HIGHWAY II

HIGHWAY II1

CHAPTER - 1CHAPTER - 1INTRODUCTION

HIGHWAY II - Inroduction

Introduction2

Contents:

General

Overview of pavement structures pFlexible pavements

Rigid pavements

B i d i d tBasic design data


General3

The field of pavement design is dynamic, The concepts are changing with time as technology develops and new equipment emerges for site investigation material and traffic data collection investigation, material and traffic data collection, and new data become available. Observing the performances of the already g p yconstructed roads, highway engineers become aware that pavement performance is dependent on the subgrade soils subgrade soils. With the knowledge of soil mechanics, pavement design was made with soil classification.


g

General Cont’d4

Increase in traffic

usage and development necessitated a g pof heavy transport means

Deterioration of more rational approach of

pavements due to trucks and aircrafts

ppdesign.


General Cont’d5

This led to full-scale and laboratory experiments in y pdifferent countries at different capacities.

Results of laboratory experiments conducted under varying soil, climatic, and loading conditions in different countries have given rise to understanding and development of the existing design methods and development of the existing design methods.


General Cont’d6

Principles of pavement design are common to all p p gproblems and localities,

Different highway agencies in different countries use different design manuals prepared to suite

their local conditions and

available materials of constructionavailable materials of construction.


Overview of Pavement Structures7

Pavements are designed and constructed to provide g pdurable all-weather traveling surfaces for safe and speedy movement of people and goods with an

t bl l l f f t t acceptable level of comfort to users.

A pavement structure is a layer structure which supports the vehicle load on its surface and transfers supports the vehicle load on its surface and transfers and spreads the load to the subgrade without exceeding either the strength of the sub grade or the g g ginternal strength of the pavement itself.


Overview Cont’d8

The basic idea in building a pavement for all-weather use by vehicles is to prepare a suitable sub grade, provide necessary drainage and construct a pavement that will:pavement that will:

Have sufficient total thickness and internal strength to carry expected traffic loads, and distribute them over the sub grade soil without overstressingsoil without overstressing.Have adequate properties to prevent or minimize the penetration or internal accumulation of moisture, andHave a surface that is reasonably smooth and skid resistant at Have a surface that is reasonably smooth and skid resistant at the same time, as well as reasonably resistant to wear, distortion and deterioration by vehicle loads and weather.


Overview Cont’d9

The functional requirements of pavements are q pachieved through careful considerations of:

selection of pavement type,

l i f i l b d f i l selection of materials to be used for various pavement layers and treatment of subgrade soils,

structural thickness design for pavement layers, g p y ,

subsurface drainage design for the pavement system,

surface drainage and geometric design, and

id bili f fridability of pavement surface.


Overview Cont’d10

EARTH ROADSDesigned for a very low traffic where the soil can be trafficable

Used when there is economic limitation

Th l b d il b d h ffi l d The natural sub grade soil can be made to carry the traffic load after clearing and shaping

Such earth roads give seasonal services and g

Require reshaping after seasonal changes.


Overview Cont’d11

GRAVEL ROADSBetter than earth roads,

Constructed by spreading gravel over the subgrade, shaping and compacting to avoid excessive strain at the sub grade leveland compacting to avoid excessive strain at the sub grade level

Usually provides services in all seasons with less frequent reshaping as compared to earth roads.

Designed to carry low to medium traffic & serve as stage construction.

The surface material should be kept to certain standard such as The surface material should be kept to certain standard such as grading and plasticity.


Overview Cont’d12

Pavements are generally classified into two g ycategories,

Flexible pavements

i id Rigid pavements.

The basis for classification is the way by which traffic loads are transmitted to the subgrade soil through loads are transmitted to the subgrade soil through the pavement structure.


Flexible Pavements13

Provides sufficient thickness for load distribution through a multilayer structure

the stresses & strains in the subgrade soil layers are within the required limits.

the strength of subgrade soil would have a direct b i th t t l thi k f th fl ibl bearing on the total thickness of the flexible pavement.

Designed to take advantage of the decreasing Designed to take advantage of the decreasing magnitude of stresses with depth.



It has low flexural strength and the load is largely g g ytransmitted to the sub grade soil through the lateral distribution of stresses with increasing depth.

The pavement thickness is designed such that stresses on the subgrade soil are kept within its bearing capacity and the sub grade is prevented from bearing capacity and the sub grade is prevented from excessive deformation.

