CONTAINER TERMINAL AND INTERMODAL RAIL YARD OPERATIONAL AREA CONSIDERATION FOR PAVEMENT DESIGN

3780 Kilroy Airport Way, Suite 600, Long Beach, California 90806 (562) 426-9551

DISCLAIMER This Design Guide was prepared for the sole purpose of providing general information on the selected subject matters. However, this Design Guide is only intended to provide general guidance related to container terminals and intermodal rail yard operational areas, and this information, is not intended for use for any specific project. The use of this Guide for actual projects should only be done in conjunction with the services of a qualified engineer or consultant to assure that specific project circums tances are taken into consideration. While all reasonable care has been taken in the preparation of this Design Guide, Moffatt & Nichol does not guarantee the correctness of the data or information contained within, and disclaims any responsibility or liability in connection with its use. Photographs and drawings of equipment used in this publication are for illustration only and do not imply preferential endorsement of any particular manufacturer by Moffatt & Nichol and their contributors.

CONTAINER TERMINAL AND INTERMODAL RAIL YARD

OPERATIONAL AREA CONSIDERATION FOR PAVEMENT DESIGN

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Executive Summary

Traffic disruptions and the cost associated with rehabilitating and maintaining distressed or failed pavements in container terminals signifies the importance of optimizing pavement design procedures within these facilities. This pavement design guide aims at providing general concepts and instructions on the pavement design of the heavily loaded conditions encountered in container terminals and intermodal rail facilities. The guide stresses the importance of the coordination between the pavement designer and terminal planner; this is because the design guidelines are greatly dependent on the loading conditions associated with the different terminal operation schemes. The guide starts by giving an overview of typical container terminal areas focusing on the different operational loading conditions and their significance on the pavement design. The different container terminal operational areas are: the wharf, the container storage yard, the intermodal rail yard, the truck gate facility, and the buildings and automobile parking. With the modernization of container terminals, several options became available to accomplish the required tasks in each of these areas. The loading conditions in each sector vary with the type of equipments used and the nature of commodities handled. Section 2 of the guide describes the equipment configuration, motion, and usage in the terminal. It classifies the terminal operational options according to the different equipment used within each area. For the container yard operations, three options are presented: the use of rubber tire gantry (RTG’s), front-end loaders (FEL’s), or straddle carriers. The usage conditions along with the corresponding truck motion are discussed for each of these options. Similar analyses portraying the operation scenarios for the RTG’s and FEL’s in the intermodal yard are presented. Section 2 also describes the machinery loads involved in operating wheeled container yards and gate areas. Having configured the terminal usage and operation schemes, the next step is calculating the corresponding pavement loads. Section 3 provides a guide for calculating the design loads and design load repetitions in a container terminal. The pavement is subject to both dynamic loading from container handling equipment and static loading from corner castings on containers and either dolly wheels or sand shoes on the chassis. Different equipment types, container load distributions, tire loads, axle and tire configurations, and repetition of loads are considered for different areas. Typical specifications for different makers are provided for each equipment type. An analysis procedure for determining the container weight distribution is presented. Depending on the container terminal operational area and equipment used, typical load repetition calculations are derived. Two approaches for computing load repetitions are discussed; the first requires converting the various loads and repetitions to equivalent single axle loads (ESAL), and the second characterizes the loads directly by the number of axles, configuration, and weight. Equipment weight distribution and wheel loads are stated as seen in the British Port Association 1982 Heavy Duty Pavement Manual. Accounting for the contact stress and wheel loads, damages to the pavement are quantified using PAWL’s (Port Area Wheel Load). Section 3 concludes by presenting a comprehensive example to demonstrate the analysis schemes discussed in the chapter.



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Section 4 of the manual details the process of site investigation. Proper site investigation is essential for enabling an economic pavement design and safety and predictability during the construction operations. Typically, site investigation is carried out by geotechnical consultants, and it aims at determining the properties of the soils within the influence zones below the underside of the pavement. Different options and approaches for improving the ground soil conditions, in order to reduce the consequences of the problems experienced in port facilities, are discussed in this section. Section 5 discusses the influence of the subgrade on the pavement type, section and performance for a particular type of operation. Failure to characterize the subgrade properties can result in high maintenance costs or premature pavement failure. This section sets out the material characteristics that affect the pavement performance, and the test methods that can be used to determine design values. It details the classification of soils as either fine or coarse grained, granular or cohesive soils. The section also describes the soil mass volume relationships, different classifications, and moisture density relationships. In-situ and lab testing procedures for determining these properties are also presented in this section. Building on the acquired knowledge about the terminal operation and subgrade properties, it is up to the designer to select a suitable pavement design. Three pavement designs are presented in this guide: hot mixed asphalt (HMA), Portland cement concrete pavement (PCCP) and roller compacted concrete pavement (RCCP). The design selection is based on the designer’s vision as to how the pavement will perform. Generally, the site environmental conditions, the traffic loads and speed, the pavement structure, and the design life/cost play a major role in determining the performance of the pavement. Not all pavement options are suitable for all operational areas. HMA pavement is not usually considered in areas subject to heavy wheel loads. While PCCP (jointed or continuously reinforced) are considered applicable for most operational areas, RCCP is best suited for large contiguous areas subject to heavy loading conditions. Section 6 stages the details of the design, construction, and quality assurance of HMA. The HMA design yields a flexible pavement that is both rut resistant and durable. Three major design procedures for HMA mix design are discussed in this section: Marshall, Hveem, and Superpave. All three procedures share common steps:

1) materials selection; 2) selection of the design aggregate structure; 3) determination of the optimal asphalt content; 4) evaluation of moisture sensitivity.

The primary difference between the three approaches is the laboratory compaction method and the effort used in the determination of the optimal asphalt content. The layered elastic analysis theory, Section 7, is used for the analysis of the thickness of the HMA pavement. It is based on the fact that the stresses and strains, which develop in the pavement and subgrade due to a wheel load application on a flexible pavement, are distributed



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according to the elastic properties of the various layers. A pavement design software, Kenlayer, can be used to analyze the pavement sections and develop strains at critical points in the pavement. It analyzes elastic multilayer systems under circular loads and superimposes values for multiple loads. It also has some iterative capabilities for the analysis of nonlinear viscoelastic layers. The section concludes by presenting a design example for flexible pavements using the methods discussed in section 6. Section 8 provides the design guidelines for PCCP, a system of subgrade soil, base course material, and the surface course of Portland cement concrete. The concrete used for PCCP must meet the combined requirements of durability under repeated heavy loads, dimensional stability to minimize shrinkage and curling, and non-reactivity of its constituent material. Joints are typically used in non-reinforced concrete pavements to limit warping and curling stresses which are due to temperature and moisture gradients through the slab, prevent control cracking due to volume changes, prevent damage to immovable structures, and facilitate construction. The thickness of the designed pavement is based upon provid ing a sufficient structural capacity. The key structural design factors include:

1) slab thickness; 2) slab concrete flexural strength; 3) foundation support (from base and subgrade); 4) wheel loads and repetition loads.

The PCCP thickness analysis, warping stress analysis, temperature reinforcement analysis, and dowel bar analysis are demonstrated in two design examples at the end of section 8. Section 9 provides the guidelines for the design of roller compacted concrete pavements. RCC is a zero-slump concrete consisting of dense graded aggregates, cement and water. Because of its low water content, it is usually placed using asphalt pavers and densified by compacting with vibrating rollers. The design philosophy of RCC pavements is based on limiting the stresses in the pavement to a level such that it can withstand repeated loadings of this stress magnitude without failing in fatigue. The critical stress is the maximum tensile stress at the bottom of the concrete slab. Several methodologies for calculating this stress are well developed and documented in the literature. Knowing the expected traffic expressed in terms of wheel loads, load configuration, and number of load applications expected over the design period, the designer varies the following parameters to optimize the flexural strength of the RCC pavement:

1) modulus of subgrade reaction; 2) flexural strength of the concrete mix; 3) thickness of concrete slab.

Design examples are provided at the end of the section to demonstrate the design methodology discussed in this section.



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Section 10 of this guide introduces the Pavement Management System (PMS). PMS is a decision making tool that assists the engineer, budget director, and management to make cost effective-decisions regarding maintenance and rehabilitation for a pavement network. Section 11 present some of the PMS software packages currently used for pavement management. The following flow chart is designed to enable the user to smoothly navigate through this design manual.



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Determine Container Terminal Operation:

Terminal Planner (Section 2)

Calculate Wheel Loads and Load Repetitions

(Section 3)

Site Investigation & Subgrade Properties:

Geotechnical Engineer (Sections 4 & 5)

Pavement Design, Thickness Analysis

Hot Mixed Asphalt, HMA

(Section 6)

Layered Elastic Analysis

(Section 7)

Portland cement Concrete, PCC

(Section 8)

Roller Compact Concrete

(Section 9)

Pavement Management (Sections 10 & 11)



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1. Introduction.......................................................................................................................... 1-1

1.1 Description of the Pavement Design Guide ................................................................... 1-1 1.2 Container Terminal Operation Area............................................................................ 1-1

1.2.1 Wharf Area........................................................................................................................................................1-3 1.2.2 Container Storage Yard.................................................................................................................................1-3 1.2.3 Intermodal Rail Yard .....................................................................................................................................1-4 1.2.4 Truck Gate Facility .........................................................................................................................................1-5 1.2.5 Buildings and Automobile Parking .............................................................................................................1-5



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1. Introduction

1.1 Description of the Pavement Design Guide

Pavement is one of the most important facility in container terminals and occupies a significant amount of the costs for container terminal constructions and maintenance. This pavement design guide, prepared for the Port of Los Angeles (POLA), provides general concepts and instructions on pavement design but tailored for the intensive loading conditions encountered in container terminals and intermodal rail facilities. Detailed design examples are also included to illustrate those concepts. Targeted at a United States audience, this guide is intended to provide a comprehensive reference of alternative design procedures and material options available to the engineers undertaking the design of pavement for such a facility, both inside and outside the pavement community. After coving these pavement concepts, you should, in general, be able to:

− Describe the concept of container terminal and intermodal rail yard operations; − Describe the pavement concept covered; − Describe the typical equipment, methods and procedures used for pavement design; − Implement typical pavement design analysis for container terminals; − Develop a number of appropriate solutions for economic analysis; − Apply these concepts and methods into practice;

In this pavement design guide, the following topics will be covered:

− State of the art container terminal and intermodal rail pavement design; − Container terminal and intermodal rail yard operational area; − Container terminal operational options; − Typical container handling equipment and the load repetition analysis; − Site investigation to determine characteristics of subgrade materials; − Subgrade test and analysis to determine design values; − Flexible pavement design; − Layered elastic analysis and the Asphalt design example; − Rigid Pavement Design and the Portland Cement Concrete (PCC) pavement analysis examples; − Roller Compacted Concrete (RCC) pavement design; − Pavement management and Pavement Management System (PMS) software;

The rest of this chapter describes typical container terminal operational areas and the importance of identifying these areas in the pavement design. 1.2 Container Terminal Operation Area

Pavement designer has to consider dividing the container yard area into various operational areas based on the anticipated variety of type of traffic and wheel loads. This will allow optimizing the pavement cost by providing appropriate pavement thickness for each operational area. Identifying the limits of each operational area for current and future operation would require the pavement designer to work closely with the container terminal planner.



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Container terminal complex includes wharf, container storage yard, intermodal rail yard, truck gate facility, container handling equipment parking areas, buildings, and automobile parking areas. These operational areas are identified on a typical container terminal layout in Figure 1-1.

Figure 1-1 - Typical Container Terminal Layout

Container facilities buildings include administration, maintenance buildings, and various service facilities. Intermodal rail facility includes area for working tracks (loading and unloading of containers), area for storage tracks (storing loaded or empty cars), container storage area, and some times a separate truck gate facility. The intermodal facility operational areas are shown on Figure 1-2.

Figure 1-2 Intermodal Facility Operational Areas



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Pavement designers need to work closely with the container terminal and intermodal facility planners to understand the startup operationa l areas and future possible changes within the operational areas. Since the operational changes can be made by just changing yard striping, the pavement designer needs to understand the possible changes and provide an appropriate pavement section that would allow changes in mode of operation in the future. 1.2.1 Wharf Area

Wharf is where the transfer of containers from ship to shore and from shore to ship occurs. The most common method employed in moving containers from ship to shore and shore to ship is using a container gantry crane that handles one or two 20-foot containers or a single 40 foot container. However, some container terminals have started to deploy container cranes that can lift four 20 foot or two 40 foot containers. These cranes are available with different capacities, different outreach and inreach, and leg spread. Most of the current cranes have 100 ft. leg spread. There are several methods of moving containers from the storage area to the wharf or from the wharf to storage area. The most common methods are chassis with yard tractors and straddle carriers. In addition three truck traffic lanes and hatch cover storage area are required on the land side of the crane rail. Hatch covers range in sizes from 30 to 55 feet. Typical wharf area is presented on Figure 1-3.

Figure 1-3 - Typical Wharf Area

1.2.2 Container Storage Yard

Container storage yard is where containers are stored for duration prior to leaving the terminal on ship, rail, or truck. Transporting within the container yard are used for chassis with yard or road tractors, and straddle carrier. In smaller terminals and as a backup top loader type of equipment can be used to transport containers. In automated terminals containers are transported using automated guided vehicles (AGVs) or automated lifting vehicles (ALVs). The major equipment used for storing containers in container yard are wheeled (container on chassis), rubber tire gantry (RTG), straddle carrie r, top loader or other similar equipments, and rail mounted gantry (RMG). Terminals may use combination of RTG and top picks to store containers.



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Most terminals have designated import, export, and empty container storage areas. In the US where the chassis are owned by the shipping industries the container terminals have designated chassis storage areas as well. Typical container terminal storage yard is presented on Figure 4.

Figure 1-4 - Typical Container Terminal Storage Yard

1.2.3 Intermodal Rail Yard

An intermodal rail facility is used to stage, load and unload containers to and from the ports. Double stack trains are loaded and unloaded by standard container handling equipment. A typical intermodal facility consists of working tracks, storage tracks, arrival and departure tracks, and a run around track. The pavement designer needs to work with the terminal planner to identify the tracks that will be paved and all possible affected operational modes such as: top picks, RMGs, RTGs, reach stacker. They will also need to identify areas designated for pre-staging inbound and outbound containers. Typical container storage yard is presented on Figure 1-5.

Figure 1-5 - Typical Container Storage Yard – Intermodal Rail Yard



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1.2.4 Truck Gate Facility

Container terminal and Intermodal rail gate facilities have very similar functions. They are used to obtain information on the incoming and outgoing container trucks for operational and security purposes. Prior to implementation of technologies, incoming trucks would be stopped by security, followed by a transaction process via communication pedestals, and finally a physical inspection of container and chassis by mechanics. Some or all of the processes have been automated and/ or eliminated. However, even the most automated gates require trucks to stop for processing. The Pavement designer should make assumptions that the gate will be operating 7 days a week with very limited tolerance for maintenance during its operation. The stop and go nature of the gate operation should also be considered in selecting the pavement material as well as the over all pavement thickness. A typical Gate facility is presented on Figure 1-6.

Figure 1-6 – Typical Gate Facility

Most of the container handling equipment is located near the maintenance and repair facility areas. The current and future types of equipments that would be stored in this area should be identified prior to designing the pavement system. 1.2.5 Buildings and Automobile Parking

Typical container terminals and Intermodal rail require administration buildings, maintenance and repair facilities and other operational buildings that have designated employee and visitors parking areas. Prior to development of pavement sections pavement designer should work closely with the terminal planner in identifying current and possible future use of these areas. The following chapters will discuss: operational options, pavement subgrade, flexible and ridge pavements, and pavement management.



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2. Container Terminal Operational Options ................................................................................. 1

2.1 Grounded Container Yard Operations with RTGs .......................................................... 1 2.1.1 Equipment Motions ............................................................................................................................................1 2.1.2 Container Truck Motions .................................................................................................................................2 2.1.3 Usage.......................................................................................................................................................................3

2.2 Grounded Container Yard Operations with Front-End Loaders ..................................... 4 2.2.1 Machine Configuration .....................................................................................................................................4 2.2.2 Equipment Motions ............................................................................................................................................6 2.2.3 Truck Motions .....................................................................................................................................................7 2.2.4 Usage.......................................................................................................................................................................8

2.3 Grounded Container Yard Operations with Straddle Carriers ........................................ 9 2.3.1 Machine Configuration .....................................................................................................................................9 2.3.2 Equipment Motions ............................................................................................................................................9 2.3.3 Strad-Truck Interchange................................................................................................................................11 2.3.4 Usage.....................................................................................................................................................................12

2.4 Intermodal Yard Operations with RTGs or Travelifts................................................... 13 2.4.1 Machine Configuration ...................................................................................................................................13 2.4.2 Equipment Motions ..........................................................................................................................................13 2.4.3 Truck Motions ...................................................................................................................................................14 2.4.4 Usage.....................................................................................................................................................................14

2.5 Intermodal Yard Operations with Front-End Loaders .................................................. 14 2.5.1 Machine Configuration ...................................................................................................................................14 2.5.2 Equipment Motions ..........................................................................................................................................15 2.5.3 Truck Motions ...................................................................................................................................................15 2.5.4 Usage.....................................................................................................................................................................16

2.6 Wheeled Container Yard Operations ............................................................................. 16 2.6.1 Machine Configuration ...................................................................................................................................16 2.6.2 Truck Motions ...................................................................................................................................................18 2.6.3 Usage.....................................................................................................................................................................18

2.7 Gate Areas with Highway Tractors and Chassis ............................................................ 19 2.7.1 Configuration.....................................................................................................................................................19 2.7.2 Usage.....................................................................................................................................................................19



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2. Container Terminal Operational Options

This section describes typical operational options in the modern container terminals. 2.1 Grounded Container Yard Operations with RTGs

Figure 2.1 shows a typical modern rubber-tired gantry crane in container yard operations.

Figure 2-1 Rubber-Tired Gantry Crane in Container Yard Operations

Deltaport, Vancouver, British Columbia

The typical modern RTG spans a space that includes six container stacks and a truck travel lane, and has a gage of about 77 feet. Other widths are common. RTG height is expressed in terms of the maximum effective stack height, plus the pass-over space. The machine in Figure 2-1 has a “one-over-four” configuration. Other heights, up to one-over-six, are common. The most common machine has eight wheels, such as that shown in Figure 2-1. Some older machines have four wheels, one wheel on each leg. A few machines have sixteen wheels, in eight dual-wheel trucks. Each truck can be rotated 90°. 2.1.1 Equipment Motions

The following equipment motions are defined:

Hoist: Vertical motion with the main hoist drive.

Trolley: Horizontal motion perpendicular to the gantry runway, with the trolley drive.

Gantry: Horizontal motion parallel to the gantry runway, with the gantry drive.



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Virtually all container handling is done with only the hoist and trolley motions. Gantrying with a container is not generally done, because unequal weight distribution makes precise steering difficult. Gantry motion perpendicular to the runways is possible in dedicated areas. There are three ways to traverse an RTG perpendicular to its runway:

Spin Trucks: Spin all trucks 90°, traverse to a new position, and spin trucks back to their original position.

Turn Around Truck : Spin all trucks but one, so that their rotation axes pass through the static truck. Turn the entire RTG 90° about the static truck, spin the trucks back, traverse, and repeat.

Turn Around Center: Spin all trucks, so that their rotation axes pass through the RTG center-point. Turn the entire RTG 90° about the center-point, spin the trucks back, traverse, and repeat.

All three of these motions generate high friction loads on the pavement, and are frequently done at embedded metal plates. The “Spin Trucks” method is the most common. 2.1.2 Container Truck Motions

Container trucks commonly traverse the entire length of the RTG block in a single lane, with a bare chassis part of the way, and a loaded chassis the rest of the way. In many terminals, adjacent RTG blocks are laid out to create some weaving and bypass room for trucks, as shown in Figure 2-2 and Figure 2-3.

Runway

Runway

Runway

Runway

Stacks

Access Lane

Bypass Lane

RTG

Truck

Figure 2-2 Truck Access and Bypass Lanes for RTGs

RTGs in Same Orientation



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Runway

Runway

Runway

Stacks

Access Lane

Access Lane

RTG

Truck Bypass Lane

Figure 2-3 Truck Access and Bypass Lanes for RTGs RTGs in Opposing Orientation with Shared Bypass

Where weaving and bypass lanes are available, trucks will generally use them only if the access lane is obstructed downstream. 2.1.3 Usage

RTGs are used in conditions requiring high storage density and frequent container re-handling between adjacent stacks. The need to re-handle means that some empty slots will always be needed. Figure 2-4 depicts the empty spaces required to accommodate re-handling containers. The container in the white slot labeled “T” is the target for retrieval. The containers in the grey slots labeled “1”, “2”, etc., need to be moved to the corresponding white slots, which need to be left empty. This reduces the effective stacking height.



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RTG 6 Wide, 1+6 High5.2 Effective Height

RTG 6 Wide, 1+4 High3.5 Effective Height

T54321 5 4 3 2 1

T321 3 2 1

Figure 2-4 Container Rehandling Space for RTGs

A typical work sequence for an RTG retrieval operation would be as follows:

− Truck arrives adjacent to target storage location with a bare chassis. − RTG is assigned, and gantries to truck’s location. − RTG re-handles obstructing containers to other stacks without gantrying. − RTG retrieves target container, and sets it on the truck chassis. − Truck departs with loaded chassis.

Export loads are typically arranged to mimic the ultimate ship stowage pattern. In many RTG terminals, a single set of adjacent export stacks would have a single common ship-stowage designation. Import loads are typically arranged in the order they are retrieved from the ship, since the order of delivery to the gate is unknowable. These patterns minimize the number of gantry moves required during ship operations, but maximize the number of gantry moves required during gate operations. The need to keep open slots for re-handling, along with the tendency to sort containers within RTG blocks, tends to limit overall RTG space utilization. When calculating annual truck trips through RTG operating areas, this reduced utilization needs to be taken into account. 2.2 Grounded Container Yard Operations with Front-End Loaders

2.2.1 Machine Configuration

“Front-end loader” (FEL) is a generic term for a broad class of equipment. All types of FEL pick up a container in a position cantilevered outside and in front of the machine’s wheelbase. FELs come in three common configurations:



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Top-Pick (TP): The spreader is mounted on a vertical mast. The container is picked up by its four top corner castings. The machine is used for both loads and empties. Top-picks frequently have a forklift attachment that allows picking up loaded 20-foot containers by their bottom forklift slots.

Side-Pick (SP): The spreader is mounted on a vertical mast. The container is picked by the two top corner castings closest to the FEL. The machine is used for empties only.

Reach-Stacker (RS): The spreader is mounted on a hydraulically-lifted, extensible boom. The container is picked up by its four top corner castings. The machine is used for both loads and empties, and can handle containers at some distance from the machine.

Figure 2-5 shows a typical top-pick. Figure 2-6 shows a typical side-pick. Figure 2-7 shows a typical reach-stacker.

Figure 2-5 Typical Top-Pick FEL with Spreader at 20'



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Figure 2-6 Typical Side -Pick FEL Serving 7-High Stack

Figure 2-7 Typical Reach-Stacker FEL with Spreader at 20'

2.2.2 Equipment Motions

All FELs having rotating rear trucks and are fairly maneuverable. The following motions are defined:

Hoist: Vertical motion along the mast on TPs and SPs, or vertical motion of the boom on RSs



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Extend: Extension of the boom on RSs.

Travel: Straight-line motion of the FEL.

Turn: Spinning of the rear truck, and rotation about one of the front trucks.

Most container handling is done without turning, simply traveling forward and backward perpendicular to a storage stack. TPs and SPs can only access the top-most container in the outer-most stack in any container block. If re-handling is required, the obstructing container must be moved to an adjacent block. This requires the FEL to do the following:

− Load re-handled container − Back up

Turn Traverse to the next block Turn Align to the block Set the re-handled container Back up Turn Traverse to the original block Turn Align to the block

− Load target container

Reach stackers have some ability to re-handle containers into the stack second from the front, but re-handling is usually done the same as for TPs and SPs. This sequence takes quite a bit of time, and so most FELs are restricted to operations involving simple fore-and-aft motions. 2.2.3 Truck Motions

Trucks commonly traverse the entire length of the FEL block in a single lane, with a bare chassis part of the way, and a loaded chassis the rest of the way. The gap between adjacent FEL storage blocks is fairly large, frequently 65’ or more, so there is usually room for maneuvering. However, simultaneous access of both adjacent FEL blocks can reduce this flexibility. Figure 2-8 shows a common FEL and truck traffic configuration.



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Access Lane

Access Lane

FEL

FEL Tire Path

Truck

Figure 2-8 Truck Access for FELs Working Adjacent Blocks

Note the intersection of the FEL and truck tire paths in Figure 2-8. This area is subject to numerous repetitions, since the FEL must retreat each time to clear the truck access lane, then advance all the way to the face of the container stack. In grounded CY operations, the stacks are in fixed locations, and so the FEL tire wear patch does not vary over time. 2.2.4 Usage

FELs are used in conditions requiring high storage density, in which container re-handling is expected to be rare or non-existent. The long cycle time for re-handling between blocks makes re-handling very expensive and unproductive. A typical work sequence for an FEL retrieval operation is as follows:

− Truck arrives, and stops short of the FEL travel path. − FEL arrives, aligns to the block, and advances across the truck access lane to the face of the

block. − FEL picks the container, and retreats to clear the truck access lane. − Truck advances, aligning to the FEL. − FEL advances, and sets the container on the truck. − FEL retreats or hoists to clear the truck. − Truck departs.

A typical work sequence for an FEL storage operation is as follows:

− Truck arrives, and aligns to the stack. − FEL arrives, and aligns to the truck. − FEL advances, and picks the container from the truck.



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− FEL retreats or hoists to clear the truck. − Truck departs. − FEL advances across the truck access lane to the face of the block. − FEL sets the container atop the stack. − FEL retreats to clear the truck access lane.

TPs are commonly used to handle pre-sorted export loads. RSs are less-commonly used. SPs are commonly used to handle empties. FELs are almost never used to handle import loads, because the randomness of retrieval order generates a high re-handle incidence. In facilities where FELs are used to handle imports the stack height and width is kept at two or less containers. As with RTGs, export loads are sorted in FEL blocks according to ship stowage designations. During ship load-out operations, all of the containers in a block will be considered logically interchangeable, so that the FEL can always work the most accessible container and avoid re-handling. Empties in FEL blocks are sorted according to their physical type and ownership. During delivery of empties to the ship or a trucker, all of the containers in a block will be considered logically interchangeable, minimizing the need for re-handles. Some physical types, e.g., “dry 40-foot standard cubes” are quite common, and generate large, full blocks. Some physical types or ownership categories are rare, and generate poorly utilized blocks. The need to avoid re-handling in FEL blocks places a practical limit on the utilization of these areas. Utilization will vary from terminal to terminal, based on local commercial patterns. These utilization patterns need to be considered when calculating annual FEL and truck trips. 2.3 Grounded Container Yard Operations with Straddle Carriers


Figure 2-9 shows a typical modern straddle carrier. Straddle carriers (strads) combine the ability to stack and transport containers over long distances. Most straddle carriers are eight-wheeled machines, with the steering of the wheels coordinated to generate a tight turning radius. Most strads are built for “one-over-two” operations. Some terminals are now using “one-over-three” straddle carriers. One high strads are also available as transporters only. 2.3.2 Equipment Motions

Straddle carriers can drive equally well, forward or backward. The operator’s cab is at the top, at one end. The driver is typically on a swivel chair, and can orient to see either direction of travel. However, many drivers prefer to drive longer distances with the cab forwards, because visibility and safety are improved. Many terminals have operating rules that dictate this behavior.



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Figure 2-9 Typical Straddle Carrier, One -Over-Two

The hoist and spreader move vertically, with some limited ability to adjust spreader position for fine alignment to stacks. Long-distance travel is supposed to be done with the container in the lowered position, so that stability is increased. There is usually a transition between long-distance travel over the open roadway and motion over container stacks. During this transition, the spreader is raised and the strad slows down to ensure proper alignment. There is limited clearance between stacked containers and the inner face of the drive equipment. Travel speed over stacks is reduced, and the driver must take some care to avoid striking the stacked containers. It has been found that when traversing long strad stacks, the driver’s attention may wander, increasing the probability of collision. Any irregularities in the pavement may cause the strad to wander, further increasing the probability of collision. To minimize collision probability, the length of strad stacks is generally limited to twelve or fourteen 20-foot slots. Figure 2-10 shows a typical stack configuration in a straddle carrier storage area. It is important to note that adjacent blocks of containers share strad tire paths, so that strads may not pass one another in adjacent blocks. This is done to maximize storage density. It affects the number of tire passes over any one tire path.



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StacksStradTire Paths

Figure 2-10 Typical Strad Stack Configuration

Storage run positions are painted onto the pavement, and do not vary much with time. The strad tire wear paths can stay in one place for years, concentrating load repetitions in fairly tight bands. 2.3.3 Strad-Truck Interchange

Strad-based terminals have an interchange area where trucks and straddle carriers can exchange containers. This area is generally laid out for maximum safety and visib ility, because of the hazards inherent to the operation. The layout of this area will vary considerably between terminals, depending on local safety practices, truck-driver skill, and strad-driver skill. Figure 2-11 shows the interchange area at Portsmouth Marine Terminal in Virginia.

Figure 2-11 Strad/Truck Interchange Area

Portsmouth Marine Terminal, Virginia

Figure 2-12 shows the layout of a typical strad/truck interchange area. The layout of the area allows strads to simultaneously serve adjacent trucks. The tire paths between adjacent interchange slots are not



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shared. Depending on local safety rules, trucks may either be backing into the interchange slot, or driving forward into it from inside the strad work zone. “Herringbone” configurations are also common.

Strad

Truck

InterchangeSlot

DriverZone

Tire Paths

Figure 2-12 Strad/Truck Interchange Area

2.3.4 Usage

Strads are used in conditions requiring moderate storage density and high productivity. Strads are capable of effective re-handling. Figure 2-13 shows the empty spaces required to accommodate re-handling of containers in 1-over-3 and 1-over-2 configurations. Terminal operators typically want to limit the distance a strad driver needs to move to find an open slot for a rehandled box. This requires that a certain number of slots be kept clear, reducing the effective stacking height.

11

Strad 1+2 High1.75 Effective Height

Target

Target2

Strad 1+3 High2.50 Effective Height

12 1

Figure 2-13 Container Rehandling Space for Strads

Strads are used for both loaded and empty container operations, although many terminal operators prefer to keep the bulk of their empty containers in side-pick configurations for higher density. Each container storage or retrieval operation typically requires that the strad traverse the entire length of the storage run.



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Export loads are typically sorted in runs corresponding to ship stowage patterns, so re-handles are relatively rare. Re-handling is more common in import load areas, and the additional strad motions up and down the run need to be considered in calculating load repetitions. 2.4 Intermodal Yard Operations with RTGs or Travelifts


Figure 2-14 shows an RTG serving an intermodal double -stack rail car.

Figure 2-14 RTGs Serving Intermodal Doublestack Car

The configuration of the machine is similar to that used in grounded container yard operations. One common difference is the presence of a stabilizer system that restricts the side-sway of the spreader. This stabilizer system is critical in the handling of trailers, as it allows the rapid attachment of trailer kingpins to support stanchions on piggyback cars. Stabilizer systems are more common in inland intermodal yards, where domestic trailer operations are more common. Maritime intermodal yards frequently use standard, non-stabilized, wire-rope RTGs. 2.4.2 Equipment Motions

The motions of the RTG are similar to those described in Section 2-1.1 for grounded container yard operations using RTGs.



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2.4.3 Truck Motions

Trucks commonly traverse the length of the RTG run along bypass lanes, because of the great length of many of the rail car “cuts”. See Figure 2-15 below. The trucks weave into the loading access lane just upstream of the target location, and weave back to the bypass lane when they are clear of the RTG. 2.4.4 Usage

Figure 2-15 shows one common layout for high-density intermodal working tracks, using RTGs. There are many variations on this theme, based on the dimensions of the RTGs, the nature of the truck and rail traffic, and the configuration of the site.

Runway

Runway

Runway

Runway

Access Lane

Access Lane

Bypass

Bypass

RTG Rail Car

Truck

Tracks

Tracks

Figure 2-15 Typical RTG Intermodal Rail Layout

The amount of gantrying by the RTGs is much less than in grounded container yard operations, because the RTGs are generally working in a systematic way from one end of the track to the other. There are, of course variations between terminals, but most RTG assignments are pretty well-organized. The utilization of double -stack rail equipment is fairly high, so it is reasonable to assume, for the purposes of traffic counts, that cars arrive loaded and depart loaded. 2.5 Intermodal Yard Operations with Front-End Loaders


Figure 2-16 shows an FEL working an intermodal double -stack car.



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Figure 2-16 Front End Loader Serving Intermodal Car

Top-picks and reach-stackers are commonly used on intermodal operations. Side-picks are not commonly used. Reach-stackers have the advantage of being able to reach a second track, by extending the boom. This is particularly useful in serving tracks set against a terminal boundary. FELs are capable of serving curved working tracks, while RTGs are not. 2.5.2 Equipment Motions

The motions of FELs in serving rail cars are similar to those described in Section 2.2.2 for ground container yard operations. The FEL typically moves fore and aft, turning frequently to move from car to car. The area of pavement immediately adjacent to the track sees a great deal of traffic, as depicted in Figure 2-17. In grounded CY operations, the stacks are in fixed locations, and so the FEL tire wear patch does not vary over time. In intermodal operations, the alignment of cars is not constant, as each train has different mixture of car and platform lengths and positions. The tire wear patch shifts constantly, spreading the repetitions over a much greater area. 2.5.3 Truck Motions

Trucks generally traverse the length of the working track segment along the access lane, as shown in Figure 2-17. The access lane thus sees the combined traffic of trucks running parallel to the track, and FELs moving back and forth perpendicular to the tracks.



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2.5.4 Usage

Figure 2-17 shows one common layout for high-density intermodal working tracks, using top-picks. There are many variations on this theme, based on the nature of the truck and rail traffic, and the configuration of the site. Note the differing car alignments, and their impact on the location of FEL tire wear paths.

Track

Track

Track

Track

Access Lane

Access Lane

Access Lane

Access Lane

FEL

FEL Tire Path Truck

Rail Car

Figure 2-17 FEL and Truck Access for Inermodal Operations

2.6 Wheeled Container Yard Operations


Figure 2-18 shows a typical wheeled storage row.

Figure 2-18 Typical Wheeled Storage Row



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In wheeled container storage, containers are mounted and parked on street-capable chassis. While parked, the chassis are sitting on their landing legs, which can be retracted for travel. The pads on the landing legs generate a high ground pressure, frequently causing local pavement damage. Street chassis have twist locks at each corner to secure the container for road travel. Chassis for 40’ containers are just over 40’ long. They have a “gooseneck” which mates to a well built into the underside of the standard container. Chassis for 20’ containers are generally 28’ or longer, to avoid exceeding highway axle load limits. Containers may also be mounted on dedicated terminal chassis, known as “bomb carts”. Bomb carts are not generally street-legal, because they are wider than 8 feet. They are equipped with flare guides at each corner, making container mounting faster and easier. Bomb carts are typically 40’ or 45’ long, and can hold two 20’ containers with a total rated load of 48 long tons. Figure 2-19 shows the rear flare guides on a typical bomb cart.

Figure 2-19 Rear Flare Guides on a Bomb Cart

A mixture of in-terminal tractors, and off-terminal, or “street”, trucks typically accesses wheeled container storage. The configuration of street trucks varies considerably. Terminal tractors are much more uniform, and differ from street trucks in a number of ways:

− Shorter wheel base − Hydraulically-liftable “fifth wheel” − Tighter turning radius − Single rear axle

The hydraulic -lift wheel on termina l tractors allows them to back under a parked chassis, pick the chassis up off its landing legs using the fifth wheel, hook up the brakes and electrics, and drive away. The



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terminal tractor can park chassis just as quickly. The act of lowering the chassis using the fifth wheel increases the impact load under the landing leg pads, exacerbating pavement damage. A typical terminal tractor is shown in Figure 2-20.

Figure 2-20 Typical Terminal Tractor

2.6.2 Truck Motions

Removing a chassis from storage is a fairly simple truck motion. Placing a chassis into storage generally requires some maneuvering, especially for street tractors. Parking slots are typically ten feet wide, and long-wheelbase tractors have some difficulty backing a 40-foot chassis gracefully into this width. The access aisles running between rows of parked containers frequently double as general traffic circulation roads for the terminal. As such, the number of truck repetitions is not directly related to just the storage and retrieval operations within a row. Truck repetitions within a row will depend on the overall traffic layout of the terminal. If the terminal is amply supplied with dedicated arterial circulation roads, traffic will be diminished in the storage rows. 2.6.3 Usage

Wheeled storage is used where low storage density is acceptable, and high container accessibility is required. Wheeled storage is used for import and export loads, and for empties. Wheeled storage is commonly used for reefer containers, since plugging, unplugging, and servicing reefers is easier when they are mounted and accessible. Peak storage utilization is typically very high, because re-handling is not required in any circumstance. When utilization is high, drivers may have to search a bit to find an empty slot to park a chassis in. This increases driving time, and increases the number of pavement load repetitions. When wheeled storage is in use, bare chassis can make up a considerable portion of the total storage demand. At times, the high population of bare chassis mandates that their storage be densified. Figure 2-21 shows a typical high-density storage area for bare chassis. Note these chaises are stacked to save yard spaces.



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Figure 2-21 High Density Bare Chassis Storage

2.7 Gate Areas with Highway Tractors and Chassis

2.7.1 Configuration

There are many different configurations in use for gate complexes. In general, however, they have in common a number of basic components:

Queuing Lanes: In-stream queuing space for trucks waiting for processing.

Remote Processing Stations: Locations where the truck driver can interact with terminal staff through telecommunications equipment, without leaving the truck cab.

Scales: Weigh scales.

Inspection Stations: Locations where the truck is visually inspected, and paperwork is exchanged.

Holding Areas: Locations where trucks are parked awaiting resolution of problem transactions, or are otherwise out of the main gate traffic stream.

Only street tractors pass through terminal gates, and only with street-legal chassis. Neither terminal tractors nor bomb carts are suitable for open-road use, and they are generally not registered as such. The configuration of street trucks varies widely, based on local commercial conditions. A typical gate can process about 20 to 25 trucks per hour, per lane. The number of gate lanes is established through queuing analysis based on the exact nature of the gate process. 2.7.2 Usage

A typical truck process through a gate requires many stops and starts, within queuing areas, at processing and inspection stations, at stop-lines established to protect pedestrians, and around holding areas. Gate traffic tends to be concentrated at the interfaces between the gate and road, and gate and container yard. Within the gate, truck traffic is diffused across many processing lanes, spreading the repetition load out to a considerable degree.



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3. Typical Container Handling Equipment Wheel Load Calculation........................................ 3-1 3.1 Container Handling Tires and Pressures ...................................................................... 3-1 3.2 Yard Equipment........................................................................................................... 3-2

3.2.1 RTG’s ..................................................................................................................................................................3-2 3.2.2 Straddle Carriers .............................................................................................................................................3-3 3.2.3 Top Picks............................................................................................................................................................3-3 3.2.4 Side Picks............................................................................................................................................................3-4 3.2.5 Reach Stackers..................................................................................................................................................3-5 3.2.6 Yard Hustlers....................................................................................................................................................3-6

3.3 Container Distribution.................................................................................................. 3-6 3.4 Static Loads .................................................................................................................. 3-8 3.5 Typical Load Repetition Analysis for Container Terminals and Intermodal Facilities . 3-8

3.5.1 Entrance Gate ...................................................................................................................................................3-9 3.5.2 Wheeled Storage Area ....................................................................................................................................3-9 3.5.3 Side/Top Pick and Truck Operations ...................................................................................................... 3-10 3.5.4 RTG and Truck Operation ........................................................................................................................ 3-11

3.6 Equipment Weight Distribution and Wheel Loads ......................................................3-14 3.6.1 RTG .................................................................................................................................................................. 3-14 3.6.2 Side or Top Pick ............................................................................................................................................ 3-15 3.6.3 Yard Trucks ................................................................................................................................................... 3-17

3.7 Pavement Damage .......................................................................................................3-18 3.7.1 Damage ............................................................................................................................................................ 3-18 3.7.2 Proportional Damaging Effect.................................................................................................................. 3-19 3.7.3 Average Damage............................................................................................................................................ 3-19 3.7.4 Critical Damage............................................................................................................................................. 3-19 3.7.5 Total Damage of a Plant and Wheel Proximity Factors..................................................................... 3-20

3.8 Equivalent Load Repetitions ........................................................................................3-21 3.8.1 RTG .................................................................................................................................................................. 3-21 3.8.2 Yard Trucks ................................................................................................................................................... 3-21 3.8.3 Side and Top Picks........................................................................................................................................ 3-22

3.9 A Comprehensive Wheel Load Calculation Example ...................................................3-22 3.9.1 Key Notations ................................................................................................................................................. 3-23 3.9.2 RTG Operation – RTG Repetitions ......................................................................................................... 3-23 3.9.3 RTG Operation – Truck Repetitions ....................................................................................................... 3-24 3.9.4 Side/Top Pick Repetitions ........................................................................................................................... 3-24 3.9.5 Damage – Top Pick ....................................................................................................................................... 3-25 3.9.6 Damage –RTG ............................................................................................................................................... 3-31 3.9.7 Design Summary ........................................................................................................................................... 3-33



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3. Typical Container Handling Equipment Wheel Load Calculation

One important function of the pavement on the container handling equipment runways is to distribute repetitive load into earth structures. Therefore, calculation of design load and design load repetitions (Load Repetition: Number of time that an area undertaking a certain amount of load.) plays an important role in the pavement design. This section provides a guide on calculation of design load and design load repetitions in a container terminal. Different equipment types, container load distribution, tire load, axle and tire configuration, and repetitions of loads are considered for different areas such as RTG runways and top pick operation area. At the end of the section, a comprehensive example is presented to illustrate the described concepts and methods. 3.1 Container Handling Tires and Pressures

Container handling equipment, including FELs, RTGs, strads, hustlers with bomb carts, hustlers with chassis, and street legal trucks with chassis, is typically used in container terminals and intermodal rail facilities. Table 3-1 lists typical tire pressures for different makers and different tire sizes of container handling equipment.

Table 3-1. Typical Tire Pressures

Tire Pressures Maker Size psi. bars

Goodyear 11R22.5 144 9.9 Nokian 14.00-24 161 11.1

Goodyear 14.00-24 144 9.9 Kalmar spec. 14.00-24 138 9.5

AVE 14.00-24 148 10.2 Goodyear 16.00-25 152 10.5

Nokian 16.00-25 131 9.0 Nokian 16.00-25 170 11.7

Kalmar spec. 16.00-25 116 8.0 AVE 16.00-25 142 9.8

Goodyear 18.00-25 131 9.0 Goodyear 18.00-25 167 11.5

Paceco spec. 18.00-25 139 9.6 Nokian 18.00-25 165 11.4

Kalmar spec. 18.00-25 131 9.0 AVE 18.00-25 147 10.1

Nokian 18.00-33 145 10.0 Goodyear 18.00-33 144 9.9

AVE 18.00-33 145 10.0 Goodyear 21.00-25 112 7.7

Kalmar spec. 21.00-25 116 8.0 AVE 21.00-25 114 7.9

Other manufacturers: Michelin General Tire



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3.2 Yard Equipment

This section presents various yard equipments, such as RTGs, straddle carriers, top picks, side picks, reach stackers, and yard hustlers. Pictures, typical dimensions, and typical specifications for different makers are provided for each equipment type. 3.2.1 RTG’s

Figure 3-1 A typical RTG

Kalmar 402315-2045C

• 16 wheels, 5+1 lift, 40.6t max lift, 125.6t dead weight, 16.00-25 tires. • 8 wheels, 5+1 lift, 40.6t max lift, 127.8t dead weight, 18.00-25 tires.

PACECO PTD 200503

• 8 wheels, 5+1 lift, 40.6t max lift, 126.0t dead weight, 18.00-25 tires. Other manufacturers: Noel (Gottwald) PMC Taylor Fantuzzi



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3.2.2 Straddle Carriers

Figure 3-2 A typical Straddle Carrier

Kalmar CSC

• 8 wheels, 4 container stack capacity, 50t max lift, 74.95t dead weight, 16.00-25 tires.

Kalmar Shuttle Carrier

• 4 wheels, 2 container stack capacity, 50t max lift, 45t dead weight, 18.00-33 tires.

Other manufactures: Belotti Nelcon Noel (Gottwald) MHI 3.2.3 Top Picks

Figure 3-3 A typical Top Pick



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Kalmar DCF450CSG

• 6 Wheels, 5 container stack capacity, 100,000 lbs. max container weight, 165,000 lbs. dead weight, 18.00x33 tires.

Kalmar DCF410CSG

• 6 wheels, 5 container stack capacity, 90,000 lbs. max container weight, 154,000 lbs. dead weight, 18.00x33 tires.

Taylor 954

• 6 wheels, 4 container stack capacity, 95,000 lbs. max container weight, 157,800 lbs. dead weight, 18.00x25 tires.

Other manufacturers: Hyster Fantuzzi 3.2.4 Side Picks

Figure 3-4 A typical Side Pick Kalmar DCE80-45 E8

• 6 wheels, 7/8 (9.5’/8.5’ containers) container stack capacity, 17,600 lbs. max lift, 81,600 lbs. dead weight, 12.00x24 tires.

Kalmar DCE100-45 E8

• 6 wheels, 7/8 (9.5’/8.5’ containers) container stack capacity, 25,400 lbs. max lift, 92,400 lbs. dead weight, 12.00x24 tires.

Kalmar DCD70-40 E5

• 6 wheels, 5 container stack capacity, 15,400 lbs. max lift, 68,100 lbs. dead weight, 12.00x20 tires.

Other manufacturers: Taylor Hyster Fantuzzi SMV



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3.2.5 Reach Stackers

Figure 3-5 A typical Reach Stacker

Kalmar DRF4000C-450C

• 6 wheels, 5-4-3 (9.5’) 5-5-4 (8.5’) stacking capacity, 99,200 max lift, 194,000 dead weight, 18.00x25 tires.

Kalmar DRS4527-4531


Kalmar DRD450-80S


Other manufacturers: Taylor Hyster Fantuzzi SMV



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3.2.6 Yard Hustlers

Figure 3-6 A typical Yard Hustlers

Ottawa 50

• 6 wheels, 63,300 maximum capacity, 14,500 dead weight, 11R22.5 tires

Ottawa DOT/EPA 60


Kalmar YT-50


Other manufactures Magnum Capacity of Texas 3.3 Container Distribution

Heaviest load will cause most damage but may only make up less than one percent of the containers transported. Therefore, to accurately analyze heavily loaded port pavements it is important to understand the weights of cargoes that will be handled. Such container distribution will be used to calculate proportional damage effect, as seen in section 3.7.2. Typical container weights range from approximately 10,000 to 67,000 pounds. Containers over 67,000 pounds are within a very small percentage and generally overweight for highway transport. A vessel discharge report summarizing all containers sizes and weights discharged and loaded during a vessel call in representative month can be obtained from a container terminal operator. A simplified tabulation of the combined import/export container distribution for a container terminal in the northwest is shown in Table 3-2 below. Figure 3-7 shows the comparison between measured and assumed container distributions. It should be noted that container weight distributions are highly sensitive to changes in the types of commodities handled. Therefore, the pavement designer should work closely with terminal planners to understand possible changes to commodities types in the region.



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Table 3-2. Container Weight Distribution

0%

5%

10%

15%

20%

25%

30%

35%

0-10,0

00

10,001

- 25,0

00

25,001

- 35,0

00

35,00

1 - 40

,000

40,001

- 45,0

00

45,001

- 50,0

00

50,001

- 55,0

00

55,001

- 60,0

00

60,001

- 65,0

00

65,001

- 70,0

00

72,501

- 100,

000

Container Weight (pounds)

Per

cen

tag

e o

f In

ven

tory

Measured Vessel Distribution Assumed Yard Distribution

Figure 3-7 Measured vs. Assumed Container Distribution

Using the assumed container distribution discussed above, container handling equipment wheel loads, tire contact pressure, and tire contact radius (Typical pavement design generally assumes the tire loads is uniformly distributed over a circular area.) for each load increment can be tabulated. A typical table for straddle carrier is shown in Table 3-3. Empty container handler wheel loads, with and without an empty refrigerated container are shown in Table 3-4.

Container Weight Range (pounds)


Container Weight Distribution

0 – 10,000 10,000 (empty box) 25% 10,001 – 25,000 25,000 17% 25,001 – 35,000 35,000 12% 35,001 – 40,000 40,000 7% 40,001 – 45,000 45,000 8% 45,001 – 50,000 50,000 8% 50,001 – 55,000 55,000 8% 55,001 – 60,000 60,000 7% 60,001 – 65,000 65,000 6% 65,001 – 70,000 70,000 1%

72,501 – 100,000 100,000 1%



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Table 3-3. Kalmar CSC-350 Straddle Carrier Wheel Loads


Single Wheel Load (pounds)

Tire Contact Radius (inches)

Tire Contact Pressure (psi)

0 17,088 6.12 145 10,000 18,338 6.34 145 25,000 20,213 6.66 145 35,000 21,463 6.86 145 40,000 22,088 6.96 145 45,000 22,713 7.06 145 50,000 23,338 7.16 145 55,000 23,963 7.25 145 60,000 24,588 7.35 145 65,000 25,213 7.44 145 70,000 25,838 7.53 145 100,000 29,588 8.06 145

Table 3-4. Taylor TEC-155H Wheel Loads With or Without An Empty Container


Front Axle Dual Wheel Load (pounds)

Front Axle Single Tire Contact Radius (inches)

Front Tire Contact Pressure (psi)

Rear Axle Single Wheel Load (pounds)

Rear Axle Single Tire Contact Radius (inches)

Rear Tire Contact Pressure (psi)

0 22,000 5.40 120 11,900 6.15 100 11,000 31,167 6.43 120 8,233 5.12 100

3.4 Static Loads

In addition to dynamic loading from container handling equipment, port pavements are typically subjected to static loading from corner castings on containers and either dolly wheels or sand shoes on chassis. Corner castings measure 7-inches by 6 3/8-inches and project approximately ½ -inch below the container base. While containers may be stacked in a block arrangement up to four high, it is unlikely that all containers in the stack will be fully loaded. Two high container stacks exert an average load of approximately 120,950 pounds and a contact stress of 677 pounds per square inch. Chassis dolly wheels are typically 4-inches wide by 9-inches diameter. The contact area of each wheel is approximately ½-inch by 4-inches and generates a stress of 5,600 psi. Sand shoes are typically 6-inches by 9-inches and exert a contact stress of 280 psi.

3.5 Typical Load Repetition Analysis for Container Terminals and Intermodal Facilities

Different areas in container terminals may have different equipment and subject to different load repetitions. This section presents formulas of typical load repetition calculation for different areas in a container terminal. Areas of the yard that can be converted to other use, such as the conversion of wheeled parking to side-pick empty storage or top-pick storage to RTG storage, need to be designed for more severe loading



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condition. In order to achieve the maximum flexibility, some terminals use a uniform design for the majority of the pavement. Typically, there are two approaches to compute load repetitions of vehicles. One approach is to convert various loads and repetitions to an equivalent number of standard or equivalent loads. This is called ESAL (Equivalent Single Axle Loads) approach. The most common equivalent loads used in the U.S. is the 80 kN (18,000 lbs). Another more complex but more accurate approach characterizes loads directly by number of axles, configuration and weight. No conversion to ESAL is involved. In the following sections, both approaches are discussed. 3.5.1 Entrance Gate

Obtain the estimated throughput capacity per year for the terminal in Twenty Equivalent Units (TEUs) and a conversion factor from lifts to TEUs from terminal planners. Also obtain the assumed percentage (%) of the total throughput going through the gate (DT). If there is no on-dock rail intermodal facility the 100% of the throughput would go through the gate. Use the following equation to compute Equivalent Single Axle Loads (ESAL). Given:

C4 = TEU/Lift (typical number of TEU per lift between 1.7 to 1.85)

C5 = Transactions/Lift (typical number of truck transaction per lift between 1.5 to 2)

DD =50 % (directional split, 50% in and 50% out)

DL = 90% (% of traffic in the preferred lane)

DT = % (% of lifts moved by truck – 100% for no on-dock intermodal facility)

TF = 3 ESAL/Trans (estimated number of ESAL per transaction)

YC = total annual terminal capacity in TEUs

We have:

Design Lane ESAL’s = YC / C4 • C5 • DT • DD • DL • TF (3-1)

3.5.2 Wheeled Storage Area

Given:

PS = estimated number of wheeled storage slots

C5 = 2 Transactions/Slot (typical number of truck transaction per slot)

TF = 3 ESAL/Trans (estimated number of ESAL per transaction)

SU = estimated slot utilization – between 70 to 90%

DW = assumed average chassis/container dwell time



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We have:

Design ESAL’s = PS • SU • 365 / DW • C5 • TF (3-2)

3.5.3 Side/Top Pick and Truck Operations

It is assumed the containers will be delivered using truck and stacked using side or top-picks. Assuming that the storage area has the configuration as shown in the Figure 3-8, the calculations are as follows: In the Side/Top Pick yard, the heaviest traffic will be directly in front of the first row. At this location there are two types of traffic - Side/Top Loader and Truck traffic. The Side/Top Pick traffic is limited to the number of boxes in the first row, while the truck traffic is defined by the size of the whole stack, because the trucks follow each other along the length. For Side/Top Picks, the storage area can be accessible from only one side or two sides. If Side/Top Picks and trucks can access both side, the repetitions will be decreased to a half. In the calculation, the variable, "Number of accessible sides (C7)", is added for this purpose.

Given:


DW = assumed average container dwell time in days

C4 = TEU’s per lift (typical number of TEU per lift between 1.7 to 1.85)

C5 = trips per box (2 for Side/Top Pick area)

C6 = moves per trip

C7 = number of accessible sides (1 or 2)

L = length of the stack in TEU’s

W = width of the stack in TEU’s

H = height of the stack in TEU’s



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Figure 3-8 Dimensions of a yard block

We have:

Truck Load Repetitions = C5 • C6 • (365 / DW) • SU • L • H • W / C4 / C7 (3-3)

Side/Top Pick Load Repetitions = C5 • C6 • (365 / DW) • SU • H • W / C7 (3-4)

3.5.4 RTG and Truck Operation

We use the following method to compute RTG repetitions. For truck operation in the RTG area, same formula as in side or top pick area is used. Two scenarios needs to be considered: RTG Gantrying and RTG Lifting. • Scenario 1: RTG Gantrying Case I: RTG retrieving boxes In order to compute RTG repetitions, we need to count how many times RTG pass a point along a run way in a block. If a uniform distributed storage block (i.e., boxes in a block have equal dwell times averagely) is assumed, it is easy to see that the worst point at which the maximum repetition occurs is at the middle point along the run way. The following argument is used to compute the RTG repetitions at the middle point for the case that RTG takes boxes out of a block, as shown in Figure 3-9.

L H

W



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Figure 3-9 illustration of RTG repetitions

When taking a box out of a block, there is a chance that the RTG will cross the middle point. This will happen only when the RTG and the box are at the different side of the block. The probability of this event is: PG = Prob( RTG cross the middle point) = Prob(RTG at the left and box at the right) + Prob(RTG at the right and box at the left) = ½ · ½ +½ · ½ = 0.5 (under the assumption of uniform distribution) This is the probability that one operation of RTG will cross the middle point. The number of times the RTG cross the middle point is obtained by multiplying the probability with the number of operations per year. During peak/semi peak times when there is more than one truck waiting for a box, the Operator may get the closest box first, creating an efficiency factor (C8). This factor will always be less than one, but can be adjusted according to port productivity. The busier they are, the more trucks are waiting, which means the potential for efficiency raises, causing the factor to go down. Thus, the load repetition for RTG gantrying when receiving boxes is given by: Efficiency factor × Prob( RTG cross the middle point) × (Number of operations/year) = C8 · PG · (365/DW) · SU · H · W · L / C4/C9

Case II: RTG receiving boxes When putting a box into the storage area, there will be less gantry reps than taking out a box, because the RTG Operator can put the box in the first available space. Thus, the formula for the case of retrieving boxes to compute load repetitions may still be used since that is the worse case. Combining Case I and Case II, we obtain the following formulas.

Truck L/2 L/2

The middle point along the run way, where the maximum repetition occurs.



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Given:


DW = assumed average container dwell time in days

C4 = TEU’s per lift (typical number of TEU per lift between 1.7 to 1.85)

C5 = trips per box (2 for RTG area)

C7 = number of sides (1 for a RTG setup)

C8 = efficiency factor (1: inefficient, 0.5: efficient, .25: very efficient)

C9 = number of RTG cranes working stack

L = length of the stack in TEU’s

W = width of the stack in TEU’s

H = height of the stack in TEU’s

PG = Probability that an RTG crosses the worst point along the run way (1/2 for a uniform

distributed storage block)

We have:

Truck Load Repetitions = C5 • C6 • (365 / DW) • SU • L • H • W / C4 (3-5)

RTG Retrieval Load Repetitions (retrieving boxes) = C8 · PG · (365/DW) · SU · H · W · L / C4/C9 (3-6)

RTG Storage Load Repetitions (receiving boxes) = same as (3-6) (3-7)

• Scenario 2: RTG Lifting Calculation methods are as follows: The RTG repetitions when lifting can be computed by counting the boxes will go into and out of a bay. For each box, there will be one lift in and one lift out (C5 = 2). Thus, we have: RTG Lifting Repetitions = C5 · C6 · (365 / DW) · SU · H · W (3-8)



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3.6 Equipment Weight Distribution and Wheel Loads

Weight distribution and wheel load calculations are stated as seen in the British Ports Association’s 1982 heavy duty pavement manual (refer as British Manual from here on). This section summarize the formulas used to calculate wheel loads for RTG, side or top picks, and yard trucks. 3.6.1 RTG

For RTG, when the container is at the right-most (or left-most) position, the weight distribution (as shown

in Figure 3-10) gives the maximum wheel loads.

A1 = 1 – (xc/ x2) (3-9)

A2 = xc/ x2 (3-10)

W1 = fD • ( ( (Wc•A1) / M ) + U1 ) (3-11)

W2 = fD • ( ( (Wc•A2) / M ) + U2 ) (3-12)

Where:

W1 = wheel load of engineless side

W2 = wheel load of engine and container side

Wc = weight of container

x2 = distance from side 1 to side 2 (wheel to wheel)

xc = distance from side 1 to the center of the lifted container when it is fully trolleyed to side

2 (engine side)

U1 = unladen weight of gantry crane on each wheel of side 1

U2 = unladen weight of gantry crane on each wheel of side 2

A1, A2 = weight distribution ratios

M = number of wheels on each side

fD = dynamic factor (See British Manual for values, typically 1.0, 1.1, and 1.2.)



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Figure 3-10 Weight distribution – RTG

3.6.2 Side or Top Pick

The weight distribution for the side or top pick is as shown in Figure 3-11. We have:

A1 = -x2 / ( x1 – x2) (3-13)

A2 = -x1 / ( x2 - x1) (3-14)

B1 = ( xT - x2 ) / ( x1 – x2 ) (3-15)

B2 = ( xT -x1 ) / ( x2 - x1) (3-16)

W1 = fD • ( (Wc•A1) + (WT•B1) ) / M (3-17)

W2 = fD • ( (Wc•A2) + (WT•B2) ) / M (3-18)

W1 W2

x2

xc

Wc



3-16 JN: 5552-06

Where:

W1 = front wheel load

W2 = rear wheel load


WT = weight of vehicle

x1 = distance from container center to front wheels

x2 = distance from container center to rear wheels

xT = distance from container center to lift’s center of mass

A1, A2, B1, B2 = weight distribution ratios

M = number of wheels on the respective axle (usually 2 for rear, and 4 for front)

fD = dynamic factor

Figure 3-11 Weight distribution – Top Pick

Wc

W1 WT

W2

x2

xT

x1



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3.6.3 Yard Trucks

The weight distribution is as shown in Figure 3-12. We have:

A = xc / x3 (3-19)

B = xB / x2 (3-20)

W1 = ( ( WC• (1 - A) •(1 – B) / M1 ) + U1 ) • fD (3-21)

W2 = ( ( WC• (1 - A) • B / M2 ) + U2 ) • fD (3-22)

W2 = ( ( WC• A / M3 ) + U3 ) • fD (3-23)

Where:

W1 = front wheel load

W2 = rear wheel load

W3 = trailer wheel load


U1 = unladen load on front axle wheels

U2 = unladen load on rear axle wheels

U3 = unladen load on trailer wheels

x2 = distance between front and rear wheels

x3 = distance between fifth wheel and trailer wheel

xB = distance between front wheels and fifth wheel

xC = distance between fifth wheel and container center of mass

A, B = weight distribution factors

M1 = number of wheels on front axle

M2 = number of wheels on rear axle

M3 = number of wheels on trailer

fD = dynamic factor



3-18 JN: 5552-06

Figure 3-12 Weight distribution – Yard Truck

3.7 Pavement Damage

Different magnitudes of wheel loads will cause different degrees of damages to the pavement. Typical pavement design will use a single load and load repetition as the design criteria. Therefore, different wheel loads and repetitions due to different container weights should be combined into a single wheel load and repetition. Such a conversion is based on the pavement damage. The damage calculation is modified from the British Ports Association’s 1982 heavy duty pavement manual to accept imperial U.S. unit values (pounds and pounds per square inch). Damages account for how both contact stress (tire pressure) and wheel loads combine to degrade the pavement, and are quantified using PAWL’s (Port Area Wheel Load). The following Equations are used for all yard equipment.

3.7.1 Damage

D = (W / 26455) 3.75 × (P / 116 )1.25 (3-24)

Where:

D = damage (PAWL)

W = wheel load on a single tire (lbs.)

P = tire pressure (psi)

WC

x3 xB

x2

W3 W2 W1

xC



3-19 JN: 5552-06

Note that the relationship between damage and wheel load is exponentia l, and increasing wheel loads will causing much more damages than increasing pressures. The above formula only calculates damage caused by a single wheel. Damage caused by equipment should be combined using the method presented in the section 3.75.

3.7.2 Proportional Damaging Effect

The damage value D along can be deceiving since an 88,000 pound container creates the greatest damage, but only makes up less than one percent of the containers transported. Because of this a proportional damaging effect is often calculated using the container distribution measured for the container terminal, as discussed in the section 3.3.

DP = D • f (3-25)

Where:

DP = proportional damaging effect (PAWL)

D = damage (PAWL)

f = container frequency/distribution (%)

3.7.3 Average Damage

Average damage is the mean of the damages (DP).

DA = average damage = mean (DP) (3-26)

3.7.4 Critical Damage

The critical damaging effect is the damage value (D) of the container (critical load) with the largest proportional damage value (DP).

DC = critical damage = max (DP) (3-27)

Typically, the wheel load causing the critical damage will be used as the design wheel load.



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3.7.5 Total Damage of a Plant and Wheel Proximity Factors

Damages (in PAWLs) calculated for each wheel of a plant (i.e., a piece of equipment) should be added together along the line of the plant’s moving direction. If only one wheel of the equipment is considered, the strain under the wheel is maximized directly under the center of the wheel and decreased along with the increase of the radius. If two wheels of the equipment are close enough to each other, the strain under each wheel will increase a certain amount. The factors determine the amount of increase is called proximity factors, which can be found in the British Ports Association’s 1982 heavy duty pavement manual. The wheel configuration of a yard truck and the associated proximity factors are illustrated by the Figure 3-13.

Figure 3-13 Wheel configuration of a yard truck

Figure 3-13 shows the wheel configuration of a yard truck. On each side of truck, there are four tractor rear wheels and four trailer rear wheels. If the interaction between two wheels in the X direction is considered, the wheel proximity factor is 1.42. If the interaction between two wheels in the Y direction is considered, the wheel proximity factor is 1.95. Note that these two factors cannot be added up into one factor since their actions are in different directions. Instead, the total PAWLs should be calculated using the two factors respectively and the maximum PAWLs is taken as the final total PAWLs. Thus,

Dx = 25.175.3

375.3

275.3

1

1162645542.1

22645542.1

226455

×

×+

×

×+

PWWW

(3-28)

DY = 25.175.3

375.3

275.3

1

1162645595.1

22645595.1

226455

×

×+

×

×+

PWWW

(3-29)

Where: Dx = total damage combined along the X direction (PAWLs); DY = total damage combined along the Y direction (PAWLs); W1, W2 and W3 = single wheel load (lbs) P = tire pressure (psi)

W1 4×W2

4×W2

4×W3

4×W3

fp=1.42

fp=1.95 fp=1.95

fp=1.42 X

Y

Wheels

W1



3-21 JN: 5552-06

The final total damage for a plant is the maximum of the above two, which is the DY in this case. 3.8 Equivalent Load Repetitions

The equivalent load repetition is the equivalent number of movements (repetitions) of the critical load causing the critical damage. Various equipments’ equivalent repetitions are combined to give the design life of a given area. The calculated repetition is the number of movements in one year. For a design life of 20 years, the design life equivalent load repetitions can be obtained by multiplying the equivalent load repetition by 20.

3.8.1 RTG

Given:

Req = equivalent load repetitions

DAi = average damage for a given dynamic factor

DE = unladen damage

DC = critical damage

fDi% = percentage of movements that experiences the given dynamic factor (total percentages

must sum to equal 100%)

RAi = lifting repetitions of the average load for the given dynamic factor

RG = gantry load repetitions

The equivalent load repetition for RTG is,

Req = { (DE • RG) + (fD1% • RA1 • DA1) + (fD2% • RA2 • DA2) + …} / DC (3-30)

3.8.2 Yard Trucks

Given:


DA = average damage



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DE = unladen damage


RA = lifting repetitions of the average load

RE = unladen load repetitions

The equivalent load repetit ion for yard trucks is,

Req = { (DE • RE) + (RA • DA) } / DC (3-31)

3.8.3 Side and Top Picks

Given:


DAi = average damage for a given dynamic factor

DE = unladen damage


fDi% = percentage of movements that experiences the given dynamic factor (total percentages

must sum to equal 100%)

RAi = lifting repetitions of the average load for the given dynamic factor

RE = unladen repetitions

The equivalent load repletion for side or top picks is,

Req = { (DE • RE) + (fD1% • RA1 • DA1) + (fD2% • RA2 • DA2) + …} / DC (3-32)

3.9 A Comprehensive Wheel Load Calculation Example

This section presents a comprehensive example calculating critical load and load repetitions for Top Pick and RTG areas, using the background described in the previous sections. The usage of the formulas is illustrated in the following tables and charts.



3-23 JN: 5552-06

3.9.1 Key Notations

The following notations are used in the example: SU estimated slot utilization – between 70 to 90% DW assumed average container dwell time in Days C4 TEU’s per lift (typical number of TEU per lift between 1.7 to 1.85) C5 trips per box (1 / No. of empty spaces per address) C6 moves per trip C7 number of sides C8 efficiency factor (1: inefficient, 0.5: efficient, .25: very efficient) C9 number of RTG cranes L length of the stack in TEU’s W width of the stack in TEU’s H height of the stack in TEU’s R repetitions (the number of times passing in front of each address or the stack length) PG Probability that a gantry will cross a point

3.9.2 RTG Operation – RTG Repetitions

The calculation is bases on the formulas presented in the section 3.5.4. 3.9.2.1 RTG Repetitions When Gantrying

Given: L = 45 TEU W = 6 TEU H = 5 TEU SU = 75% DW = 5 Days C4 = 1.75 C5 = 1/3 C6 = 1 C8 = 0.5 C9 = 2 cranes PG = 0.5 Using the formula (3-6) and (3-7), we have, Load repetitions (Storage) = C8 · PG · (365/DW) · SU · H · W · L / C4/C9 = .5 · .5 · (365 / 5) · .75 · 5 · 6 · 45 / 1.75 / 2 = 5279 REP/YEAR Load repetitions (Retrieval) = C8 · PG · (365/DW) · SU · H · W · L / C4/C9 = .5 · .5 · (365 / 5) · .75 · 5 · 6 · 45 / 1.75 / 2 = 5279 REP/YEAR Total repetitions when gantrying = 5279 + 5279 = 10558 REP/YEAR Note that all gantry moves are unloaded.



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3.9.2.2 RTG Repetitions When Lifting

Given: W = 6 TEU H = 5 TEU C4 = 1.75 C5 = 2 C6 = 1 SU% = 75% DW = 5 Days Using the formula (3-8), we have, RTG repetitions when lifting = C5 · C6 · (365 / DW) · SU · H · W = 2 · 1 · (365 / 5) · .75 · 5 · 6 = 3285 REP/YEAR Note that all the above repetitions are loaded. 3.9.3 RTG Operation – Truck Repetitions

Given: L = 45 TEU W = 6 TEU H = 5 TEU C4 = 1.75 C5 = 2 C6 = 1 SU% = 75% DW = 5 Days Using the formula (3-5), we have, Truck Repetitions = C5 • C6 • (365 / DW) • SU • L • H • W / C4 = 2*1*1*365/5*0.75*45*5*6/1.75 = 84,471 REP/YEAR Note that half of the above truck repetitions will be loaded and half will be unloaded. Thus, Unloaded truck repetitions in RTG area = 84471/2 = 42,386 REP/YEAR Loaded truck repetitions in RTG area = 84471/2 = 42,386 REP/YEAR 3.9.4 Side/Top Pick Repetitions

The calculation in this section is based on the formulas presented in the section 3.5.3.



3-25 JN: 5552-06

Given: L = 24 TEU W = 6 TEU H = 5 TEU DW = 5 Days SU = 75% C4 = 1.75 C5 = 2 C6 = 2 (picks) = 1 (trucks) C7 = 2 sides Using the formula (3-4), we have, Side/Top Loader Storage Repetitions = C5 • C6 • (365 / DW) • SU • H • W / C7 = 2*2*(365/5)*0.75*5*6/2 = 3285 REP/YEAR Using the formula (3-3), we have, Truck Stack Delivery Repetitions = C5 • C6 • (365 / DW) • SU • L • H • W / C4 / C7 = 2*1*(365/5)*0.75*5*6*24/1.75/2 = 22526 REP/YEAR Note that half of the above repetitions will be loaded and half will be unloaded. Thus, we have, Unloaded Side/Top Loader Storage Repetitions = 3285/2 = 1643 REP/YEAR Loaded Side/Top Loader Storage Repetitions = 3285/2 = 1643 REP/YEAR Unloaded Truck Stack Delivery Repetitions = 22526/2 = 11263 REP/YEAR Loaded Truck Stack Delivery Repetitions = 22526/2 = 11263 REP/YEAR 3.9.5 Damage – Top Pick

The damage calculation in this section and the following sections is based on the formulas presented in the section 3.6 and 3.7. Due to the complexity of the calculation, a spreadsheet model is developed to compute the critical load and the equivalent critical load repetition. The spreadsheet model is presented here as an example of pavement damage calculation. Inputs are highlighted with the yellow color and final outputs are highlighted with the red color. Step-by-step calculation is not shown in the table due to the limited space.



3-26 JN: 5552-06

Top Pick Operation: fD = 1.0 fD = 1.1 fD = 1.2

x1 9.19 x2 27.94 xT 18.78 A1 1.49 A2 -0.49 B1 0.49 B2 0.51 Equipment Weight, WT 154000.00 Number of Tiers, M 4 Tire Pressure, P 144.00 Unladen Damage, DE 10.73 15.34 21.26 Unladen Wheel Load 39,398.33 43,338.17 47,278.00 Average Damage, DA 68.05 97.28 134.82 Average Wheel Load 75,425.41 82,967.96 90510.497

Critical Damage, DC 98.49

140.81 195.13

Critical Wheel Load 83,493.67

91,843.03 100,192 Maximum Damage 841.13 1202.50 1666.44 % of fD = 1.0 0.50 % of fD = 1.1 0.40 % of fD = 1.2 0.10 Top Pick Load Repetition Average Load, RA 1643(1)

Unladen, RE 1643(1)



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Truck Repetition Top Pick Area

Number of Front Wheels on Tractor, M1 2 Number of Rear Wheels on Tractor, M2 8

Number of Wheels on Trailer, M3 8 Load on Front Wheels - Unladen , U1 6000 Load on Rear Wheels - Unladen, U2 4000 Load on Trailer Wheels - Unladen, U3 4000 xC 21.0 xB 18.0 x2 18.0 x3 42.0 A 0.5 B 1.0 Tire Pressure, P 144.0 Unladen Damage, DE 0.06 Unladen Wheel Load 4,000.00 Average Damage, DA 0.48 Average Wheel Load 7138.73978 Critical Damage, DC 0.68 Critical Wheel Load 7,850.00 Maximum Damage 5.80 % of fD = 1.0 100% % of fD = 1.1 % of fD = 1.2 Truck Repetitions Top Pick Area Average Load, RA 11263(1) Unladen, RE 11263(1)

Design Life (Years) 1

Design life equivalent load repetition for critical loading 1,682 Design Load (lb) 83,494

Note:

(1) The load repetitions are calculated in the section 3.9.4.

(2) The calculation of equivalent load repetition considers both top picks and trucks.



3-28 JN: 5552-06

The following table presents the calculation of proportional damaging effects for top-picks. fD = 1.00

container frequency front corner rear wheel Front rear Total Proportional weight (lbs) % loads loads PAWL PAWL PAWL Damage

WC f W1 x 2(1) W2 D DP 0 0.00 37602 39398 4.898 5.835 10.733 0.000

2200 0.00 39241 38859 5.748 5.541 11.289 0.000 4400 0.00 40880 38320 6.701 5.258 11.959 0.000 6600 0.00 42519 37781 7.765 4.986 12.751 0.000 8800 4.00 44158 37242 8.948 4.725 13.673 54.692

11000 4.00 45797 36703 10.259 4.473 14.732 58.929 13200 4.00 47436 36164 11.705 4.232 15.937 63.747 15400 0.00 49075 35625 13.295 4.000 17.295 0.000 17600 0.00 50714 35086 15.038 3.778 18.816 0.000 19800 0.08 52353 34547 16.943 3.565 20.508 1.641 22000 0.26 53992 34008 19.020 3.361 22.380 5.819 24200 0.65 55631 33469 21.277 3.165 24.442 15.887 26400 1.07 57270 32930 23.724 2.978 26.703 28.572 28600 1.39 58909 32391 26.372 2.800 29.172 40.549 30800 1.66 60548 31852 29.231 2.629 31.860 52.887 33000 2.49 62187 31313 32.310 2.466 34.776 86.593 35200 2.58 63826 30774 35.621 2.310 37.932 97.864 37400 2.97 65465 30235 39.174 2.162 41.337 122.770 39600 3.83 67104 29696 42.981 2.021 45.002 172.358 41800 4.83 68743 29157 47.052 1.887 48.939 236.374 44000 4.38 70382 28618 51.398 1.760 53.158 232.832 46200 4.94 72021 28079 56.033 1.638 57.671 284.895 48400 4.36 73660 27540 60.966 1.524 62.490 272.455 50600 4.75 75299 27001 66.211 1.415 67.626 321.221 52800 4.93 76938 26462 71.779 1.312 73.091 360.337 55000 5.04 78577 25923 77.683 1.214 78.898 397.644 57200 5.61 80216 25384 83.936 1.122 85.058 477.177 59400 7.02 81855 24845 90.550 1.035 91.586 642.932

61600(2) 8.54 83494 24306 97.539 0.954 98.492 841.126 63800 7.72 85133 23767 104.915 0.877 105.792 816.712

66000 4.33 86772 23228 112.692 0.805 113.497 491.441 68200 1.97 88411 22689 120.884 0.737 121.621 239.593 70400 0.70 90050 22150 129.504 0.673 130.178 91.124 72600 0.47 91689 21611 138.567 0.614 139.181 65.415 74800 0.51 93328 21072 148.087 0.558 148.645 75.809 77000 0.37 94967 20533 158.077 0.507 158.584 58.676 79200 0.30 96606 19994 168.553 0.459 169.011 50.703 81400 0.20 98245 19455 179.529 0.414 179.943 35.989 83600 0.02 99884 18916 191.021 0.372 191.393 3.828 85800 0.02 101523 18377 203.043 0.334 203.377 4.068 88000 0.01 103162 17838 215.611 0.299 215.910 2.159



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Note: (1) For front corner loads W1 is doubled, this is done because the front two wheels are so close that

they behave, to an extent, like one large wheel. This must be accounted for in order to calculate the damage. Realistically the multiplying factor will most often be a value between 1.95-1.98 depending on the exact wheel spacing.

(2) The highlighted row is the row with critical load. The following table presents calculation of proportional damaging effects for trucks. fD= 1.00

container frequency front wheel rear wheel trailer wheel X Y total

Damage

weight (lbs) %

loads - Tractor

loads – tractors load PAWL PAWL PAWL

Wc f W2 W3 W1 Dx DY D(1) DP

0 0.00 6,000.00 4,000.00 4000.00 0.02 0.06 0.06 0.00 2,200 0.00 6,000.00 4,137.50 4137.50 0.02 0.07 0.07 0.00 4,400 0.00 6,000.00 4,275.00 4275.00 0.03 0.07 0.07 0.00 6,600 0.00 6,000.00 4,412.50 4412.50 0.03 0.08 0.08 0.00 8,800 4.00 6,000.00 4,550.00 4550.00 0.03 0.09 0.09 0.37

11,000 4.00 6,000.00 4,687.50 4687.50 0.03 0.10 0.10 0.41 13,200 4.00 6,000.00 4,825.00 4825.00 0.04 0.11 0.11 0.45 15,400 0.00 6,000.00 4,962.50 4962.50 0.04 0.13 0.13 0.00 17,600 0.00 6,000.00 5,100.00 5100.00 0.05 0.14 0.14 0.00 19,800 0.08 6,000.00 5,237.50 5237.50 0.05 0.15 0.15 0.01 22,000 0.26 6,000.00 5,375.00 5375.00 0.05 0.17 0.17 0.04

24,200 0.65 6,000.00 5,512.50 5512.50 0.06 0.18 0.18 0.12 26,400 1.07 6,000.00 5,650.00 5650.00 0.06 0.20 0.20 0.22 28,600 1.39 6,000.00 5,787.50 5787.50 0.07 0.22 0.22 0.31 30,800 1.66 6,000.00 5,925.00 5925.00 0.08 0.24 0.24 0.40

33,000 2.49 6,000.00 6,062.50 6062.50 0.08 0.26 0.26 0.65

35,200 2.58 6,000.00 6,200.00 6200.00 0.09 0.28 0.28 0.73 37,400 2.97 6,000.00 6,337.50 6337.50 0.10 0.31 0.31 0.91 39,600 3.83 6,000.00 6,475.00 6475.00 0.10 0.33 0.33 1.27 41,800 4.83 6,000.00 6,612.50 6612.50 0.11 0.36 0.36 1.73

44,000 4.38 6,000.00 6,750.00 6750.00 0.12 0.39 0.39 1.70 46,200 4.94 6,000.00 6,887.50 6887.50 0.13 0.42 0.42 2.06 48,400 4.36 6,000.00 7,025.00 7025.00 0.14 0.45 0.45 1.96 50,600 4.75 6,000.00 7,162.50 7162.50 0.15 0.48 0.48 2.29 52,800 4.93 6,000.00 7,300.00 7300.00 0.16 0.52 0.52 2.55 55,000 5.04 6,000.00 7,437.50 7437.50 0.17 0.56 0.56 2.80 57,200 5.61 6,000.00 7,575.00 7575.00 0.18 0.59 0.59 3.33 59,400 7.02 6,000.00 7,712.50 7712.50 0.20 0.64 0.64 4.46 61,600 8.54 6,000.00 7,850.00 7850.00 0.21 0.68 0.68 5.80 63,800 7.72 6,000.00 7,987.50 7987.50 0.22 0.72 0.72 5.59



3-30 JN: 5552-06

66,000 4.33 6,000.00 8,125.00 8125.00 0.24 0.77 0.77 3.34 68,200 1.97 6,000.00 8,262.50 8262.50 0.25 0.82 0.82 1.62 70,400 0.70 6,000.00 8,400.00 8400.00 0.27 0.87 0.87 0.61 72,600 0.47 6,000.00 8,537.50 8537.50 0.29 0.93 0.93 0.44 74,800 0.51 6,000.00 8,675.00 8675.00 0.30 0.98 0.98 0.50 77,000 0.37 6,000.00 8,812.50 8812.50 0.32 1.04 1.04 0.39 79,200 0.30 6,000.00 8,950.00 8950.00 0.34 1.11 1.11 0.33 81,400 0.20 6,000.00 9,087.50 9087.50 0.36 1.17 1.17 0.23 83,600 0.02 6,000.00 9,225.00 9225.00 0.38 1.24 1.24 0.02 85,800 0.02 6,000.00 9,362.50 9362.50 0.40 1.31 1.31 0.03 88,000 0.01 6,000.00 9,500.00 9500.00 0.42 1.38 1.38 0.01

Note:

(1) The calculation of total PAWL considering proximity factors as seen in the British Ports Association heavy duty pavement manual, as described in the section 3.7.5. The total damage D is the maximum of the Dx and DY.

(2) The highlighted row is the row with critical load.



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3.9.6 Damage –RTG

RTG Operation: (77') fD=1 fD=1.1 fD=1.2

PACECO 126t 5+1 Lift

xC 67.17 x2 77

Unladen Weight of RTG on each wheel of side 1 (lb), U1 42327 Unladen Weight of RTG on each wheel of side 2 (lb), U2 27119 Number of Wheels on Each Side, M 4 A1 0.13 A2 0.87 Tire Pressure, P 139.4 Unladen Damage, DE 191.78 274.17 379.95 Unladen Wheel Load 42,327.10 46,559.81 50,792.52 Average Damage, DA 426.67 609.98 845.32 Average Wheel Load 52,387.62 57,626.38 62,865.14 Critical Damage, DC 539.14 770.77 1068.14 Critical Wheel Load 55,760.43 61,336.48 62,865.14 Maximum Damage 4604.24 6582.34 9121.94 % of fD = 1.0 0.75 % of fD = 1.1 0.25 % of fD = 1.2 0.0 RTG Load Repetition Average Load, RA 3285(1) Gantry (Unladen), RG 10558(1) Truck Repetitions RTG Area Average Load, RA 42386(2) Unladen, RE 42386(2) Design Life (Years) 1

Design life equivalent load repetition for critical loading 6,677 Design Load (lb) 55,760

Note:

(1) RTG repetitions are calculated in the section 3.9.2. (2) Truck repetitions are calculated in the section 3.9.3.



3-32 JN: 5552-06

RTG Wheel Load and Damage Sample Calculations fD = 1

container wheel Proportional weight frequency load Damage Damage lbs % lbs PAWL PAWL WC f W D DP

0 0 42,327 191.78 0.00 2200 0 42,807 200.06 0.00 4400 0 43,287 208.59 0.00 6600 0 43,766 217.40 0.00 8800 4 44,246 226.47 905.88

11000 4 44,726 235.82 943.26 13200 4 45,206 245.44 981.77 15400 0 45,685 255.35 0.00 17600 0 46,165 265.56 0.00 19800 0.08 46,645 276.05 22.08 22000 0.26 47,125 286.85 74.58 24200 0.65 47,604 297.96 77.47

26400 1.07 48,084 309.38 201.09 28600 1.39 48,564 321.11 343.59 30800 1.66 49,044 333.17 463.11 33000 2.49 49,524 345.56 573.63 35200 2.58 50,003 358.28 892.11 37400 2.97 50,483 371.34 958.06 39600 3.83 50,963 384.75 1142.70 41800 4.83 51,443 398.51 1526.28 44000 4.38 51,922 412.62 1807.30 46200 4.94 52,402 427.10 2109.90 48400 4.36 52,882 441.95 1926.92 50600 4.75 53,362 457.18 2171.60 52800 4.93 53,841 472.78 2330.82

55000 5.04 54,321 488.78 2463.43 57200 5.61 54,801 505.16 2833.96 59400 7.02 55,281 521.95 3664.07 61600 8.54 55,760 539.14 4604.24 63800 7.72 56,240 556.74 4298.03 66000 4.33 56,720 574.76 2488.71 68200 1.97 57,200 593.20 1168.61 70400 0.7 57,679 612.08 428.45 72600 0.47 58,159 631.39 296.75 74800 0.51 58,639 651.14 332.08 77000 0.37 59,119 671.35 248.40 79200 0.3 59,599 692.01 207.60 81400 0.2 60,078 713.13 142.63 83600 0.02 60,558 734.72 14.69 85800 0.02 61,038 756.79 15.14 88000 0.01 61,518 779.33 7.79



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3.9.7 Design Summary

3.9.7.1 Top Pick

Design Load: 1,682 lbs Design Load Repetitions: 83,494 REP/YEAR

Pressure: 144 psi

1.9’

W1

Front Corner Load W1 x 1.98



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8.25’

3.9.7.2 RTG

Design Load: 6,677 lbs Design Load Repetitions: 55,760 REP/YEAR Pressure: 139 psi

W



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4. Site Investigation.................................................................................................................. 4-1 4.1 Methods of Ground Improvement ................................................................................ 4-1

4.1.1 Options ................................................................................................................................................................4-2 4.2 Global Ground Improvement ....................................................................................... 4-2

4.2.1 Surcharging and Wick Drains ......................................................................................................................4-2 4.2.2 Removal and Replacement............................................................................................................................4-3 4.2.3 Shallow Stabilization .......................................................................................................................................4-3 4.2.4 Dynamic Compaction......................................................................................................................................4-4

4.3 Transitions .................................................................................................................... 4-5 4.3.1 Vibro-Compacted Stone Columns...............................................................................................................4-5 4.3.2 Pressure Grouting ............................................................................................................................................4-5 4.3.3 Articulations ......................................................................................................................................................4-5

4.4 Localized Improvement................................................................................................ 4-6 4.4.1 Vibro-Compacted Concrete Columns ........................................................................................................4-6 4.4.2 Jet Grouting .......................................................................................................................................................4-6 4.4.3 Deep Soil Mixing ..............................................................................................................................................4-7 4.4.4 Geopier System.................................................................................................................................................4-7



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4. Site Investigation

The purpose of site investigation is to determine the location, characteristics, and extent of the subgrade materials that will be affected by the pavement construction and the operations on the pavement. The site investigation must obtain sufficient information to enable an economic pavement design and to enable construction operations to be undertaken in a safe and predictable manner. Skimping on the extent of the investigation may result in conservative design input or even undersign of the pavement section, and may lead to unpredicted conditions being encountered during construction that could affect the price of the construction contract. In the long term, an effect site investigation with a thorough scope tailored to address pavement requirements is likely to be more cost effective than interpreting values from a basic investigation aimed at the design of the structural elements of the development. The wheel loads from the heaviest container handling equipment operating on the pavement are likely to influence the soils within six to ten feet below the underside of the pavement, or formation level. These soils will be subject to repeated, short duration, moving loads. The strength and stiffness properties of the soils are therefore important. The imposed loads from the container stack are likely to affect the soils to a greater depth. The deeper soils will be subject to medium term, stationary loads. The consolidation properties of these soils are therefore important. The purpose of the site investigation is to determine the properties of the soils within these zones of influence. The investigation should include determining the depth to bedrock or to competent layers, the extent, depth and thickness of weak or soft layers and the depth to the water table or any perched water. As the types of testing change with depth below formation, it is important to have an understanding of the final elevations on the terminal. It may be the case that several feet of fill will be required over the area proposed for the terminal, and therefore some of the critical materials may not be present at the site. 4.1 Methods of Ground Improvement

Port and rail yard facilities are generally flat in grade to enable safe and efficient operation of the equipment. With the large depths of compressible soil, the variable fill regimes and buried obstructions, settlements takes place, often with large-scale surface distortion created by the differing loading conditions. On such flat surfaces this settlement can lead to ponding of surface water, which can penetrate into the pavement and subgrade. The ingress of water into the pavement and subgrade can accelerate pavement damage, and result in areas of high maintenance and potential loss of use. Increased grades can often hamper equipment operation and provide safety concerns. It can also lead to equipment and vehicle damage. Settlement problems are not merely confined to the surface furnishings. They can also cause problems to drainage runs, sub-surface utilities and communication ducts. The poor bearing capacities of the soils mandate deep foundations for buildings and other structures and fixtures. Frequently, differential settlement can lead to problems at light pole foundations, crane rails and buildings that are often supported on piles. These resistant islands or break-points across large areas of an unsupported dockside area provide more sources of differential settlement. The challenge is to utilize a construction process that will increase the bearing capacity of the soils so that deep foundations can be avoided. The shallow foundations resulting from the increased bearing capacity will then settle in sympathy with the adjacent areas. The Geopier system has the potential to do just this. As with other continuously heavily trafficked areas such as intermodal and automotive yards, this will



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reduce the loss of use of large areas of paving, reduce disruption to operations and prevent diminishing throughput. 4.1.1 Options

There are a number of different approaches that can be adopted to reduce the consequences of the problems experienced in port, facilities. These include undertaking global ground improvement to the soils, forming transition zones between areas and providing soil improvement that will be sympathetic to ground movement. When reviewing the potential options for these large external areas, several conditions have to be satisfied, as each has a technical and commercial consideration. 4.1.1.1 Option 1 – Global Ground Improvement

The first approach is to improve the ground globally so that settlements are minimized and predictable, and such that the bearing capacity is improved. There are a few different options that can be employed to achieve this. They include surcharging, removal and replacement, shallow stabilization and dynamic compaction. Frequently a mix of two systems is employed when a crust of imported or stabilized material is placed after settlement has occurred, to help increase the bearing capacity. This solution is often insufficient to support heavy point loads. 4.1.1.2 Option 2 – Transitions

The second approach is to provide localized improvement that eases the transition between soft ground and areas supported on deep foundations such as piles. This can be achieved by local use of the global systems described above as well as by using vibro-compacted stone columns, stabilization by pressure grouting or by including articulations that will accommodate the movement. It can be beneficial to select a pavement system around such locations that can quickly and easily be reapplied to compensate for extremes of settlement. 4.1.1.3 Option 3 – Localized Improvement

The final approach is to create a zone that will have increased bearing capacity, but that will settle in a controlled manner and at a similar rate to surrounding areas. This can be achieved by using vibro-compacted concrete columns, vibro-compacted stone columns, jet grouting or deep soil mixing. This type of solution can also be achieved by the use of Geopiers. 4.2 Global Ground Improvement

4.2.1 Surcharging and Wick Drains

Surcharging is one of the most common ground improvement techniques in the backland development of port areas. In this method, material is spread over the area to be treated to a predetermined height causing primary consolidation to occur. The height is designed so that the applied load exceeds any future loading resulting from fill material, construction work and stored cargo. The primary consolidation under the surcharge generally exceeds the long-term consolidation under the permanent loading conditions. As such, settlement potential can be greatly reduced. In addition the materials are densified so that they have greater stiffness and bearing capacity.