Its structural strength and smoothness depends to a Its structural strength and smoothness depends to a large extent on the deformation of the subgrade soil.


Flexible Pavement16



Flexible Pavement Typical Applicationsyp ppTraffic lanes

Auxiliary lanes

RRamps

Parking areas

Frontage roadsFrontage roads

Shoulders



Advantages to Flexible PavementAdjusts to limited differential settlementEasily repairedAdditional thickness added any timeAdditional thickness added any timeNon-skid properties do not deteriorateQuieter and smootherT l t t f t tTolerates a greater range of temperatures

Disadvantages to Flexible PavementLoses some flexibility and cohesion with timeLoses some flexibility and cohesion with timeNeeds resurfacing sooner than PC concreteNot normally chosen where water is expected



Generally, two types of construction have been used y, ypfor flexible pavements,

conventional flexible pavement and

f ll d h h l full-depth asphalt pavement.


Conventional Flexible Pavements20

Conventional flexible pavements are multilayered p ystructures with

better materials on top where the intensity of stress is high and

i f i i l h b h h i i i l inferior materials at the bottom where the intensity is low.

This design principle makes possible to use local materials and usually results in a most economical materials and usually results in a most economical design.



A conventional pavement normally consists of seal coat, surface course, tack coat, prime coat, base coat, prime coat, base course, sub base course, compacted subgrade, and natural subgrade natural subgrade.

The use of various courses is based on either necessity or yeconomy and some of the courses may be omitted.



Surface course: -The surface course is the top course of an asphalt pavement,

sometimes called wearing course.

I i ll d b d d d h h l i It is usually constructed by dense graded hot asphalt mix.

It is a structural part of the pavement, which must be tough to resist distortion under traffic and g

provide a smooth and skid-resistant riding surface.

The surface must be waterproof t t t th ti t d to protect the entire pavement and

subgrade from the weakening effect of water.



Base course: -The base course is the layer of material immediately beneath the surface course.

It may be composed of well graded crushed stone It may be composed of well-graded crushed stone (unbounded), granular mixed with binder, or stabilized materials.

It is the main structural part of the pavement and provides a level surface for laying the surface layer.

If constructed over the sub grade, it prevents intrusions if the g , pfine subgrade soils into the pavement structure.



Sub base course: -It is the layer of material beneath the base course constructed using local and cheaper materials for economic reason on top of the subgrade of the subgrade.

It provides additional help to the base and the upper in distributing the load.

It facilitates drainage of free water that might get accumulated below the pavement.

If the base course is open graded, the sub base course with p g ,more fines can serve as a filter between the sub grade and the base course.



Sub grade: -gIt is the foundation on which the vehicle load and the weight of the pavement layers finally rest.

It is an in situ or a layer of selected material compacted to the It is an in situ or a layer of selected material compacted to the properly drained desirable and compacted to receive the pavement layers.


Full- depth asphalt pavements26

are constructed by placing one or more layers of hot-y p g ymix asphalt directly on the sub grade or improved sub grade.

This concept was conceived by the asphalt institute and is generally considered the most cost-effective and dependable type of asphalt pavement and dependable type of asphalt pavement

for heavy traffic and

quite popular in area where local materials are not availableq p p


Rigid Pavements27

Are constructed of cement concrete slabs A rigid pavement, by virtue of its rigidity, can be able to effect a slab action to spread the wheel load over the entire slab area.entire slab area.The structural capacity of the rigid pavement is largely provided by the slab itself. F h f b d il h h For the common range of subgrade soil strength, the required rigidity for a Portland cement concrete slab can be achieved without much variation in slab thickness. The effect of subgrade soil properties on the thickness of rigid pavement is less important than that of flexible pvt.


Rigid pavements28

Derive their capacity to withstand vehicle loads from p yflexural strength or beam strength due to high modulus of elasticity.

Because of high flexural strength, the vehicle load on cement concrete slab is distributed over a relatively wider area of the soil than flexible pavements and wider area of the soil than flexible pavements and thus variation in the subgrade soil strength has little influence.


Rigid pavements29


Rigid pavements30

The flexural strength also permits the slab to bridge g p gover minor irregularities under it.

Thus, the performance of rigid pavements is more governed by the strength of the concrete slab that the subgrade supports.