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Surcharging can be accomplished in a number of ways, subject to the constraints of time and cost. Providing twenty or more feet of fill over the whole area can be the most expedient option, but it requires the import and subsequent export of large quantities of material. If time permits, it is more economical to undertake a rolling surcharge program, whereby one section of the site is surcharged after another, as the material is moved around the site. However, this can take a matter of years rather than months. The time for primary consolidation to occur is a factor of many geotechnical parameters, but one of the most important is the length of the drainage path. By shortening the drainage path, the duration of loading can be reduced. One of the most common procedures for achieving this is to install vertical wick drains so that there is a permeable connection between the materials being consolidated and the surface, or to other free draining layers. Vertical drains can be installed to depths in excess of 100 feet. When the drainage path leads to the surface, it is necessary to install a drainage blanket under the surcharge if the surcharge material is not free draining in and of itself. The price of surcharge is often only dependent upon the cost of transport and machinery required to bring material to site and spread it. The system can be highly economical. However, the time necessary to generate the maximum available level of compaction can be prohibitive. Rarely is a three or four week window of opportunity available once the development clock starts ticking, let alone the year or often longer time period demanded for effective surcharging. The improvements in bearing capacity achieved by this system may be insufficient to support heavy foundation loads, and other improvement systems may need to be used locally. 4.2.2 Removal and Replacement

This system involves the excavation of large areas of material that will create problems in the final development. This is more commonly used at shallow depths, but can also be used locally for deeper pockets in the areas of proposed structures. Generally these materials are too weak, too elastic or too wet to be treated. Removing large volumes of material can create issues with disposal and can have financial and program implications if the work is extensive. For older ports and rail yards the presence of buried obstructions could make major excavation work difficult and more expensive. Problems can frequently be experienced when excavation reaches the water table or very soft underlying soils, where equipment can become bogged down. It is frequently necessary to include geotextiles and / geogrids in the replacement layers to avoid overly deep excavations, and to achieve the required long term stiffness in the crust. The stiffer the near surface or crusted soils can be made, the better the distribution of load to soft and highly compressive soils at depth. At best this solution is slow and expensive, and as a settlement preventative measure, might be only partially successful. There are rarely any significant gains in bearing capacity at the depths of foundations, unless the removal has been carried out to significant depths. In order to get the best out of this form of surface densification, this process needs to be combined with different techniques of ground improvement. 4.2.3 Shallow Stabilization

This process involves shallow stabilization or modification of the poor soils with lime, cement or other additives or modifiers. This is a process that involves in-place mixing of near surface soils with



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quantities of lime, cement or other modifier, transforming the existing near-surface soils into a hard and durable layer that is ideal for the construction of a port pavement. However, shallow soil stabilization is a thin layer form of treatment although it can be carried out in multiple thickness layers is rarely suitable for localized deep treatment. This form of stabilization is unlikely to offer much protection against settlement, particularly if settlement is an on-going consequence of load and time versus deep-seated soft alluvial estuarine soils. In order to get the best out of this form of surface densification, this process needs to be combined with different techniques of ground improvement. 4.2.4 Dynamic Compaction

The Dynamic Compaction (DC) process is used to create a stiffened soil raft of limited thickness over a large surface area. The raft of improved ground can safely and continuously provide settlement resistance, and the technique can cope with changes in ground conditions, buried obstructions and variations in groundwater levels. Typical treatment depths in clays and silts are up to 25 feet and in sands and gravels up to 30 feet. The construction process depends on the material to be compacted. It is a universally tried and tested system having been around for many years. The simplicity of site operation i.e. pounding the site surface with a large weight dropped from a great height belies the complexity of interaction within the soils matrix. Essentially, DC injects high levels of energy into the ground, which in turn responds by particle re-distribution and achieved stiffening. However the practical drawbacks inherent with the process very often preclude its use. Large cranes are required to lift and drop sizeable flat tamper weights of up to 20 tons, and vibration tends to limit the technique’s suitability for many port applications. The size of the treatment area can discount many technically responsive sites with 8,000 square feet normally being the absolute minimum area where cost efficiency of the DC process can be considered. The need to provide a thick granular working blanket together with the consequence of reducing the working level of the site further limits the attraction of the DC process particularly on existing sites. Modern techniques of using shaped tamper weights have generated true three-dimensional ground distortion with lower levels of vibration. Dropping shaped tamper weights at regular grid centers requires far less effort in energy input for a similar output of ground stiffness than can be expected from high energy drops using flat plates, and can provide increases in stiffness in much thinner depths of soil. Smaller rigs are purpose built and workable site areas can be reduced in size without compromising cost-efficiency. Dynamic Compaction, although quick and relatively cheap to carry out, can only look to improve ground to modest levels of bearing capacity. Attempts to produce big improvement percentages attract risks of much larger plant and equipment, (which may be difficult to source in some parts of the world), progressively greater levels of applied energy and resultant vibrations as well as major cost penalties.



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4.3 Transitions

4.3.1 Vibro-Compacted Stone Columns

The use of vibro-compacted stone columns is a well understood ground improvement technique. Its versatility and low operational costs have made this system a popular choice for many years. It can be used to treat clays and silts to a depth approaching 75 feet and in sands and gravels to a depth of around 100 feet. The construction method depends on the native soils. Stone columns are nearly always installed using a vibrator suspended from a crane or operating within purpose built leaders, which frequently have the advantage of providing a pull-down force. Penetration of the ground is usually a function of the weight and frequency of vibration of the lance. Stone is tipped in to the vertical hole produced on withdrawal of the vibro lance. Re-insertion of the lance into successive charges of stone causes the surrounding indigenous soils to be laterally displaced during penetration of the lance. More modern developments of ‘bottom feed’ equipment allow stone infill to be discharged at the toe of the each column thereby eliminating any risk of soil collapse, which can occur on withdrawal of the lance in soft or waterlogged conditions. The quality of the stone column whether formed with top feed or bottom feed process, is largely similar. When attempting to cap an area treated by stone columns a thick stone blanket is required. Otherwise in time pavements can become deformed as the heads of the stone columns punch through as the ground settles around them. The use of geogrid reinforcement can mitigate against this problem. While the provision and placement of a stone blanket may not adversely affect the overall efficiency offered by stone columns, it serves to illustrate the relatively low state of change produced within the near surface soils. When it comes to using stone columns for the support of large open areas, particularly those with high and/or variable loading conditions, there are limitations. While stone columns produce a level of improvement, unless they terminate in competent soils, their ability to create their own stiffened soil raft is limited as the confining pressure of the stone columns cannot be maximized in very soft ground. This is a consequence of the relatively low value of input energy used to form the stone column. 4.3.2 Pressure Grouting

In some soil types the upper layer of material can be improved by pressure grouting to depths of up to ten feet. Cementitious materials in slurry form are injected into the ground under pressure. This material fills the seams and voids in the soil and stiffens the materials forming a crust. As a settlement preventative measure, this system might be only partially successful. It may also be insufficiently deep to distribute the loads from foundations into the underlying soils. 4.3.3 Articulations

Localized areas found between structure and external service yard can be designed as a form of articulation or ‘rocker’ slab, which as the name suggests, allows for normal movements irrespective of on-going settlements. While rocker slabs may be a solution for particular applications, they can never provide an operationally friendly solution for large storage areas or service yards.



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Problems associated with on-going settlement are often not addressed. For example in an area of container stacking, where the surface is finished with crushed stone or sand, make-up for settlement deflection can be relatively cheap and expedient. However the overall disruption to container handling equipment can be dramatic and expensive. As more material is added to make up for on-going settlement, the time between maintenance intervals can often get shorter, rather than longer, as the surcharge effect of the additional material creates its own settlement. 4.4 Localized Improvement

4.4.1 Vibro-Compacted Concrete Columns

Another process, which can be loosely described as ground improvement, is the use of vibro-compacted concrete columns (VCC). These can be formed with a specially adapted vibro-lance or vibrated hollow mandrel. Either way, the construction sequence is similar in that penetration is achieved from ground level to a suitable stratum whereupon high slump concrete or grout is pumped through the lance as it is slowly retracted. The main difference between a VCC and a conventional pile is the function of the head. It is possible to produce an enlarged mushroom-shaped head of pre-determined size with its level terminating at the site platform. Concrete columns can be spaced accurately to pre-determined dimensions, before a transfer mattress of compacted granular material, usually complete with multiple layers of geogrid reinforcement, is placed over the column heads. The pavement or floor is placed on top of the mattress with no physical connection to the VCCs below. This allows the finish to be designed as ground bearing rather than the much more expensive alternative of being fully suspended. While attractive in principle, VCCs can have serious drawbacks. The installation mandrel usually has very limited ability to overcome buried obstructions but unlike stone columns the re-positioning of VCCs and the altering of the pre-designed grid spacing can have a serious effect on the workability of the transfer mattress. Also the installation of VCCs and placement of a transfer mattress, rarely less than 2 feet thick, can pose problems for working levels. It would seem counterproductive and extremely expensive to reduce the operational platform by the thickness of the transfer mattress before commencing the installation of VCCs. 4.4.2 Jet Grouting

Jet grouting is a construction process that can be used to stabilize the ground to depths of around 100 feet. It forms stiff columns or panels of soil-cement. It can be used to stabilize most soils, from soft clays and silts to sands and gravel, and is suitable for mass treatment, linear treatment and inclusions. Initially, a vertical borehole is drilled to the required depth. Very high-pressure (4,000 -7,000 psi) water/cement slurry mixtures are pumped into the soil through one or more small nozzles at the foot of the drill string. The jets completely break up the soil structure and mix the soil particles with the water/cement slurry to create a homogeneous mass that solidifies in time. The work typically progresses from the bottom of the borehole to the top. Excess material rises back up the borehole and is removed from site as it emerges. Controlling the rotation of the drill rods enables either columns or panels to be



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formed. Columns are formed when the drill rods are rotated during lifting. Panels are formed by lifting the drill rods without rotation. There are three traditional jet grouting systems: single, double or triple. The high velocity and pressure of the single jet system cuts and mixes the soil in-place. In double jet system, a shroud of compressed air is pumped to surround the slurry jet, which enhances the penetration of the jet into the soil, increasing the width of treatment. In the triple jet system, the cement slurry is pumped at a lower pressure at the bottom of the drill string while high pressure water, surrounded by a shroud of compressed air, cuts and removes the soil during the withdrawal of the drill rods. Selection of the most appropriate system is generally a function of the in situ soil, the application, and the physical characteristics required for that application. 4.4.3 Deep Soil Mixing

The Deep Soil Mixing (DSM) process results in improved bearing capacity, reduced permeability, and increased structural support. It uses a crane-mounted turntable or a self-contained drilling rig to rotate and advance single or multiple shafts of augers and mixing paddles into the soil. The mixing paddles are selected based on site requirements and will usually vary from three to six feet in diameter. Due to the spacing of the shafts and placement of the mixing paddles, there is continuous overlap with adjacent soil-cement columns. This technique is generally used for depths of up to 100 feet. The shafts are slowly rotated into the ground by the drilling rig. The auger flights loosen the soil and the paddles continue the mixing process. As the ground is penetrated, cement slurry is pumped through the center of each shaft and out of holes in the paddles so that it mixes with the loosened soil. As the shafts advance to a greater depth, the soil-cement mixture is remixed by additional mixing paddles spaced along each shaft. The slurry helps to fluidize the soil around the paddles and assists in the breaking up of the soil into smaller pieces. After final depth is reached, the shafts remain lowered to the bottom of the hole for several rotations while the settings are changed. At this point, the shafts are withdrawn to the surface. The mixing process is repeated while continuing to pump slurry to the paddles at a reduced rate to achieve complete mixing. The series of mixing paddles intermittently mix the soil in place. They are of limited length along the shaft so that they do not carry soil up to the ground surface. However, as the soil is being loosened and cement slurry is being introduced into the ground, excess material comes to the surface and needs to be disposed of. This is a similar combination of the cement slurry and soil particles to that remaining in the ground in the soil cement columns. 4.4.4 Geopier System

Geopier comprises in essence large size stone or aggregate columns. It is partly a displacement and partly a replacement process, making it unique amongst foundation systems. Geopier is not an untried technique, but has been in use for ground improvement under building foundations for many years in the United States. It is used as an intermediate solution between shallow and deep foundations where foundation loads are too great for some poorer soils. It has also been used to improve the load carrying capacity in some good quality soils. Buildings of up to sixteen stories and with foundation loads of 200 kips have used the process. In-situ driven gravel columns were also used many years ago in Europe by contractors who could not afford or find vibro-lances for sale or lease but wanted to take advantage of the benefits available from the burgeoning ground treatment market.



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For each Geopier column a vertical access hole is bored with a conventional power auger. The depth typically ranges from 5 feet up to 20 feet depending upon the load and soil conditions. The weak material is removed form the hole during the excavation / auguring process. The hole is then backfilled with competent, well graded aggregate material in a series of 1 foot layers. Each layer is tamped with a specially designed tamper that imposes impact ramming energy to the surface of the layer until a predetermined density or level of distortion is achieved. This sequence of infilling and in-situ compaction is repeated until the operating platform level is reached. Further Geopiers are formed in a grid over the area / foundation to be loaded. The interaction with the surrounding ground is clearly many times better than could be produced by any vibro lance during the construction of other stone columns. This can be proved by the volume of stone used and the cross-sectional area of the resulting column. The ramming process not only causes compaction of the aggregate, but also causes it to displace laterally into the softer sides of the hole. This causes the soil to be stressed and confined. This process increases the bearing capacity of the soil and reduces its settlement potential. The overall increase in ground stiffness and the high column density which can be achieved with this process is such that failure of the resulting Geopier column will not take place due to bulging into the surrounding ground but as a consequence of shearing of the column/soil interface. Down-the-hole tampers produce a stone column of very high compressive strength. Another significant advantage offered exclusively by Geopier is the ability to accommodate tension loads. Bearing plates and stressing bars can be installed prior to the in-situ filling and staged compaction and relatively high levels of uplift can be resisted.



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5. The Subgrade........................................................................................................................ 5-1 5.1 Introduction.................................................................................................................. 5-1 5.2 Definitions ..................................................................................................................... 5-1 5.3 Soil Types ..................................................................................................................... 5-2 5.4 Soil Properties .............................................................................................................. 5-4

5.4.1 Mass-Volume Relationships ..........................................................................................................................5-4 5.4.2 Classification .....................................................................................................................................................5-6 5.4.3 Moisture-Density Relationships ................................................................................................................ 5-10



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5. The Subgrade

5.1 Introduction

The subgrade generally has the largest influence on the pavement type, section and performance for a particular type of operation. Materials in the upper part of the subgrade will be affected by the full range of loads applied to the pavement, be they static or moving. Materials at a greater depth below the pavement surface may not be affected by all of the traffic, but the increased load from stored cargo and additional fill material will cause a change in their load environment. This is particularly the case in many marine terminals where the terminal area has been developed beyond the natural shoreline. In these situations the materials used for fill will be placed over the sea bed, which may be poor quality material, but uneconomical to remove to competent strata. Fill placement may also be undertaken with little opportunity for a high standard of compaction. Improvements undertaken after fill placement can be time consuming or costly. Failure to accurately characterize the subgrade properties as they will occur under the pavement can result in high maintenance requirements or in premature pavement failure. This is a complex issue as the eventual characteristics that occur under the pavement are likely to be different from the properties that presently exist at the site, and greatly benefits from the designer’s experience. Changes in the moisture content and in the state of compaction are likely to occur during construction and through the life of the pavement. In some cases the existing ground surface may be well below the surface required to achieve the design elevations. In addition, the subgrade materials will be variable both in location and depth, as a consequence of differing constituent soils and properties. An overly cautious interpretation of the soil properties could have significant economical impact on the project. This section of the pavement design guideline sets out the material characteristic that affect pavement performance, and the test methods that can be used to determine design values. In-place testing for site investigation as well as laboratory testing is covered. The significance of the various procedures and tests are described along with a method to account for the material variability when selecting design values. Where possible, the text focuses on the soils that are more commonly encountered in the Port, although a broader oversight is given. Details are also included on construction requirements and monitoring. At the end of this section there is a brief description of some of the available techniques of ground improvement that can be considered for use under the pavements and terminal structures. These descriptions are not intended to be comprehensive, but the pavement designer should be aware of the way these techniques can affect pavement performance, particularly at locations where they start or terminate. 5.2 Definitions

The following paragraphs set out the basic meanings of terms used for subgrade materials under pavements. Many of the terms are in common use in the Los Angeles area, but some additional terms have been borrowed from national and international sources to provide a fuller set of descriptions. Natural Ground or soils consists of rock and mineral particles of various sizes, water and air, and are described as:

Topsoil: This is generally encountered at the surface of undeveloped land and is highly organic. It is not suitable for use under a pavement, but may be appropriate for landscaping purposes.



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Sub-Soil: This is generally composed of uncemented or weakly cemented, inert mineral particles that are formed by the weathering of rock. The void space between the particles may contain water and air. It may contain some traces of organic matter. The sub-soil may have good or poor properties as a pavement subgrade, and as such may be suitable for fill material or may need to be removed prior to constructing the pavement. Bedrock : This is the solid material of the Earth’s crust. It can form a very strong subgrade but is rarely exposed at pavement levels. The bed rock can support high loads and does not experience significant deflections. The bedrock is often the source of aggregates for construction purposes.

Fill Material may be natural or man-made materials imported from an external source. Much of the fill material used at the Port has been won from the channel dredging work and from other offshore sources. In most applications it has been hydraulically placed. This entails pumping a suspension of soil particles in water, from the dredging operation onto the land. The solid particles settle out and the water drains off the site through settling basins. Coarse particles settle before the fine particles resulting in a variable fill product. The Subgrade comprises the natural and man-made materials that the pavement is constructed over. In the majority of the Port’s terminals the subgrade consists of fill material from natural sources that have been placed over many years. The Formation is the interface between the pavement and the subgrade. This is a borrowed term, but is very useful in establishing the top of the subgrade. It is the level at which the design values for the subgrade are determined. Materials below this interface are not considered part of the pavement structure. A Capping Layer is imported material used to create a working platform over poorer subgrade materials. The capping layer material may not have a high level of quality control, but will be distinctly better than the underlying material. It will be constructed in accordance with defined procedures. The formation is typically at the top of the capping layer when this material is present. Improved subgrade is a working platform created by modifying the existing subgrade materials. The improvement can be the result of mechanical treatment, or by the addition of other materials such as aggregates or chemicals in low quantities. In essence, this layer may be considered as a capping layer formed from the local materials and additives, and as such, the formation is typically at its top surface. Embankment is material imported from a borrow area and compacted above the ground or tidal water level in a controlled manner. The degree of compaction will frequently increase as the height of the embankment increases, as it is not practical to achieve high degrees of compaction immediately over softer substrates. 5.3 Soil Types

Different soil types result from weathering of bedrock. Physical weathering of bedrock by wind, water, frost, gravity, plants, etc. produces granular soils. Gravel and coarse sand particles are typically spherical or cubical rock fragments containing several minerals. Fine sand and silt particles are predominantly spherical or cubical mineral grains.



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Soils can be coarse grained or fine grained, dependent on whether they pass the No. 200 sieve. The engineering properties of coarse grained soils are highly influenced by the gradation and particle shape and texture. Moisture does not have a significant influence on the performance of coarse grained granular soils. The properties of fine grained soils are influenced by electrical charges. Moisture can have a significant influence. The structure of granular soils is arranged with each particle in direct contact with most of their neighbors. There are voids between the particles where they are not in contact, and the structure may range from very loose with a lot of void space to very dense with little void space. Poorly graded granular soils have many particles of similar size and comparatively large voids between them. Well graded materials have smaller particles between the larger particles, partially filling the voids and making them smaller. There is no bonding of the particles. A. Granular Soils

1. Coarse Grained

Boulders are pieces of bedrock retained on a 12" square sieve Cobbles are pieces of bedrock retained on a 3" square sieve Gravel is particles of bedrock retained on a No.4 sieve (4.75mm) Sand is particles of bedrock retained on a No. 200 sieve (75µm)

2. Fine Grained

Silt is particles of bedrock passing a No. 200 sieve, and has a Plasticity Index less than 4 Chemical weathering occurs when water and chemical agents leach minerals from bedrock and granular soils to produce groups of crystalline particles that are finer than 0.002 mm. Clays are almost exclusively platy shaped mineral grains that have a high surface to mass ratio. As such their properties are affected by surface forces. Clay minerals have significant negative charges on their surfaces. The structure of cohesive soils is highly influenced by the inter-particle forces. When the negative charges are on the faces and edges of the particles they are kept apart , but some clay minerals develop positive charges on their edges that result in the edges being attracted to the faces of other particles. Both physically weathered soils particles and chemically weathered soil particles are present in many soils. B. Cohesive soils

1. Fine Grained

Clay consists of mineral grains passing a No. 200 sieve, and has a Plasticity Index of 4 or greater. Individual grains are finer than 5µm

Some soils remain relatively close to the location of their parent rock. These soils are known as residual soils. Other soils are transported long distances by ice, wind, water or other processes. The soils transported by rivers are known as alluvial soils, and are predominantly composed of sand, silt and clay



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particles. Many of the soils in the harbor area are alluvial soils. These are frequently used as the fill materials in the terminals. SOIL PROPERTIES

GW-GM Well graded gravel with silt GW-GC Well graded gravel with clay GP-GM Poorly graded gravel with silt GP-GC Poorly graded gravel with clay SW-SM Well graded sand with silt SW-SC Well graded sand with clay SP-SM Poorly graded sand with silt SP-SC Poorly graded sand with clay CL-ML Silty clay SC-SM Silty, clayey sand

5.4 Soil Properties

5.4.1 Mass-Volume Relationships

A sample of soil consists of dry solids, water and air. The relationships between the mass and volume of these components are used in the calculation of several important soils properties. Density, dry density, relative density, water content, void ratio, degree of saturation and porosity can be determined, leading to the development of further parameters. These include the state of compaction, the permeability and the potential for settlement. Under most conditions a soil is partially saturated and contains dry solid, water and air. These are represented in the three-phase diagram below. When a soil is completely dry or completely saturated it will only have two phases, with the water content and air content being zero respectively.



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Figure 5-1 Three phase diagram of soil

Symbols Total Mass of the soil: M Total Volume of the soil: V Mass and volume of dry solids : Ms and Vs Mass and volume of water: Mw and Vw Mass and volume of air: Ma and Va The Volume of Voids (Vv) is the volume of the air and the volume of the water.

Vv = Va + Vw The Bulk Density (∆) of the soil is the ratio of its mass to its volume.

∆ = M / V The Dry Density (∆d) is the ratio of the mass of dry solids to the total volume.

∆d = Ms / V The Relative Density (∆r) or Specific Gravity (Gs) is the ratio of the mass of dry solids to the mass of an equal volume of water.

∆r = Gs = Ms / (Vs x ∆w) The Water Content (w) or moisture content (m) is the ratio of the mass of dry solids to the mass of water.

AIR

WATER

SOLIDS

Va

Vw

Vs

Vv

V

Ma

Mw

Ms

M



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w = m = Mw / Ms

The Air Content (A) is expressed as

A = n (1-Sr) or A = (e – w x Gs) / (1 + e) The Degree of Saturation (S) is the ratio of the volume of water to the volume of voids.

S = Vw / Vv The Void ratio (e) is the ratio of the volume of voids to the volume dry solids.

e = Vv / Vs The Porosity (n) is the ratio of the volume of voids to the total volume of the soil.

n = Vv / V The void ratio and porosity are related as follows:

e = n / (1 – n) or n = e / (1 + e) The volume and mass of a soil can be determined on undisturbed specimens of the soil. The moisture content of the soil can be determined by drying a test specimen in an oven until it reaches a constant mass. ASTM D 2216 sets out a typical procedure. The water content is calculated as the difference between the mass of the specimen in its natural condition and in its dry condition. Specific gravity of fine grained soils where all particles pass the No. 4 sieve can be determined in accordance with ASTM D 854. If coarser particles are retained on the No. 4 sieve they should be tested in accordance with ASTM C127. 5.4.2 Classification

Soil materials can be classified dependent on several different properties. These include their particle size distribution, their Atterberg limits, The particle size analysis of soils is undertaken using the test methods set out in ASTM D 422. This test method consists of two procedures. The first test procedure involves passing a sample of soil through a nest of sieves to determine the distribution of particle sizes larger than a No. 200 sieve. The top sieve has the largest apertures and the size of the apertures decreases by approximately half with each successive sieve. The smallest sieve is the No. 200 sieve. Typical sieve sizes may include 3", 2",1-1/2", 1", 3/4", 3/8", No. 4, No. 8, No. 10, No. 16, No. 20, No. 30, No. 40, No. 50, No. 60, No. 100, No. 140 and No. 200. However, the procedure may be undertaken with sieves above a No. 10 sieve, and then with sieves No. 10 and below. The nest of sieves is agitated to cause the particles to drop through each sieve until they reach a sieve that has apertures that are too small for them to pass. The original mass and the mass retained on each sieve, including the bottom collection pan are measured. The results are presented as the amount retained on each sieve, or more commonly as the amount passing each sieve.



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Figure 5-2 Equipment to do particle size analysis using sieves.

The second procedure is used to determine the distribution of particle sizes smaller than a No. 200 sieve. It involves a sedimentation process using a hydrometer, as shown in Figure 5-3. The sample is thoroughly soaked and dispersed in distilled water and allowed to settle. Hydrometer readings are taken are set intervals during the sedimentation period to determine the specific gravity of the suspension. The larger particles settle out more quickly than the smaller particles, changing the hydrometer readings. Stokes’ Law is used to calculate the size of particles that have settled a known distance in the suspension at each interval. Using the data a particle size distribution can be prepared. Typical sizes that are reported are 0.074 mm, 0.005 mm and 0.001 mm.

Figure 5-3 Sedimentation process using a hydrometer



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The results are plotted on grain size distribution charts as shown below and a curve is drawn through the points. Steep curves represent uniformly graded materials with a narrow range of article sizes. Flat curves represent well graded materials with a wide range of particle sizes. The shape of the curve can be used for comparing different soil samples. Two coefficients are used for this purpose. The uniformity coefficient (Cu) is determined by dividing the particle size at 60% passing (D60) by the particle size at 10% passing(D10). The coefficient of curvature (Cc) is determined by dividing the particle size at 30% passing (D30) squared, by the product of the particle size at 60% passing and the particle size at 10% passing.

Cu = D60 / D10

Cc = D302 / (D60 X D10)

The particle sizes are used to describe the textural classification of the soils. The following definitions are used, and are described more fully in ASTM D 2487. Gravel: passing the 3" (75 mm) sieve and retained on the No.4 (4.75 mm) sieve Coarse gravel: passing 3" (75 mm) sieve and retained on the 3/4" (19 mm) sieve Fine gravel: passing 3/4" (19 mm) sieve and retained on the N0. 4 (4.75 mm) sieve Sand: passing the No. 4 (4.75 mm) sieve and retained on the No. 200 (0.0075 mm) sieve. Coarse sand: passing the No. 4 (4.75 mm) sieve and retained on the No. 10 (2.0 mm) sieve. Medium sand: passing the No. 10 (2.0 mm) sieve and retained on the No. 40 (0.425 mm) sieve. Fine sand: passing the No. 40 (0.425 mm) sieve and retained on the No. 200 (0.075 mm) sieve. Silt: 0.075 mm to 0.005 mm Clay: 0.005 mm to 0.001 mm The particles size distribution can also provide an indication of performance of the material as a subgrade, but experience and great care is required. Additional testing should always be used to determine the actual properties required. Generalizations include that the coarser a soil the better the engineering properties. The coarser the soil the more permeable it will be. The finer a soil is the greater the capillary forces. The gradation curves can also be used for approximating properties and requirements during stabilization work. The Atterberg Limits are named after Albert Atterberg, who originally defined six limits of consistency of fine grained soils. They included the upper limit of viscous flow, the liquid limit, the sticky limit, the cohesion limit, the plastic limit and the shrinkage limit. Today the Liquid Limit (LL) and the Plastic Limit (PL) are the only ones regularly used. Occasionally the Shrinkage Limit (SL) may be determined. Two indices are also used regularly with the Atterberg limits. These are the Plasticity Index (PI) and the Liquidity Index (LI). Figure 5-4 and Figure 5-5 show the preparation and equipment for Atterberg Limits test.



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Figure 5-4 Atterberg Limits test preparation

Figure 5-5: Equipment used for Atterberg Limits test

The Liquid Limit is the water content at the boundary between the semi-liquid state and the plastic state of the soil. Test apparatus described in ASTM D 4318 includes a flat brass cup mounted on an edge pivot. It is lifted and dropped a set distance onto a rubber using a cam mechanism. A soil sample is mixed with a set amount of water to form a paste. The paste is placed in the cup. Leveled off and grooved with a standard tool. The cup is dropped repeatedly until the groove closes over half an inch. The Liquid Limit is defined as the water content that will cause it to close after twenty five drops.



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The Plastic Limit is the water content at the boundary between the plastic state and semi-solid state of a soil. It is determined by molding a plastic sample of the soil mixed with water into a ball and then into a 1/4" diameter roll as described in ASTM D 4318. It is them rolled on a glass surface utill the thread is 1/8" diameter. The plastic limit is the water content at which the thread starts to break up both longitudinally and transversely at the 1/8" diameter. The Shrinkage Limit is the point where no further volume reduction occurs on drying, but the degree of moisture saturation is still 100 percent. It is typically assumed to represent the amount of water required to fill the voids of a cohesive soil. It can be used to evaluate the shrinkage potential and the likelihood of crack development in cohesive soils. The Plasticity Index is the difference between the Liquid Limit and the Plastic Limit. It is the rage of water content through which the soil exhibits plastic behavior. The Liquidity Limit is the ratio of difference between the natural water content and the Plastic Limit of the soil to its Plasticity Index. It is beneficial for clarifying the consequence of the natural water content of the soil. The soil will behave as a solid when its Liquidity Limit is less than zero, and as plastic if it is between zero and one. The soil will behave as a viscous liquid when the Liquidity Limit is greater than one. The Liquid Limit and the Plasticity Index are used to classify fine grained soils in accordance with ASTM D 2487. When the Liquid Limit is plotted against the Plasticity Index on the Plasticity Chart, clays are above the A-Line and silts are below. High plasticity soils are above 50% LL and low plasticity soils are below. These properties can also provide an indication of performance of the material as a subgrade, but experience and great care is required. Additional testing should always be used to determine the actual properties required. Generalizations include that the higher the Liquid Limit the poorer the properties of the soil. Also a low plasticity Index is indicative of granular materials. The properties can also be useful in determining the type of stabilizing agent that might be suitable. 5.4.3 Moisture -Density Relationships

The engineering properties of soils increase as the density of the soils increase. It is therefore important to have a thorough understanding of the compaction characteristics of the soils in the subgrade. Considering the Phase Diagram above, the compaction process involves reducing the air space (Va) from the soil by reorienting and packing the partic les more closely together. The water content (Vw) does not change until the voids become completely full of water (Vv = Vw). To achieve further compaction, the water content needs to be reduced and further compaction can occur up to the point where the particles have reached their maximum packing density. Some moisture is necessary to act as a lubricant so that the particles can be more readily reoriented. At low water contents most soils become more difficult to compact. The relationship between moisture content and density should be thoroughly understood to ensure that the optimum density of each soil type is achieved during construction. There are two test methods that are used to this end, referred to generally as Proctor test and the modified Proctor test. The former was proposed by R. R. Proctor in 1933. The procedure involves compacting a sample of the subgrade soil in a standardized 4" or 6" diameter mold using a 5.5 lb. hammer dropped 25 or 56 times from a height of 12". The modified test was developed to more closely simulate the compactive effort that can be achieved with modern vibratory compaction equipment, as shown in the Figure 5-6. This procedure uses a higher



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specific energy input (approximately 56 ft-lbf/ft3 as opposed to 12,400 ft-lbf/ft3 in the standard test). The procedure involves compacting soil in the standardized molds using a 10-lb. hammer dropped 25 or 56 times from a height of 18 in. The tests are repeated at several different moisture contents.

Figure 5-6: Vibratory compaction equipment

When the moisture content is plotted against dry density a curve is produced, and typical curves from both tests are depicted. The peak on each curve represent the maximum test density and the optimum moisture content that relates to that density and compactive effort. The dry density can be calculated from the following equation when the air content and the water content are known.

∆d = Gs x ∆w (1 - A) / (1 + w x Gs)



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The maximum dry density at any moisture content occurs when the air content (A) is zero. As noted above, as the compactive effort is increased the maximum density increases and the optimum moisture content reduces. However, the air content is similar. In general, the coarser the soil the greater the maximum dry density, and the lower the plasticity the greater the maximum dry density.



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6. Hot Mix Asphalt Design, Construction, and Quality Assurance............................................ 6-1 6.1 Introduction.................................................................................................................. 6-1 6.2 Distresses in Flexible Pavements ................................................................................... 6-2

6.2.1 Rutting ............................................................................................................................................................... 6-2 6.2.2 Fatigue Cracking............................................................................................................................................. 6-5 6.2.3 Low-Temperature Cracking ........................................................................................................................ 6-6 6.2.4 Age-Related Cracking.................................................................................................................................... 6-6 6.2.5 Moisture Damage ............................................................................................................................................ 6-6 6.2.6 Raveling ............................................................................................................................................................. 6-7 6.2.7 Rate of Deterioration...................................................................................................................................... 6-8

6.3 HMA Mix Design........................................................................................................ 6-10 6.3.1 Step 1: Materials Selection .........................................................................................................................6-10 6.3.2 Step 2: Selection of the Design Aggregate Structure...........................................................................6-18 6.3.3 Step 3: Determination of Optimum Asphalt Content .........................................................................6-22 6.3.4 Step 4: Evaluation of the Moisture Sensitivity......................................................................................6-45



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6-1

6. Hot Mix Asphalt Design, Construction, and Quality Assurance

6.1 Introduction

Prior to beginning to design a pavement, it is important for the designer or design team to develop a vision as to how that pavement will perform. This is important because there can be trade offs in the design process between certain performance expectations. For example, most designers will want a flexible pavement to be both rut resistant and durable (resistant to cracking and raveling). One of the most common methods of achieving rut resistance in hot mix asphalt (HMA) pavement is to increase the laboratory compaction effort, which in turn reduces the design asphalt content. While this does improve resistance to rutting, durability tends to be decreased as a consequence. However, there are choices that can be made during materials selection to help achieve both goals. Another example might be that although the designer desires the pavement to last for 30 years without structural strengthening or rehabilitation, there is only sufficient budget to provide a pavement that will be expected to last for 10 years. Then a designer may need to consider which performance elements can be sacrificed while still providing a good foundation for future strengthening or upgrade. A typical list of performance expectations for a flexible or HMA pavement is as follows:

• Rut Resistant • Durable

– Resists Cracking – Resists Raveling

• Resists Surface Indentation • Good Surface Drainage • Smooth • Flexible • Skid Resistant • Readily Repairable • Economical

With the exception of being readily repairable, all of these performance parameters are affected by the design, construction, and quality assurance process. If only one of these elements: design, construction, or quality assurance is neglected, the pavement may not perform as desired. Skid resistance is generally not a concern for a port terminal due to the low traffic speeds. Once the designer has a vision of how the pavement will be expected to perform, the designer needs to consider the following factors which will determine that performance: § Environment § Traffic loads and speed § Pavement Structure § Design life/Cost

Environmental conditions are influenced by the location of the site. Materials selection for a pavement designed for Los Angeles, CA would be different than materials selection for Boston, MA, particularly in terms of binder grade. More information on binder grade will be provided in a later section.



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6-2

Traffic loads will vary depending on the purpose of the pavement. A parking lot for port employees or empty containers will have significantly different loadings as compared to a container terminal. Further within a container terminal, differing loads can be expected between a rubber-tire gantry crane, port picker and straddle carrier. The rubber-tire gantry crane will produce extremely channelized traffic This channelization will tend to increase the propensity for permanent deformation or rutting. For an HMA pavement, slower moving traffic is also more likely to cause rutting. For port pavements, all traffic in container terminals, intermodal facilities and gate areas can be considered as slow moving. Even if the correct materials are specified, the pavement may not perform if the pavement thickness or structural design is not adequate. Too thin a pavement can lead to rutting and/or fatigue cracking regardless of the materials selected. Poor or improper pavement drainage can also lead to premature pavement failure. Certain material selections can be made, such as the inclusion of anti-stripping additive, good in-place density and rich bottom layers to help guard against damage from moisture resulting from shallow pavement cross-slopes or high water tables. These measures are not a substitute for pavement drainage, where necessary. Finally, the designer and materials engineer will need to consider cost. Limited budgets may force the use of thinner pavements and/or lower quality materials. These choices, although required by economic necessity, will reduce tend to reduce the performance of the pavement. Under no circumstances should quality assurance be sacrificed by the owner in order to “buy” more expensive materials. 6.2 Distresses in Flexible Pavements

When discussing materials choices for flexible pavements, it is first advantageous to understand what distress mechanisms typically effect flexible pavements. It is also helpful to understand which distresses are more affected by pavement structural or thickness design and which are more affected by materials selection. Types of distresses in HMA pavements may include: § Rutting § Cracking (fatigue, shrinkage, and thermal) § Bleeding § Roughness (typically due to construction or one or more of the above) § Weathering § Raveling

6.2.1 Rutting

There are three mechanisms that lead to rutting of HMA pavements: mechanical deformation, consolidation, and shear flow. Mechanical deformation or structural rutting, illustrated in Figure 6-1, results from inadequate base or subgrade support or inadequate pavement thickness. Localized mechanical deformation might be attributed to soft spots in the subgrade or poor drainage. Soft spots can often be identified at the time of construction by proof rolling.



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6-3

Figure 6-1 Schematic of Structural Rutting.

HMA pavements are typically constructed at approximately 7 to 8 percent in-place air voids. The pavement is expected to densify or consolidate under traffic to approximately 4 percent air voids. This consolidation can result in a limited amount of rutting on the pavement surface. The actual amount of deformation which occurs tends to be less than that predicted based on vertical consolidation (Figure 6-2). If however the pavement densifies to less than 2 percent air voids, bleeding and or shear flow rutting may occur. Most HMA mix design systems are primarily concerned with the prevention of shear flow rutting. Shear flow rutting results from instability of the HMA. Figure 6-2 shows a schematic of a pavement exhibiting shear flow rutting. Note the characteristic “humps” of material on either side of the wheel path which helps to differentiate this from other kinds of rutting. Shear flow rutting is exacerbated by heavy slow moving loads or starting and stopping traffic. Shoving, due to starting and stopping, is a similar phenomenon.



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6-4

2000 NCAT Test Track

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Predicted Rutting based on Densification, mm

Mea

sure

d W

ire L

ine

Rut

ting

afte

r 10

M

illio

n E

SA

Ls, m

m

PG 67 Upper and Lower PG 70 Upper and LowerPG 76 Upper PG 67 Lower PG 76 Upper and Lower

Figure 6-2 Predicted Rutting due to Consolidation Compared to Measured Rutting

Figure 6-3 Schematic of Shear Flow Rutting.



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6-5

There can be a number of causes for shear flow rutting. The following is a partial list of causes, which will be discussed in more detail under materials selection: § Rounded aggregate (coarse or fine), § Excessive fines, § Improper gradation, § Moisture damage, § Low voids, § Low viscosity asphalt, § High asphalt content.

6.2.2 Fatigue Cracking

Fatigue cracking is a progressive form of deterioration which occurs in the wheelpath. Typically, it will start as a longitudinal crack but has also been observed initially as a series of transverse cracks. As the cracking continues, the cracks will interconnect forming “alligator” cracking as shown in Figure 6-4. Finally, the cracked area may begin to pump fines from the base and subgrade, rut and/or pothole. Cracking may initiate at the bottom of the pavement structure due to bending or at the top of the pavement structure. Prevention of bottom up fatigue cracking is one of the two distresses typically designed for when determin ing the pavement structure or thickness. Bottom-up fatigue cracking can be delayed or prevented by minimizing the tensile strain at the bottom of the asphalt layer. Bottom-up fatigue cracking is not typically observed in highway pavements over 10 to 12 inches thick. Although bottom-up fatigue cracking is primarily related to pavement thickness, materials choices, such as binder grade, in-place density and asphalt content can influence the occurrence of fatigue cracking.

Figure 6-4 Typical Fatigue Cracking.



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Top down cracking is not believed to be related to pavement thickness. Various theories have been developed to explain the occurrence of top down fatigue cracking. In many instances it is believed to be related to construction, particularly paver segregation. Other theories suggest that radial tires may place the pavement surface under the center of the tire in tension. 6.2.3 Low-Temperature Cracking

Low temperature cracking is an environmental distress. Stresses and strains are induced in the pavement as the surface of the pavement cools. Cracking can initiate at the surface of the pavement based on a single occurrence of a low temperature below the critical cracking temperature of the pavement. Once a crack is initiated, it will typically progress to the full depth of the asphalt layer. In a highway pavement, low-temperature cracks are characterized by a transverse crack for the full width of the pavement with typical longitudinal spacing of 20 to 100 feet (6 to 30 meters). Low temperature cracking would not be expected to be a concern in Los Angeles, CA. Low-temperature cracking is also believed to occur from thermal fatigue, where the pavement eventually cracks from repeated heating and cooling cycles. Thermal fatigue may be of concern in areas with daily temperature extremes, such as desert areas. Low-temperature cracking is primarily affected by the properties of the asphalt binder. 6.2.4 Age-Related Cracking

There are a number of forms of age related cracking. One of the most common forms is block cracking. Block cracking is typically only observed in large paved expanses such as airfields or container terminals where there is little traffic. The mechanisms for block cracking are similar to low temperature cracking. Their occurrence in areas with low traffic is related to thixotropic hardening or embrittlement of the asphalt binder. This can be exacerbated by low pavement density (Roberts et al, 1996). 6.2.5 Moisture Damage

Moisture damage is often referred to as stripping. Stripping defines the condition where the asphalt separates from the aggregate in the presence of moisture or an adhesive failure of the binder from the aggregate. Figure 6-5 shows an example of coarse aggregate stripping in an underlying layer. Moisture damage can also result in a loss of integrity of the asphalt binder or cohesive failure. Moisture damage in the lower layers of a pavement can result in dramatic failures. Moisture damage may occur in the lower layers of a pavement due to high water tables, or permeable surface layers. Surface seals, such as coal tar, can also trap moisture vapor in the pavement structure, resulting in moisture damage.



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6-7

Figure 6-5 Stripping in Underlying Layer.

A number of factors can contribute to the likelihood of moisture damage. Cross-slopes, pavement smoothness, spacing of drains and presences of pavement subsurface drainage can all affect the possibility for moisture damage to occur. Materials selection and construction also play significant roles. Larger nominal maximum aggregate size mixes tend to be more permeable at a given in-place density than smaller nominal maximum size aggregates (NMAS). Similarly, for a given nominal maximum aggregate size, coarse graded mixes tend to be more permeable than fine graded mixes are. Lower asphalt content mixes will be more susceptible to moisture damage (for a given NMAS) than higher asphalt content mixes. Some aggregate types, for instance granite, tend to be more susceptible to moisture damage than other types, such as limestone. Hydrated lime or liquid anti-stripping agents can be added to the mixture to improve the adhesion between the aggregate and binder. Construction plays a large role in the potential for moisture damage. Segregation and low in-place density increase the likelihood for pavement permeability. Once water enters the pavement structure, it will be trapped unless proper pavement drainage is in-place. 6.2.6 Raveling

Raveling is a progressive loss of fines or coarse aggregate from the pavement surface. There are a number of potential causes for raveling, including: moisture damage, low density, low asphalt content and high fines content or a combination thereof. Figure 6-6 shows an example of raveling attributed to low density and low asphalt content after six months. Poor quality aggregates can also lead to surface deterioration in the form of popouts due to wetting and drying or freezing and thawing.



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6-8

Figure 6-6 Loss of Fines Raveling after Six Months.

6.2.7 Rate of Deterioration

As a pavement begins to experience deterioration, the pavements life can be extended, in an economical manner through the prompt application of preventive maintenance and repairs. If the pavement condition is allowed to continue to deteriorate unabated, the pavement will reach a point where the deterioration rate will accelerate resulting in the need for more extensive rehabilitation or reconstruction, a much more costly alternative (Figure 6-7). Similarly, a poorly constructed pavement, possibly due to poor or inadequate construction inspection and quality assurance testing will begin its life at a lower point on the deterioration curve and deteriorate more rapidly resulting in a shorter service life (Figure 6-8). A pavement management system is necessary to ensure that repairs are preventive maintenance and repairs are performed in a cost effective manner. Good quality assurance testing, preferably by an independent lab, and good construction inspection are necessary to ensure that the pavement is constructed as designed.



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Figure 6-7 Pavement Performance Curve.

Figure 6-8 Comparison of Pavement Performance Curves for Expected and Problem Construction

Quality.



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6.3 HMA Mix Design

There are four steps to the mix design process, shown in Figure 6-9.

1. materials selection; 2. selection of the design aggregate structure; 3. determination of optimum asphalt content; 4. evaluation of moisture sensitivity;

Three major mix design procedures will be discussed: Marshall, Hveem and Superpave. All three mix design systems generally share the same four steps. The primary difference between the design systems is the laboratory compaction method and effort used in the determination of the optimum asphalt content. For the Marshall and Hveem systems, guidelines for materials selection were typically developed by the specifying agency. Materials selection consists of selecting the appropriate asphalt binder and coarse and fine aggregates. Once the component coarse and fine aggregates are selected, the blend gradation of aggregates must be designed. Then the optimum asphalt content for a given blend of aggregates must be determined. Finally, moisture damage can be a concern regardless of the design system, so the moisture susceptibility of the mixture should be tested. The following sections describe the four steps of the mix design process in detail. The primary difference of the three major mix design are discussed in the step 3, determination of optimum asphalt content. 6.3.1 Step 1: Materials Selection

6.3.1.1 Asphalt Binders

Asphalt binder is referred to by a number of names: asphalt, asphalt cement, oil and tar. In this text, it will typically be referred to as binder or asphalt. Asphalt and tar are very different materials. Asphalt is generally a by-product of the distillation (refining) of crude oil, although it can be naturally occurring, such as Trinidad Lake Asphalt. The amount of asphalt produced from a given quantity of oil is dependent on the crude source and refining techniques. Asphalt is soluble in petroleum products, such as gas and oil. Tar is resistant to petroleum products. It is a byproduct of the distillation of coal to produce coke. Coke is used as a fuel to smelt iron ore since it is smokeless. The International Agency for Research on Cancer characterizes preparations that include more than 5 percent crude coal tar as class 1 carcinogens. For a variety of environmental and health exposure reasons, tar is generally only used as a surface coating in areas where fuel resistance is important. Asphalt binders are viscoelastic materials. As such, the engineering properties of asphalt depending on the loading time and temperature. At cold temperatures, asphalt acts as an elastic solid. At intermediate (in-service) temperatures, asphalt can have both viscous (flow) and elastic behavior. If a can of asphalt were turned on its side at room temperature, over a period of several hours the contents would begin to flow out of the can. At higher temperature, the asphalt flows faster. At very high (mixing) temperatures, asphalt will behave as a viscous liquid. Thus rate of loading and the temperature of the asphalt when it is loaded are important considerations when selecting and asphalt binder.



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A number of systems have been developed to “grade” or specify asphalt binders based on their engineering properties. The penetration test was adopted for grading asphalt cements by ASTM in 1903. The penetration test measures the distance that a truncated sewing needle penetrates an asphalt samples under a 100 g load in 5 seconds at a temperature of 77 °F. The penetration is the depth of penetration in 0.1 mm, e.g. a penetration value of 60 indicates the needle penetrated the sample 6 mm. The penetration grading system was adopted as ASTM D946. One of the main disadvantages of the penetrations system was it only measured the stiffness of the asphalt at one temperature. The performance of a binder at 77 °F may be deceptive to its performance at higher (summer) or lower (winter) temperatures due to the concept of temperature susceptibility, which will be discussed later. Also, there were no tests to indicate the properties of the binder at mixing and compaction temperatures. Penetration grading is still used in Europe in conjunction with other tests such as softening point. In 1963, the viscosity grading system was developed by the Federal Highway Administration (FHWA) and the Asphalt Institute to address problems during construction and at high temperatures (warm summer). Viscosity is a fundamental engineering property and is defined as resistance to flow. The viscosity of the binder was measured at two temperatures, 140 and 275 °F. The first was selected to represent typical pavement temperatures on a warm summer day. Note that pavement temperatures are almost always higher than air temperatures. The second temperature was selected to determine the binder properties near typical mixing and compaction temperatures. Absolute viscosity tests are performed at 140 °F according to ASTM D 2171. A Cannon-Manning viscometer is placed in a temperature controlled water bath. The viscometer is charged with asphalt. The asphalt is then conditioned to the test temperature. Asphalt does not readily flow on its own at 140 °F, so a slight vacuum is applied to one end of the viscometer during the test. The viscosity is determined from the time it takes the asphalt to flow past two timing marks. The viscosity is reported in units of Poise or Pascal•Seconds (1 Pa•Second = 10 poises). At 275 °F, a Zietfuchs Cross-Arm Viscometer is used to measure viscosity according to ASTM D2170. The viscometer is placed in a temperature controlled oil bath. At this temperature the asphalt will readily flow. A slight vacuum is used to initiate flow over the siphon point after which flow will continue under the influence of gravity and is termed the kinematic viscosity. The viscosity is again determined by measuring the time it takes the binder to flow past two timing marks. Kinematic viscosity is reported in units of centistokes (cSt) or mm2/s. Kinematic viscosity can be converted to absolute viscosity by multiplying by the specific gravity of the binder. The viscosity grades are specified in ASTM D 3381. In addition to the absolute and kinematic viscosity, ASTM D 3381 includes the penetration test at 77 °F and an absolute viscosity test on the thin-film oven (TFO) residue. The thin-film oven simulates the expected aging of the binder which occurs during mixing and construction. Because the asphalt is exposed to high temperatures in a thin film during mixing and construction, the binder will age or stiffen due to the loss of lighter fractions (oils) from the binder. A sample of the binder is placed in a pan in a thin (1/8 in.) layer and heated in a forced draft oven to 325 °F for 5 hours. Commonly used viscosity or AC grades were AC-10 and AC-20. States in the southeastern U.S. later developed AC-30, a grade readily suited to that climate. An AC-20 has a viscosity of 2000 ± 400 poise at 140 °F. Two criticisms of the viscosity grading system were that it did not provide safeguards against low temperature cracking and it was not suitable for modified binders. The viscosity grading system was



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the most widely used grading system in the U.S. up to the adoption of the Superpave Performance Graded Binder System. Later in the 1960’s the Aged Residue (AR) grading system was developed in an effort lead by the California Department of Highways. This system was developed to address concerns over tender mix problems during construction. This system is similar to the AC grading system except that the tests are performed on the aged residue resulting from the rolling thin-film oven test (RTFO). The RTFO test is similar in purpose to the TFO test. In the RTFO test a sample of binder is placed in a glass jar. The jar is placed on a rotating rack in a 325 °F oven for 75 minutes. The rotation of the rack coats the inside of the bottle with a thin film of binder. It also prevents a scum from forming on the surface of the binder which might prevent additional aging of the binder (this can occur in the TFO test). A nozzle blows dry compressed air into the bottle with each revolution. Only the penetration test is performed on the original binder. Absolute viscosity, kinematic viscosity and penetration are performed on the RTFO aged residue. The penetration on the original binder is only used to calculate a percentage of retained penetration after aging. The specifications for AR grades are provided in ASTM D3381 Table 3. The AR grading system is highly regional and was only used by agencies on the west coast. The system has no tests on the original (unaged) binder produced by the supplier. Testing times are slightly longer due to the aging period. In addition, the AR grading system has the same two criticisms as the AC grading system. In 1994, the Performance Graded (PG) Binder system was released. The PG Binder system was a product of the Strategic Highway Research Program, a five-year, 50 million dollar (on asphalt) effort. The PG binder system is unique in that it provides specifications for the binder over the complete range of temperatures expected during construction and in-service. The system also examines three states of expected aging, the original or unaged binder (that which is delivered by the supplier), the RTFO aged binder (the stiffness expected on the roadway immediately after construction), and the pressure aging vessel (PAV) residue. The PAV residue represents the stiffness of the binder after 5 to 8 years of in-place aging. The PG system is based on climatic pavement temperatures, traffic speed (or loading rate), and traffic volume. As noted previously, “PG” stands for performance grade. The first number represents the average 7-day maximum pavement temperature for which the binder would be resistant to rutting, e.g. a PG 64-XX would be expected to be resistant to rutting to a pavement temperature of 64 °C (147 °F) at normal traffic speeds. The second number is the minimum pavement temperature for which the binder would be expected to be resistant to low temperature cracking, e.g. a PG XX-22 would be expected to be resistant to low temperature cracking to a temperature of -22 °C (-8 °F). The properties of the binder at mixing and compaction temperatures are measured using the rotational or “Brookfield” viscometer on the original binder according to AASHTO T316. The rotational viscometer essentially measures the kinematic viscosity of the binder. A rotational viscometer measures the torque required to turn a spindle of specified dimensions within a cup of asphalt binder at a specified temperature. The torque is converted to a viscosity by the unit. The PG Binder specification includes a maximum viscosity of 3.0 Pa•S at 135 °C (275 °F) to ensure that the binder can be pumped into the asphalt plant. Typically tests are carried out at both 275 and 325 °F in order to determine the mixing and compaction temperature of the binder. This procedure tends to overestimate the mixing and compaction temperature of a modified binder. The suppliers recommendation should be used for the mixing and



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compaction temperatures for a modified binder. Overheating a modified binder may destroy the modifier resulting in a softer (less stiff) binder. The performance of the binder with respect to rutting or permanent deformation is measured on both the original and RTFO aged binder using the dynamic shear rheometer according to AASHTO T315. Testing is conducted at the high temperature binder grade, e.g. a PG64-XX is tested at 64 °C. The dynamic shear rheometer basically applies an oscillatory load to a wafer of the binder sandwiched between two parallel plates and measures the resulting strain (controlled stress rheometer) or applies a known strain and measures the resulting stress. The test is conducted at an oscillatory frequency of 10 Hz, which approximates 60 mph. The minimum specification value for the original (1.0 kPa) or the RTFO aged (2.2 kPa) binder stays the same regardless of the test temperature. The performance of the binder with respect to fatigue cracking is also measured using the dynamic shear rheometer. However the testing is conducted on the PAV residue. Binder which has previously been subjected to RTFO aging is subject to heat and pressure for a period of 20 hours in the PAV to simulate 5 to 8 years of in-place aging. Both fatigue and low temperature cracking are more likely to occur as the binder ages. Because the PAV aged binder is so stiff, testing is conducted using an 8 mm diameter parallel plate instead of a 25 mm diameter parallel plate. He testing is conducted at an intermediate temperature which is based on the high and low temperature grade. For example, the intermediate tests for a PG 64-22 are conducted at 25 °C (77 °F). A maximum stiffness of 5,000 kPa is specified at the appropriate intermediate test temperature. The performance of the binder with respect to low temperature cracking is measured with the bending beam rheometer (BBR) and if specified, the direct tension test. A pair of beams is cast from the PAV residue to perform the BBR test (AASHTO T313). The BBR test simulates the response of the binder due to a rapidly moving cold front. As the temperature of the pavement drops, tensile stresses are induced in the pavement. The pavement will stretch of relax some of this stress. However, if the stress exceeds a critical level, the pavement will crack. Even the most rapidly moving cold front may take several hours to pass. In order to avoid such a long test time, the principle of time-temperature superposition is used. Basically, if asphalt is tested at a faster loading rate or low temperature it will be stiffer. Therefore, the BBR test is performed in 4 minutes at a temperature that is 10 °C warmer than the expected low pavement temperature. The effect of the faster loading rate and warmer temperature counteract one another making the test more convenient to run. Two parameters are measured in the BBR test, the creep stiffness and relaxation rate (m-value) at 60 seconds. A maximum creep stiffness of 300 MPa and a minimum m-value of 0.300 are specified regardless of the grade low temperature. The direct tension test (AASHTO T314) is used to better characterize the fracture properties of some modified binder systems. Selection of the PG binder grade for a project is done through an evaluation of climatic data, expected loading rate, and the expected number of repetitions. Climatic data is readily accessible using LTPPbind, a software package developed for FHWA. LTPPbind can be downloaded for free at: www.ltppbind.com/. The program allows you to select weather stations by GPS coordinates (latitude and longitude) or by name and location. For Los Angeles WBO, the climatic grade which provides 98 percent reliability is a PG 64-10. Specifying a climatic grade of binder with 98 percent reliability suggests that there is only one chance in 20 that the specified pavement temperatures would be exceeded. The base climatic grade is then modified for traffic speed and volume of truck traffic or other heavy loading. The Superpave system recommends a one grade high temperature bump for slow moving traffic



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and a two grade high temperature bump for standing traffic. Thus, a designer would select a PG 70-10 for a site with a base climatic grade of PG 64-10 expected to receive slow moving traffic. An argument can easily be made that all port traffic is slow moving. Transfer areas and security booths would be classified as having standing traffic. Further, areas with heavily channelized flow, such as where a rubber tired gantry crane runs would most likely meet the requirements for a grade bump based on loading repetitions. So a site with a PG 64-10 might be bumped to a PG 76-10 for transfer areas, security booths and RTGC runways. LTPPBind can be used to examine changes in binder grade as a function of depth. Shear flow rutting typically occurs in highways in the upper 4 inches of the pavement structure. Therefore, high temperature bumps should be considered to a depth of 4 inches. Mechanistic -empirical pavement analysis techniques could be used to examine vertical strain and shear with depth for heavier loading such as a port picker, straddle carrier or RTGC. There is a general rule of thumb for PG binders that if the high and low temperature numbers are added together (ignoring the minus sign) and they exceed 90, then the binder will need to be modified. For example, A PG 76-10 would be 86, which means that it is borderline. Many west coast crude sources are considered to be of lower quality and therefore may require modification. There are numerous methods of modification available for asphalt binder. Some of the most common are, § Polymers

o Elastomers o Plastomers

§ Air Blowing § Acid modification

Elastomeric polymers are preferred by many agencies. Elastic polymers form networks within the binder which result in a greater elastic response as compared to a viscous response by the binder. That is when a load is applied to the pavement, the asphalt is more likely to deform under the load but then return to its original position. Elastomeric polymers are also believed to improve the fatigue and reflective cracking resistance of the binder and in some cases improve resistance to moisture damage. Examples of elastomeric polymers include: § Homopolymers

o Natural Rubber § Random copolymers

o Styrene Butadiene Rubber (SBR) also known as latex § Block copolymers

o Styrene Butadiene Diblock (SB) o Styrene Butadiene Styrene (SBS)

Plastomers generally only stiffen the binder and do not improve the elastic properties of the binder. For this reason cracking has been a concern with some plastomers. Some common examples of plastomers might include: Novaphalt, Vestoplast and Polybilt. Novaphalt is produced using low density polyethylene (LDPE), the same polymer plastic milk jugs are made from. Separation can be a concern with some types of polymers. If the polymer is not properly cross-linked and or agitated in the tank it can separate from the asphalt binder. Such binders are said to lack storage



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stability. Some polymer such as natural rubber, recycled tire rubber and Novaphalt are generally blended on site at the contractor’s plant. Air blowing has been used as a refining technique for many years to stiffen (increase the high temperature grade of binders. Basically, the binder is aged under controlled conditions at the refinery. This technique only improves the rutting susceptibility of the binder. Acid modification has received more attention in recent years. There are multiple types of acid that can be used to modify acids. Some types are better than others. Poly-phosphoric acid (PPA) would be a preferred type for acid modification. Table 6-1 shows a comparison between the properties of two different types of acid used to modify asphalt. It should be noted that the effectiveness of acid modification varies by crude type. Acid modification can be very beneficial with Venezuelan base crude sources. It has been reported to have little effect on west coast crude sources. One potential concern with acid modification is an increased susceptibility to moisture damage. In some cases, mixes with binders modified with PPA can have increased moisture susceptibility. Unreacted acidity in the binder could react with basic materials such as standard amine based anti-stripping agents or lime. This would both neutralize Table 6-1 Acid Modification Phosphoric

Acid Poly- Phosphoric Acid (PPA)

Chemical Formula H3PO4 Hn+2(PnO3n+1)

Viscosity (room temp., cps) 10 max. 800 min.

Free Water Content 15% min. 0%

Molecular Weight (g/mol) 98 258 min.

the anti-stripping agent and could result in a softer binder grade. Appropriate liquid anti-stripping agents are available for use with PPA. The PG binder grading system is supposed to be blind to the type of modification. Agencies that desire a specific kind of modification, such as an elastic polymer, have resorted to PG+ specifications. Examples of PG+ specifications might be the addition on a maximum phase angle for the DSR test performed on the original binder or a minimum elastic recovery values. The phase angle is a measure of the elastic response of the binder. Most neat (unmodified) binders have a phase angle close to 90 degrees. Maximum phase angle specifications of 60 to 70 are used to ensure the inclus ion of elastic polymers. 6.3.1.2 Aggregate Properties

Aggregate properties can be categorized to reflect a few performance concerns: tests related to specific gravity and absorption (used to calculate volumetric properties which will be discussed later), tests for aggregate durability, tests for aggregate angularity and texture and tests for aggregate shape.



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The Superpave mix design system codified the aggregate properties often specified by agencies with other mix design systems. Superpave specifies by consensus and source properties. Consensus properties vary by traffic ESALs but are to be consistent throughout the U.S. Source properties are set by the agency to reflect local geology. The consensus aggregate properties include: § Fine Aggregate Angularity (AASHTO T304) – used to prevent too much rounded natural sand

which may lead to tenderness of the mix during construction and rutting. § Sand Equivalent (AASHTO T176) – used to reduce clay-like particles in the mix. The asphalt

may stick to the clay –like particles coating the aggregate particles and then strip in the presence of moisture.

§ Flat and Elongated Particles (ASTM D4791) – Flat or elongated particles may break under the roller exposing uncoated faces or reorient under traffic leading to flushing.

§ Coarse Aggregate Angularity (ASTM D5821) – used to prevent uncrushed gravel particles which may lead to rutting or shear instability.

The fine aggregate angularity or uncompacted voids in fine aggregate test is based on the premise that materials that are more angular, e.g. crushed particles, or particles that have more surface texture will not pack together as tightly as rounded or smooth particles would. It also recognizes the fact that not all natural sands are rounded or bad. Some natural sand can be beneficial in a mix design. The equipment needed to conduct the uncompacted voids test is shown in Figure 6-9. Superpave specifies AASHTO T304 mehtod A, which uses a standardized gradation. A standardized gradation is used to compare angularity, since varying percentages of material passing the 0.075 mm (No. 200) sieve could alter the results even for materials with the same angularity. The bulk specific gravity of the fine aggregate is required to calculate the volume of the aggregate in the cylinder of known volume. The Superpave criteria for uncompacted voids are specified on the blend of fine aggregate, not an individual stockpile.

%100))((

×÷−

=V

GMVvoidsduncompacte sb

where, V = the calibrated volume of the cylinder in cubic centimeters (approximately 100), M = the mass of the uncompacted aggregate, struck off in the cylinder, and



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Gsb = the fine aggregate specific gravity.

Figure 6-9 Uncompacted Voids in Fine Aggregate Apparatus. Two source properties are specified in the Superpave mix design system, LA Abrasion and sulfate soundness. LA Abrasion (AASHTO T95/ ASTM C131) is a measure of expected breakdown during handling, mixing and placement. Such breakdown can alter the HMA gradation resulting in a mixture that does not meet volumetric properties. This breakdown can generally be accounted for in the design process. The sulfate soundness test is used to evaluate the durability of aggregate sources to freezing and thawing as well as wetting and drying. Sulfate soundness is performed according to AASHTO T104. Either magnesium or sodium sulfate can be used too conduct the test. Researchers believe the results from the magnesium sulfate soundness test are better correlated with performance. The test was developed in the 19th century to simulate freezing and thawing. A sample of the aggregate is soaked in a saturated sulfate solution. The saturated aggregates are then placed in a drying oven. When the sulfate crystallizes in the pores of the aggregate, it creates pore pressure similar to freezing water. Results from the micro-deval test have been correlated to the sulfate soundness test. The micro-deval test also provides a measure of an aggregates abrasion resistance.



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Table 6-2 Comparison of Aggregate Criteria for Equivalent Traffic Property Port of LA Item P401 Superpave Coarse Aggregate Angularity, % 1 and 2 crushed faces

NA/90 85/70 95/901

Flat and Elongated Particles, maximum to minimum dimension exceeding 5:1 ratio

NA 8 Max. 10 Max.

Uncompacted voids in fine aggregate NA NA 45 Min.1

Natural Sand, % 10 Max. 15 Max. NA Sand Equivalent value 50 Min. 45 Min. 45 Min.1

1Varies by traffic level. 6.3.2 Step 2: Selection of the Design Aggregate Structure

Gradation bands are generally specified by a nominal or a maximum aggregate size. The Superpave mix design system attempted to standardize the definitions of nominal and maximum aggregate size.

§ Nominal maximum aggregate size (NMAS) is defined as one sieve size larger than the first sieve to cumulatively retain more than 10 percent of the blend (or have less than 90 percent passing).

§ Maximum aggregate size is one sieve size larger than the nominal maximum aggregate size. Superpave includes gradation control points for 4.75, 9.5, 12.5, 19.0, 25.0 and 37.5 mm NMAS mixes. It is generally believed that mixes with larger NMAS are “stronger” or more rut resistant than mixes made from smaller aggregate. Larger NMAS mixtures are probably more resistant to indentation than smaller NMAS mixes are. However, it would be unlikely that even a 25 mm NMAS mix could resist indentation from hatch covers or even the corners of containers. The asphalt content of a mixture is driven by the total surface area of the aggregate that must be coated with asphalt. Smaller particles have more surface area for an equivalent volume of aggregate than larger particles have. Therefore, larger NMAS mixtures tend to have lower optimum asphalt contents than smaller NMAS size mixtures. Mixtures with lower asphalt contents are also less likely to rut. The tradeoff comes in terms of durability. Larger NMAS mixtures tend to be more permeable to water at a given in-place density. They also tend to be more prone to durability problems, such as raveling, and more susceptible to construction problems, such as segregation. Therefore, a surface course produced with a smaller NMAS aggregate, such as 12.5 or 19.0 mm is advisable. Superpave gradations are represented by a 0.45 power curve. The x-axis is a logarithmic plot of the sieve size opening, in mm, raised to the 0.45 power. The y-axis is the percent passing the corresponding sieve size. The maximum density line is drawn from the origin to 100 percent passing the maximum sieve size. The maximum density line is supposed to represent the gradation for which the particles would pack together resulting in the minimum void space between the particles or the gradation that would result in the densest packing of the aggregate. The Superpave mix design system originally included a football shaped area along the maximum density line between the 0.300 (No. 50) sieve and the 2.36 mm (No. 8) sieve referred to as the restricted zone. Many natural sands have a “hump” in their gradation or a larger percentage of material retained near the 0.600 mm (No. 30) sieve. The restricted zone was another tool to work in conjunction with the fine



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aggregate angularity test to preclude excess amounts of natural sand. Research has shown that many mixes with good performance, both historically and based on laboratory performance tests pass through the restricted zone. Consequently, the restricted zone has been eliminated from current Superpave specifications. Superpave only includes a minimum number of control points and not a gradation band such as that historically used by other mix design systems/specifications. Control points include the 0.075 mm (No. 200), 2.36 mm (No. 8), and NMAS sieve size. Figure 6-10 illustrates the various components of the Superpave gradation bands including the now defunct restricted zone.

Figure 6-10 Superpave Gradation Band for 12.5 mm NMAS Mixture The Superpave system gives the designer great freedom when developing a mix design and is adaptable to a wide range of materials. However from the owner’s standpoint, it can result in mixes with very different appearance and potentially performance. Figure 6-11 illustrates three different gradations produced from the same aggregate stockpiles. All three gradations would be considered dense-graded. Gradations below the maximum density line are called coarse graded mixes. Gradations that are above the maximum density line are called fine graded mixes. Gradations close to the maximum density line are the most densely graded mixes. The appearance of the three gradations in terms of surface texture can vary dramatically. Airfields tend to specify fine to densely graded mixtures to reduce the chance for foreign object damage. Figure 6-12 shows a comparison of the 25.0 mm NMAS gradation bands for the X-mix used by Port of LA, the FAA P401, and the Superpave control points. Figure 6-13 shows a comparison of the 19.0 mm



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NMAS gradation bands for the Y-mix used by Port of LA, the FAA P401, and the Superpave control points. As can be seen from Figure 6-12 and Figure 6-13, The Port gradations are consistently coarser than the P401 mixes. The extremes of the Port and P401 gradations correspond to the Superpave control points. When performing a mix design, it is important to account for the expected breakdown of the aggregate. Ideally, the expected breakdown would be known for a given aggregate source based on experience. If not, the addition of 1 percent passing the 0.075 mm (No. 200) sieve is a reasonable starting point. The additional dust can be collected from the baghouse or by sieving the fine aggregate. There are a number of methods to batch aggregate samples for mix design. For large samples, e.g. more than 5,000 g, the aggregates can be dumped into a pan and “bulk batched” using a flat bottom scoop. It is important that the scoop is used run along the bottom of the pan. Smaller samples, such as those used in Marshall design, require fractionation. The aggregates can be combined as for bulk batching and then fractionated into all of the sieve sizes for precise control of the gradation. The two draw back of this method are that it is then impossible to change the aggregate percentages (particularly if natural sand or crushed aggregates from different sources are used), and adherent fines can stick to the coarse aggregate. The second method is to fractionate each aggregate source or stockpile individually. Some designers will only fractionate the material down to the 2.36 mm (No. 8) sieve. This authors experience suggests that such a combined fine fraction is easy to segregate resulting in variable test results during mix design. Regardless of the method used to batch or combine the aggregates it is absolutely necessary to run a washed gradation on a sample batched in the same manner as the samples prepared for mix design to determine the gradation of the batched samples matches the design gradation. Ignoring this step invites a great deal of frustration.

9.5 mm Nominal Sieve Size

0.60

1.18

2.36

4.75

9.50

12.5

0

0.07

50.

15

0.30

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Per

cent

Pas

sing

Blend 1Blend 2Blend 3

Figure 6-11 Examples Coarse, Dense and Fine Gradations

Fine

Coarse



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2.36

1.18

0.60

0.30

0.15

0.07

5

37.5

0

25.0

0

19.0

0

12.5

0

9.504.75

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Per

cent

Pas

sing

X-Mix

P401

Figure 6-12 Comparison of X-Mix, P401 and Superpave



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1.18

0.60

0.30

0.15

0.07

5

25.0

0

19.0

0

12.5

0

9.50

4.75

2.36

0

10

20

30

40

50

60

70

80

90

100

Sieve Size (mm)

Per

cent

Pas

sing

X-Mix

P401

Figure 6-13 Comparison of Y-Mix, P401 and Superpave

6.3.3 Step 3: Determination of Optimum Asphalt Content

Three systems of mix design will be discussed: Marshall, Hveem and Superpave. All three use, to one extent or another, the concept of volumetric properties to determine the optimum asphalt content of the mix. Therefore, a brief introduction to volumetric properties will be provided first. 6.3.3.1 Volumetric Properties

Volumetric properties are based on the fact that all matter has mass and occupies space. Volumetric properties are the relationship between mass and volume. Two concepts are commonly used to describe these relationships, density and specific gravity. Density is the unit weight of the material, typically expressed in lbs/ft3 or kg/m3. Unit weight is equal to:

WGWeightUnit γ×= where, G = specific gravity of the material, and γW = the density of water, either 62.4 lbs/ft3 or 1.000 g/cm3. Specific gravity is the ratio of the mass to the volumes of an object to that of water at the same temperature.



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WaterVolumeWaterMass

SolidVolumeSolidMass

G =

In the metric system, since the density of water is 1.000, this simplifies to the mass of an object over the volume of the object. Five different gravities, defined below, are used in the calculation of volumetric properties for HMA: § Gb = Specific gravity of the binder, typically close to 1.03 § Gsb = Bulk specific gravity of the aggregate § Gse = Effective specific gravity of the aggregate § Gmb = Bulk specific gravity of the mixture § Gmm = Maximum specific gravity of the mixture

The bulk specific gravity of the fine aggregate is determined according to AASHTO T84 or ASTM C127. The bulk specific gravity of the coarse aggregate is determined according to AASHTO T85 or ASTM C128.

voidssurfacepermeablewaterofVolumeaggregateofVolumedryovenMass

Gsb +=

,

The volume of the water permeable surface voids (Figure 6-14) is calculated by determined the mass of the aggregate in the saturated surface dry (SSD) condition. Basically the aggregate is saturated and then partially dried until there is no free water on the surface. Coarse aggregate particles are dried with a towel and the SSD conditioned determined visually by a color change as the surface goes from wet to dry. Fine aggregate particles are dried with moving air. A sample of the fine aggregate is compacted in a cone and the cone lifted. A slight slump indicates that the SSD condition has been met. This is subjective by nature and can be complicated by angular crushed fine aggregates or those with high dust contents. Examples of both SSD conditions are shown in Figure 6-15. It is easier to determine the apparent gravity of the aggregate, Gsa, which ignores the surface voids. The effective aggregate gravity (Gse) can easily be determined from the theoretical maximum specific gravity (Gmm) or Rice test. Gse ignores the portion of the surface voids that are filled with asphalt cement when measuring the volume to determine the aggregate specific gravity. Thus, Gsa measures the smallest aggregate volume, then Gse, and Gsb uses the largest aggregate volume. Which results in Gsa being the largest specific gravity, then Gse, and finally Gsb will always be the smallest specific gravity. This relationship can be used when evaluating test results to look for potential errors. Gsb and Gse can be very close together if the water absorption is small.



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Figure 6-14 Aggregate Surface Voids Included in Determination of Gsb

Figure 6-15 Fine and Coarse Aggregate SSD State.

The measurement of the surface voids is important since they will be partially filled with asphalt (to a lesser degree than with water). This asphalt, which is absorbed into the aggregate pores, does not act to glue the aggregate particles together in the pavement. Therefore, Gsb should always be used when determining the voids in mineral aggregate (VMA) in the Marshall and Superpave design systems. The bulk specific gravity of the compacted HMA sample (Gmb) is another important volumetric property. The sample could be compacted in the laboratory using a Marshall Hammer, Hveem Kneading Compactor, or Superpave Gyratory Compactor, or it could be a core cut from the pavement. The Gmb of a compacted HMA samples is typically determined according to AASHTO T166 or ASTM D2726. Both methods use Archimedes’s Principle (and really the fine and coarse aggregate methods) to determine Gmb. First, the dry mass of the sample is determined. For a field core, this step can be determined last, after the core has been dried to a constant mass in an oven. The drying temperature varies depending on the whether the AASHTO or ASTM procedure is being used. Next, the mass of the samples suspended in a water bath at 77 °F (25 °C) is determined. Archimedes’s Principle states that the volume of a samples is equal to the mass of water (at a specified temperature and hence density) displaced by the object. If you were measuring the apparent specific gravity of the sample, the dry mass and weight in water would be



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sufficient, but since we want to know the bulk specif ic gravity we must also determine the SSD mass to account for the volume of surface voids. The SSD mass of a compacted HMA sample is determined by quickly blotting the surface of the samples to remove the surface moisture and then determining its mass.

waterundersampleofMasssamplesSSDofMasssampledryofMass

Gmb −=

If the air voids of the compacted HMA sample are too high, water can drain out of the sample before the SSD condition can be determined, introducing an error. An example might be that the technician blots the surface, water droplets reappear and the technician continues to blot the sample. This action leads to an erroneously high Gmb. The samples should be quickly blotted and then placed on the scale. If water drains onto the scale, that mass should be considered as part of the SSD mass of the samples. Both AASHTO T166 and ASTM D2726 are only valid for samples with water absorptions less than 2 percent. Other methods such as paraffin coated samples (ASTM D1188) or the Corelok method (ASTM D6XXX) are specified for samples with high water absorptions. The air voids of a compacted HMA sample are used in determining the optimum asphalt content during design, monitoring production of the mix in the field and ensuring the quality of the in-place pavement. In order to determine the air voids of the compacted HMA sample, both the Gmb and the theoretical maximum specific gravity (Gmm) must be measured. Gmm is basically the mass of the asphalt and aggregate divided by the voidless volume of the asphalt and aggregate (100 percent density). Gmm is determined according to AASHTO T209 or ASTM D2041. First, the dry mass of a loose (uncompacted) sample of HMA is determined. Then the sample subject to a vacuum and agitation while under water to remove all of the air (Figure 6-16) Then the volume of the sample is determined by weight under water or determining its mass in a calibrated pycnometer filled to it calibration line. As described previously, specific gravity is the dry mass divided by the volume.

Figure 6-16 Maximum Specific Gravity Setup



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The voids in mineral aggregate (VMA) are used in the design of HMA to help ensure the durability of the mixture. VMA is the total void space between the aggregate particles in a compacted HMA sample, some of which is filled with asphalt and some of which is filled with air. If the VMA of a mixture is too low, there will be insufficient room for enough asphalt binder to adequately coat the aggregates and provide cohesion between the aggregate particles. The calculation of VMA is shown below:

−×−=

sb

bmb

GPG

VMA)100(

100

Pb or AC% is the asphalt content of the mixture expressed as a percentage of the total mixture weight (not by the mass of the aggregate). “100-AC%” is also referred to as percent stone. AC% may be known or it may be determined using the ignition test or a solvent extraction. The portion of the VMA that is filled with asphalt is called the voids filled with asphalt (VFA). If the VFA of a mixture is too low, durability may suffer; if the VFA is too high the mixture may be susceptible to rutting. The calculation for VFA is shown below:

VMAvoidsairVMA

VFA)(

100−

×=

Superpave and some agency specifications will specify air voids, VMA and VFA. However, only two are necessary to control the mixture as can be seen from the calculation for VFA. If all three are specified, then the acceptable range for a single property is likely compromised. Gse can be calculated knowing the asphalt content, Gmm, and Gb as shown below.

−

−=

b

b

mm

bse

GP

G

PG

1

)1(

Gse can be useful for a number of reasons. First, it is used in the calculation of the percentage of binder which is absorbed into the aggregate, which in turn is used to calculate the effective binder content in the Superpave mix design system. Second, the Gse of the aggregate should remain relatively constant, assuming that the water absorption and Gsb of the aggregate are not changing. The equation for Gse can be rearranged to calculated Gmm. The equation for Gmm suggests that there is a straight line relationship between asphalt content and Gmm, e.g. if you plot Gmm versus AC%, the resulting data over a range of AC% should result in a straight line. This relationship can be used during mix design to predict Gmm values at other asphalt contents or it can be used during production as a check on the AC% and Gmm testing.

+

−=

b

b

se

bmm

GP

GP

G1

1



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6.3.3.2 Marshall Mix Design

6.3.3.2.1 Historical Background Bruce G. Marshall began the development of what later became known as the Marshall mix design procedure around 1939 while employed by the Mississippi State Highway Department. Marshall developed the stability test; flow measurements were added by the U. S. Army Corps of Engineers. Marshall was retained by the Corps during their studies. Initially, samples of HMA for the stability and flow tests were compacted with a modified American Association of Highway Officials (AASHO), California Bearing Ratio (CBR) field hammer. The modified AASHO hammer consisted of a 10 pound hammer (weight) dropped 18 inches; the load was transferred to the sample through a 1.95-inch diameter foot. Samples were compacted in a 4-inch diameter mold with a target compacted height of 2.5 inches. The diameter of the compaction foot was later modified to 3 7/8 inches. The Corps of Engineers was charged with selecting a method of HMA mix design to deal with the increasing tire pressures found on military aircraft. Aircraft weights began increasing during World War II. As the weight of the aircraft increased, tire pressures were also increased to minimize the size of the landing gear. At the beginning of World War II, tire pressures were approximately 100 psi. By the end of World War II, tire pressures had increased to approximately 200 psi. The Corps of Engineers constructed a number of HMA, sand asphalt and double surface treatment sections with varied asphalt contents. Loading was applied with a modified scraper pulling a load cart. The net tire contact pressures were 106, 146 and 139 psi for the 15,000, 37,000, and 60,000-lb wheel loads, respectively. Net pressures were used to account for the block nature of the tire tread. The performance of the pavement sections were monitored as a function of wheel passes, 3500 passes for the 15,000 lb load and 1500 passes each for the 37,000 and 60,000 lb loads (Figure 6-17). The 50-blow on each face compaction effort was developed out of this study. The Corps of Engineers concluded that tire pressure was more important than load in its effect on pavement performance. In summary the Corps of Engineers note (10), “The results of this study indicate that the quantity of asphalt is the most important factor in a paving mixture. Where there is too much asphalt in the mix the resultant pavement will “flush” and the pavement will rut and shove under traffic. Too little asphalt produces a brittle pavement that will crack and ravel. From the standpoint of durability, it is desirable to include as much asphalt as possible.”



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Figure 6-17 Traffic Compaction Data for Mix 11, Crushed Limestone with Medium Filler Content.

Aircraft tire inflation pressures continued to increase in the late 1940’s and early 1950’s. Tire pressures doubled from the approximately 100 psi net tire pressure used in the first field study to 200 psi. White reports (11), additional tests were conducted on the original test sections using both 30,000 lb wheel load with a 200 psi tire pressure and 15,000 lb wheel load with a 240 psi tire pressure. From these efforts it was determined that 69 blows from a 10-lb hammer falling 18 inches on a 3 7/8-inch diameter foot were appropriate for the increased tire pressures. This was later adjusted to the 75-blow Marshall. McLeod (16) first suggested the concept of designing for minimum VMA to ensure durability in 1956. VMA is the total void space filled with either air or asphalt between the compacted mineral aggregate, which is believed to be related to durability. He argued that VMA and VFA should be calculated with the effective binder content and aggregate bulk specific gravity to avoid errors with absorptive aggregates (12). In 1957, McLeod reaffirmed his belief that the effective binder content and aggregate bulk specific gravity should be used to calculate the VMA and air voids of the compacted HMA sample (13). McLeod stated: “Values for percent voids in mineral aggregate and for percent air voids can be defined precisely for compacted bituminous paving mixtures that are made with non-absorptive aggregates.” He added: “For compacted paving mixtures that contain absorptive aggregates, values for percent voids in the mineral aggregate and for percent air voids, should be calculated by means of (a) the ASTM bulk specific gravity of the aggregate, and (b) the effective bitumen content of the paving mixture.” McLeod’s objections to the use of apparent and effective aggregate specific gravities (which are substantially easier to measure) result from their failure to differentiate between the portion of the binder that is coating the aggregate particle and the portion of the binder that is absorbed in the aggregate. Without this differentiation, it is difficult to relate observations from the laboratory design to fie ld performance in terms of both permanent deformation and durability. In 1962, the Asphalt Institute published a new version of MS-2 that included the first “modern” version of the Marshall mix design procedure including volumetric analysis based on effective binder content (14). Eventually, mechanical Marshall Hammers were developed to reduce the effort required by the operator to produce samples. These tended to produce less compactive effort than a hand-held hammer. This is attributed to the operator moving the handle during compaction, producing a slight kneading action (15). To compensate, alternatives to the flat-foot, static base mechanical hammer were developed including the slant-foot, static base, and rotating base mechanical hammers. The Marshall mix design procedure was



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expanded to include 1 ½ inch maximum aggregate by developing a 6-inch diameter mold with a 75-blow compaction effort (16). By 1984, 38 out of 50 states were using the Marshall mix design procedure to design HMA.