H th j f t id d i th d i f Hence the major factor considered in the design of pavement is the structural strength of the concrete.


Rigid pavements31

Rigid Pavement Typical Applicationsg yp ppHigh volume traffic lanes

Freeway to freeway connections

E i i h h ffiExit ramps with heavy traffic

Advantages of Rigid PavementGood durabilityGood durability

Long service life

Withstand repeated flooding and subsurface water without deterioration


Rigid pavements32

Disadvantages of Rigid Pavement g gMay lose non-skid surface with time

Needs even sub-grade with uniform settling

M f l j iMay fault at transverse joints


Rigid pavements33


Rigid pavements34

The subgrade may provide a uniform support for the slab.

However where the sub grade soil cannot provide a uniform support, there is always a necessity to build a base or subbase course under cement concrete slabsubbase course under cement concrete slab.


Rigid pavements35

Main reasons for providing base course under cement concrete slab are:Control of pumping: -

P i i d fi d th j ti f t d b dPumping is defined as the ejection of water and subgradesoil through joints, cracks, and along the edges of the pavements.Pumping occurs when there is void space under the slab due to temperature curling of the slab, deformation of the subgrade or both and erodible material under the slab is saturated. It leads to faulting and cracking of the slab if not corrected in time.


corrected in time.

Rigid pavements36

Control of frost action: -f fHeave caused by increase in volume of freezed water and the formation and continuing expansion of ice lenses causes the concrete slab to break and soften the subgradecauses the concrete slab to break and soften the subgradeduring frost melting period.

This occurs when the soil within the depth of frost ppenetration is frost susceptible (e.g. clay), there is a supply of moisture and the temperature freezes for a sufficient period of timesufficient period of time.


Rigid pavements37

Improvement of drainage: -p f gwhen the water table is high and close to the ground surface, a base course can raise the pavement to a desirable elevation above the water table above the water table.

An open graded base course provides an internal drainage system capable of rapidly removing water that seeps through

t k d j i t it t th d id pavement cracks and joints carry it away to the roadside.

Dense-graded or stabilized base courses can also serve as waterproofing layer.


Rigid pavements38

Control of shrinkage and swell: -When the change in moisture causes subgrade to shrink or swell, the base course can serve as a surcharge load to reduce the amount of shrinkage and swell in addition to its use of improving drainage. Measures that are taken to reduce entering water in to the subgrade further reduce the shrinkage and swell potentials.

As working platform for construction: -A base course can be used as a working platform for heavy construction equipment construction equipment. Under severe weather conditions a base course can keep the surface clean and dry and facilitate the construction work.


Types of concrete pavement39

Concrete pavements can be classified in to four ptypes:

Jointed Plain Concrete Pavement (JPCP),

i d i f d ( ) Jointed Reinforced Concrete Pavement (JRCP),

Continuous Reinforced Concrete Pavement (CRCP), and

Pre-stressed Concrete Pavement (PCP).Pre stressed Concrete Pavement (PCP).


Rigid pavements40



In Jointed Unreinforced Concrete Pavements (JUCP),

the pavement consists in an unreinforced concrete slab cast in place continuously and divided into bays of predetermined place continuously and divided into bays of predetermined dimensions by the construction of joints.

The bays dimensions are made sufficiently short so as to ensure that they do not crack.

The bays are linked together by tie bars, which is to prevent horizontal movement and thus ensure load transfer through gaggregate interlock.



Jointed Unreinforced Concrete Pavements (JUCP), ( ),


Joints accommodate shrinkage during drying.


In Jointed Reinforced Concrete Pavements (JRCP) ( )the pavement consists generally in a cast in place concrete slab divided in reinforced concrete bays separated by joints.

The reinforcement is made to prevent developing cracks from The reinforcement is made to prevent developing cracks from opening.

The bays are linked together by tie bars to prevent horizontal movement and thus ensure load transfer through aggregate interlock.

The amount of distributed steel increases with the increase in joint spacing and is designed to hold the slab together after cracking.



Continuously Reinforced Concrete Pavements y(CRCP)

are reinforced concrete pavements designed joint-free for the purpose of eliminating joints which are the weak spots in rigid purpose of eliminating joints, which are the weak spots in rigid pavements.

The elimination of joints would decrease the thickness of pavement required.

The expansion and contraction movements are prevented by a high level of sub-base restraint. g

The frequent transverse cracks are held tightly closed by a large amount of continuous high tensile steel longitudinal reinforcement


reinforcement.


Continuously Reinforced Concrete Pavements y(CRCP)



The prestressed concrete pavements p phave less probability of cracking and fewer transverse joints and therefore result in less maintenance and longer pavement life life.

has been used more frequently for airport pavements than for highway pavements because the saving in thickness for airport

t i h t th th t f hi h tpavements is much greater than that for highway pavements.


Composite pavements47

Composite pavements are pavements composed of b l d h i h lcement concrete as a bottom layer and hot-mix asphalt as

a top layer to obtain an ideal pavement with the most desirable characteristics. The cement concrete slab provides a strong base and the hot-mix asphalt provides a smooth and non-reflective surface surface. However, this type of pavement is very expensive and is rarely used as a new construction. Composite pavements include rehabilitated concrete pavements using asphalt overlays and asphalt pavements with stabilized bases.


Composite pavements48

For flexible pavements with untreated bases, p ,the most critical tensile stress or strain is at the bottom of asphalt layer,

while for composite pavements the most critical location is at while for composite pavements the most critical location is at the bottom of the cement concrete slab or stabilized bases.

A disadvantage of this construction is the occurrence gof reflection cracks on the asphalt surface due to the joints and cracks in the rigid base layer.


Comparison of Rigid and Flexible pavements 49

The following main differences between rigid and g gflexible pavements can be cited.

The manner in which vehicle loads are transmitted to subgrade

i lif d i iDesign life and precision

Maintenance requirements

Initial costInitial cost

Suitability for stage construction

Surface characteristics

Permeability and

Traffic dislocation during construction.


Highway and Airport Pavement50

Airport pavements are generally thicker than p p g yhighway pavements and require better surfacing materials due to:

h h f l ll h h fThe gross-weight of an airplane is usually greater than that of a heavy truck, but the number of load repetitions on airport pavements is usually smaller than that on highway pavements.

The arrangement and spacing of wheel loads on airport and highway pavements are different.

A typical tyre pressure on highway pavements is much lesser A typical tyre pressure on highway pavements is much lesser than that of airport pavements


Highway and Airport Pavement51

Vehicle loads are applied near to the edge of highway pavements but far away from the outside edge of airport pavements.

Unlike highway pavements airfield pavements are Unlike highway pavements, airfield pavements are subjected to an impact loading.

The design load of airport pavements is the wheel load of the largest aircraft during takeoff time due to heavy fuel weight. Although wheel loads can be used as design loads number of repetitions of standard axles is the loads, number of repetitions of standard axles is the commonly used design parameter for highway pavements


Basic Design Factors52

Design factors can be divided into four broad gcategories:

traffic loading,

i environment,

materials and

failure criteria.failure criteria.


Traffic loading53

The loading applied by traffic is one of the major g pp y jfactors affecting the design and performance of pavements.

The most important aspects of traffic loading that are considered in the analysis and design of pavements are:pavements are:

The configuration,

magnitude and g

repetitions of axle loads


Traffic loading54

The principal function of pavement structure is to protect the sub grade from the loading imposed by traffic.

The magnitude of maximum loading is commonly t ll d b l l l d li it controlled by legal load limits.

Traffic surveys and loadometer studies are often used to establish the relative magnitude and occurrence of establish the relative magnitude and occurrence of various loadings to which a pavement is subjected.

Prediction or estimation of the total traffic that will use a pavement during its design life is a very difficult but obviously important task.


Axle-loads and configurations55

Axle loads affect primarily the stresses and strains d l d i h l l f hdeveloped in the lower layers of the pavement. Although much publicity is given to the physical size and gross weight of vehicles, it is the individual wheel or axle-gross weight of vehicles, it is the individual wheel or axleload that is critical in pavement design and performance. Vehicle size and weight may have a devastating effect on the environment but will not necessarily increase the environment but will not necessarily increase pavement wear. Heavier loads are usually carried on a larger numbers of axle or wheel thereby maintaining or even reducing the individual wheel or axle loads, although their number may be increased.


y


Single Axle Single Tire o o

Singe Axle Dual Tires oo oo

Tandem Axle Dual Tires oo oooo oo

Tridem Axle Dual Tires oo ooTridem Axle Dual Tires oo oo(Special heavy duty oo oohaul trucks) oo oo


haul trucks) oo oo


Small vehicles use single axles with single wheels.