6.3.3.2.2 Marshall Mix Design Procedure In the Marshall mix design procedure, once the materials are selected and a design gradation is selected, a series of samples are mixed and compacted over a range of asphalt contents encompassing the expected design asphalt content. Typically, samples are compacted at four asphalt contents which each vary by 0.5 percent. Three to four samples should be compacted at each asphalt content. The Marshall method typically does not include any short-term oven aging to simulate the aging and absorption of the binder that typically occurs when a mix goes through an asphalt plant. Therefore, the aggregate temperature should be adjusted so that the resulting HMA temperature, after mixing, is equal to the desired compaction temperature. The asphalt binder should be maintained at the mixing temperature determined from the kinematic or rotational viscosity tests, or in the case of a modified binder the supplier’s recommendations. Typically, an aggregate temperature 50 to 75 °F above the recommended mixing temperature for the asphalt binder suffices. Similarly, the compaction temperature should be determined from either the kinematic and absolute viscosity data or the supplier’s recommendation. Some designers will reheat the mixture to the compaction temperature after mixing. If this is done, it should be done uniformly, for instance by placing the samples in the oven for 30 minutes at the compaction temperature. A paper disk is placed in the bottom of the mold. The samples are loaded into a mold, spaded 10 times across the center and 15 times around the perimeter of the mold. A second paper disk is placed on top of the sample and then the sample is compacted with 50 or 75 blows on each face. The samples are allowed to cool in the mold until they can be handled without a glove. The samples are then jacked out of the mold and the paper disks removed. In some cases a heat gun, hair dryer, or blow torch are required to facilitate the removal of the paper disks. According to AASHTO T245, the specimens are then to cool overnight before completing testing. During production, this practice is seldom followed. Instead the samples are cooled in front of a fan for approximately one hour. AASHTO T245 requires that automatic Marshall Hammers be calibrated to a manual hammer. Typically, the required number of blows for an automatic hammer (Figure 6-18) is higher than the specified (50 or 75) number of blows with the manual hammer.



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Figure 6-18 Automatic Marshall Hammer.

The air voids of the cooled sample are determined as described previously. The heights of the samples are measured. The target height is 2.5 inches. The samples height is also used to correct the stability measurements. The samples are then placed in a 140 °F (60 °C) water bath for 30 minutes. The bath temperature was selected to represent typical pavement temperatures on a warm summer day. The samples is taken out of the water batch and immediately loaded into a Marshall stability and flow breaking head and then tested for stability and flow (Figure 6-19). The sample is loaded at a rate of 20 inches per minute. The stability is defined as the peak load carried by the sample and the flow is the vertical deformation at the peak load.



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Figure 6-19 Marshall Stability and Flow Press.

The asphalt institute procedure uses three criteria to determined optimum asphalt content using the Marshall Method. The optimum asphalt content is the average of the asphalt content that produces 4 percent air voids, maximum stability and maximum unit weight. The flow and VMA values are then compared to the acceptable ranges at the optimum asphalt content. The Asphalt Institute procedure and most agency specification varied criteria based on expected traffic. Table 6-3 presents typical Marshall criteria. The stability values are most affected by the viscosity of the binder at 140 °F (60 °C) and the angularity of the aggregate. High flow values generally indicate a plastic mix which may be subject to permanent deformation, whereas low flow values tend to indicate high voids and the potential for durability problems. As mentioned previously, VMA is used to help ensure the durability of the mixture. Smaller particles have a greater surface area for the same volume of material. Therefore mixes made with smaller NMAS aggregate require more asphalt to provide the same film-thickness of asphalt coating than larger NMAS mixes. Therefore minimum VMA requirements increase with decreasing NMAS as shown in Figure 6-20.

Table 6-3 Marshall Design Criteria Property/Traffic Light

< 104 ESAL Medium 104 < ESAL<106

Heavy > 106 ESAL

Compaction, blows 35 50 75 Stability, lb (N) 750 (3336) 1200 (5338) 1800 (8006) Flow 0.1 in (0.25 mm) 8 to 18 8 to 16 8 to 14 Air Void, % 3 to 5 3 to 5 3 to 5 VMA, % Varies with aggregate size



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Figure 6-20 Minimum VMA as a Function of Aggregate Size.



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6.3.3.3 Hveem Mix Design

6.3.3.3.1 Historical Background Francis N. Hveem was first exposed to asphalt as a young employee of the California Division of Highway. By 1929, Hveem observed that coarser gradations tended to require less road oil than finer gradations and made the connection that the surface area of the aggregate varied with gradation. Hveem identified a method for calculating (estimating) the surface area of aggregate. Hveem realized that in addition to surface area, the optimum asphalt content, or at least the point where the optimum asphalt content was exceeded and stability decreased was affected by the surface texture of the aggregate. A “surface factor” was used by Hveem in combination with the calculated surface area to determine the optimum asphalt content. Although an experienced engineer could adjust for texture and absorption of various aggregates, Hveem later developed the centrifuge kerosene equivalent (CKE) test to estimate the surface constant (a combination of surface area, absorption and adjustment for surface texture) of the fine aggregate. Vallerga and Lovering (8) quote Hveem’s own summary of his mix design philosophy in 1937 as follows,

“For the best stability, a harsh, crushed stone with some gradation, mixed with only sufficient asphalt to permit high compaction with the means available. For greatest resistance to abrasion, raveling, aging and deterioration, and imperviousness to water, a high asphalt content, broadly speaking, the richer the better. For impermeability, a uniformly graded mixture with a sufficient quantity of fine sand (fine sand is more important than filler dust). For non-skid surfaces, a large quantity of the maximum sized aggregate within the size limits used. For workability and freedom from segregation, a uniformly graded aggregate. To reduce the above factors to as simple a consideration as possible, it seems to be the best rule to use a dense, uniformly graded mixture without an excess of dust and to add as much oil or asphalt as the mixture will tolerate without losing stability.”

[Currently, we would describe “uniformly” graded as “well” or “dense” graded]. Graphically, this philosophy is summarized in Figure 6-21.



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Figure 6-21 Stability and Durability as a Function of Asphalt Content (8)

6.3.3.3.2 Hveem Mix Design Procedure Once the asphalt binder, aggregates, and design gradation are selected as discussed previously, the first step in conducting a Hveem mix design is to calculate the estimated surface area of the aggregate. The surface area is estimated using the surface area factors and the gradation percent passing as shown in Table 6-4.

Table 6-4 Surface Area Factors Sieve Size (mm) Percent Passing1 Surface Area

Factor (SAF) Surface Area, m2/kg (ft2/lb) Percent Passing x SAF/100

Maximum size 100 0.4 (2)2 0.4 4.75 mm (No. 4) 0.4 (2) 2.36 mm (No. 8) 0.8 (4) 1.18 mm (No. 16) 1.6 (8) 0.600 mm (No. 30) 2.9 (14) 0.300 mm (No. 50) 6.2 (30) 0.0150 mm (No. 100) 12.4 (60) 0.075 mm (No. 200) 33.0 (160) SA = ∑m2/kg (ft2/lb)

1Percent passing of design gradation (blend) 2Surface area factor for ft2/lb shown in ()



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The next step is to determine the CKE to correct for the surface texture of the fine aggregate. A 100 g sample of the fine aggregate (100 percent passing the No. 4 sieve) is saturated in kerosene. The sample is then subjected to 200 times gravity in a centrifuge, after which the aggregate was weighed to determine the percent of kerosene retained by mass of dry aggregate. If the fine aggregate type was similar to the coarse aggregate, then the bitumen index or the quantity of asphalt required to coat one unit of the area of aggregate could be determined directly from the CKE test; otherwise a separate test could be performed to determine the surface factor of the coarse aggregate (9). The surface capacity of the coarse aggregate is performed by soaking a sample of the coarse aggregate in S. A. E. 10 oil for five minutes, and then allowing the sample to drain for 15 minutes at 140°F before determining the percent of retained oil. The coarse aggregate surface factor is used to correct the fine aggregate surface factor. These procedures, either the surface area calculation or the surface factors can be used to estimate optimum binder content. Correction factors are also included for aggregate specific gravity and the viscosity of the asphalt. Nomographs are then used to estimate the optimum bitumen ratio. Is should be noted that the bitumen ratio calculates the asphalt content as a percent by aggregate weight. The bit umen ratio can be converted to an AC% by total weight of mix as follows:

100100

% ×÷

=RatioBitumen

RatioBitumenAC

Samples are then batched and mixed as described previously. Typically, a minimum of four asphalt contents and up to seven asphalt contents are used to produce specimens. If four asphalt contents are used, samples would be prepared at the optimum asphalt content predicted from the surface area and CKE, optimum – 0.5 percent, optimum + 0.5 percent and optimum + 1.0 percent. After mixing, the samples are oven aged in a flat pan for 15 hours at 140 °F (60 °C) prior to compaction. Samples are compacted using the Hveem Kneading Compactor (Figure 6-22). The kneading compactor primarily uses a triangular shaped compaction foot. The sides of the foot are slightly radiused and the points of the triangle are rounded. The foot applies a kneading action to the surface of the sample without impact, which allows reorientation of the aggregate particles similar to that which occurs under a roller or traffic in the field.



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Figure 6-22 Kneading Compactor.

Approximately half of the batch is placed in a 4-inch diameter mold and rodded 20 times in the center of the mold and 20 times around the perimeter then the remainder is added and rodded in the same manner. The mold is placed in the compactor and 10 to 50 blows are applied with a 250 psi pressure. Typically, 20 blows typically being sufficient to precompact the mixture. The mold rotates 1/6 of a turn after each tamp. After precompaction, 150 tamping blows are applied at a pressure of 500 psi. The sample is then reheated to 140 °F (60 °C) for 1.5 hours and then a 1000 psi static load to level the specimen using the “double plunger method.” This laboratory compaction method generally exceeds the compaction provided by either a Marshall Hammer or a Superpave Gyratory compactor. A pyramid scheme is used to select the optimum asphalt content using the Hveem mix design procedure as shown in Figure 6-23. The first step is to examine the surface of the compacted sample for flushing after the 150 tamping blows have been applied. The asphalt contents that exhibit moderate to heavy flushing are to be discarded. Moderate flushing would be described if paper sticks to the surface, but no distortion is observed. Heavy flushing would result in asphalt puddle on the surface or distortion of the surface of the sample. At least one of the trial asphalt contents should result in medium or heavy flusing.



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Figure 6-23 Hveem Mix Design Pyramid

Hveem wanted to evaluate the stability of the HMA. He hypothesized that depending on the roughness and angularity of the aggregate, the film thickness at which the particles would become overly lubricated by the asphalt and therefore unstable would vary (9). The stabilometer (Figure 6-24) evolved into a hydraulic device into which a compacted sample of asphalt was loaded. The sample was loaded vertically on its flat surface and the radial force transmitted to the surrounding hydraulic cell is measured. The stability value is calculated as follows:

222.0)(

2.22

2 +−

=

hv

h

PPDP

S

where, Pv = vertical pressure (400 psi), Ph = horizontal pressure at a vertical pressure of 400 psi, and D2 = displacement of sample in number of turns of handle.



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Figure 6-24 Hveem Stabilometer.

The minimum recommended stability values are: § 30 minimum – Light Traffic § 35 minimum – Medium Traffic § 37 minimum – Heavy Traffic

Samples representing asphalt contents that do not meet the minimum stability value are eliminated next in the pyramid scheme. After completion of the stabilometer test, the Gmb of the samples are determined as described previously. The final asphalt content is selected as the highest asphalt content which meets the minimum stability and has at least 4 percent air voids.



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6.3.3.4 Superpave Mix Design

6.3.3.4.1 Historical Background The Superpave Mix Design System was a product of the Strategic Highway Research Program (SHRP). The SHRP project was a five-year (1988 to 1993) congressionally funded transportation research project with a total funding of 200 million dollars, 50 million of which was spent on asphalt research. During planning for the SHRP project, premature pavement rutting was a serious concern in the U. S. as were concerns regarding low temperature cracking. The development of a new binder specification was an early goal of the research. The development of a new mix design system evolved as the research progressed. Numerous universities participated in the SHRP research. The University of Texas at Austin under Dr. Tom Kennedy headed the synthesis of the design system. 6.3.3.4.2 Superpave Mix Design System It is important to understand the Superpave Mix Design System, unlike the previous mix design procedures was designed to function as a system including the following parts: § Materials Selection

o Asphalt binder o Aggregates

§ Volumetric Mix Design § Moisture Sensitivity Testing § Performance Testing for Critical Pavements.

The Superpave Mix Design System is Summarized in AASHTO M323 and AASHTO R 35.

As described previously, the PG binder specification was developed to specify and grade asphalt binders. Binders for a specific paving job were to be selected using climatic data with the high temperature grade modified by the traffic speed and volume. Previously, individual agencies had set their own aggregate requirements for the Marshall and Hveem mix design procedures. As described previously, Superpave attempted to codify aggregate selection through the consensus aggregate properties and source aggregate properties. The consensus aggregate properties vary by traffic level, but are to be uniformly applied within the Superpave system. Allowances for local materials are made the the “source” properties where agencies can set limits for aggregate degradation (LA Abrasion) and freeze-thaw durability (Soundness) based on locally available materials. The Superpave Consensus aggregate properties are summarized by traffic level in Table 6-5. All of the Superpave consensus aggregate properties are tested on the blend of aggregates, not the individual stockpiles. Tests can be performed on an individual stockpile and then mathematically combined to produce the blend result. The Superpave mix design method recognizes that stresses decrease with depth in the pavement structure. Therefore, criteria are separated depending on whether the majority of the layer is less than or greater than a depth of 4 inches (100 mm).

Although Port loadings in wharf and container areas may not be directly transferable to ESALs, a traffic loading of between 3 and 30 million ESALs is probably appropriate for heavily loaded areas. Designs for higher traffic loadings would produce more rut resistant pavements. Employee parking areas would be represented by lower traffic levels.



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Table 6-5 Superpave Consensus Aggregate Properties Design ESALs (Million)

Coarse Aggregate Fractured Faces, % Minimum

Uncompacted Void content of Fine Aggregate2, % Minimum

Depth from Surface Depth from Surface < 100 mm > 100mm < 100 mm > 100mm

Sand Equivalent Value, % Minimum

Flat and Elongated Particles3, % Maximum

< 0.3 55/- -/- - - 40 - 0.3 to <3 75/- 50/- 40 40 40 10 3 to <10 85/801 60/- 45 40 45 10 10 to <30 95/90 80/75 45 40 45 10 >30 100/100 100/100 45 45 50 10

185/80 refers to 85 percent with at least one fractured face and 80 percent with at least two fractured faces as measured by ASTM D5821 on the +4.75 mm material. 2Uncompacted Void Content of Fine Aggregate Measured using AASHT T304, Method A 3Percentage of flat and elongated particles exceeding the maximum to minimum dimensional ratio of 5:1 on the +4.75 mm material.

The Superpave mix design system recommended additional source properties, whose specification limits were to be set by the agency based on locally available materials. Source properties include: LA Abrasion, Sulfate Soundness and Deleterious materials. Deleterious materials are clay, coal or other soft materials. These materials may cause popouts in the pavement surface. The Superpave gradation requirements are based on NMAS. When using the Marshall or Hveem mix design procedures, agencies typically adopted relatively narrow gradation bands with controls on most sieve sizes. Superpave gradations use relatively few controls including: 0.075 mm, 2.36 mm and NMAS sieve sizes. The Superpave control points are shown for the 25.0, 19.0 and 12.5 mm NMAS in Table 6-6. As noted previously, the Superpave mix design system originally included the restricted zone to help prevent excessive quantities of rounded natural sand. Research showed that many mixes with good historical performance passed through the restricted zone and that the restricted zone was redundant if the uncompacted voids test was used. Overall, the Superpave criteria allow the designer a great deal of freedom. Some agencies have added or tightened the ranges, particularly by increasing the minimum percent passing on the 2.36 mm sieve to prevent excessively coarse mixes. Coarse mixes tend to be more permeable at the same in-place air void content.

Table 6-6 Superpave Aggregate Gradation Control Points for Selected NMAS 25.0 NMAS 19.0 NMAS 12.5 NMAS Sieve Size, mm

(in) Min. Max. Min. Max. Min. Max. 37.5 (1 ½) 100 25.0 (1.0) 90 100 100 19.0 (3/4) 90 100 100 12.5 (1/2) 90 100 9.5 (3/8) 4.75 (No. 4) 2.36 (No. 8) 19 45 23 49 28 58 1.18 (No. 16) 0.075 (No. 200) 1 7 2 8 2 10



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The Superpave mix design system recommends that three design aggregate structures with varying gradation be developed and that trial samples be prepared at each of the gradations. This practice is advisable if the designer has little or no familiarity with the aggregate source. With limited experience a designer can choose a blend that will meet the specification requirements, it may not, however, be the optimum aggregate blend. If possible, a design produced under another mix design system, such as Marshall or Hveem should be used as a starting point if the designer has no prior experience with Superpave. Once the design aggregate structure is selected, samples are batched for a volumetric mix design. Superpave Gyratory Compactor (SGC) samples are 150 mm (6 inches) in diameter and have a target height of 115 mm (4.5 inches). Therefore, SGC samples require a greater mass of material, typically 4500 to 5000 grams of mix depending on the specific gravity of the aggregate. The larger sample size was selected for SGC samples in order to provide more representative samples for larger aggregate sizes. Because of the larger sample size, bulk batching, discussed previously, can be used more readily with SGC samples. It is still paramount that a washed gradation be performed on a batched sample in order to ensure that the batched sample represents the target design gradation. The rotational viscometer is used to determine the mixing and compaction temperature ranges for unmodified asphalts. Typically, two tests are run at 135 and 165 °C (275 and 325 °F). The results are plotted on a log-log graph of temperature versus viscosity as shown in Figure 6-25. The mixing and temperature ranges are then picked off the graph from the recommended viscosity ranges of approximately 0.17 ± 0.02 Pa•s for mixing and 0.28 ± 0.03 Pa•s for compaction. For modified asphalts, the supplier’s recommendations for mixing and compaction temperatures should be used. Research is currently in progress to identify a better method for the determination of mixing and compaction temperatures. Overheating certain polymer modification systems can damage the polymer resulting in a softer binder.



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Temperature, C

Vis

cosi

ty, c

P

Control PG 64-22

0.1

1

10

52 58 88 100 150 165 180 200

Mixing Range

Compaction Range

64 76 8270 120 135

100

500

Figure 6-25 Example Mixing and Compaction Temperature Chart from Rotational Viscometer.

Once the HMA sample has been mixed, the sample is spread out in a thin lift in a pan and aged for two hours at the compaction temperature according to AASHTO R30. This aging simulates the expected aging of the mixture that will occur during mixing, storage, hauling and compaction. Asphalt will also be allowed to absorb into the aggregate during this time period. The SGC molds should be preheated to the compaction temperature. The HMA is to be gathered from the aging pan and loaded into the SGC mold all at once, not by repeated scooping from the aging pan. This can be accomplished by scooping the mix into a metal “taco” or making a “burrito” out of brown craft paper. The burrito method works best for mixtures prone to segregation (coarse base mixes). SGC samples are not rodded before compaction. The mold is then loaded into the SGC.



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Figure 6-26 SGC Characteristics.

The SGC was based off the Texas gyratory compactor, but adopted the approximate gyration angle and vertical pressure of the French Gyratory Press. The operating characteristics of the SGC are shown in Figure 6-26. There are a number of brands and models of SGCs. Although SGCs are required to be evaluated under AASHTO PP35, which compares them to either the original Pine AFGC125X or the Troxler 4140, research has shown that different models of SGC can produce different compactive efforts. Differences in the angle of gyration due to differences in machine compliance are believed to cause the differences in compactive effort and the resulting differences in Gmb. Originally, the angle of gyration was measured external to the gyratory mold. Devices have been developed to measure the internal angle of gyration inside the mold and under load. Although these devices were originally used in conjunction with HMA, two new devices, the Pine Rapid Angle Measurement Device and the Troxler Dynamic Angle Validator II, are available which measure the dynamic interna l angle (DIA) of gyration without mix. The Superpave Mixture and Aggregate Expert Task Group has recently recommended that all SGCs be calibrated to a DIA of 1.16 ± 0.03 degrees with one of the two mixless internal angle devices. The number of gyrations used to compact samples in the SGC is similar to the number of blows used to compact a Marshall samples. Higher numbers of gyrations are recommended for higher traffic levels as shown in Table 6-7. The SGC records the samples height with each gyration. Knowing the sample height, diameter of the mold (150 mm) and sample mass the density of the sample can be estimated at any gyration level. The estimated density is then corrected for the surface voids by determining the samples Gmb after compaction. The correction factor is assumed to be constant at every gyration. Three parameters are considered on the SGC compaction curve, Ninitial, Ndesign, and Nmaximum as shown in Figure 6-27, a plot of log gyrations versus sample density. The Ninitial criteria are believed to indicate the potential for tenderness in the mix during compaction. Tenderness is a condition where the mix moves in front of the roller if the mix is too hot. It is different from the “tender zone,” which will be



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discussed later. If the mix compacts too rapidly in the SGC, it may be susceptible to tenderness. Ndesign is the number of gyrations where the volumetric properties of the mix are evaluated and the optimum asphalt content selected. Nmaximum is supposed to simulate the density of the Table 6-7 Design Gyration Levels.

Compaction Parameter Design ESALs (millions) Ninitial Ndesign Nmax < 0.3 6 50 75 0.3 to <3 7 75 115 3 to < 30 8 100 160 ≥ 30 9 125 205

Figure 6-27 SGC Compaction Curve.

pavement near the end of its service life after trafficking. If a pavement compacts to more than 98 percent of Gmm (less than 2 percent air voids), then the pavement is susceptible to bleeding and rutting. If the SGC sample compacts to greater than 98 percent of Gmm at Nmaximum gyrations the pavement was believed to be susceptible to rutting. Revisions to the Superpave Mix Design System based on the NCHRP 9-9 research changed the SGC procedure such that routine design and quality control samples were compacted to Ndesign gyrations. Once optimum AC% was determined, the Nmaximum criteria could be checked during design. After short term oven aging, SGC samples are compacted to Ndesign gyrations. The samples are immediately jacked out of the mold and the end papers removed. The samples are allowed to cool. Then the Gmb of the compacted sample is determined as described previously. The Gmb, Gmm, and Gsb are used to calculate air voids, VMA and VFA as described previously. Superpave specifies that one additional property be calculated, the dust to effective binder content ratio. To do this, first the effective asphalt content must be calculated. The effective asphalt content is the portion of the asphalt content



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6-45

which is not absorbed into the surface voids of the aggregate. The effective asphalt content (Pbe) is calculated as follows:

)()()(( sbsesbsebsbbe GGGGGPPP ×÷−××−= where, Ps = percent stone = 100 – AC%, Pb= AC% Other terms defined previously.

The dust to effective asphalt content is then the percent passing the 0.075 mm sieve based on a washed gradation divided by Pbe. The volumetric criteria for the Superpave Mix Design System vary by traffic level and NMAS as shown in Table 6-8 and the minimum VMA requirements by NMAS are shown in Table 6-9.

Table 6-8 Superpave Design Requirements Required Density, %Gmm Design

ESAL (Million)

Ninitial Nmaximum

Air Voids, %

VMA, % VFA, % Dust to Effective Binder Ratio

<0.3 ≤91.5 ≤98.0 4.0 70-80 0.6-1.2 0.3 to <3 ≤90.5 ≤98.0 4.0 65-78 0.6 3 to <10 ≤89.0 ≤98.0 4.0 65-75 0.6 10 to <30 ≤89.0 ≤98.0 4.0 65-75 0.6 ≥30 ≤89.0 ≤98.0 4.0

Varies by NMAS, See Table 9

65-75 0.6

Table 6-9 Superpave Minimum VMA Requirements NMAS, mm Minimum VMA, % 37.5 11.0 25.0 12.0 19.0 13.0 12.5 14.0 9.5 15.0 4.75 16.0

6.3.4 Step 4: Evaluation of the Moisture Sensitivity

The final step in any volumetric mix design procedure, be it Marshall, Hveem, or Superpave, is an evaluation of the moisture susceptibility of the mixture at optimum asphalt content. Moisture susceptibility, often referred to as stripping is the condition where the asphalt separates from the aggregate or the asphalt binder itself weakens in the presence of binder. If the binder separates from the aggregate, this is called an adhesive failure or stripping. If the binder fails within itself it is called a cohesive failure. The most commonly used test for determining moisture susceptibility is the tensile strength ratio (TSR) test (AASHTO T283). The test method specifies that samples be compacted to 7 ± 0.5 percent air voids. This air void level was chosen to simulate typical in-place air void contents. The



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test method was originally developed for 4-inch diameter by 2.5 inch tall samples. SGC samples 150 mm in diameter and 95 mm tall can also be tested. With the SGC, preparing samples 95 mm tall with an air void content of 7% is relatively easy. A volumetric calculation is done to estimate the mass of material required to give 7% air voids or 93% density. Typically, the target density must be reduced by 1.5% to account for surface voids.

21525.05.95.91arg ×××××= πmmGmassetT

The SGC is then set to compact to a specified height (95 mm) instead of a specified number of gyrations. A similar calculation can be used to estimate the required mass for Marshall or Hveem samples, but the number of blows or tamps needs to be adjusted to achieve the required height. This can be a trial and error process. A minimum of six samples need to be prepared and generally eight are prepared to ensure that six samples with the appropriate air void content are obtained.

Based on AASHTO T283, specified by the Superpave Mix Design System, the loose mix is to first be aged for 16 ±1 hours at 140 °F (60 °C) and then heated to compaction temperature for 2 hours prior to compaction. The cooled samples are bulked and then are supposed to age at room temperature 24 ± 3 hours. Some agencies have waived the 16 hour oven cure and 24 hour counter cure. The samples are divided into two subsets a dry and a conditioned subset. The samples in the conditioned subset are then saturated with water using a vacuum. The required degree of saturation is 70 to 80 percent. The saturated samples are wrapped tightly in plastic wrap. After saturation there is an optional (for the ASTM method) 16-hour freeze cycle. This option should be used by all agencies regardless of whether or not it freezes in their climate. The freeze cycle produces pore pressure in the mixture, similar to that produced in a saturated pavement under loading. After the freeze cycle, the conditioned samples are placed in a 140 °F (60 °C) water bath for 24 hours. The plastic wrap is removed as soon as possible in the hot water bath. Finally, both the dry (wrapped in plastic) and conditioned samples are placed in a 77 °F (25 °C) water bath for 2 hours. The indirect tensile strength is then determined at a loading rate of 2 inches per minute using a fixture similar to that shown in Figure 6-28. The TSR is reported as the ratio of the average conditioned tensile strength to the average unconditioned tensile strength. Superpave requires a minimum TSR of 0.80. Certain aggregate types, such as granite or siliceous material are more susceptible to moisture damage than other aggregate types. Mixtures that fail TSR can be addressed in a number of manners. Liquid anti-striping agents, primarily amines, can be added to the binder either at the terminal or at the HMA plant. These additives alter the surface chemistry between the asphalt and binder, improving adhesion. Hydrated lime can also be added to the mix. Hydrated lime should be added to damp aggregate or in a slurry form to allow a chemical reaction to occur between the lime and the surface of the aggregate. The addition of hydrated lime does increase the material passing the No. 200 sieve in the mixture. It also tends to reduce the optimum asphalt content, even at the same dust content. Many agencies consider hydrated lime to be the best material for reducing the likelihood of moisture damage.



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Figure 6-28 TSR Fixture and Press.



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7. Layered Elastic Analysis ....................................................................................................... 7-2 7.1 Theory .......................................................................................................................... 7-2 7.2 Software........................................................................................................................ 7-3 7.3 Empirical Stiffness........................................................................................................ 7-3

7.3.1 Asphalt Concrete ............................................................................................................................................. 7-3 7.3.2 Cement Treated Base..................................................................................................................................... 7-4 7.3.3 Aggregate Base Course and Sub-base Course........................................................................................ 7-5 7.3.4 Subgrade ............................................................................................................................................................ 7-6

7.4 Design Life .................................................................................................................... 7-7 7.5 Permanent Deformation ............................................................................................... 7-8 7.6 Structural Cracking...................................................................................................... 7-9

7.6.1 Asphalt Concrete ............................................................................................................................................. 7-9 7.6.2 Cement Treated Base...................................................................................................................................7-10

7.7 Design example for flexible pavements........................................................................ 7-11 7.7.1 Input Data.......................................................................................................................................................7-11 7.7.2 Operations.......................................................................................................................................................7-13 7.7.3 Design Method...............................................................................................................................................7-13 7.7.4 Subgrade ..........................................................................................................................................................7-14 7.7.5 Pavement Sections.........................................................................................................................................7-14 7.7.6 Computer output...........................................................................................................................................7-15



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7. Layered Elastic Analysis

7.1 Theory

When a wheel load is applied to a flexible pavement it causes stresses and strains to develop in the pavement and subgrade. The stresses and strains are distributed according to the elastic properties of the various layers. Consider a homogeneous half space with an elastic modulus (E) and Poisson’s ratio (ν ) with a circular load acting on top of the half space, having a radius (a) and a uniform contact pressure (q). Then consider a small element with its center at depth (z) below the load and distance (r) from its center. The element has two horizontal faces, two radial faces and two tangential faces Theory determines that nine stresses act on this element. There are three normal stresses acting perpendicular to the faces of the element. These are the vertical stress (sz), radial stress (sr) and

tangential stress (st). There are also six shearing stresses acting parallel to the faces of the element. These are rtτ (which equals trτ ), rzτ (which equals zrτ ) and ztτ (which equals tzτ ). These stresses can be calculated at any point using Boussinesq’s equations. Under condition under center of load, the following stresses and strains formulas are given. Vertical Stress and Strain

+−=

3 22

3

1za

zqzσ

+−

++−

+=

3 22

3

22

221

1

za

z

za

zE

qzν

νν

ε

Horizontal Stress and Strain Radial and tangential are equal under center of load

++

+

+−+=

3 22

3

22

)1(221

2 za

z

za

zqr

ννσ

++

+

−−−+=3 22

3

22

)1(221

2)1(

za

z

za

zE

qr

νννε

Vertical Deflection ( ∆ )

−+−+

+

+=∆

azza

za

aE

qa 22

22)21(

)1(ν

ν



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The elastic strains corresponding to each normal stress are determined from the following equations

vertical strain ( ))(1

trzz Eσσνσ +−=∈

radial strain ( ))(1

ztrr Eσσνσ +−=∈

tangential strain ( ))(1

rztt Eσσνσ +−=∈

7.2 Software

Kenlayer pavement design software can be used to analyze the pavement sections and develop strains at critical points in the pavement. It analyses elastic multilayer system under circular loads and superimposes values for multiple loads. It can use an iterative approach for nonlinear layers, collocated at various times for viscoelastic layers. The program can also consider variations in material properties. The program can determine the design life based upon fatigue cracking, or upon permanent deformation. However, these are not recommended procedures for the pavements at the port Input parameters required to run the program are the Z coordinates, and the layer properties. These include thickness, Poisson’s ratio , elastic modulus and unit weight. It also requires the interface details between each layer and details on nonlinear and viscoelastic layers. The load information required to run an analysis includes the contact pressure, contact radius, the axle spacing, the wheel spacing and the number of repetitions. It also requires the response positions for calculating the stresses and strains in X-coordinates and Y-coordinates. Critical locations are at the top of unbound layers where vertical strain is limiting factor that leads to permanent deformation. This typically controls the pavement thickness when bound layers are thin. The other critical location is at the bottom of bound layers where horizontal strain is limiting factor. This leads to fatigue cracking that controls the pavement thickness when bound layers are thick 7.3 Empirical Stiffness

7.3.1 Asphalt Concrete

As noted above, the elastic propertie s of asphalt concrete are greatly affected by the mix properties, the pavement temperature, the age of the asphalt concrete layer and the speed of the container handling equipment. As such the stiffness of the layer will be different for each load repetition. The potential range of elastic modulus (E) and Poisson’s ratio (Λ) normally encountered are:

E = 100,000 – 1,000,000 psi.

ν = 0.3 – 0.4



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To streamline the analysis process it is beneficial to select one value that will represent the elastic properties over the life of the pavement. The following values are typical for the surface course and base course under slow moving heavy wheel loads over the life of the pavement.

New surface course: E = 250,000 psi. and ν = 0.40

Existing uncracked surface course: E = 600,000 psi. and ν = 0.35

Old cracked surface course: E = 400,000 psi. and ν = 0.30

Failing surface course E = 200,000 psi. and ν = 0.25

Suggested design values E = 450,000 psi and ν = 0.35

New base course: E = 400,000 psi. and ν = 0.40

Existing uncracked base course: E = 700,000 psi. and ν = 0.35

Old cracked base course: E = 500,000 psi. and ν = 0.30

Failing base course E = 300,000 psi. and ν = 0.25

Suggested design values E = 550,000 psi and ν = 0.35 7.3.2 Cement Treated Base

The compressive strength of cement treated base is typically between 500 psi and 1,000 psi. At these strengths the material can be mixed in place, but plant mixing is preferred. The elastic properties of cement treated base are dependent on the strength of the cured material, which is in turn dependent on the quality of the materials and the amount of cement used in the mix. The elastic modulus can be derived from compressive tests or from the specified minimum strength. The Poisson’s ration does not change. One standard equation to determine the uncracked elastic modulus is as follows:

E = 57,000 x fc0.5 and

ν = 0.2 where

fc = compressive strength

Cement treated base undergoes shrinkage as it cures, and this will result in a series of cracks. The cement treated base will not be as strong in these locations, and as such it is necessary to consider the cracked modulus. This can be taken as half of the uncracked modulus. As cracking is assumed to have occurred, it is not necessary to verify the fatigue life properties.



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7.3.3 Aggregate Base Course and Sub-base Course

Aggregate base course and sub-base course are constructed using unbound graded aggregates. These may be virgin materials, but there is a general preference for recycled granular products. These are most commonly the result of crushing concrete and asphalt concrete and recycled granular materials. Several different types of aggregate base are specified in the Standard Specifications for Public Works Construction “Greenbook”. Crushed aggregate base (CAB) is graded crushed rock that is required to have a minimum R-value of 80. Crushed miscellaneous base (CMB) is a crushed graded recycled aggregate that is also required to have a minimum R-value of 80. It is available in a fine and coarse gradation. Processed miscellaneous base (PMB) is a partially crushed graded recycled product that is required to have a minimum R-value of 78. It is also available in a coarse or fine gradation. Select sub-base is required to have a minimum R-value of 60 and is available in a coarse or fine gradation. The most common material used for aggregate base at the Port of Los Angeles is CMB. The elastic modulus of aggregate base and sub-base layers is dependent on the state of stress, the quality of the materials, the moisture conditions and the quality of construction, particularly the degree of compaction. The state of stress is dependent on the wheel load and the properties of the underlying subgrade. Many computer programs have routines that will calculate the modulus of the unbound layer based upon these conditions. Research has shown that this relationship holds true for light wheel loading as encountered in highway design, but that it is far more complex for heavy wheel loads found in airports and marine terminals. Therefore it is recommended that these routines are not used and that specific values are input based upon alternative approaches. One such approach for heavy wheel loads considered by the Corps of Engineers is to calculate the elastic modulus of the unbound layer based upon the thickness of the layer and the elastic modulus of the underlying layer. Two equations are used dependent on the quality of the material, i.e., whether they are base or sub-base materials. The maximum value of a base material will be 100,000 psi using these equations. Very high values should be used with caution and it is recommended that the maximum value used for a port pavement should be limited to 80,000 psi. The maximum value of a sub-base material will be 40,000 psi. These equations are as follows: For base layers

( )tEtEE nnn 10110101 loglog10.2log52.101 ++ −+= where

En = elastic modulus of the layer under consideration

En+1 = elastic modulus of the immediate underlying layer

t = thickness For sub-base layers

( )tEtEE nnn 10110101 loglog56.1log18.71 ++ −+= where



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En = elastic modulus of the layer under consideration

En+1 = elastic modulus of the immediate underlying layer

t = thickness To use these equations to calculate the elastic modulus of the different layers is necessary to sub-divide the sub-base and base into a series of layers. Typically these can be of the thickness that will be used for construction of each lift of each course. As such, layer thickness will generally be between 6 in and 8 in. The process starts from the bottom of the unbound layers. The modulus for the bottom layer should always be determined from the equation for sub-base layers. The elastic modulus for the underlying layer is that of the subgrade. For the second layer the equation for the appropriate material will be used. The modulus for the first layer and the thickness of the second layer will be used. The process is repeated to the top layer of material. The modulus of all base layers should be adjusted downward to a maximum 80,000 ps i if they are higher. If the layered elastic analysis program does not have the ability to consider the total number of layers considered in the equations, the average value for the base and sub-base should be used. Poisson’s ration for unbound granula r layers is dependent on the quality of the material and the moisture conditions. For crushed aggregate base materials the Poisson’s ratio (Λ) can be taken as 0.3. If the materials are naturally occurring or there is a high moisture content the ration will be 0.35. 7.3.4 Subgrade

The subgrade soils can be highly variable in character across the project site for a marine terminal. This is particularly relevant where the site has varied history of previous uses or fill operations. It is therefore important that all soil types are properly identified and characterized for design. It is strongly recommended that a 200 ft grid of test positions is set out on the site so that there will be adequate characterization of the soils. If inadequate testing is undertaken, the likelihood of premature failure or excessive pavement cost can be significant. It is not generally viable to vary the pavement design for each soil encountered, but some degree of fine tuning of the pavement can be undertaken when there are trends occurring over larger areas. The subgrade properties used in design are its resilient modulus and Poisson’s ratio. These can be determined directly from laboratory repetitive triaxial testing or derived from other laboratory tests and in-place testing. For the resilient modulus these include laboratory and in-place CBR tests, hand-held DCP tests and MEXE probe tests. The latter two provide equivalent CBR values. These tests are described in greater detail in other sections of this document. Poisson’s ratio can be estimated based upon the soil type and engineering judgment. There are several different relationships for converting CBR values into the resilient modulus in fine grained soils. In the most common method the resilient modulus can be determined from the CBR value as follows:

MR = 1500 x CBR It is generally considered necessary to limit the resilient modulus of subgrade materials to 30,000 psi. irrespective of test properties. If the pavement is a rehabilitation project a high level of information can be determined from FWD testing.



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As a last resort, the resilient moduli can also be estimated on the basis of the material type and engineering judgment. The following table sets out some typical values of resilient modulus and Poisson’s ratio for different subgrade types: After the test values or estimated values have been determined for each grid point, and assigned to defined pavement areas it is necessary to develop the appropriate design values for each area. The design value is generally take as the 85-percentile value. That is, the value at which 85 percent of the test results are higher. The remaining 15 percent will be below the design value, but this does not necessarily mean that these locations will fail prematurely. Very low results can be treated as soft areas and some additional depth of subgrade can be removed and replaced with better quality material, or these areas can be treated or modified. In addition, the variability in traffic loads and patterns will result in only part of this area being fully loaded. Local experience over the long term with certain subgrade materials may enable the use of a lower percentile value, or indicate the need for a higher one. 7.4 Design Life

Flexible pavements are considered to fail in a few different ways. These include permanent deformation (particularly rutting), structural cracking and environmental cracking. Permanent deformation results from repetitive wheel load applications on the pavement, or more correctly vertical stress and strain applications to the pavement and subgrade materials. The subgrade is most susceptible to permanent deformation. Structural cracking also results from repetitive wheel load applications on the pavement, or horizontal stress and strain applications to the pavement materials. The bottom of asphalt concrete or cement treated base is the most susceptible to structural cracking. Environmental cracking results from expansion and particularly contraction of the materials as a result of temperature changes, and from shrinkage of asphalt concrete as it ages. The top of asphalt concrete is the most susceptible to environmental cracking. Failure criteria are subjective issues, and arise from several aspects of the pavement performance. This may include ride quality, moisture penetration resistance and repair methods. They therefore vary with the type of application and the authority having jurisdiction. Typically for highway pavements the permanent deformation condition is defined as rut depths of 1/2 in to 1 in. For airports, similar criteria are used. Port pavements typically experience rut depths of up to 2 in before issues arise. For mechanistic design it is beneficial to represent the failure criteria in terms of strain. Much research has been undertaken to determine the strains at which permanent deformation limits are reached. There are several different models as a result of laboratory testing programs and pavement performance monitoring. Structural and environmental cracking is usually defined as a tensile failure of the asphalt concrete or cement treated base, and the initiation of cracking over 15 to 25 percent of the pavement. Many research programs have been carried out in this regard to develop limiting strain relationships. The design life of a pavement is generally considered as the point at which the cumulative strain repetitions from the design load have reached the allowable strain repetitions for the critical layer in the pavement or in the subgrade. As mentioned above, for load related failure this will normally be a vertical compressive strain at the top of an unbound layer or a horizontal tensile strain at the bottom of the bound layer. This does not necessarily mean that the pavement will no longer support traffic, but that it will have failed according to the definition of failure used in the design method. Rutting will continue to progress at an increasing rate and cracks may take some time to propagate beyond their point of initiation. For a port pavement that has significantly variability in the wheel loads and traffic patterns, and further



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variability in material properties, some pavement areas will fail before the design life has been reached and other will survive for a longer period. 7.5 Permanent Deformation

Permanent deformation can occur in the asphalt concrete layers, the unbound pavement layers and in the subgrade. Deformation in the asphalt concrete is generally minimized by the selection of the constituent material, the mix design process and quality of construction. Numerical fatigue relationships exist that can model permanent deformation in the asphalt concrete, but these are not generally considered for port pavement design, and are not included herein. Permanent deformation in the unbound pavement layers such as aggregate base and sub-base are also small because of the quality of the materials. However, these can be verified using the same fatigue relationships as used for the subgrade. It should be noted that improper material selection and construction quality can result in excessive deformation in these layers. The subgrade is the most critical layer for permanent deformation. There are many different theoretical relationships that have been developed for subgrade failure in highway conditions. There are fewer relationships developed from studies with heavy wheel load such as aircraft gear. One such relationship has been used by the FAA and Corps of Engineers. This relationship relates the allowable number of repetitions of the design wheel load to the specific level of vertical compressive strain from the layered elastic analysis of the pavement system, and the elastic modulus of the layer. The relationship is as follows:

B

z

AN

∈

= 000,10

where

N = allowable repetitions

A = 0.000247 + 0.000245log10MR

MR = elastic modulus of layer

z∈ = vertical tensile strain in layer

B = 0.0658E0.559 Figure 7-1 is a graphical representation of the relationship for typical subgrade materials :



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ALLOWABLE VERTICAL SUBGRADE STRAIN

800

900

1,000

1,100

1,200

1,300

1,400

10,00

020

,000

30,00

040

,000

50,00

060

,000

70,00

080

,000

90,00

0

100,0

00

110,0

00

120,0

00

130,0

00

140,0

00

150,0

00

160,0

00

170,0

00

180,0

00

190,0

00

200,0

00

210,0

00

220,0

00

230,0

00

240,0

00

250,0

00

Load Repetitions

Mic

rost

rain

CBR 5

CBR 10

CBR 15

CBR 20

Figure 7-1 Allowable Vertical Strain for Subgrade

Several layered elastic analysis programs have built-in permanent deformation routines that can be used to develop the design life of the pavement. Care should be taken in using these routines as many are the result of highway load related research. It is recommended that the computed strains are taken from the layered elastic analysis output and are analyzed separately. 7.6 Structural Cracking

7.6.1 Asphalt Concrete

Structural cracking occurs at the bottom of the asphalt concrete layer. Several theoretical relationships have been developed for asphalt concrete. For particular locations the fatigue relationships can also be determined through laboratory testing on the proposed materials. For cracking at the bottom of the asphalt concrete it is recommended that the relationship used by the FAA and Corps of Engineers is adopted. This relationship relates the allowable number of repetitions of the design wheel load to the specific level of horizontal tensile strain from the layered elastic analysis of the pavement system, and the elastic modulus of the layer. The relationship is as follows:

EN h 101010 log665.2log0.568.2log −∈−= where




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h∈ = horizontal tensile strain in asphalt concrete

E = elastic modulus of asphalt concrete Figure 7-2 is a graphical representation of the relationship for typical asphalt concrete materials:

ALLOWABLE HORIZONTAL TENSILE STRAIN AC

0

100

200

300

400

500

600

700

800

900

10,00

020

,000

30,00

040

,000

50,00

060

,000

70,00

080

,000

90,00

0

100,0

00

110,0

00

120,0

00

130,0

00

140,0

00

150,00

0

160,0

00

170,0

00

180,0

00

190,0

00

200,0

00

210,00

0

220,0

00

230,0

00

240,0

00

250,0

00

Load Repetitions

Mic

rost

rain

200,000 psi300,000 psi

400,000 psi600,000 psi

Figure 7-2 Allowable Horizontal Tensile Strain for Asphalt Concrete

7.6.2 Cement Treated Base

Structural cracking occurs at the bottom of the cement treated base layer. Only a few theoretical relationships have been developed for cement treated base material. Fatigue properties for tensile strain can be determine from repetitive load tests undertaken on beams of cement treated base. Several tests should be run at different stress levels (40%, 60%, and 80%), and fatigue properties should be calculated from deflections after 100, 1,000 and 10,000 cycles). For cracking at the bottom of the chemically stabilized layers (including portland cement and lime) it is recommended that the relationship used by the Corps of Engineers is adopted. This relationship relates the allowable number of repetitions of the design wheel load to the specific level of horizontal tensile strain from the layered elastic analysis of the pavement system. The relationship is as follows:

N = 10C where




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C = h∈− 0578.011.9

h∈ = Horizontal tensile microstrain in cement treated base Figure 7-3 is a graphical representation of the relationship:

ALLOWABLE HORIZONTAL TENSILE STRAIN CTB

60

65

70

75

80

85

90

10,00

020

,000

30,00

040

,000

50,00

060

,000

70,00

080

,000

90,00

0

100,0

00

110,0

00

120,0

00

130,0

00

140,0

00

150,0

00

160,0

00

170,0

00

180,0

00

190,0

00

200,0

00

210,0

00

220,0

00

230,0

00

240,0

00

250,0

00

Load Repetitions

Mic

rost

rain

Figure 7-3 Allowable Horizontal Tensile Strain for Cement Treated Base

7.7 Design example for flexible pavements

This chapter describe an design example for flexible pavements using the methods discussed in the previous section. The design analysis is done by using the Kenlayer computer software. Firstly preparation of the input data is discussed. Then the design method using the software is presented. The output from the computer software is also attached. 7.7.1 Input Data

7.7.1.1 Material Properties

7.7.1.1.1 Subgrade It is assumed that a geotechnical investigation has been undertaken for the area of the proposed pavement. Boreholes were formed and samples recovered for laboratory testing. The geotechnical report indicates that the ground conditions comprise recent fill materials including sand, silt and clay. The surficial soils on which the pavement will be constructed consist of loose to medium dense silty sand with a thickness of 15 to 30 feet. The soils are variously classified as SP, SM and SP-SM with a range of SPT blow



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counts between 5 and 20. The water table was a minimum of 12' below the underside of the pavement section. Undisturbed samples of the surficial soils within 10' of the underside of the pavement were taken from the boreholes at several locations to determine in-place density. The densities ranged between 90.3 pcf and 110.6 pcf. Compared with the maximum dry density of 117.2 pcf determined in accordance with ASTM D1557 during the laboratory test program, these values indicate in-place relative densities of between 77% and 94%. The majority of the results were between 85% and 90% relative density. Bulk samples of the surficial soils within 10' of the underside of the pavement were taken at eight locations for laboratory CBR testing. The soaked CBR values were determined in accordance with ASTM D1883, for in-place densities and relative densities of 90% and 95% of maximum dry density determined in accordance with ASTM D1557. The four in-place density CBR values were 3.0, 4.0, 4.5 and 6.5. The CBR values at 90% relative density were 7.0, 8.5, 13.0, 13.0, 14.0, 15.0, 15.5 and 16.0 at 0.1 inches penetration. At 95% relative density they were 18.0, 19.5, 23.5, 25.0, 26.0, 26.0, 26.0 and 32.0 at 0.1 inches penetration. The design CBR will be selected from this data as the 15th percentile for each relative density. The design CBR values are therefore 3.5, 8.7 and 19.7 respectively. For the analysis of the pavement section it is necessary to convert the design CBR values into equivalent elastic modulus values. Using a factor of 1,500 the elastic moduli become approximately5,200 psi, 13,100 psi and 29,600 psi respectively for in-place density and 90% and 95% relative density. These values can be used in a layered subgrade approach in the analysis. The specification for subgrade preparation will require that the top 12 inch layer of the subgrade is compacted to a minimum of 95% relative density (ASTM D1557) and the underlying 12 inches are compacted to a minimum of 90% relative density (ASTM D1557). To examine the interaction of one layer over the top of another to evaluate an equivalent composite modulus a Barker and Brabston analysis can be undertaken. The sub-base equation will be used for the subgrade materials. Using a foundation modulus of 5,200 psi for the natural soil creates a similar profile of elastic modulus values. This analysis indicates that the combined effective in-place elastic modulus under the pavement will be approximately 18,500 psi. This value can be used for a uniform subgrade approach in the analysis as an alternative to the multi-layered approach. The pavement section analysis method also requires that a Poisson’s ratio is selected for the subgrade. This value is not obtained in the soil testing, but should be appropriate for the SP, SM and SP-SM materials in their eventual in-place condition. The ground water level was recorded to be approximately 12' feet or greater below the underside of the pavement. As the soils are relatively fine grained but well above the water table a Poisson’s ratio of 0.4 is considered appropriate. 7.7.1.1.2 Aggregate Base Two types of aggregate base generally are available to the Port of Los Angeles for its paving projects. In most cases the port has traditionally used crushed miscellaneous base (CMB) in preference to crushed aggregate base (CAB). This is a recycled material including crushed concrete and asphalt. The contractors have the option of crushing and reusing the removed existing pavement materials, provided they comply with the specification for CMB. The Specification states that the CMB is to be compacted to a relative density of at least 97% of the maximum dry density determined in accordance with ASTM D1557. It is to be spread and compacted in lifts no greater than 6" thick. The available aggregate base



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will be Crushed Miscellaneous Base complying with the Greenbook Specification. It will have a minimum R value of 80. The elastic modulus value of the aggregate base is required for the pavement analysis. The elastic moduli of unbound aggregates are stress dependent, and vary as a result of the modulus of the underlying layer and the thickness of the lift. In theory the values will change each time the layer thicknesses change. However, to simplify the analysis one option is considered and subsequently fine tuned to verify the final section. The initial value will be determined assuming an 18 inch thick CMB layer using Barker and Brabston techniques to develop the design elastic modulus. Three 6" lifts will be considered for this purpose over the 18,500 psi composite subgrade modulus. This analysis indicates that the values of the three CMB layers are 40,900 psi, 67,500 psi and 87,400 psi from bottom to top. This provides an average value of 65,300 psi. The Poisson’s ratio used in the pavement section analyses is 0.35. This is a typical value for relatively free-draining, well-compacted aggregate base materials. 7.7.1.1.3 Asphalt Concrete The proposed asphalt concrete mixtures used at the Port are mixtures specially developed by the Port of Los Angeles, and are referred to as Class X and Class Y. These were developed to provide stiffer asphalt concrete with greater resistance to indentation under corner castings and chassis legs. The elastic modulus of asphalt concrete is variable dependent on several factors, including age, temperature and loading time. The elastic modulus increases with age as the asphalt cement oxidizes and hardens. It reduces as the asphalt cement becomes warm following exposure to high air temperatures and exposure to sunlight. It also reduces as the loading time increases for slow moving vehicles. For this analysis an elastic modulus of 450,000 psi for the top lift and 550,000 psi for the bottom lift will be used. A Poisson’s ratio of 0.35 is a typical value used for the asphalt concrete. A crack suppression layer of asphalt concrete with a lower modulus has also been considered at the bottom of the bound layer. This material will have greater fatigue properties so that cracking is offset. 7.7.2 Operations

7.7.2.1 Design Wheel Load

Top-Picks: The top-picks will be Taylor THDC 955 machines. The top-picks have a capacity of lifting up to 80,000 lbs, but the critical wheel load will occur when the container weight is 24 long tons and there is a dynamic factor of 1.2. The dual wheel load used for design will be 91,513 lbs, and the tire pressure will be 120 psi. There will be the equivalent of 6,000 annual repetitions of this wheel load over 20 years for a total of 120,000 repetitions. 7.7.3 Design Method

7.7.3.1 Computer Program

The design analysis will be undertaken using the Kenlayer computer program. This program computes stresses, strains and deflections at selected positions in the pavement structure. For a single wheel load the critical conditions occur under the center of the wheel. For dual wheels, these positions are typically at the center of the two tires. Both of these positions should been analyzed. The critical strains are



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typically at the bottom of the asphalt concrete and at the top of the subgrade. All layers are considered to be linear elastic and all interfaces are considered to be fully bonded. No subdivision of layers will be undertaken in this example. The following pages set out the printout from the Kenlayer program for each of the options considered. The principal tensile strain at the bottom of the asphalt concrete layer (position 1) and the principle compressive strain at the top of the subgrade (position 2) are considered for fatigue life criteria. 7.7.3.2 Failure Criteria

Pavement materials fail by fatigue. The repeated application of stresses well below the failure condition will cause cumulative damage resulting in eventual failure. Relationships have been developed by various authorities to enable calculation of number of repetitions of an established strain before failure. 7.7.3.3 Asphalt Concrete

The fatigue factors used for the calculation of the allowable horizontal tensile strain at the bottom of the asphalt concrete are set out in the flexible pavement design section of this guide. The relationship is as follows:

EN h 101010 log665.2log0.568.2log −∈−= where


h∈ = horizontal tensile strain in asphalt concrete E = elastic modulus of asphalt concrete

7.7.4 Subgrade

The fatigue factors used for the calculation of allowable vertical compressive strain in the top of the subgrade are set out in the flexible pavement design section of this guide. The relationship is as follows:

B

z

AN

∈

= 000,10

where N = allowable repetitions A = 0.000247 + 0.000245log10MR MR = elastic modulus of layer

z∈ = vertical tensile strain in layer B = 0.0658E0.559

7.7.5 Pavement Sections

7.7.5.1 Alternate Sections

A realistic starting point for evaluating the pavement thickness is to assume that it will be approximately 20+ inches thick. Initial analyses were undertaken using 7 inches of asphalt concrete over 15, 17 and 19 inches of crushed miscellaneous base. Comparative designs were undertaken thickening the asphalt concrete by 1 inch and reducing the base course by a similar amount. Refer to the following summary.



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As can be seen from the results, the increase in asphalt concrete thickness has little effect ( approximately 5% increase) on the design life of the pavement and in all cases the pavement sections will not reach their required design life for this parameter. However, the subgrade achieves the required design life when the pavement thickness reaches 26 inches thickness. A further series of sections were analyzed including a 2 inch layer of softer asphalt concrete under the Class X mix. As this mix has a lower modulus it has a higher allowable strain limit. As evident in the summary, the pavement develops an adequate life for both subgrade and asphalt concrete criteria when the pavement is thinner. The two options selected are

3" Class Y asphalt concrete surface course 4" Class X asphalt concrete base course 2" Class D asphalt concrete crack suppression layer 15" crushed miscellaneous base course

or 31/2" Class Y asphalt concrete surface course 41/2" Class X asphalt concrete base course 2" Class D asphalt concrete crack suppression layer 12" crushed miscellaneous base course

As the former pavement option (24" thick) provides double the life expectancy of the second option (22" thick) at the subgrade level, this option allows the asphalt concrete to be replaced at the end of the design life without requiring full depth replacement of the pavement. 7.7.6 Computer output

******************************************************************************************** * * * 3 + 4 AC on 15 CMB * * * ********************************************************************************************

MATL = 1 FOR LINEAR ELASTIC LAYERED SYSTEM

NDAMA = 0, SO DAMAGE ANALYSIS WILL NOT BE PERFORMED

NUMBER OF PERIODS PER YEAR (NPY) = 1

NUMBER OF LOAD GROUPS (NLG) = 1

TOLERANCE FOR INTEGRATION (DEL) -- = .00100 NUMBER OF LAYERS (NL)------------- = 4 NUMBER OF Z COORDINATES (NZ)------ = 2 LIMIT OF INTEGRATION CYCLES (ICL)- = 80 COMPUTING CODE (NSTD)------------- = 9

THICKNESSES OF LAYERS (TH) ARE : 3.00000 4.00000 15.00000 POISSON'S RATIOS OF LAYERS (PR) ARE : .35000 .35000 .35000 .40000 VERTICAL COORDINATES OF POINTS (ZC) ARE: 6.99000 22.01000 ALL INTERFACES ARE FULLY BONDED FOR PERIOD NO. 1 ELASTIC MODULI OF LAYERS ARE: .450000E+06 .550000E+06 .653000E+05 .185000E+05

LOAD GROUP NO. 1 HAS 2 CONTACT AREAS CONTACT RADIUS (CR)--------------- = 11.02000 CONTACT PRESSURE (CP)------------- = 120.00000 NO. OF POINTS AT WHICH RESULTS ARE DESIRED (NPT)-- = 2 WHEEL SPACING ALONG X-AXIS (XW)------------------- = .00000 WHEEL SPACING ALONG Y-AXIS (YW)------------------- = 24.00000 POINT NO. AND X AND Y COORDINATES ARE : 1 .00000 .00000 2 .00000 12.00000

PERIOD NO. 1 LOAD GROUP NO. 1

POINT VERTICAL VERTICAL VERTICAL MAJOR INTERMEDIATE MINOR VERTICAL MAJOR MINOR HORIZONTAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL NO. COORDINATE DISP. STRESS STRESS STRESS STRESS STRAIN STRAIN STRAIN STRAIN 1 6.99000 .6586E-01 .6753E+02 .6801E+02 -.1556E+03 -.2101E+03 .3553E-03 .3564E-03 -.3263E-03 -.3263E-03 1 22.01000 .5515E-01 .2152E+02 .2225E+02 .1730E+01 .6776E-01 .1109E-02 .1164E-02 -.5149E-03 -.5149E-03


******************************************************************************************** * * * 3 + 4 AC on 17 CMB * * * ********************************************************************************************









POINT VERTICAL VERTICAL VERTICAL MAJOR INTERMEDIATE MINOR VERTICAL MAJOR MINOR HORIZONTAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL NO. COORDINATE DISP. STRESS STRESS STRESS STRESS STRAIN STRAIN STRAIN STRAIN 1 6.99000 .6374E-01 .6853E+02 .6899E+02 -.1485E+03 -.2017E+03 .3471E-03 .3483E-03 -.3161E-03 -.3161E-03 1 24.01000 .5220E-01 .1949E+02 .2016E+02 .1336E+01 -.9632E-01 .1013E-02 .1063E-02 -.4700E-03 -.4700E-03

POINT VERTICAL VERTICAL VERTICAL MAJOR INTERMEDIATE MINOR VERTICAL MAJOR MINOR HORIZONTAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL NO. COORDINATE DISP. STRESS STRESS STRESS STRESS STRAIN STRAIN STRAIN STRAIN 2 6.99000 .6628E-01 .6100E+02 .6100E+02 -.5094E+02 -.1931E+03 .2662E-03 .2662E-03 -.3575E-03 -.3575E-03 2 24.01000 .5475E-01 .2131E+02 .2131E+02 .1884E+01 -.1535E+00 .1114E-02 .1114E-02 -.5098E-03 -.5098E-03

******************************************************************************************** * * * 3 + 4 AC on 19 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3.5 + 4.5 AC on 14 CMB * * * ********************************************************************************************









POINT VERTICAL VERTICAL VERTICAL MAJOR INTERMEDIATE MINOR VERTICAL MAJOR MINOR HORIZONTAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL NO. COORDINATE DISP. STRESS STRESS STRESS STRESS STRAIN STRAIN STRAIN STRAIN 1 7.99000 .6359E-01 .5908E+02 .5956E+02 -.1609E+03 -.2150E+03 .3463E-03 .3475E-03 -.3264E-03 -.3264E-03 1 22.01000 .5425E-01 .2066E+02 .2135E+02 .1691E+01 .1666E+00 .1062E-02 .1114E-02 -.4892E-03 -.4892E-03

POINT VERTICAL VERTICAL VERTICAL MAJOR INTERMEDIATE MINOR VERTICAL MAJOR MINOR HORIZONTAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL PRINCIPAL NO. COORDINATE DISP. STRESS STRESS STRESS STRESS STRAIN STRAIN STRAIN STRAIN 2 7.99000 .6637E-01 .5396E+02 .5396E+02 -.8681E+02 -.2118E+03 .2882E-03 .2882E-03 -.3642E-03 -.3642E-03 2 22.01000 .5693E-01 .2249E+02 .2249E+02 .2349E+01 .1193E+00 .1162E-02 .1162E-02 -.5306E-03 -.5306E-03

******************************************************************************************** * * * 3.5 + 4.5 AC on 16 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3.5 + 4.5 AC on 18 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3 + 4 + 2 AC on 13 CMB * * * ********************************************************************************************






THICKNESSES OF LAYERS (TH) ARE : 3.00000 4.00000 2.00000 13.00000 POISSON'S RATIOS OF LAYERS (PR) ARE : .35000 .35000 .35000 .35000 .40000 VERTICAL COORDINATES OF POINTS (ZC) ARE: 8.99000 22.01000 ALL INTERFACES ARE FULLY BONDED FOR PERIOD NO. 1 ELASTIC MODULI OF LAYERS ARE: .450000E+06 .550000E+06 .300000E+06 .653000E+05 .185000E+05





******************************************************************************************** * * * 3 + 4 + 2 AC on 15 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3 + 4 + 2 AC on 17 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3.5 + 4.5 + 2 AC on 12 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3.5 + 4.5 + 2 AC on 14 CMB * * * ********************************************************************************************











******************************************************************************************** * * * 3.5 + 4.5 = 2 AC on 16 CMB * * * ********************************************************************************************











PAVEMENT SECTIONPosition 1 Position 2 22 inches 24 inches 26 inches

3 + 4 AC on 15 CMB -3.26E-04 -3.69E-04 35,413 reps3 + 4 AC on 17 CMB -3.16E-04 -3.58E-04 41,262 reps3 + 4 AC on 19 CMB -3.08E-04 -3.49E-04 46,538 reps3.5 + 4.5 AC on 14 CMB -3.26E-04 -3.64E-04 37,604 reps3.5 + 4.5 AC on 16 CMB -3.15E-04 -3.52E-04 44,399 reps3.5 + 4.5 AC on 18 CMB -3.07E-04 -3.43E-04 50,679 reps

3 + 4 + 2 AC on 13 CMB -3.64E-04 -4.02E-04 115,006 reps3 + 4 + 2 AC on 15 CMB -3.51E-04 -3.88E-04 137,289 reps3 + 4 + 2 AC on 17 CMB -3.41E-04 -3.78E-04 158,084 reps3.5 + 4.5 + 2 AC on 12 CMB -3.53E-04 -3.88E-04 137,820 reps3.5 + 4.5 + 2 AC on 14 CMB -3.40E-04 -3.74E-04 166,732 reps3.5 + 4.5 + 2 AC on 16 CMB -3.29E-04 -3.62E-04 194,147 reps

PAVEMENT SECTIONPosition 1 Position 2 22 inches 24 inches 26 inches

3 + 4 AC on 15 CMB 1.16E-03 1.22E-03 26,847 reps3 + 4 AC on 17 CMB 1.06E-03 1.11E-03 107,448 reps3 + 4 AC on 19 CMB 9.73E-04 1.02E-03 412,885 reps3.5 + 4.5 AC on 14 CMB 1.11E-03 1.16E-03 54,756 reps3.5 + 4.5 AC on 16 CMB 1.02E-03 1.07E-03 204,584 reps3.5 + 4.5 AC on 18 CMB 9.38E-04 9.85E-04 767,910 reps

3 + 4 + 2 AC on 13 CMB 1.09E-03 1.14E-03 73,283 reps3 + 4 + 2 AC on 15 CMB 1.00E-03 1.05E-03 276,579 reps3 + 4 + 2 AC on 17 CMB 9.20E-04 9.66E-04 1,048,302 reps3.5 + 4.5 + 2 AC on 12 CMB 1.05E-03 1.09E-03 147,784 reps3.5 + 4.5 + 2 AC on 14 CMB 9.62E-04 1.01E-03 539,525 reps3.5 + 4.5 + 2 AC on 16 CMB 8.85E-04 9.30E-04 1,923,368 reps

REPETITIONS UNTIL ASPHALT CONCRETE CRACKING

REPETITIONS UNTIL SUBGRADE RUTTING

PAVEMENT THICKNESSHORIZONTAL STRAIN

VERTICAL STRAIN PAVEMENT THICKNESS



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8. Concrete Pavement........................................................................................................... 8-1 8.1 Introduction...................................................................................................................... 8-1 8.2 Portland Cement Concrete Materials ............................................................................... 8-2

8.2.1 Cement Types................................................................................................................................................... 8-2 8.2.2 Supplementary Cementitious Materials ................................................................................................... 8-4 8.2.3 Concrete Aggregates ...................................................................................................................................... 8-5 8.2.4 Admixtures........................................................................................................................................................ 8-6

8.3 Concrete Mixing ............................................................................................................... 8-7 8.3.1 Water .................................................................................................................................................................. 8-7 8.3.2 Mix Proportioning .......................................................................................................................................... 8-8 8.3.3 Concrete Batching, Transporting, and Placing ...................................................................................... 8-9 8.3.4 Quality Control ..............................................................................................................................................8-11

8.4 Thickness Design for Non-Reinforced Concrete Pavement ............................................. 8-14 8.4.1 Fatigue Damage .............................................................................................................................................8-14

8.5 Joint Design for Non-Reinforced Concrete Pavement ..................................................... 8-16 8.6 Analys is of PCC pavement.............................................................................................. 8-20

8.6.1 Warping Stress Analysis .............................................................................................................................8-20 8.6.2 Temperature Steel Analysis .......................................................................................................................8-22 8.6.3 Dowel Bar Analysis.......................................................................................................................................8-23

8.7 Design Examples............................................................................................................. 8-24 8.7.1 Concrete Pavement Analysis Examples – Top Picks...........................................................................8-24 8.7.2 Concrete Pavement Analysis Examples – RTG Runway...................................................................8-32



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8. Concrete Pavement 8.1 Introduction Portland Cement Concrete Pavement (PCCP) is a system of subgrade soil, base course material, and the surface course of Portland cement concrete. The appropriate design of a PCCP section requires information on the properties of the subgrade soil and base course material, environmental impacts such as climate, water table, and drainage, concrete properties, and the type of equipment, wheel loads, and load repetitions. Prior to designing the pavement section, information about the on-site material (subgrade), available granular bases, and concrete materials must be determined. It is most important to design the pavement using a flexural strength that can be readily attained with the local materials. Using higher than normal strengths may produce a thinner pavement section, but will create problems with concrete production. The subgrade soil properties including its load bearing capacity are determined from field and laboratory tests of materials sampled during the site investigation. The subgrade evaluation, determination of the subgrade modulus reaction (k value), and improvement are discussed in the Subgrade section of this study. The granular base material adds strength to the overall pavement section and also provides a strong, stable working platform for the paving operation. The strength and durability of the base depends upon the aggregate gradation, and durability and soundness of the aggregate. Using the base material Modulus of Subgrade Reaction (k value) of the aggregate base, a composite k value at the top of the base material is required for concrete pavement design. At its base level, concrete is an artificial rock composed of aggregates bound by a cementitious paste. How the aggregates are combined and the paste proportioned defines the strength, durability, and overall quality of the concrete. Concrete used for PCCP must meet the combined requirements of durability under repeated, heavy loads, dimensional stability to minimize shrinkage and curling, and non-reactivity of its constituent material. The concrete mix is proportioned to attain the flexural strength assumed in the pavement design. Depending upon the local environment, different mix proportions may be prepared to accommodate hot and cold weather placing operations. The basic concrete materials - Portland cement, supplementary cementitious materials, aggregates, and chemical admixtures will be discussed in this section. Climate and drainage considerations include the expected maximum and minimum daily temperatures and the evaluation of the drainability and frost susceptibility of subgrade and base materials. The projected load repetitions for the design life of the pavement are required to design concrete slab thickness. Determinations of load repetition for various operational areas are discussed in the section 3 of this study. The determination of design wheel loads is a critical input in designing the PCCP section. The wheel configurations and wheel loads for the typical container terminal and intermodal facility equipment are provided in the section 3 of this study.



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8.2 Portland Cement Concrete Materials This section provides general guidelines for the selection of Portland cement, supplementary cementitious materials, aggregates, and chemical admixtures.

8.2.1 Cement Types

Two types of Portland cement are generally available: ASTM C 150, Standard Specification for Portland Cement and ASTM C 595, Specification for Blended Hydraulic Cements. The C150 cements are the most common and are the basis of the C 595 cements. This standard provides for eight types to specific purposes:

Type I Normal Type IA Normal, air-entraining Type II Moderate sulfate resistance, low-alkali option, moderate heat option Type IIA Moderate sulfate resistance, low-alkali option, moderate heat option, air-

entraining Type III High early strength Type IIIA High early strength, air-entraining Type IV Low heat of hydration Type V High sulfate resistance

When selecting the type of cement for PCCP pavement, consider the environmental conditions, available aggregates, and method and speed of construction. The Type IA, IIA, and IIIA cements are manufactured with an interground air-entraining agent. Generally, these cements are not commercially available. Type I cement is used in general construction where no special properties are needed, where there are no concerns about the presence of alkali reactive aggregates, and where concrete is not exposed to sulfates. This cement would not be suitable for concrete work on projects sited on sulfate soils or in a saltwater splash zone. Type II cement is used when concrete has a moderate sulfate exposure. To maximize the sulfate exposure benefit of Type II cement, the water:cementitious ratio should be kept low, see Table 8-1. The cement can also be manufactured with a low-alkali option meaning it can provide some mitigation when used with alkali reactive aggregates. This issue will be discussed more fully in the aggregate section. Type II cement is typically manufactured as a lower heat of hydration cement. This reduces the temperature rise and allows larger masses of concrete to be placed without the associated thermal cracking, especially in hot weather. Table 8-1 Types of Cement Required for Concrete Exposed to Sulfate Attack Relative Degree of Sulfate Attack

Percentage Water-Soluble Sulfate (as S04) in Soil Samples

Sulfate (as SO4) in Water Samples (parts/mi lion)

Cement Type

Negligible 0.00 to 010 0 to 150 I Positive 0.10 to 0.20 150 to 1,500 II Severe 0.20 to 2.00 1,500 to 10,000 V* Very Severe 2.00 or more 10,000 or more V+pozzolan** * Or approved Portland-pozzolan cement providing comparable sulfate resistance when used in concrete.



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** Should be approved pozzo Ian that has been determined by tests to improve sulfate resistance when used in concrete with Type V cement. Cement Type Type III cement is used when high early strength is required. Chemically it is similar to Type I cement, but Type III has a finer grind. Type III cement is generally used where early strengths are desired and is not a common paving cement, except for projects under severe time restraints where strengths are needed in one week versus the typical 28-days. Type IV cement is used for mass concrete such as gravity concrete dams or other very large structures where the heat rise from cement hydration must be minimized and strength can be attained in months not days. This cement is a special order item. Type V cement is used for concrete that has an extreme sulfate exposure. Again, for it to provide the best protection, the water:cementitious ratio must be kept low. In California, it is not uncommon to see cements manufactured to the requirements of both Type II and Type V and to be denoted on the mill certificate as Types II/V. ASTM C 595 is a standard for five classes of blended cements used in concrete construction like C 150 cements. The main difference is the C 595 cements are blended with a pozzolan or blast-furnace slag. While these cements are not common on the West Coast, their use will increase as the demand for more environmentally friendly construction products increases. Both slag and pozzolans such as fly ash are recycled industrial waste products. The types of C 595 cements are:

Type IS Portland blast- furnace slag cement Type IP or Type P Portland-pozzolan cement Type I (PM) Pozzolan-modified Portland cement Type S Slag cement Type I(SM) Slag-modified Portland cement

A Type IS cement is manufactured by intergrinding blast-furnace slag with Portland cement clinker, separately ground slag is blended with clinker, or a combination of intergrinding and blending. The Type IS cement is used for general construction and may be manufactured with air-entraining (A), moderate sulfate resistance (MS), or moderate heat of hydration (MH) optional properties. Type IP and Type P are Portland-pozzolan cements made by intergrinding or blending Portland cement clinker with a pozzolan, such as fly ash. Type IP performs similarly to a C 150 Type I cement. Type P may be designated as a low heat of hydration (LH), moderate sulfate resistant (MS), or air-entraining (A) cement. Type I(PM) pozzolan-modified Portland cements are used for general construction. The pozzolan content is less than 15% of the finished cement and may have a MS, MH, or A optional property. The Type S slag cement contains a minimum of 70% slag cement combined with Portland cement. It may be air-entrained. Type I(SM) slag-modified Portland cement is a general construction cement manufactured by intergrinding Portland cement clinker and granulated blast-furnace slag or by blending Portland cement



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with ground granulated blast-furnace slag or by a combination of the two. The slag content is less than 25% of the finished cement. It may have optional properties of A, MS, or MH. Cement is composed of four broad materials – lime, iron, silicate, and alumina. The amount of each material is varied depending upon the type of cement being manufactured. Controlled proportions of finely ground materials are blended and fed into a sloped, rotating kiln heated to 2500 to 2800 0F. The material exiting the kiln is a marble -sized cement “clinker”. After cooling, the clinker is processed through a ball mill where it is pulverized to a size that nearly all of it passes the No. 325 mesh sieve (45 micrometer). During the final step, gypsum is added. This sulfate addition provides regulation of the setting time and assists in improve shrinkage and strength development. Portland cement is a hydraulic material that is both exothermic and endothermic . When mixed with water, Portland cement forms a calcium silicate hydrate and calcium hydroxide and releases heat. When the external temperature is low, the cement hydration is retarded resulting in slower set times and strength gains. The calcium hydroxide is known as efflorescence and imparts no beneficial property to the concrete. In fact, it allows external chemicals ready access to the concrete.

8.2.2 Supplementary Cementitious Materials A supplementary cementitious material (SCM) is one that when used in conjunction with Portland cement contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity or both. The most common SCMs are

Fly Ash ASTM C 618, Class C (mildly cementitious) Class F (low-calcium) Blast Furnace Slag ASTM C 989 Silica Fume ASTM C 1240 Metakaolin ASTM C 618, Class N Natural Pozzolan ASTM C 618, Class N

These finely divided materials are either siliceous or aluminosiliceous will react with the calcium hydroxide produced during cement hydration to form calcium silicate hydrate. As discussed in the previous section, several of these SCMs are used to produce blended cements (ASTM C 595). Portland Cement + H2O => Calcium Silicate Hydrate (CSH) + Ca(OH)2 Ca(OH)2 + Supplementary Cementitious Material (high silica content) => CSH When determining how much supplementary cementitious material to use in a mix design, it is important to understand the reaction between the proposed cement and the different SCMs. The above equations depict a chemical reaction and not every combination of cement and SCM is equal. Some SCMs may react better with one cement than another. Therefore it is important to conduct sufficient trial batches to determine the correct proportions for the project at hand. Because fly ash is the most commonly used SCM, additional discussion of its properties when used with C 150 cement is warranted. Fly ash is the by-product of coal fired electrical power plants. As the coal is burned, the non-volatile matter fuses into spherical shapes and are carried away with the exhaust gases. Prior to exiting the exhaust stack, these spheres are collected by electrostatic precipitators. Fly ash is primarily silicate glass which imparts two beneficial properties to concrete. First, the spherical shape aids



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in the workability of the concrete. This is especially important with either or both crushed coarse aggregate and manufactured sand. Second, the silicate content reacts with the Ca(OH)2 to produce additional Calcium Silicate Hydrate (CSH). Note that the additional CSH is not produced until sufficient Ca(OH)2 is produced for there to be a reaction. If cement is replaced with fly ash, as is most often the case, the initial strengths will be lower since there is less cement in the mix. The fly ash mix strengths generally equal or exceed the non-fly ash mixes between 28 and 42-days. This must be confirmed with each cement to fly ash combination since it is a chemical reaction.

8.2.3 Concrete Aggregates

Aggregates are classified as light weight, normal weight, or heavy weight. This discussion is limited to normal weight aggregates which are used in majority of container terminal pavement construction. Concrete aggregate comprises approximately 60% to 75% of the concrete volume and effects concrete’s workability, pumpability, finishability, durability, volume stability, and strength. Coarse and fine (sand) aggregates are commonly defined by ASTM C 33, Standard Specification for Concrete Aggregates. Coarse aggregates consist of natural or crushed stone larger than 0.2 in up to 1-1/2 in. (sieve sizes #4 to 1-1/2 in). Natural coarse aggregate is mined from waterways or pits. Since very little stream bed mining occurs today, most coarse aggregate is crushed from larger stone. Fine aggregate is either natural sand or manufactured by crushing coarse aggregate. Both coarse and fine aggregates can be manufactured by crushing and recycling old concrete. The recycled aggregate is generally blended with fresh aggregate, especially for the sand portion, in concrete for new pavements. Using recycled aggregate will require additional testing to determine the percentages of recycled versus fresh and the presence of injurious chemicals. However, there is the potential for savings in the form of hauling and burying old concrete in landfills and the use of limited virgin aggregate resources. The aggregate shape and texture affect the workability of fresh concrete and strength of hardened concrete. Angular, elongated, or irregular shaped aggregates will increase paste requirements compared to smooth, round, natural aggregates. Elongated aggregates may also cause problems with segregation during handling. While rough texture surfaces may increase mechanical bond, an elongated shape may also indicate an aggregate with weak fracture planes. This may have an adverse effect on the hardened concrete strength. Aggregate cleanliness and the presence of silts and clays impact the bond between the cement paste and the aggregate and increase water demand. Both chemical and physical durability of aggregate must be considered. Physical durability concerns the soundness, wear resistance and freeze-thaw characteristics of the aggregate. The most common tests are ASTM C 88, Sodium Sulfate Soundness, and C 535, Los Angeles Rattler. For projects located in freeze-thaw areas, if there is no local experience with an aggregate, it should be tested in accordance with C 666, Resistance of Concrete to Rapid Freezing and Thawing. This will determine if the aggregate is susceptible to D-cracking. D-cracking is related to aggregates that are expansive when saturated with water and then frozen. The pressure exerted by the repeated expansion is great enough to fracture the concrete along a joint.



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For significant projects, the aggregates should be investigated for potential alkali-silica reaction between the cement and aggregate. Local agencies, such as the highway department, may have already determined the reactivity of the available aggregates. Alkali-silica reactivity produces a gel that expands and slowly cracks the concrete creating serviceability problems. For aggregates found to be reactive, testing of various cements and supplementary cementitious materials can determine the most efficient combination to combat the problem at hand. As an example, C 150 Type II cement with the low alkali option and 25% low calcium C 618 Class F fly ash are specified by Caltrans. There are other harmful materials that are easily determined as parts of an aggregate qualification investigation. It is advisable that the local agencies requirements for specifications on soundness, wear resistance, and freeze-thaw damage are followed. Aggregate gradation influences the amount of cement that is required, the handling characteristics of the plastic concrete, and the hardened concrete properties. ASTM C33 sets gradation limits for coarse and fine aggregates. While it is important to have aggregates that fall within the gradation limits for both coarse and fine aggregates, it is more important to have a well graded combined gradation that minimizes the amount of fine aggregate. There are 4 advantages of such a gradation: Volume stability – more coarse aggregate and less sand equates to less water and less shrinkage More workability – easier to place and finish Mix does not segregate Greater strength and durability To achieve a well-graded mix, additional aggregates, usually in the form of a 3/8” maximum size aggregate may have to be added. The maximum aggregate size for pavement slabs should not exceed 1.0 to 1.5 inches. Slipform paving machines can easily handle 1.5 inch aggregate, but this size is not always available. The advantage of the larger size aggregate is slightly less cement and water contents and less drying shrinkage. If reinforcement is used, the maximum size should not exceed ¾ of the minimum clearance between reinforcing bars and forms.

8.2.4 Admixtures

Admixtures are any material other than cement, supplementary cementitious material, aggregate, or water added to concrete batch immediately before or during mixing to improve performance or appearance. The typical admixtures are air-entraining agents, water-reducers, set accelerators, set retarders, and high-range water-reducers. Admixtures can also be used to reduce shrinkage, control hydration, inhibit corrosion, reduce permeability, and add color. This discussion will focus on the first set of admixtures which are used to improve the handling and consolidation of plastic concrete resulting in improved performance and material characteristics of hardened concrete. As concrete aggregates become more manufactured having a coarser texture, the workability imparted by air-entraining is as significant as its ability to protect concrete against freeze-thaw damage. The round air-bubbles impart workability to the concrete. It should be noted that the same air bubbles also block water bleeding to the surface which may result in plastic shrinkage cracking, especially on windy days. The same lack of bleeding also closes off the concrete to external chemical attack. Water-reducing admixtures have three effects on the concrete mixture. The cement content is reduced to maintain a constant water:cement ratio



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The water content is reduced and strength increased with no change in slump The water and cement contents are maintained and the slump is increased. The use of a high-range water-reducer which increases the slump from the 2”-3” range to over 7” may appear to be inconsistent with paving concrete. Properly designed, the concrete mix can be self-consolidating. When placed in fixed forms, this type of mix has a labor-savings advantage. Table 8-2 summarizes the principal advantages and disadvantages of major types of admixtures. Table 8-2 Admixture Effects of Concrete Properties Admixture Type Fresh Concrete Hardened Concrete Air-Entrained

Improve workability Reduced bleeding Reduced segregation

Improved freeze-thaw resistance Improved sulfate resistance Increased potential for plastic shrinkage Reduced strength

Water-Reducing 5% minimum water reduction Improved workability May increase bleeding May entrain air

Increased strength Increased impermeability Improved durability

Set-Retarding Retarded initial set for difficult placements

Possible increased shrinkage Reduced early strength

Set-Accelerating Note: Calcium chloride is not recommended when metal is embedded in concrete.

Sets quicker Increased early strength May increase final strength May increased shrinkage

Water-Reducing Set-Retarding 5% minimum water reduction Improved workability Retarded initial set

Increased seven-day strengths Increased impermeability Improved durability

High-Range Water Reducing Note: May be combined with a set-retarder.

10% minimum water reduction Increased slump Increased workability Reduced consolidation required

Increased strength Increased impermeability Improved durability

8.3 Concrete Mixing This section provided general guidelines for the section of water, mixing proportioning, concrete batching, transporting, and placing, and quality control.

8.3.1 Water Portland cement concrete is a hydraulic material requiring water to hydrate the cement. Traditionally, any water considered to be potable has been acceptable for batching concrete. Clean water regulations no longer permit the dumping of concrete plant water into waterways. This includes water used to wash-out



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trucks returning to the batch plant. These waters are collected in reclaiming systems and the water is used as part of the batch water for fresh concrete. The solids content will vary from 2.5% to 10%. Test cylinders made with this water will be at least 90% of the strength of concrete made with distilled water at seven-days of age. Concrete mix water also has limits for chloride, sulfate, alkalis, and total solids by mass.

8.3.2 Mix Proportioning Concrete mixes are proportioned based upon three principles Strength is inverse to the water:cementitious ratio (w/c) Water demand is inverse to the maximum size aggregate used Well-graded combined coarse and fine aggregates produce the best strengths and finishes and are the most durable For non-air entrained concrete, a general guide is 2000 psi concrete has a w/c of 0.7 lb/lb compared to a 0.4 lb/lb for a 4000 psi concrete. At a constant cement content, the addition of water dilutes the cement paste decreasing the concrete strength. The water demand for a given slump is governed in part by the maximum sized aggregate (MSA). A larger MSA has less surface area per volume compared to a smaller MSA. Given that cement requires approximately 3 gallons to fully hydrate 94 pounds of cement, the absolute w/c is 0.25 lb/lb. The mix water in excess of 0.25 lb/lb is the “water of convenience” that imparts workability and placeability to the concrete. This water also increases drying shrinkage. As an example, for a mix designed with a total of 6 sks of cement and a water content of 36 gallons, the water of convenience is 18 gallons. If the MSA were decreased and the total mix water went to 42 gallons, the cement content would be increased to 7 sacks to maintain the w/c, but the water of convenience would increase to 21 gallons and increased drying shrinkage would be anticipated. If the cement content were not increased, the w/c would increase, the strength would decrease, the water of convenience would increase to 24 gallons, and drying shrinkage would further increase. Well-graded combined coarse and fine aggregates minimize the amount of water needed to produce concrete of a given workability and decrease the drying shrinkage. Together, the concrete produces the best strength and is the most durable. Mixes can be proportioned following prescriptive criteria, trial batches, or empirical data. There are advantages and disadvantages to each method. Prescriptive criteria mixes specify certain mix properties, such as minimum cement content, maximum slump, maximum size aggregate, without considering equipment, labor, and environmental conditions. The advantage is that the mixes rarely fail in strength. However, the concrete characteristics govern the work instead of having the concrete work for the contractor. Any innovation in placing, finishing, or improving the operation is limited by the inherent concrete characteristics. A project stretching over several climate changes will be penalized by the handcuffs of detailed prescriptive mix criteria. As the weather changes, the concrete additives and placing conditions should change. Trial batched mix proportioning utilizes the materials engineer’s expertise in developing a mix that will meet the project specifications and match the contractor’s equipment, environmental conditions, and job restrictions to produce a performance concrete . The degree to which concrete can be made to perform



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may be limited by the specificity of the specifications for minimum cement content, maximum, maximum size aggregate, etc. Empirical mix proportioning is based upon statistical data, such as strength and slump, for a given set of concrete making materials combined with the contractor’s desired equipment performance, site conditions, and environment. The mix can be proportioned to follow general material specifications and still be a performance mix. Once the mix is proportioned, trial batches can be performed to verify the strength, workability, and other properties. The details of mix proportioning methods are found in the American Concrete Institute’s guide for proportioning ACI 211 and in the Portland Cement Association’s publication Design and Control of Concrete Mixtures.

8.3.3 Concrete Batching, Transporting, and Placing Concrete batching is a highly controlled, computerized process of accurately weighing tons of material into either a central mix plant or in a dry mix plant. The differences between the two are in a central mix plant concrete is batched into a stationary mixer drum and mixed at high speed before being discharged into the delivery vehicle. The delivery vehicle for paving projects is usually a dump truck. For commercial operations, truck mixers are the typical delivery method. Dry batch plants weigh and deposit the materials directly into the truck mixer drum where it is mixed enroute to the project. Truck mixers are generally not used on slip-form paving projects due to a lower discharge rate of concrete. They are effective on fixed form projects. The process of weighing, mixing, and delivery of concrete is covered in ASTM C 94, Standard Specification for Ready Mixed Concrete. Aggregate stockpiles should be segregated by size with no overlap of different sizes. Bins should be of sufficient size to contain the aggregate and not be overfilled. When the aggregate is stored on the ground, a solid concrete floor is preferable, but storage directly on grade is acceptable provided the loader operator feed the batch plant always picks up material above the bottom of the stockpile. Cement and supplementary cementitious materials must be stored in separate locked silos. There should be a key checkout system to prevent introducing cement to a SCM silo or vice versa. The consequences are obvious. Likewise, chemical admixtures must be securely stored in separate containers to insure there is no mingling of admixtures until they are introduced into the concrete. Concrete batching is a planned sequence of events that produces consistently produces uniform concrete of consistent workability and strength. A similar sequence is followed whether the concrete is batched in a central mix plant or dry batched. Water is the first element added followed by the air-entraining agent, if used and then by any water-reducer. Coarse aggregates then fine aggregates begin to be added. After the coarse aggregate addition is well underway, the cementitious materials are added. Note that to save space for weigh hoppers, the cement and SCM can be weighed in the same hopper if the cement is weighed first. The cement and SCM addition is completed before the aggregate. The water and aggregates end their charging together. It is important that the drum be damp, but contain no excess water prior to the charging process. Admixtures must be added individually and not mixed prior to entering the



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drum. Coarse aggregates are required to be in the drum prior to the cement addition. If not, the cement will pack against the head of the drum or form balls. Both conditions lead to non-uniform mixes. After the truck is batched, the driver will wash off any excess dust and cement from the exterior, but must not add water to the mix without authorization from the batch man or technical services. The goal of concrete transportation is deliver concrete of consistent slump, air content, and workability with every load. Dump trucks should have the load covered to prevent evaporation unless the transport is very close to the project. Mixer trucks should slowly turn the drum in transit to keep the concrete from setting. While waiting on the project, the drum should remain in motion. Constructing concrete pavement requires six steps:

• Placing the concrete in a form • Consolidating • Finishing/texturing • Jointing • Curing • Joint sealing Concrete pavement forms can be fixed or moving. Slip form paving is the oldest system. It utilizes steel forms set to the height of the finished pavement. The forms are the mold for the pavement section and establish the grade and alignment and provide the track for the paving equipment. The pavement smoothness is dependent upon the care with which the forms are set. For a successful fixed form pavement, the subgrade or base must be stable and built to the specified tolerances. A stringline is used to set the forms to the correct elevation. The stringline must be established by an accurate survey and once established not be moved. Concrete is placed with some type of form riding equipment. The size of the equipment varies with the project from simple vibrating screeds for single lands to large bridge machines for multiple lane paving.

Regardless, the same placing principles apply:

• Place the concrete uniformly across the face of the pavement • Consistently and adequately consolidate the concrete • Keep the placing equipment consistently in a forward motion • Everytime the placing equipment stops, smoothness suffers • Float the surface • Finish to proper grade – cross section • Remember, the form is the mold If dowel bar baskets are used, anchor them to the subgrade and mark on the form where the baskets are located. Once the concrete is placed, the saw cutter will not be able to see them. It is important that the joints be sawed over the dowel bars. Deformed tie bars, if used, should be secured to the form to prevent being moved during the concrete placement. Slip form paving is a process of extruding extremely dry concrete through a moving paving machine. The concrete is placed in front of the paver, consolidated, formed into a shape, and extruded at the correct elevation, alignment, and finish. The first step is to construct a sound, durable base that extends at least



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3’ beyond the edge of the pavement section. Since the paving train will ride on this base, it must be kept clear and clean. An accurately constructed base will save concrete and enhance the pavement smoothness. Any elevation change will be reflected in the finished product. Second, the stringline that the paving machine reads for elevation control must be accurately surveyed. Once established, the stringline cannot be touched. Nothing can be draped over it and care must be taken to not trip on it. The finished surface is a direct reflection of the care taken to establish and maintain the stringline. Smooth dowels can be placed either with dowel baskets anchored to the subgrade or installed with an automatic dowel bar inserter. If dowel baskets are used, mark the centerline of the basket on the grade outside the track line prior to paving. For dowels installed with a DBI, have the machine automatically mark the dowel’s centerline on both sides of the pavement. To construct a smooth, durable pavement, the concrete must be delivered in consistent quantities so the paving machine never stops and the concrete must have a consistent slump. It does not matter if the concrete is discharged directly in front of the mixer, placed with a spreader, or placed with a belt placer. The important item is consistent workability at a constant rate. For either fixed or slipformed pavement, once the concrete is placed, any touch-up finishing can be done with a 10’ highway straight edge and the final texture applied. The pavement should be cured immediately with a pigmented curing compound. For slipformed pavement, the sides of the pavement should be cured immediately. The sides of fixed form pavements should be cured when the forms are removed. Insure that the curing compound is applied evenly. At the conclusion of the day, check the totes that contained the curing compound for the presence of any unused pigment. Joints should be cut as soon as possible. Mark the joints to be cut over dowel bars using the marks placed before the paving started. Green sawing the joints will greatly reduce the incidence of random drying cracking. If green joints will not be widened and sealed, the joint should be sprayed with curing compound as soon as it is cut. Joints that will be widened and sealed do not need to be cured.

8.3.4 Quality Control Quality control is the responsibility of every person on the project. One department or entity may be designated as the responsible party for making inspections and taking test samples, but since quality cannot be inspected in only built in, everyone is responsible for the final product quality. The intent of quality control testing is to obtain random samples using repeatable procedures to obtain reproducible results. This section will address the concrete quality control tests for fresh and hardened concrete and the significance of them. Since the American Concrete Institute started the certification program for concrete field technicians in 1981, the overall quality of concrete construction has improved as more individuals became knowledgeable about the basic field tests and the randomness of testing was decreased. The first step to improving field quality control is requiring that all field testing be performed by technicians qualified to at least ACI Field Level I. Additional certifications through ACI are available for laboratory technician, strength test technician, and concrete transportation inspector. Before any acceptable test can be performed, the initial sample of concrete must be properly taken. ASTM C 172 specifies that the concrete sample shall be taken within a 15 minute period at two or more



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regularly spaced intervals from the middle portion of the load (emphasis added). This means that slump tests, cylinder tests, and unit weight tests made from the first concrete down the chute are invalid because the concrete sample was invalid. Once the sample has been taken, it should be remixed within a wheel barrow or other sampling container before the remaining tests are made. The sample should also be covered to prevent evaporation. The concrete’s temperature is measured in accordance with ASTM C 1064. This test can be performed while the other tests are being conducted since it requires only placing a calibrated thermometer in the concrete and waiting for the temperature to stabilize. The slump test (C 143) measures the consistency (workability, placeability) of the concrete. It does not equate to compressive or flexural strength, except under extremely controlled laboratory conditions. The batching tolerances for conventional concrete preclude any strength prediction based upon slump results. Slump tests are best used to judge the consistency of the batching process. If there are sudden changes in the slump, either up or down, then there has been a change in one of the constituent materials, such as a gradation change or water content. For slipformed concrete, the slump test is not needed; the machine indicates whether the concrete is at the correct slump; if the slump is too high, the sides will fall and require a hastily erected sideform. Two tests are available to determine the air content of concrete. The volumetric method (C 173), also called the rollometer, uses an approximately 1/8th cf container to test for the concrete’s total air content. This meter can be used with either normal or lightweight aggregate. Test method C 231 is the pressure method and is not used with lightweight aggregate since the applied pressure would also measure any air contained in the vesicular space of the lightweight aggregate. An advantage of the pressure meter is the ability to also obtain a rapid unit weight test C 138). The device has an approximate volume of .25 cf. Note that this half the size required for a unit weight test to resolve yield questions, but it does provide a reasonable number to monitor the concrete. For a given concrete sample, the unit weight measured with a .25 cf container will be higher than when measured with a .5 cf container. The consolidation procedures are the same for both containers resulting in more effort being imparted to the smaller container, thus a higher unit weight. The quality control testing does not depend upon these differences but on the deviations from test to test when a consistent size container is used. An increase in unit weight indicates a decrease in air or water content or an increase in cement or aggregate. Conversely, decreases in unit weight are an alert for increases in water or air content or decreases in cement or aggregate content. Decreases in air content may signal long-term problems with freeze-thaw durability. Increases in water content may portend drying shrinkage problems and increased susceptibility to outside, injurious chemical attack. If there is a question about the yield of a mix design, the procedure outlined in C 94 is to test the unit weight of three separate loads using a calibrated .5 cf unit weight container. The average unit weight is then divided into the total batch weight, including any field added water, of each truck. This will provide the volume in cubic feet for each load which can be compared to the ordered volume. Test samples (C 31) for strength can be either cylinders or flexural beams. It is important to understand that neither sample represents the strength of the concrete in-place. The test samples only indicate that the concrete as batched and sampled is capable of producing the tested strength. If the strength is less than that specified, then an investigation should be conducted to determine first if the tested sample was correctly made, stored, and tested, then if the in-place concrete is under-strength. It is important to note the general field curing times for strength samples. For concrete that being tested for conformance to the design strength, the samples must be initially stored in the field at 60 0F to 80 0F and then placed under



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standard laboratory conditions (72.3 0F, 90% relative humidity) within 48 hours of being fabricated. If they cannot be in a laboratory condition within 48 hours, at 24 + 8 hours shall be stripped from their molds in the field and cured at 73 0F either in a water bath or fog room. Test specimens that receive non-standard curing, especially exposure to drying, exhibit lower strengths. Test cylinders are the most common method of determining concrete strength. Laboratories and technicians are comfortable fabricating, storing, and testing 6” diameter by 12” high cylinders. Flexural beams are an uncommon item for most laboratories and technicians. The procedure for fabricating beams is straight forward, but the degree of care needed to properly fabricate a beam is not met in many cases. The beams are sensitive to drying on the exposed surface which will be vertical during the testing phase. Any slight drying shrinkage crack on this surface will prematurely fail the beam. Also, the longer the samples are out of standard laboratory curing, the more difficult it becomes to obtain the design strength. For paving projects, a good quality control program can incorporate both beams and cylinders. During the mix development stage, both beams and cylinders are made and compared. A minimum compressive strength is selected and field quality control is performed using cylinders. Random beam tests are made to verify that the cylinder tests are accurately reflecting the minimum design strengths. When developing a field concrete quality control plan, note that C 31 requires slump, air content, and temperature tests for each set of strength samples. Also, provide for adequate labor to retrieve samples on weekends and holidays. Samples made on Friday must either be picked up and placed in laboratory conditions on Saturday or be placed in a field laboratory condition as previously discussed within 48 hours. In addition to standard samples, ultrasonic and maturity methods can be used to determine the in-situ strength of hardened concrete. The ultrasonic procedure passes an ultrasonic wave through a concrete test sample before it is broken. After testing a number of samples, a plot is made relating sound velocity to strength with higher strengths equating to faster sound. In the field, measurements are taken and strengths computed. The maturity method, C 1074, is based upon a trial batch of concrete. A temperature probe measures the temperature of one specimen while other samples kept at the same condition are tested. For each test, the time, temperature, and strength are recorded. A time/temperature Maturity factor (M) is calculated and plotted against the strength. The resulting curve is accurate to + 5%. During construction, temperature probes are cast in the concrete and monitored. When the desired M factor is reached, the concrete is assumed to be at the design strength. Laboratory quality control tests for hardened concrete are typically for compressive (C 39), flexural (C 78 – third point loading, C 293- center point loading), and splitting tensile (C 496) strengths. The third point loading test is more representative of the field loading condition than the center point. Other procedures detail capping of specimens (C617) and the determination of concrete’s modulus of elasticity (C 469). Laboratory trial batching of concrete is covered in C 192. If there is a question about the strength of a sample, test cores should be obtained using the procedure of C 42. Aggregate quality control tests have been discussed previously in the aggregate section.



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8.4 Thickness Design for Non-Reinforced Concrete Pavement The thickness design procedure is based upon providing a sufficient structural capacity of pavement system for a sufficient structural capacity of a pavement system for specific type of container handling equipment loading. The key structural design factors include: Slab thickness Slab concrete flexural strength Foundation support (from base and subgrade) Equipment load repetition and wheel loads It is also assumed that a relatively short joint spacing and adequate load transfer at the joints are provided.

8.4.1 Fatigue Damage Repeated equipment loading results in fatigue damage in the concrete slabs which results in microcracking at bottom of the slab. These cracks work their way to surface of the slab, eventually dividing the slab into two or more pieces. In addition, if pumping and loss of support occur at slab corners, critical stress could increase until a corner break develops. The slab and foundation are characterized using the Westergaard theory. All stress can be computed us ing computer programs developed by Portland Cement Association. The important design assumption is that adequate load transfer is provided at joints so that the load stress that occur at joints are not significantly higher than the stress at the interior of the slab. Adequate load transfer is provided at joints by a stabilized base, keyways, mechanical load transfer device or aggregate interlock. The cracking of a non reinforced jointed concrete slab with relatively short joint spacing is controlled by: The magnitude of flexural stress caused by the equipment loading The flexural strength of the concrete The number of stress applications The number of allowable stress applications to crack the concrete slab is controlled by the ratio of critical stress to flexural strength of the concrete. The relationship used in design procedure to relate stress/flexural strength ratio to the number of stress applications to cracking was developed by the PCA is shown on Table 8-3. The lower the ratio of the critical stress to flexural strength the larger the number of load applications that the slab can carry before cracking.



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Table 8-3 Stress-Strength Ratio and Allowable Coverage Table

Stress-Strength Ratio

Allowable Coverage

Stress-Strength Ratio

Allowable Coverage

0.45 2,300,000 0.63 14,000 0.46 1,700,000 0.64 11,000 0.47 1,300,000 0.65 8,000 0.48 1,000,000 0.66 6,000 0.49 720,000 0.67 4,500 0.50 540,000 0.68 3,500 0.51 400,000 0.69 2,500 0.52 300,000 0.70 2,000 0.53 240,000 0.71 1,500 0.54 180,000 0.72 1,100 0.55 130,000 0.73 850 0.56 100,000 0.74 650 0.57 75,000 0.75 480 0.58 57,000 0.76 370 0.59 42,000 0.77 280 0.60 32,000 0.78 210 0.61 24,000 0.79 160 0.62 18,000 0.80 120

The following five key design inputs are needed to determine the required slab thickness: • Design concert flexural strength • K value at top of Base • Design wheel load • Load repetition The 28-day third point loading flexural strength is used for pavement design. The design flexural strength should be as high as practical and economical but not less than 650 pounds per square inches. The actual mean flexural strength in the field will be grater than the design flexural strength. The k value is the ratio of unit pressure to deflection of a 30-inch diameter rigid steel plate. The k value on the subgrade and at the top of the base layers is determined using ASTM D196 method of testing. The value used for design is that obtained at the top of base. The combined base and subgrade should have a minimum design k value of 200 pounds per cubic inch to prevent excessive permanent deformation of the subgrade due to slab corner deflections. A base course of sufficient thickness and quality should be used to achieve this modulus. However, in no case should design be based on a k value greater than 500 pounds per cubic inch. The critical load shall be determined as shown in section 3. The design equipment repetition is calculated as shown on section 3.



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8.5 Joint Design for Non-Reinforced Concrete Pavement The performance of PCCP, especially at joints, is directly related to the strength of the subgrade. For example, cement-treated subbases have a joint effectiveness in excess of 80% after 1,000,000 equivalent single-axle loads compared to 40% for untreated subgrades. Joints are used to limit curling and warping stresses in pavement which are due to temperature and moisture gradients through the slab, prevent control cracking due to volume changes, prevent damage to immovable structures, and facilitate construction. Most of joints are classified as expansion, contraction and construction joints. Expansion joints allow for expansion of the pavement and reduction of high compressive stress at critical locations in the concrete pavement in hot weather. Expansion joints are placed the full depth of the slab. Use expansion joints at all intersections of pavements with fixed structures, at non-perpendicular pavement intersections, and between existing and new concrete pavement when joints in adjacent slab are not aligned. Expansion joints are not otherwise required within the non-reinforced concrete pavement. See Figure 8-1 for expansion joint details.

Figure 8-1 Isolation/Expansion Joints

Contraction (weakened plane) joints are used to control cracking in the pavement due to volume changes resulting from a temperature decrease or moisture decrease and, limit curling and warping stress from temperature and moisture gradients in the pavement. Form contraction joints in concrete by partial depth



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sawing or by installing sawable inserts. The saw cut joint or formed groove provides a weakened plane which will crack through the full slab depth during shrinkage and contraction of concrete as it cures. Contraction joints are required in the transverse direction and in the longitudinal direction depending upon slab thickness and spacing of construction joints. See Figure 8-2 for contraction joints.

Figure 8-2 Transverse Contraction Joints

Construction Joints are used between paving lanes or when abutting slabs are placed at different times. Longitudinal and transverse expansion may be required. Transverse construction joints will be required when it necessary to stop concrete placement for a length of time suffic ient to allow the concrete to begin to set. Longitudinal construction joints are generally spaced 20 to 50 feet apart depending on the construction equipment. Locate all transverse construction joints at the same location as regularly spaced transverse joints. Provide for load transfer or a thickened edge.



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Figure 8-3 Longitudinal Construction Joints

See typical longitudinal construction joints shown in Figure 8-3. Some of the typical longitudinal construction joint types are keyed joint, butt joint, and thickened edge joint. Keyways have been used extensively to provide load transfer along the longitudinal joints. However, there has been substantial amount of keyway failure under heavy loading on thinner slabs. Keyed joints should only be used on slabs 9 inches thick or greater. Butt joint may be considered for longitudinal construction joints on pavements less than 9 inches thick constructed with stabilized base. Thickened edge joint may be considered for construction joint for any pavement thickness and base type. Standard joint spacing for pavements is 12.5 (longitudinal) by 15(transverse) feet. For slabs having a thickness greater than 12 inches, joint spacing can be increased to a maximum of 20 feet. Transverse joint spacing shall not vary from longitudinal joint spacing by more than 25 percent. Figure 8-4 shows standard joint spacing.



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Figure 8-4 Typical Spacing of Jointed Plain Concrete Pavement

(source: http://training.ce.washington.edu/WSDOT/Modules/02_pavement_types/02-6_body.htm)

Properly designed joint must provide adequate load transfer across the joint. Load transfer efficiency is normally defined as the ratio of deflection of the unloaded side to the deflection of then loaded side of the joint. Good load transfer will aid in preventing deterioration such as corner breaks, transverse and longitudinal cracking, faulting, pumping, and spalling. Different amount of load transfer can be obtained through the use of aggregate interlock, dowel bars, keyways, a stabilized base or combination of these. Aggregate interlocking can provide adequate load transfer across joints when pavement is originally constructed, or during hot weather. However, as joint movements due to temperature variation and load applications increase, and joint begins to open, aggregate interlock is lost and load transfer is greatly reduced. Dowel bars are used to provide load transfer load transfer and prevent excessive vertical displacements of adjacent slabs. Attention shall be paid to quality control during construction when using dowel bars. Keyways may be used to provide load transfer along longitudinal construction joints. Stabilized base can be used to improve load transfer effectiveness by reducing joint deflection through increased support across a joint. Use stabilized base for all slabs less than 9 inches. Where thickened edge joints are used, the stabilized base is not required. Joint sealants are used to provide a seal to reduce infiltration of water and incompressible.



8-20 JN: 5552-06

8.6 Analysis of PCC pavement Analysis of PCC (Portland Cement Concrete) pavement should include consideration of the following issues: • Warping Stress Analysis • Temperature Steel Analysis • Dowel Bar Stress Analysis • PCC Slap load stress analysis • Fatigue Analysis • Unreinforced thickness requirements • Final reinforced slab thickness requirements

8.6.1 Warping Stress Analysis This is a stress caused by daily temperature variation. The magnitude of warping stress in PCC pavement is primarily dependent on slab size or geometry. During daytime, horizontal expansion at the top of the slab is greater than the horizontal expansion at the bottom. The slab tends to warp and induce tensile stress at the bottom of slab. This stress is in addition to the load induced tensile stress. Slab warping are evaluated along x & y-axis, as well as edge at the interior of the slabs. Stress analysis is accomplished by Bradbury’s analysis of Westerguard’s slab bending moment equations.

2

tte

CE ∆=

ασ (edge)

−+∆

= 221

12 µµα

σCCE tt

i (interior)

Where:

eσ = edge stress

iσ = interior stress E = Modules of Elasticity of PCC µ = Poisson’s Ratio (0.15)

tα = Coefficient of thermal expansion (5x10-6 in./in./ ºF)

t∆ = Thermal difference between top and bottom. C1 and C2 = Bradbury warping stress coefficients. The coefficient in C1 is in the desired direction, where as C2 is for direction perpendicular to this derivation. Figure 8-5 can be used to determine these coefficients. The Lx and Ly are the free length and width respectively.



8-21 JN: 5552-06

Radius of relative stiffness can be calculated using:

42

3

)1(12 kEh

lµ−

=

Where: l = Radius of relative stiffness in (in) E = Modulus of elasticity (psi) h = Thickness of pavement µ = Poisson’s ratio of the pavement k = Modules of subgrade reaction (pci) .

Figure 8-5 Warping stress coefficients curve



8-22 JN: 5552-06

If the slab is of 10ft or less warping stress is not a major factor. For slab spacing of 20ft or more, warping stress can be 60% to 100% of the flexural strength of the PCC.

8.6.2 Temperature Steel Analysis

Reinforce steel in rigid pavement system does not provide additional structural strength to the PCC. The primary purpose of steel reinforcement is to hold crack in the PCC tightly together to ensure adequate load transfer across the crack. Reinforcing steel requirements are based on “slab foundation drag theory.” The friction forces developed by the slab movement due to semiannual temperature change from the center of the slab to the free end and it must be equal to the total tension in the concrete.

hWLf

c 24=σ

Where: s c = Unit stress in the concrete (psi) W = Weight of slab (psf) L = length of slab in feet f = average coefficient of subgrade resistance h = Thickness of pavement? For x less than ½ L

−=

Lx

ff ma 32

1

Where: fa = Average resistance fm = Fully mobilized resistance

t

x∆

=1000

Where: ? t = Change of temperature L = Length of slab For x greater than ½ L

x

Lff m

a 232

=

Friction resistance forces are critical for long slabs (100ft or greater).



8-23 JN: 5552-06

8.6.3 Dowel Bar Analysis

To insure that all the transverse joints have adequate load transfer is one of the important design considerations. The best way of transferring the load for container terminal concrete pavement is using dowel bar. The sizing of the dowel bar diameter and spacing of dowel bar is based on the Timoshenko Frisberg Analysis. The analysis is based on criteria of failure where the bearing stress on the PCC by the deflected steel dowel bar is less than or equal to the allowable bearing strength of concrete. The maximum bearing stress on the concrete exerted by the dowel bar is given by :

EIzKPt

b 34)2(

ββ

σ+

=

4

4EIKb

=β

Where: K = Modulus of dowel support (1.5 x 106 pci) Pt = Transferred load ß = Relative stiffness of bar embedded in concrete I = Moment of inertia of the dowel E = Modules of elasticity, steel (29x106 psi) z = joint opening

The allowable bearing stress is given by

cb fb

f ′

−

=0.3

4

Where:

cf ′ = Compressive strength of PCC psi b = dowel bar diameter (inches)

The number of bars is calculated:

EIbfzeKP

nc

tb 3)4(8

)2(3β

β−′

+=

Where: e = Joint transfer load efficient nb = Number of bars



8-24 JN: 5552-06

8.7 Design Examples In this section, two design examples of PCC pavement are given. One is for top picks. The other is for RTG runways. The RCC thickness analysis, warping stress analysis, temperature steeling analysis and dowel bar analysis are illustrated in these examples.

8.7.1 Concrete Pavement Analysis Examples – Top Picks This example includes interior stress analysis, temperature reinforcing analysis, temperature distribution steel analysis and dowel bar analysis.

8.7.1.1 Top Pick Design Example – Interior Stress Analysis

Portland Cement Concrete Pavement Interior Stress Analysis

Mixed Traffic Loading of Kalmar DCF 410CSG Container Handler

Edge of slab thickness, t = 14 inches

Design modulus of rupture of concrete, Sc = 700 psi

Elastic modulus of concrete, Ec = 4,000,000 psi

Poisson ratio of concrete, ν = 0.15

Composite modulus of subgrade reaction, kc = 200 pci

Front tire contact stress, p f = 144 psi

Rear tire contact stress, p r = 144 psi

Radius of relative stiffness, l = 46.51 inches

1Interior Stress

Container Stress Ratio

Weight Load Estimated σi σi/Sc 4Allowable Percent

(pounds) Location Repetitions (psi) (psi) Repetitions Used

0 2Front Dual 20,420 197.9 0.28 UNLIMITED 0.00

0 3Rear Single 40,840 377.3 0.54 171,698 23.79

61600 4Front Dual 17,718 397.0 0.57 77,200 22.95

63800 4Front Dual 884 403.5 0.58 59,631 1.48

66000 4Front Dual 884 410.2 0.59 45,696 1.93

68200 4Front Dual 402 416.9 0.60 35,017 1.15

70400 4Front Dual 143 423.6 0.61 26,834 0.53

72600 4Front Dual 96 430.3 0.61 20,563 0.47

74800 4Front Dual 104 437.0 0.62 15,758 0.66



8-25 JN: 5552-06

77000 4Front Dual 76 443.6 0.63 12,124 0.63

79200 4Front Dual 61 450.5 0.64 9,217 0.66

81400 4Front Dual 41 457.2 0.65 7,063 0.58

83600 4Front Dual 4 463.8 0.66 5,434 0.07

85800 4Front Dual 4 470.4 0.67 4,181 0.10

88000 4Front Dual 2 477.0 0.68 3,217 0.06

5TOTAL FATIGUE CONSUMPTION = 55%

Is the total fatigue consumption < 100% ? YES

NOTES:

(1) Interior stress calculated using PCA computer program AIRPORT

(2) For each loaded repetition into the stack there is an unloaded repetition.

(3) For each front axle repetition there is a rear axle repetition that crosses the same (or similar) point.

(4) Look at critical wheel load and heavier wheel loads.

(5) Use Miner's Rule to evaluate cumulative damage from different load cases.



8-26 JN: 5552-06

8.7.1.2 Top Pick Design Example – Temperature Reinforcing Analysis Notes:

(1) Reinforcing steel is not typically used in traditional jointed concrete pavements, except when very large or irregularly shaped slabs are used.

(2) The addition of temperature reinforcing steel does not justify a reduction in pavement thickness. (3) Reinforce odd-shaped slabs. (i.e., L:W (Length : Width) or W:L > 1.25)

Joint Spacing:

(1) Different guidelines exist for maximum un-reinforced pavement joint spacing. See PCA, USACE, or FAA references.

(2) Common guideline is Max Length, ML = 24 × T, where T is the thickness in feet. (3) Un-reinforced slabs should not exceed 25' between joints for pavements on granular bases or 20'

between joints on stabilized bases. From thickness calculation, T = 14" (1.17')

52 UseN.G. ase)granular b (Assuming 52 82 )7(24)(1.1 ML ′∴′>′=′= Theoretically, the free slab panel size could be 25' × 25'. Note that a free edge is an untied edge. Plain, doweled, untied – key, expansion, and isolated joints are considered free edges. Assume for economic reasons a 25' × 50' panel size is determined to be more economical, determining necessary reinforcing. Slab reinforcing: Use subgrade drag theory. Slab thickness, T or h = 14" Slab length, Ly = 50' Slab width, Lx = 25'

s

f

fWhbC

A24

=

Where: b = Distance between nearest free joints (Feet); fC = Coefficient of subgrade (or subbase) resistance to slab movement.;

W = Weight of concrete (LBS/FT3); h = Slab thickness (inches); sf = Allowable stress in steel (PSI), generally taken as 2/3 yield strength; Assume: fC = 1.5 for gravel subbase;

yσ = 40,000 PSI (acceptable for grade 60 reinforcing or weld wire);



8-27 JN: 5552-06

/FTIN 64.0)000,40)(24(

)14)(150)(5.1)(50( 2==YA

Example options: # 3 @ 8" ⇒0.165 IN2/FT; # 4 @ 14" ⇒0.171 IN2/FT; W8.5 @ 6" ⇒0.17 IN2/FT; W18 or D18 @ 12" ⇒0.18 IN2/FT; W26 or D26 @ 18" ⇒0.17 IN2/FT; Keep spacing = 18";

/FTIN 082.0)000,40)(24(

)14)(150)(5.1)(25( 2==XA

Various bar and wire options exist.



8-28 JN: 5552-06

8.7.1.3 Top Pick Design Example – Temperature Distribution Steel Analysis TEMPERATURE DISTRIBUTION STEEL ANALYSIS FOR JOINTED

REINFORCED CONCRETE PAVEMENTS (JRCP)

Notes: (1) Distribution steel is not structural steel reinforcement. (2) Distribution steel holds cracks together so that load transfer is maintained through aggregate interlock. (3) Free joints are considered contraction joints, expansion joints, and unrestrained edges. (4) Subgrade friction factors shown are considered mean values. Actual values may vary significantly.

Typical Yield Strengths and Allowable Stresses for Steel

Yield Strength Allowable Stress Type and Grade of Steel (psi) (psi)

ASTM A 615, Grade 40 Billet Steel 40,000 27,000 ASTM A 615, Grade 60 Billet Steel 60,000 40,000

ASTM A 185, Cold drawn wire (smooth) 65,000 43,000 ASTM A 497, Cold drawn wire (deformed) 70,000 46,000

Typical Subgrade Friction Factors

Type of Material Beneath Slab Friction Factor (fa) Lean-Concret or Cement-treated Base

w/ Bondbreaker 4.0

Asphalt-treated gravel 5.8 Lime Stabilization 4.0 Crushed Aggregate 1.5 Fine-grained Soil 1.3

Sand 0.8

Slab Thickness h = 14inches

Slab Width Lx = 25feet (Longest distance between free joints)

Slab Length Ly = 50feet (Longest distance between free joints)

Allowable Steel Stress fs = 40,000psi (Grade 60 Reinforcing)

Density of Concrete γc = 150pcf

Subgrade Friction Factor fa = 1.5

Longitudinal Area of Steel Required Asy = 0.1641in2/ft of length

Transverse Area of Steel Required Asx = 0.0820in2/ft of width

Type of reinforcing to be used (i.e. BAR or WIRE) Type = BAR

Longitudinal reinforcing size provided (i.e. 3, 4, 5, etc.) Bary = 3

Longitudinal reinforcing spacing (inches) sy = 8inches



8-29 JN: 5552-06

Longitudinal area of steel provided Asy = 0.1657in2/ft of length

Is sufficient longitudinal steel provided? YES

Transverse reinforcing size provided (i.e. 3, 4, 5, etc.) Barx = 3

Transverse reinforcing spacing (inches) sx = 16inches

Transverse area of steel provided Asx = 0.0828in2/ft of width

Is sufficient transverse steel provided? YES



8-30 JN: 5552-06

8.7.1.4 Top Pick Design Example – Dowel Bar Analysis Use Timdshenkd Analysis to determine dowel bar size and spacing. PCA, USACE, or FAA guidelines should be used as a starting point for minimum dowel size and maximum spacing. Look at 103K Dual Wheel Load from top loader. Try 1.75" diameter @ 12" O.C.

PCIK 6105.1 ×= (Modulus of dowel support) PSIEd

61029 ×= (Modulus of elasticity for dowel)

PCIk 200= (Subgrade support)

444

4604.064

)75.1(64

ININd

Id ===ππ

INPCI

INPSIkr

hEl

INPSIINPCI

IEKd

c

dd

5.46)200]()15.0(1)[12(

)14)(104()1(12

4709.0)4604.0)(1029)(4(

)75.1)(105.1(4

25.0

2

3625.0

2

3

25.0

46

625.0

=

−

×=

−

=

=

××

=

=β

Assume: Contraction Joint Width, 52.0 ′′=z Joint Efficiently, %100=e

EFFn = 9 Bars Bars Directly Below Tire Fully Used, Then Proportional To Distance Further Away.



8-31 JN: 5552-06

Stress) Bearing(Dowel 3260)00217.0)(105.1(

00217.0)4604.0)(1029()4709.0)(4(

)]25.0)(4709.0(2)[5722(4

)2(

722,595.512/103

60

6330

#

PSIKy

INIEzP

y

nP

b

dd

t

K

EFF

K

t

=×==

=×

+=

+=

===

σ

ββ

Assume PSIf c 000,5=′

3

)5000)(75.14(3

)4( Stress, BearingAllowable

−=

′−=⇒ c

bfd

f

PSIfb 3750=

OK ∴< bb fσ



8-32 JN: 5552-06

8.7.2 Concrete Pavement Analysis Examples – RTG Runway

8.7.2.1 RTG Runway Design Example – Overview RTG runway design consists of three parts of design: 1) concrete slab design, 2) expansion joint width, and 3) dowel bar design. The concrete slab design should consider the following stresses as a minimum:

1) Concrete fatigue stress due to equivalent wheel load repetition. 2) Concrete compression and tension stresses due to different wheel positions on the concrete slab. 3) Temperature warping stress due to differences in temperature at top and bottom surfaces of a

PCC slab. 4) Concrete tensile stress caused by slab expansion and contraction due to temperature changes.

The pavement expansion joint width should be properly sized to allow concrete slab expansion and contraction. However, excess joint opening can result concrete damage during wheel load transferring through the joint. One way to insure proper load transferring between slabs is to provide dowel bars across the joint. Sample calculations of the fatigue analysis, warping analysis, load stress analysis, subgrade drag procedure, expansion joint opening, and dowel bar analysis are attached. It’s very important to note that the RTG runway is designed ONLY for RTG wheel load to travel in the longitudinal direction of the concrete slab. No protection is provided at the transverse direction. Therefore, any type of vehicle traveling across the RTG runway in the transverse direction is discouraged.



8-33 JN: 5552-06

8.7.2.2 Example – Thickness Design Thickness Design Report

GENERAL DESIGN INP UT

Design Period: 20

Years

Unit: US Units Total Design Traffic: 109000

Load Repetitions

USER DEFINED INPUT

Design Vehicle/Aircraft: Test Vehicle

Wheel/Axle Configuration: Single-Single Pavement Type: RCC

Modulus of Elasticity 3.6 million psi

Modulus of Rupture (MR): 569 psi

Modulus Subgrade Reaction (k): 250 pci

Computation Method: With Axle Rotation Loading Condition: Interior Loading

Number of Wheels: 1 Contact Area: 387 sq. Inches

Contact Pressure: 144 psi

Total Load: 55728 lbf

COMPUTATION RESULT

X_Max: 0 inches

Y_Max: 0 inches

Maximum Angle: 90 degrees

Maximum Stress: 254 psi

Stress Ratio: 0.446

OUTPUT

Allowable Total Repetitions: 181398 Allowable Daily Repetitions: 25

Final Slab Thickness: 16.0 inches

WHEEL COORDINATES inches

x: 0

y: 0

NOTE

A stress ratio (stress divided by design strength) greater than 0.75 may be too high to satisfy routine pavement design requirements (the thickness is inadequate), but may be used to evaluate the effect of unexpected heavy loads on an existing pavement. If the computed thickness for RCC pavement is less than 4" or 200 mm (20 cm), 4" or 200 mm should be used in design.

Note: the above is modified from the output of the pavement design program RCCPave.



8-34 JN: 5552-06

8.7.2.3 RTG Runway Design Example – Warping Stress Analysis

Warping (Curling) PCC Stress Analysis

The thermal gradient assumed for slab thickness 2 F / in

Slab Length (Ly) = 6 ft Slab Width

(Lx) = 50 ft

Compressive Strength of PCC (f'c)

= 4000 psi Assumed

Slab Thcikness

(h) = 16.0 inch

Pavement Modulus of Elasticity (Ec) = 3605 ksi

Poisson Ratio (u) = 0.15

Coefficient of Thermal Expansion

(At) = 0.000005

Subgrade Modulus

(k) = 250 pci

Allowable Steel Reinforcement

Stress (fs) = 24.00 ksi

Radius of Wheel

Contact (ac) = 12.12 in

Modulus of Rupture

(fr) = 632 psi fr = 10 * f'c0.5

Thermal Gradient

(Dt) = 32.00 F Dt = 3 * h

Raduis of Relative

Stiffness (l) = 47.37 in

= ( Ec * h 3 / (12 ( 1 - u2 ) * k) )0.25

Lx / l = 12.67 Ly / l = 1.52

Check Figure 1, Cx

= 1.02 Cy = 0

EDGE STRESS

Edge Stress = Cx * Ec * At * Dt / 2

= 294 psi

INTERIOR STRESS

Interior Stress = Ec*At*Dt/2*[(Cx+uCy)/(1-u^2)]

= 301 psi

CORNER STRESS

Corner Stress = Ec*At*Dt/[3*(1-u)]*(ac/l)0.5

= 114 psi



8-35 JN: 5552-06

8.7.2.4 RTG Runway Design Example – Load Stress Analysis

Load Stress Analysis

Slab Thcikness (h) = 16.00 inch

Raduis of Relative

Stiffness (l) = 47.37 in

Tire Load (W) = 60.00 kips

Tire Pressure (Ps) = 130.00 psi

Tire Contact Area (a)

= 461.54 in^2

Radius of Wheel

Contact (ac) = 12.12 in

Flexural Strength of

Rupture (fr) = 632 psi

Radius of Resisting

Section (b) = 11.36 in = (1.6*ac2 + h2)0.5 - 0.675*h

4*log (l/b) = 2.48

EDGE LOADING (TENSILE STRESS AT THE SLAB TOP)

σe = 0.572 * W * [4 * log (l/b) + 0.359] / h2

Load Stress = 381 psi

Warping Stress = 294 psi

Total Stress = 675 psi (day time temperature gradient)

f'r = 750 psi concrete flexural strength specified

? INTERIOR LOADING (TENSILE STRESS AT THE SLAB BOTTOM)

σi = 0.3162 * W * [4 * log (l/b) + 1.069] / h2



Total Stress = 564 psi (night time temperature gradient)


CORNER LOADING (TENSILE STRESS AT THE SLAB TOP)

σc = 3 * W * [1 - (ac * 20.5 / l )0.6] / h2



Total Stress = 435 psi (day time temperature gradient)




8-36 JN: 5552-06

8.7.2.5 RTG Runway Design Example – Subgrade Drag Procedure

SUBGRADE DRAG PROCEDURE

Cross-Sectional Area in Square Inches of Steel per Lineal Foot of Slab Width

As = f * L * W / 2 / fs

Allowable Steel Stress (fs = 0.75

Fy) = 45.00 ksi A307 Rebar Fy = 60 ksi

Friction Factor (f) = 1.80 ( 1.5 ~ 2.0 ) Welded Wire Fabric Fy = 70 ksi

Slab Thcikness (h) = 16.00 inch

Dead Weight of PCC Slab (W) = 200.00 psf

Slab Length (Ly) = 6.00 ft

Slab Width (Lx) = 50.00 ft

Long. Temp. Reinforcement (As)

= 0.02 in^2/ft #4 @ 18 As = 0.17 in^2/ft OK

Trans. Temp. Reinforcement

(As) = 0.20 in^2/ft #5 @ 18 As = 0.21 in^2/ft OK



8-37 JN: 5552-06

8.7.2.6 RTG Runway Design Example – Dowel Bar Analysis

Dowel Bar Analysis

Modulus of Dowel

Support (K) = 1.5E+06 pci

Applied Wheel Load

(Pw) = 55.8

Joint Opening (z) = 0.50 inch

Joint Transfer Load Efficient

(e) = 0.90

Dowel Bar

Diameter (b) = 1.50 inch Dowel Bar

Spacing (s) = 8.00

Dowel Bar Area

(A) = 1.77 in2

Dowel Bar Strength (Fy)

= 36.00

Modulus of Elasticity of Steel

(Es) = 29000000 psi

Compressive Strength of PCC (f'c) = 4000.00

Dowel Bar Moment of Inertia

(Is) = 0.25 in^4

Raduis of Relative

Stiffness (l) = 47.37

Relative Stiffners

of Bar (β) = 0.53 /inch β =( K * b / ( 4 * Es * Is )) 0.25

Number of Effective Dowels

(Neff) = 5.92 bars Neff = l / s

Load Transferred Across the Joint

(Pt) = 25.09 kips Pt = Pw * e / 2

Max Shear on

Each Dowel (Pc) = 4.24 kips Pc = Pt / Neff

Max Shear Stress on Each Dowel

(Vc) = 2.40 ksi Vc = Pc / A < 0.4 Fy O K

Deflection at Face

of Joint (yo) = 0.0023 in

yo = Pc * (2 + β ∗ z) / (4 * β3 * Es * Is)

Max Bending Moment on Each

Dowel (Mc) = 0.60 k-in Mc = Pc * z / 2

Max Bending Stress on Each Dowel (Fb) = 1.81 ksi

Fb = Mc * b / 2Is < 0.66 Fy O K

Allowable Concrete Bearing

Stress (fb) = 3333.33 psi fb = (4 - b ) * f'c / 3

Concrete Bearing Stress at Face of

Joint (σb) = 3381.08 psi σb = K * yo < fb Close Enough

?



8-38 JN: 5552-06

Shrinkage/Expansion Joint Opening

Joint Width (z) =

= C * L * ( e * ∆t -δ )

= 0.44 in

Slab Length (Lx) = 50 ft

Temperature

Change (Dt) = 70.00 degree F

Base Friction Restraint Factor

(C) = 0.80 /degree F = 0.65 Stabilized Bases

= 0.80 Granular Bases

Concrete Thermal

Expansion (e) = 6.0E-06 /degree F

= 6.6E-06 quartz = 5.3E-06 granite

= 6.5E-06 Sandstone = 4.8E-06 basalt

= 6.0E-06 gravel = 3.8E-06 Limestone

New PCC Shrinkage

Coefficient (δ) = 5.0E-04 in/in

= 8.0E-04

Indirect Tensile Strength of 300 psi or less

= 4.5E-04

Indirect Tensile Strength of 500 psi

= 2.0E-04

Indirect Tensile Strength of 700 psi or greater



JN: 5552-06

9. Roller Compacted Concrete (RCC) Pavement....................................................................... 9-1 9.1 Introduction.................................................................................................................. 9-1 9.2 RCC Design Approach.................................................................................................. 9-1 9.3 Structural Analysis and Load Configurations............................................................... 9-2

9.3.1 Distribution of Pavement Stresses .............................................................................................................. 9-2 9.3.2 Pavement Loads ............................................................................................................................................... 9-3 9.3.3 Strength and Fatigue Relationships ........................................................................................................... 9-3 9.3.4 Pavement Design............................................................................................................................................. 9-4

9.4 Materials Characterization........................................................................................... 9-4 9.4.1 RCC Aggregate ................................................................................................................................................ 9-4 9.4.2 Strength and Modulus of Elasticity............................................................................................................ 9-4 9.4.3 Subgrade Support........................................................................................................................................... 9-5

9.5 RCC Mix Design........................................................................................................... 9-5 9.5.1 Determining Maximum Density.................................................................................................................. 9-5 9.5.2 Determining Cement Content...................................................................................................................... 9-6 9.5.3 Admixtures and Freeze-Thaw Consideration......................................................................................... 9-6

9.6 RCC Pavement Performance........................................................................................ 9-6 9.6.1 Smoothness........................................................................................................................................................ 9-6 9.6.2 Cracking and Faulting ................................................................................................................................... 9-7 9.6.3 Durability, Permeability................................................................................................................................ 9-7 9.6.4 Maintenance ..................................................................................................................................................... 9-7

9.7 Construction................................................................................................................. 9-8 9.7.1 Mixing ................................................................................................................................................................ 9-8 9.7.2 Transporting..................................................................................................................................................... 9-8 9.7.3 Placing and Compacting ............................................................................................................................... 9-8 9.7.4 Shrinkage and Cracking Control .............................................................................................................9-10 9.7.5 Curing ..............................................................................................................................................................9-11 9.7.6 Weather ...........................................................................................................................................................9-11

9.8 QC/QA Methods ......................................................................................................... 9-12 9.9 Design Example .......................................................................................................... 9-13 9.10 References................................................................................................................... 9-16 9.11 Appendix Tables and Figures ..................................................................................... 9-17



9-1 JN: 5552-06

9. Roller Compacted Concrete (RCC) Pavement

9.1 Introduction

Roller Compacted Concrete (RCC) is a zero-slump concrete consisting of dense-graded aggregate and sand, cement, and water. Because it contains a relatively small amount of water, it cannot be placed by the same methods used for conventional concrete. For pavement applications, the concrete is usually placed with an asphalt paver, and densified by compacting with a vibrating roller. The low water-cement ratio (usually ranging from .30 to .40) provides for very high strengths. The use of RCC as a material to construct pavements began in the 1970’s in Canada. It was originally used by the logging industry to provide an all-weather platform for unloading logging trucks and storing and sorting logs. In the past 25 years it has gained acceptance as a strong and durable pavement material that can withstand heavy loads and severe climates with little required maintenance. RCC pavements have been successfully used for container terminals and intermodal rail yards in many parts of North America, including the following examples:

- Conley Terminal, Massachusetts Port Authority, Boston (78,000 sq.yds.) - Intermodal Terminal, Burlington Northern Santa Fe RR, Denver (126,000 sq. yds.) - Pier 300, Port of Los Angeles (40,000 sq. yds) - Intermodal Terminal, Canadian National Railway, Calgary (87,000 sq. yds.) - Norfolk International Terminal, Norfolk, VA (50,000 sq. yds)

9.2 RCC Design Approach

The approach used for designing RCC pavements for container terminals and intermodal rail yards is very similar to that used for designing conventional concrete pavements for industrial applications. This varies somewhat from design procedures used to design concrete pavements for highways because the load configurations and traffic operations are different, and there is no comparable database for industrial pavement performance as exists for highway pavements. The design approach for RCC pavements for heavy industrial applications is based upon limiting the stress in the pavement to a level such that the pavement structure can withstand repeated loadings of this stress magnitude without failing in fatigue. When wheel loads are applied to the interior of a concrete slab, it will deform in the shape of saucer. This deformation causes compression in the top of the slab, and tension at the bottom. The number of repeated stress applications that can be withstood before failure is the fatigue life. With conventional portland cement concrete and roller-compacted concrete, the relationship between stress level and fatigue has best been expressed through the ratio of the applied critical stress to the Modulus of Rupture:

Stress Ratio = Critical applied stress Modulus of Rupture where: Critical applied stress is the maximum tensile stress at the bottom of the concrete pavement slab, and



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Modulus of Rupture is the tensile strength of a concrete beam tested using third-point loading at 28 days. This relationship has been developed for roller-compacted concrete through laboratory studies of fatigue testing conducted by the Portland Cement Association (PCA) (Ref 1). In the design process, the designer considers the economic and structural tradeoffs of concrete strength, pavement thickness, and foundation support with regard to the applied wheel loads and number of expected load applications. The applied pavement stress is determined theoretically, and compared to the concrete strength, which can be tested in the laboratory for each mix design. The specifics of this design process are explained in further detail in the sections below. This procedure follows the approach used by the PCA since 1986 (Ref 2). Other design procedures used by the Federal Aviation Administration (FAA) for the design of airport pavements (Ref 3), and by the U.S. Army Corps of Engineers (Ref 4) can also be used for the design of RCC pavements, but are not covered in this design guide. 9.3 Structural Analysis and Load Configurations

As mentioned above, the applied tensile stress at the bottom of the concrete slab must be theoretically determined in order to calculate the stress ratio. The calculation of the applied stress is based on the mechanics of a slab on an elastic foundation. The magnitude of the theoretical applied tensile stress will be a function of the applied load (expressed in terms of a circular load area and magnitude), the Modulus of Elasticity of the concrete, and the assumed load position. In most terminal and intermodal yard applications, the interior loading condition can be assumed because there are no designed joints in roller-compacted concrete, and traffic operations are conducted away from the edge of the slab. 9.3.1 Distribution of Pavement Stresses

The methodology used to calculate pavement stresses was originally developed by Westergaard (Ref 5) and expanded by Pickett and Ray (Ref 6). As described above, the critical stress being evaluated is the maximum tensile stress at the bottom of the concrete slab. The basic equation (for interior loading) is:

25.03

2

)1(12

)069.1log4(316.0

−

=

+=

kEh

l

bl

hP

i

ν

σ

where: σi = tensile stress at the bottom of the interior of the concrete slab (psi) P = applied wheel load (lbs.) h = thickness of slab (in.) b = a = radius of loaded area (if a > 1.724h), or b = (1.6a2 + h2)0.5 – 0.675h ; when a < 1.724h l = radius of relative stiffness (in.)



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E = modulus of elasticity of concrete (psi) ν = Poisson’s ratio of concrete (normally assumed to be 0.15) k = modulus of subgrade reaction (psi/in, or pci) The radius of relative stiffness is a comprehensive term that incorporates the stiffness of the concrete material, the thickness of the slab (which affects the slab moment of inertia), and the stiffness of the material underlying the slab. The modulus of subgrade reaction relates the stiffness of everything underneath the slab. So, if the slab is placed on more than one layer of material, such as a subbase layer, then the k value must consider the effects of both the subbase and the subgrade. The k value can be measured in the field, using a plate bearing test. This test measures the pressure necessary to penetrate a plate into the subbase, expressed in terms of applied pressure (psi) per inch of penetration. Because of the time and expense of conducting this test in the field, estimates of k values are usually preferred, based on other material properties that can be determined in the laboratory (see Appendix Figure 1). 9.3.2 Pavement Loads

The load magnitude and area of application is the primary factor in determining the resulting stress in a pavement slab. In most cases pavement loads are not applied through a single wheel, but through multiple wheel configurations where the stresses caused by one wheel overlap the stresses caused by other nearby wheels. The stresses from these nearby wheels are cumulative, so the additive effects of multiple wheels need to be included in the design procedure. The designer must characterize the spacing between wheels, the load per wheel, and the area of load for each wheel. The area of load application (sq. in.) is most commonly determined by dividing the wheel load (lbs.) by the tire pressure (psi). If hard (non-pressurized) tires are used, the footprint area can be used. The pavement is designed for the wheel load and configuration that generates the most critical stress condition. If the terminal can be divided into different areas of operation, with different traffic conditions in each area, then significant savings can be realized by designing the pavement separately for each traffic area. If mixed traffic exists, where multiple types of traffic exist in the same area, then the contribution to fatigue must be calculated for each traffic type, and added together to make sure the total loading does not exceed 100% of the pavement fatigue life. Pavement fatigue is discussed below in more detail, and shown in the design example . 9.3.3 Strength and Fatigue Relationships

Because there is no large empirical database of pavement performance for RCC pavements, there is no way to relate critical stress to actual field performance. Instead, RCC materials are evaluated in the laboratory at different stress levels to determine the fundamental relationships that explain the fatigue behavior of RCC. The PCA design procedure for RCC pavement is based on research conducted in the mid-1980’s (Ref 2). In this research, a fatigue relationship was developed for RCC pavements, based upon the ratio of the applied flexural stress to the flexural strength. This relationship is shown in Appendix Table 1.



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9.3.4 Pavement Design

To determine the pavement design, the designer must have the expected traffic, expressed in terms of wheel loads, load configuration, and number of load applications expected over the design period. Since the design of a terminal facility is for a long period of time, a design life of 20 – 30 years is typical. For the expected number of load applications, the designer can select the following parameters, which all have an affect on either the flexural stress, or the flexural strength, of the RCC pavement: • modulus of subgrade reaction • flexural strength (and elastic modulus) of the concrete mix • thickness of the concrete slab

By evaluating the economics and other design constraints of the three factors above, the designer can select the best overall RCC pavement for a given project. The designer may decide to increase the subbase thickness, change the flexural strength of the concrete mix, or increase the thickness of the slab, depending on the pavement loading and the economics of these different changes. Once the design flexural strength is determined, then the concrete mix can be developed to meet that requirement. To make the calculation of designing the pavement slab easier, charts have been developed to aid the process. In addition, computer programs are available which greatly simplify the effort required to evaluate the pavement (Ref 7). 9.4 Materials Characterization

9.4.1 RCC Aggregate

Proper selection of aggregate is one of the most important factors that will affect the construction and performance of an RCC pavement. The aggregate must be dense-graded in order to provide stability during and after construction, and to minimize the amount of voids in the mix (since the volume of paste is much smaller in RCC than that for conventional concrete). A figure illustrating the recommended gradation from ACI 325 (Ref 8) is shown in Appendix Figure 2. Normally the nominal maximum size aggregate (NMSA) should not exceed ¾ in., and the allowable percentage passing the #200 sieve is 2 – 8 %. For high quality RCC, both the coarse and the fine aggregate fractions should be composed of hard, durable particles evaluated by standard physical property tests such as those listed for ASTM C33. 9.4.2 Strength and Modulus of Elasticity

The strength of the RCC mix is expressed in terms of the modulus of rupture (flexural strength), as determined by third-point loading. Because compressive strength testing is often more practical to complete than flexural beam tests, relationships have been developed between compressive strength and flexural strength for RCC materials. For design purposes, the following relationship is suggested:



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( ) 5.09 cr ff ′= where: rf = flexural strength (psi)

cf ′ = compressive strength (psi) A similar relationship exists for estimating the modulus of elasticity as a function of the concrete compressive strength. This relationship is:

( ) 5.0000,57 cfE ′= where: E = modulus of elasticity (psi) 9.4.3 Subgrade Support

As discussed earlier, the value of the modulus of subgrade reaction, k, can be estimated from laboratory tests such as CBR or R-value, or soil classification tests. Estimates of k based on these relationships are shown on the chart in Appendix Figure 1. In addition, the effect of on k values when using a subbase is shown in Appendix Table 2. 9.5 RCC Mix Design

The recommended method in this guide of proportioning aggregate, water, and cement to determine the project RCC mix is based on evaluating compacted laboratory specimens. The equipment and procedures are very similar to those used for determining maximum density and optimum water content for aggregates and soils. Other mix design procedures are also available, but are not discussed in detail here (see Ref 8). The mix design process begins with a selected aggregate that meets specifications previously discussed. Then the design cement content must be selected, and the optimum moisture content for proper compaction of the mix. 9.5.1 Determining Maximum Density

There are two procedures that can typically be used to determine the maximum density of RCC mixtures: 1) ASTM D1557 (using the Proctor procedure), and 2) ASTM C1435 (using a mechanical vibrating plate). Either procedure uses a specified ASTM method to compact a sample. The samples are prepared at 3 or 4 levels of moisture, and then weighed, to determine at which moisture content the material has the highest dry density. Previous research has found that the strength of RCC mixes depends significantly on the amount of compaction. If the mix is too dry, then there is not enough moisture to lubricate the particles so that they can move closer together. In addition, if too dry, an insufficient amount of cement paste will develop to spread among the soil and aggregate particles. If the mix is too wet, the water particles will take up too much volume, and the solid particles will not fit as tightly together. It is at the optimum moisture content that maximum density and maximum strength are achieved.



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9.5.2 Determining Cement Content

The desired cement content is the minimum amount that will satisfy the required design flexural strength. The cement content is typically expressed as a percentage of the total weight of solids (oven dry aggregates plus cement) in the mix. Common values of cement content range from 10% to 16%. Laboratory samples are created at optimum water content over a range of 3 – 4 cement contents, and tested in compression. Strength values are plotted versus cement content so that the designer can determine the value of cement content that will satisfy the design strength. 9.5.3 Admixtures and Freeze -Thaw Consideration

Chemical admixtures are used differently in RCC than in conventional concrete, because the much lower volume of paste makes it more difficult to incorporate many admixtures. While its low water/cement ratio helps give RCC its high-strength properties, there are times when certain admixtures may be considered, such as: Set retarders can be used to delay the setting time of the cementitious materials and are useful when there is a long haul time between the point of production and the project location. Set accelerators can be used if the intent is to speed the setting time of the RCC, such as when opening a project early to traffic. Water reducers and plasticizers can help distribute the small amount of cementitious paste uniformly throughout the RCC mix and improve speed and workability during production and placement. Air-entraining admixtures are very difficult to homogenously incorporate throughout a batch of RCC due to the extremely dry nature of the mix and are not commonly used. Whenever any admixtures are being considered for use in RCC mixes, extensive laboratory and field testing should be conducted to determine the effectiveness and proper dosage rates. Just as important as the aggregates, wate r, and cementitious materials, the correct selection of admixtures is important to the production and placement of quality RCC mixes. Many years of observing RCC pavements in cold climates have shown very good performance with regard to freeze-thaw effects (Ref 9). However, traditional laboratory evaluations of freeze-thaw durability with RCC mixes have not shown good results. Given that the good field experience has not correlated with the laboratory results, it is not recommended that freeze-thaw testing of RCC mixes be conducted. Additional information on the freeze-thaw performance of RCC can be found in Reference 10. 9.6 RCC Pavement Performance

9.6.1 Smoothness

RCC pavements are not as smooth as conventional concrete pavements. As a result, operating speeds on RCC pavements typically do not exceed 35 – 40 mph. The measurement of smoothness is usually expressed as the deviation in elevation of the pavement surface at any point along a 10 ft. straight-edge. Projects have been successfully constructed using a ¼ to 3/16 in. straight-edge tolerance. If pavement smoothness is particularly important for a RCC project, the following steps can be taken to improve the final results:

- use a maximum aggregate size no larger than ½ in.



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- do not construct the pavement in layers exceeding 8 in. in thickness (after compaction) - use a high-density paver with string-line grade control - be able to achieve compaction without excessive rolling

If high-speed operations are required, a thin (2-3 in.) layer of asphalt or bonded concrete can be placed over the RCC slab to provide a smooth travelling surface. Diamond grinding of the RCC surface has also been used, and can provide additional smoothness without the construction of a surface overlay. 9.6.2 Cracking and Faulting

Cracks will develop in an RCC pavement slab as a natural result of the shrinkage process during curing. These cracks will normally occur on a random basis every 30 – 70 ft. Because there is no bleed water in RCC, there is less shrinkage cracking than that which occurs with conventional concrete. The shrinkage cracks that occur in RCC pavements are usually small (less than 1/8 in.) and very good load transfer exists across the crack through aggregate interlock. This aggregate interlock is enhanced through the use of the dense-graded aggregates that are specified for RCC mixes. Long-term performance studies of RCC pavements (Ref 9) have shown almost no evidence of crack faulting (the vertical displacement of the pavement slab at the crack), which provides further indication of the load transfer provided by aggregate interlock. To improve the appearance of the final RCC product, control joints can be sawn every 20 – 30 ft. to eliminate most of the random shrinkage cracking. (See section below on construction of control joints). 9.6.3 Durability, Permeability

Roller Compacted Concrete, as an engineering material, can be considered to be impermeable. Because the shrinkage cracks are narrow, very little water moves through to the bottom of the slab, and good aggregate interlock has made the problems associated with pumping of RCC pavements very rare. The durability of RCC pavement is excellent, both in terms of environmental effects, and the physical wearing caused by equipment operations. In some cases a small amount of wear will occur (less than ¼ in.) on the pavement surface if it was not adequately bonded during construction. However, experience indicates that this wear will be arrested and will not increase even after years of traffic and abrasion (Ref 9). 9.6.4 Maintenance

RCC pavements have shown to require very little maintenance. Cracks are sometimes routed and sealed, but usually crack spalling is not a significant problem. The most common type of repair occurs with small areas where the RCC may have been placed by hand, or around structures. In these locations, if the RCC is not satisfactory, it can be removed and replaced with a repair using conventional concrete.



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9.7 Construction

9.7.1 Mixing

The mixing plant should be located within a 30-minute haul time from the point of RCC placement. The plant should be capable of producing an RCC pavement mixture in the specified proportions, and be able to produce a uniform mixture at a rate compatible with the paving equipment. Pugmill Plant. Pugmill plant shall be a central plant with a twin shaft pugmill mixer, capable of batch or continuous mixing, equipped with synchronized metering devices and feeders to maintain the correct proportions of aggregate, cement, pozzolan and water Rotary Drum Mixer. Rotary drum batch mixer shall be capable of producing a homogeneous mixture, uniform in color and having all coarse aggregate coated with mortar. 9.7.2 Transporting

Dump trucks for hauling the RCC material from the plant to the paver should have covers available to protect the material from drying and inclement weather. The number of trucks should be sufficient to ensure adequate and continuous supply of RCC material to the paver. The trucks should be dumped clean with no buildup or hanging of RCC material in the corners, depositing the material directly into the hopper of the paver or into a secondary material distribution system which deposits the material into the paver hopper. Dump truck delivery should be timed and scheduled so that RCC material is placed and compacted within one hour from the time it is mixed. 9.7.3 Placing and Compacting

Before placing RCC the subgrade should be graded and compacted so that a good, stable platform is available for paving. A stone subbase is often used to provide additional support for the concrete slab and reduce the chances of future pumping. RCC is usually placed with an asphalt-type paver, with the concrete placed in the paver by dump trucks. Either high-density or conventional pavers can be used. High-density pavers have been designed with tamping bars and other devices located inside the paving screed that consolidate the concrete a substantial amount during placement. The density of the mix after paving will be about 90% - 95% of maximum with the high-density pavers, compared with 80% - 85% of maximum with conventional paving equipment.



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Figure 9-1 Placement with asphalt paver and rolling of RCC.

Typical construction specifications (Ref 11) for RCC call for 96% - 98% of maximum density, so compaction after paving is necessary to meet density requirements. Smooth-wheel vibrating rollers are used to achieve compaction, with some contractors preferring to use pneumatic -tire rollers for finish rolling. A test strip is essential at the beginning of the project to determine the behavior of the RCC mix during placing and compaction, and to verify that the contractor’s equipment and rolling pattern can achieve the required density. Construction joints can be considered to be “fresh” if adjacent material is placed within 1 hour. For fresh joints, the contractor’s rolling pattern should provide for both sides of the joint to be uncompacted before kneading them together to ensure proper blending and compaction. Sometimes water or evaporation retarder is sprayed on the open face of a fresh joint to reduce drying before placement of the adjacent material.



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Figure 9-2 Construction of fresh joint within 1 hour of placing first section.

If adjacent material is placed after 1 hour, then a cold joint should be constructed. The face of the cold joint should be trimmed so that a vertical face exists and any slumped material is removed. Grout should be brushed on the face of the cold joint immediately ahead of the paver to provide better bonding when paving along a cold joint.

9.7.4 Shrinkage and Cracking Control

Concrete will shrink due to drying and hydration curing. Because of this shrinkage, the concrete can be allowed to crack naturally, or control joints can be sawn to relieve the shrinkage strains. With RCC, there is less shrinkage than conventional concrete because there is less paste in the mix. Saw cuts (typically to a depth of ¼ the slab thickness) can be performed with early entry saws with RCC, usually within 2-3 hours of compaction. Spacing between control joints is usually 20 to 30 feet, depending upon the thickness of the slab. Load transfer across the shrinkage crack is accomplished by aggregate interlock. Figure 9-3 shows the crack that forms at a control joint. No steel reinforcement or dowel bars are used in RCC.



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Figure 9-3 Side view of crack at control joint in RCC slab.

9.7.5 Curing

As with conventional concrete, curing is very important for RCC. However, RCC has no bleed water, so the main concern is drying. At least three negative things will happen if RCC is allowed to dry: 1) the concrete will experience drying shrinkage which will lead to cracking, 2) the cement will not continue to hydrate which will result in lower strengths and less durability, especially at the surface, and 3) dusting of the surface is more prevalent. To keep RCC from drying the surface should be kept moist for 7 days, or until a curing compound is applied. The surface should be gently moistened with water from the time compaction is complete. Curing compounds conforming to ASTM C 309, which are used for conventional concrete, can be used for RCC. However, because RCC has a more open surface texture than conventional concrete, the curing compound application rates are 1.5 to 2 times the application rates used for conventional concrete. 9.7.6 Weather

When the ambient temperature is 40 degrees F or less, or may reach 40 degrees F in the 24 hour period after RCC paving, all protective equipment and material must be available before paving begins in order to ensure adequate protection against the effects of cold weather. The same precautions and procedures used for cold weather construction for conventional concrete should also be used for RCC construction. Hot temperatures will make the concrete less workable and more difficult to place and compact, resulting in a poorer quality final product. High temperatures lead to higher rates of moisture evaporation, which is very important to monitor with RCC because there is so little moisture in the concrete. As temperatures



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increase from 70 degrees F to 90 degrees F, the time to initial set and final set are reduced by 20 to 30 percent. When placing RCC during hot weather, it will be to the contractor’s advantage to keep the concrete as cool as possible during placement and compaction. As ambient air temperature increases beyond 90 degrees F, the time allowed from time of mixing to completion of compaction should be reduced accordingly (for example, from 60 minutes to 30 to 45 minutes). To compensate for moisture loss during hauling and placement, additional mix water can be added at the plant. For long haul times, consideration should be given to the use of set-retarding admixtures to provide more workability time.

9.8 QC/QA Methods

Some quality control procedures for RCC are similar to those used for conventional concrete, and others are similar to those used for soil compaction. At the mixing plant, care must be made that the feed controls are calibrated and accurate. Aggregate stockpiles should be monitored for consistent moisture content and the possibility of size segregation. Monitoring the density of the compacted RCC is one of the most important quality control steps. The maximum density will be determined in the laboratory, as discussed earlier, or in the field through the use of a test strip. The engineer will specify what percentage of the maximum density must be obtained in the field. This required percentage is typically 96% - 98% of maximum, and is measured in the field using a nuclear moisture-density gauge. Care must be taken to calibrate the moisture measurements if using a nuclear gauge, since the hydrating cement in the RCC mix can affect the gauge readings. Cylinders of the RCC mix can be cast in the field, and tested for compressive strength after waiting the required number of days. In addition, cores can be taken after a number of days to determine the strength, thickness, and uniformity of the as-constructed material.

Figure 9-4 Density testing for freshly placed RCC.



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9.9 Design Example

The design example in this section follows the example given in the Section 3 of this study, where various types of traffic are tabulated for a container terminal operations scenario. The scenario provides traffic for three different types of loads: Top/Side Pick, RTG, and Trucks. In the design example below, designs are prepared for the Top/Side Pick area, and the RTG area. Both of these areas also have truck traffic that will be considered in addition to the equipment loading. For the Top/Side Pick area, the equipment loading will be considered first. Figure 9-5 shows a load distribution diagram from the load data given in the Section 3 of this study. The PCA design procedure for RCC does not consider “equivalent” loads in the design process. Instead, pavement evaluations are conducted for different loads, and the anticipated damage for the different loads is added together (as described in Section 9.3).

Cumulative Frequency of Top/Side Pick Loads

0

25

50

75

100

0 10000 20000 30000 40000 50000 60000

Front Wheel Load (lbs)

Per

cent

Figure 9-5 Cumulative load distribution for Top/Side Pick equipment.

Since it is not practical to perform calculations on every load, the load frequency is divided into quartiles, and calculations are performed on four representative loads (at 25%, 50%, 75%, and 100% of the load frequency curve). For each of the four representative loads, the load stress was calculated using the RCCPave computer program. This program uses the same procedure explained in Section 9.3, but does the calculations automatically without using manual procedures. Once the number of loads to failure for each load is calculated, then the damage can be summed for all of the four representative loads (see Table 9-1 below). For the example given, a pavement thickness of 17 inches was tried, but the sum of damage was larger than 1.0. The table shows that a thickness of 17.5 inches is satisfactory.



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Table 9-1 Design table for Top/Side Lifter equipment. Load

(lbs)

Thickness

(in)

Stress

(psi) Stress Ratio

Appl. to Failure

Number

Appl.

Fractional

Damage

46,000 17.5 331 .472 92,807 37,545 .405

39,000 17.5 283 .405 533,430 37,545 .070

35,000 17.5 255 .364 unlimited 37,545 .000

27,000 17.5 201 .287 unlimited 37,545 .000

Total .475

The same procedure was followed to evaluate the design required for the RTG area. The load distribution is shown in Figure 9-6, and the design table is shown in Table 9-2.

Cumulative Frequency RTG Load

0

25

50

75

100

40000 45000 50000 55000 60000 65000 70000

Wheel Load (lbs)

Per

cent

Figure 9-6 Cumulative load frequency for RTG area.

Table 9-2 Design table for RTG area

Load

(lbs)

Thickness

(in)

Stress

(psi) Stress Ratio

Appl. to Failure

Number

Appl.

Fractional

Damage

61,000 15.5 296 .423 329,554 111,840 .339

57,000 15.5 281 .401 578,360 111,840 .193

54,500 15.5 271 .388 unlimited 111,840 .000

50,000 15.5 254 .363 unlimited 111,840 .000

Total .532

As mentioned earlier, truck traffic (conventional trucks with legal wheel loads) operates in both the Top/Side Lifter area, and the RTG area. Therefore, the effect of the truck traffic should be added to the effect of the heavy equipment in Figure 9-5 and Figure 9-6. The evaluation of the truck traffic in the RTG



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area is shown below in Figure 9-7 and Table 9-3. This example illustrates how many facility designs are primarily affected by the heaviest loads, leading to very little or no effect from the smaller loads.

Cumulative Frequency Truck Wheel Loads

0

25

50

75

100

0 1000 2000 3000 4000 5000

Truck Wheel Load (lbs)

Per

cent

Figure 9-7 Cumulative load distribution for trucks operating in RTG area.

Table 9-3 Design table for trucks operating in RTG area Load

(lbs)

Thickness

(in)

Stress

(psi) Stress Ratio

Appl. to Failure

Number

Appl.

Fractional

Damage

4,100 15.5 54 .077 unlimited 3.4 mill. .000

Total .000



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9.10 References

1. Tayabji, S. D., and Okamoto, P.A., “Engineering Properties of Roller-Compacted Concrete”, Transportation Research Record 1136, Transportation Research Board, Washington, D.C. 1987.

2. Structural Design of Roller-Compacted Concrete for Industrial Pavements, Portland Cement Association, Skokie, Il. 1987.

3. Airport Pavement Design and Evaluation, Advisory Circular 150/5320-6C, Federal Aviation Administration, Washington, DC 1978.

4. Roller-Compacted Concrete, Engineering and Design. Publication EM 1110-2-2006, U.S. Army Corps of Engineers, Vicksburg, MS Aug 1985.

5. Westergarrd, H. M., “Theory of Concrete Pavement Design”, HRB Proc., Vol 7, Part 1, pp 175-181, 1927.

6. Pickett, G. and Ray, G. K., “Influence Charts for Concrete Pavements”, Paper 2425, ASCE Transactions, Vol 116, 1951.

7. Computer Program RCCPave2000, Portland Cement Association, Skokie, Il., 2000.

8. Production of Roller Compacted Concrete, IS332, Portland Cement Association, Skokie, Il., 2006.

9. Piggott, R.W., “Roller Compacted Concrete Pavements – A Study of Long Term Performance”, RP 366, Portland Cement Association, Skokie, Il., 1999.

10. Frost Durability of Roller-Compacted Concrete Pavements: Research Synopsis, IS692, Portland Cement Association, Skokie, Il., 2006.

11. Guide Specification for Construction of Roller-Compacted Concrete Pavements, IS009, Portland Cement Association, Skokie, Il., 2004.



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9.11 Appendix Tables and Figures

Appendix Figure 1. Correlation of K value with other material properties.



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Appendix Table 1. Fatigue relationship for RCC based on stress ratio.



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Appendix Figure 2. Recommended aggregate gradation for RCC.



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JN: 5552-06

10. Pavement Management................................................................................................... 10-1 10.1 PMS Concepts .............................................................................................................10-1 10.2 Components of a Pavement Management System........................................................10-6 10.3 Database ......................................................................................................................10-6 10.4 Maintenance Policies and Costs ...................................................................................10-6 10.5 Rehabilitation Strategies..............................................................................................10-7 10.6 Performance and Costs ................................................................................................10-7 10.7 Optimation ..................................................................................................................10-7 10.8 Prioritization and Funding ..........................................................................................10-8 10.9 Structural Analysis ......................................................................................................10-8



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10. Pavement Management

Historically , many agencies with responsibility for pavement maintenance and rehabilitation have utilized an informal ad-hoc approach for establishing needs and allocating funding. While this approach can be effective on a small scale, it is often too subjective and inefficient for large facilities such as marine terminals. However, over the last ten or so years standardized methods for improved decision making have been formalized in an integrated system, commonly referred to as a Pavement Management System (PMS). A pavement management system provides a consistent, objective and systematic procedure for setting priorities and schedules, allocating resources, and establishing budgets for pavement maintenance and rehabilitation. A PMS can also quantify information and provide specific recommendations for actions required to maintain a pavement network at an acceptable level of service while minimizing the cost of maintenance and rehabilitation. A properly developed PMS can assist the engineer, budget director, and management to make cost-effective decisions regarding maintenance and rehabilitation for a pavement network.

10.1 PMS Concepts

In its most basic form, a PMS is typically based on visually identifying pavement distresses and computing an objective pavement condition rating. The system can include other elements such as analysis of drainage, structural performance, or surface friction depending on user requirements. A PMS not only evaluates the present condition of a pavement facility, but can also be used to estimate its future condition through the use of a pavement condition indicator. By projecting the rate of deterioration, a life-cycle cost analysis can be performed for various alternatives to arrest deterioration, and the optimal time of application of the best alternative can be determined. This is critical to avoid higher maintenance and repair (M&R) costs at a later date. Figure 10-1, “Typical Pavement Condition Life Cycle” illustrates how a pavement generally deteriorates. The figure also illustrates the relative cost of rehabilitation at various times during it’s life. Note that during the first 75% of a pavements’ life, it performs relatively well. After that, however, it begins to deteriorate rapidly. The number of years a pavement stays in “good” condition depends on how well it is maintained. Numerous studies have shown that the ratio of total annual costs between maintaining a good pavement and periodically rehabilitating a poor pavement is in the order of 1 to 4 or 5.



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Figure 10-1 Typical Pavement Condition Life Cycle

To standardize characterization of pavement condition, the Pavement Condition Index (PCI) was developed. The PCI is a numerical index from 0 (failed) to 100 (excellent). The PCI is computed from prescribed visual measurements based on the type, severity, and amount (density) of observed distresses. The PCI process is depicted graphically in Figure 10-2, “Condition Survey”. The measurement process, referred to as a pavement condition survey, and computation of the PCI is described in ASTM D-6433, “Standard Practice for Roads and Parking Lots Condition Survey”. PMS software programs, such as described below, allow for automated PCI computations. A tabulation of typical flexible and rigid pavement distresses is shown in Table 10-1 and Table 10-2, “MicroPAVER Distress Mechanisms”. The table also includes the mechanisms that are primarily responsible for causing a particular distress.



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CONDITION SURVEY

PCI RATING COLOR PAVER RATING

100

86

EXCELLENT

85

71

VERY GOOD

70

56

GOOD

55

41

FAIR

40

26

POOR

25

11

VERY POOR

10

0

FAILED

Figure 10-2 Condition Survey

PAVEMENT CONDITION RATING

PCI

DISTRESS QUANTITY

DISTRESS TYPE

DISTRESS SEVERITY



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MicroPAVER DISTRESS MECHANISMS

Table 10-1 MicroPAPER Distress Mechanisms for Asphalt Surfaced Roads and Parking Areas

CODE DISTRESS MECHANISM 01 Alligator Cracking Load 02 Bleeding Other 03 Block Cracking Climate 04 Bumps and Sags Other 05 Corrugation Other 06 Depression Other 07 Edge Cracking Load 08 Joint Reflection Cracking Climate 09 Lane/Shoulder Drop Off Other 10 Longitudinal/Transverse Cracking Climate 11 Patching and Utility Cut Patching Other 12 Polished Aggregate Other 13 Potholes Load 14 Railroad Crossing Other 15 Rutting Load 16 Shoving Other 17 Slippage Cracking Other 18 Swell Other 19 Weathering and Raveling Climate

Table 10-2 MicroPAPER Distress Mechanisms for Portland Cement Concrete Roads and Parking Areas

CODE DISTRESS MECHANISM 21 Blow-up/Buckling Climate 22 Corner Break Load 23 Divided Slab Load 24 Durability ("D") Cracking Climate 25 Faulting Other 26 Joint Seal Damage Climate 27 Lane Shoulder Drop Off Other 28 Linear Cracking Load 29 Patching, Large/Utility Cut Other 30 Patching, Small Other 31 Polished Aggregate Other 32 Popouts Other 33 Pumping Other 34 Punchout Load 35 Railroad Crossing Other 36 Scaling/Map Cracking/Crazing Other 37 Shrinkage Cracking Climate 38 Spalling, Corner Climate 39 Spalling, Joint Climate

From Figure 10-1it is also significant to note that beyond a certain point, referred to as the critical PCI, the pavement deteriorates rapidly. In fact, the first 40% drop in quality typically occurs during the first



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75% of pavement life, while the next 40% occurs during only 12% of pavement life. Therefore, it is important and cost-effective to maintain a pavement above its critical PCI. As discussed, deferral of necessary maintenance or rehabilitation can increase costs 4 or 5 fold in a relatively short period. If maintenance is performed in a timely and predicable manner, the rate of deterioration can be slowed and more costly rehabilitation deferred. This concept is depicted in Figure 10-3. “PMS Preventive Maintenance Concept”.

Figure 10-3 PMS Preventive Maintenance Concept

The condition survey results will also identify whether and to what extent pavement condition is being affected by load, environmental, or other (e.g., construction related) mechanisms. This information is useful in evaluating the effectiveness of different maintenance or rehabilitation strategie s. For example, it would not be cost-effective to attempt to repair a structural distress such as alligator cracking with a seal coat, which is a functional repair method. Likewise, it may not be necessary to apply a structural repair method such as reconstruction for a functional distress such as block cracking. Further, if the pavement is experiencing load related distresses, this would indicate the need to augment the visual condition survey results with a structural evaluation that would typically include nondestructive deflection testing, cores, and borings. Future condition (i.e., PCI) can be extrapolated based on the current PCI, prior inspection results, and the last rehabilitation date. Estimates of the future PCI and deterioration rates are useful in identifying optimal maintenance and rehabilitation timing, and whether a particular pavement feature is above or below the critical PCI. Information on pavement deterioration, by itself, is not sufficient to answer questions involved in selecting cost-effective maintenance and repair strategies. For example, should a pavement be seal coated, reconstructed, or resurfaced? This type of decision requires information on the cost of various maintenance and repair procedures and their effectiveness. In other words, the proposed solution should



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be targeted toward the source of the deficiency, type of distress and associated mechanisms, and whether it will improve the pavement’s condition rating and keep the pavement in this improved condition for a time period sufficient to recover the cost of the repairs. A pavement management system, then, should enable a user to store information in a data base and use the system to identify the most cost-effective solution. 10.2 Components of a Pavement Management System

In order to take full advantage of a pavement management system, information must be collected and periodically updated, decision criteria established, alternative strategies identified, and optimization procedures that consider the entire pavement life cycle developed. A system for accomplishing these objectives will generally include the following basic elements.

• A systematic means for collecting and storing information; • An objective and repeatable system for evaluating current and future pavement condition; • Procedures for identifying alternative maintenance and rehabilitation strategies; • Procedures for predicting the performance and costs of alternative strategies; and • Procedures for identifying the optimum alternative for maintenance and/or rehabilitation.

10.3 Database

The PMS data is stored in a database that would typically include:

• Pavement Features: Dimensional hierarchal segments typically referred to as branches and sections;

• Pavement Structure: Pavement thickness and composition for each feature from as-built records, supplemented by cores, as necessary;

• Construction History: Dates, activities, and costs of major construction activities (e.g., overlay, reconstruction);

• Maintenance History: Prior maintenance activities and costs to enable evaluation of various maintenance procedures in extending pavement life;

• Traffic Data : Types of vehicles, weights, and load repetitions; and • Pavement Condition: The ability to objectively quantify pavement condition and track

the rate of deterioration is a fundamental element of the PMS. Most pavement management systems utilize the Pavement Condition Index (PCI) for establishing estimates of current and projected pavement condition (see Figure 2).

10.4 Maintenance Policies and Costs

The PMS needs to include maintenance policies and costs to repair identified pavement distresses. The repairs are categorized as a function of distress, type, and severity. For example, low severity cracking may require no action; however, medium and high severity cracking may require routing and sealing. The PMS should include maintenance policies and costs matched to each distress type and severity level.



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10.5 Rehabilitation Strategies

For pavements with PCIs below the critical PCI, or those with structural distresses, alternate strategies for rehabilitation (e.g., overlay, “mill and fill”, recycling, and reconstruction) need to be identified. The rehabilitation strategies and costs are typically related to pavement condition (i.e., PCI). Figure 10-4, “Rehabilitation Options” is an example of typical maintenance and rehabilitation options and costs as a function of PCI.

The strategy that is applied to a particular feature (section) should consider pavement condition, rate of deterioration, distress mechanisms, future utilization, and expected life of a particular alternative.

Figure 10-4 Rehabilitation Options

10.6 Performance and Costs

The expected performance of each identified maintenance or rehabilitation option needs to be identified. For example, distress repairs (i.e., maintenance) would result in recomputation of pavement condition (e.g., PCI) after the repairs. On the other hand, both overlay and reconstruction would result in a post-rehabilitation PCI of 100. However, the projected performance, cost, and longevity of the two would be different. 10.7 Optimation

In order to select a particular alternative, a procedure that evaluates several options (e.g., life cycle cost analysis) is needed.



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10.8 Prioritization and Funding

Since funding constraints must be addressed, the PMS should prioritize needs (i.e., the order in which pavements should be repaired or rehabilitated). The system should include several optimization techniques (e.g., “worst first”, repairs as a function of PCI, maintain current condition, etc.) that can be applied for selection of the option that will result in the most cost-effective utilization of funding on a long term basis. The PMS should also be capable of evaluating alternate funding scenarios and identify improvements in the overall condition of the pavement network with different funding levels. An example of the effect of different budget scenarios on condition is depicted in Figure 10-5, “Budget Scenarios”.

BUDGET SCENARIOS

Figure 10-5 Budget Scenario

10.9 Structural Analysis

Depending on the traffic utilization and amount of structural distresses identified, the PMS should allow for supplemented structural analysis. This will typically consist of nondestructive testing (NDT), or other physical tests, analysis of traffic, and analysis of structural performance. The structural analysis will help in the selection of the most appropriate rehabilitation option to meet future pavement performance expectations. Guidelines for performing nondestructive testing are included in ASTM D-4602, “Standard Guide for Nondestructive Testing Using Cyclic Loading Dynamic Deflection Equipment”; ASTM D-4694, “Standard Test Method for Deflection with a Falling Weight Impulse Load Device”; and ASTM D-4695, “Standard Guide for General Pavement Deflection Measurements”. There are also various references that describe how to utilize the data in a structural evaluation framework.

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11. PMS Software ................................................................................................................. 11-1 11.1 Overview of Network Level Analysis ...........................................................................11-1 11.2 Report Generation and Usage......................................................................................11-2 11.3 Micropaver Software ...................................................................................................11-2 11.4 Other PMS Software....................................................................................................11-3



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11. PMS Software

There are several PMS software packages that can be used for pavement management. Some are proprietary that were developed by private enterprises. A non-proprietary program that has enjoyed widespread use by local, state and federal agencies, as well as commercial users, is the MicroPAVER program. This computer program was developed by the U.S. Army Construction Engineering Research Laboratory under contract to the U.S. Departments of Transportation and Defense. Program updates have been continually supported by the Federal Aviation Administration (FAA), Federal Highway Administration (FHWA), U.S. Army Corp of Engineers, U.S. Air Force, U.S. Navy, and other agencies to meet the needs of current users. The program allows for storage of pavement condition history, nondestructive testing data, construction and maintenance history, and repair cost data. This data base provides many capabilities including evaluation of current conditions, prediction of future conditions, identification of ma intenance and rehabilitation needs, inspection scheduling, economic analysis, and budget planning. MicroPAVER not only computes and evaluates the present condition of the pavement using the pavement condition index (PCI) described in ASTM D-6433, but it can also be used to estimate the future pavement conditions. As discussed, the PCI is a numerical indicator that reflects the structural integrity and functional condition of a pavement based on objective measurements of distress type, severity, and quantity. By projecting the pavement’s rate of deterioration, a life-cycle cost analysis can be performed to test various maintenance and rehabilitation alternatives for selecting the best alternative and optimal time of application. Although the program can be used for evaluation of the entire pavement network (network level), it can also be used to support a particular rehabilitation project for a specific feature (project level). Actually, both are similar, except that the project level analysis will typically involve a higher frequency of inspection and may include additional elements to support a particular project (e.g., structural analysis).

11.1 Overview of Network Level Analysis

In network level pavement management, the system is used to identify short and long range budget needs, the current and future condition of the pavement network, and candidates for project level analysis. In addition to providing an automated inventory of the pavements being managed, MicroPAVER provides a series of programs which access the database and produce customized reports. These reports help the user making decisions regarding inspection scheduling, identification of pavements for rehabilitation, budget forecasting, identification of routine maintenance projects, evaluation of current condition, and prediction of future condition. Condition prediction is used as the basis for developing inspection schedules and identifying pavements requiring maintenance or rehabilitation. Once pavements requiring future work have been identified, a budget for the current year and for several years into the future can be developed. By using an agency’s prioritization scheme, and maintenance and rehabilitation policies and costs, and comparing the budget to actual funds available, a list of potential projects can be produced. This list becomes the link with project level management.



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11.2 Report Generation and Usage

MicroPAVER can assist in the decision making process through the use of several standard reports. Each report can be customized to include only the pavements and/or conditions of interest and can be generated to represent various budget/condition scenarios. The use of each report is briefly outlined below. • Inventory Report: This report is a listing of all pavements in the network and contains information

such as surface type, location, area, and pavement function.

• Inspection Scheduling Report: This report allows the user to schedule inspections for the next 5 years based on a pavement’s minimum acceptable condition (PCI) level and rate of deterioration.

• PCI Frequency Report: This report provides the user with an indication of overall network condition based on the PCI scale for the current and future years. The projected condition can be used to assist in planning future maintenance and repair needs and keeping management informed. Since the PCI extrapolation used assumes no major repairs have occurred between the last inspection and prediction dates, the user can see the impact on the overall network condition of deferring major repairs.

• Budget Planning Report: This report allows the user to produce 5-year projected budgets required to maintain the pavement network above a user-specified condition level. The user is required to input three forms of data: (1) min imum PCI values for each pavement type; (2) average unit repair costs based on surface type and PCI ranges; and (3) the inflation rate during the analysis period.

The report predicts the year in which the minimum PCI will be reached and calculates the cost of repair for each section. • Network Maintenance Report: This report uses the agency’s maintenance policy which is stored in

the data base and applies it to the distresses identified in the latest PCI survey. This report can be used to estimate both the type and cost of routine maintenance for development of an annual maintenance plan.

• Economic Analysis Report: This report can be used to help select the most cost-effective alternative

for a pavement repair. For each feasible alternative, the user must input initial costs, periodic maintenance costs, one-time future maintenance costs, interest rates, and discount rates. The program performs a life-cycle cost analysis and provides the user to vary interest rates, repair costs, and timing so that their effect on alternatives can be analyzed.

11.3 Micropaver Software

The MicroPAVER software package together with its user’s guide can be obtained from a distribution center. Currently, there are several distribution centers, with each center responsible for establishing individual fees for distribution and providing updates and corrections as they become available. The fees vary according to the service provided to the user (training, implementation assistance, user’s group membership, etc.). Users should contact each center and determine which one will best suit their needs. The location of the distribution centers, user manuals, and product updates are provided on the MicroPAVER website at http://WWW.cecer.army.mil/paver/.



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11.4 Other PMS Software

Pavement management systems other than MicroPAVER are used by consulting engineer firms that provide pavement evaluation and management services. The software programs used by these firms are not in the public domain and typically cannot be purchased for use by an individual or an agency.

CONTAINER TERMINAL AND INTERMODAL RAIL YARD OPERATIONAL AREA CONSIDERATION FOR PAVEMENT DESIGN

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