Larger vehicles mostly have either duel wheels or single wheels with ‘super-single’ tyres at each end of the non-t i l l till l hi l h t d steer single axles; still larger vehicles may have tandem

or multiple axles arrangements in which the successive axle are closely adjacent to one another. y j

The larger aircraft use quite complicated wheel arrangements because the weight of the aircraft has

ll t b t itt d th h t d i l usually to be transmitted through two undercarriage legs, and many wheels are necessary are necessary to obtain a reasonably low individual wheel load.


y

Type pressure58

The contact pressure is greater than the tyre pressure for low pressure tyres because the wall of tyres is in low-pressure tyres, because the wall of tyres is in compression and the sum of vertical forces due to wall and tyre pressure must be equal to the force due to the contact pressurecontact pressure.The contact pressure is smaller than the tyre pressure for high pressure tyres. H i t d i th t t i However, in pavement design, the contact pressure is generally assumed to be equal to the tyre pressure. Because, heavier axle loads have higher tyre pressures and more destructive effects on pavement the use of tyreand more destructive effects on pavement, the use of tyrepressure as the contact pressure is therefore on the safe side.


Type pressure59

Mostly, it is only the commercial vehicle that is y, yimportant in structural pavement design and a typical tyre pressure would be 0.5 MN/m2.

Aircraft tyres use pressures up to nearly 3.0 MN/m2

which can cause serious problem in the design of the materials employed in the upper layers of the materials employed in the upper layers of the pavement.


Type pressure60

The approximate shape of contact area for each tyre,pp p y ,which is composed of a rectangle and two semicircleswith the dimensions.

Based on the finite element analysis of rigidpavements, a rectangular contact area is alsoassumed with a length of 0 8712L and a width ofassumed with a length of 0.8712L and a width of0.6L, which has the same area of 0.5227L2.


Type pressure61

These contact areas are not axisymmetric and cannot be used with the layered theory be used with the layered theory. When the layered theory is used for flexible pavement design, it is assumed that each tyre has a circular contact

Thi ti i t t b t th area. This assumption is not correct, but the error incurred is believed to be small. To simplify the analysis of flexible pavements, a single i l ith th t t th d l i circle with the same contact area as the duals is

frequently used to represent a set dual tyre instead of using two circular areas. Thi ti ll lt i ti This practice usually results in a more conservative design, but may not become conservative for thin asphalt surface.


Number of repetitions62

A succession of loads has a cumulative effect on the behavior of pavements of pavements. It is therefore necessary to design the pavement for a specified number of years and to estimate the total number and magnitude of loads that will be applied during the periods magnitude of loads that will be applied during the periods specified. A widely accepted procedure of considering traffic load is the use of equivalent factor and converts each load into an qequivalent 80KN single axle load. The equivalency between two different loads depends on the failure criteria used. Equivalent factor based on permanent d f i b diff f h b d f i deformation may be different from those based on fatigue cracking. Generally, an empirical approximation of a single equivalent factor is used for practical purposes.


Speed of traffic loading63

Another factor related to traffic loading is the speed of traveling vehicles traveling vehicles. Studies showed that the stresses and deflections tend to decrease as the vehicle speed increases.

d d l d h d f l dSpeed is directly used as the duration of loading on pavements. Generally, the greater the speed is, the larger the y, g p , gmodulus and the smaller the strains in the pavement. Because of this, for a given volume of traffic, greater thickness and quality of paving materials are required for q y p g qpavements in urban areas than those in rural areas. Similarly, such requirements are considered for uphill roads and bus stop.


p

Traffic loading64

Concept of Equivalent Single Axle Load : Used to convert any load and/or combination of axles and tires into a number of ESALs based on concept of equivalent damage.equivalent damage.Equivalent damage: Compare damage caused by a wheel to damage caused by a standard wheel. It is a f i f f d (f il ) lfunction of type of damage (failure). Currently, we only have equivalency Factors for general damage.Number of Repetitions are based on equivalent Number of Repetitions are based on equivalent factors. Each load group is converted into an equivalent 18kip (80 kN) single axle load.


Traffic loading65

Contact area and tire pressurepSame load can cause more damage if pressure is high because of less contact area.

Tire pressure is not always contact pressureTire pressure is not always = contact pressure.

Speed is important.Viscoelastic Theory: speed is directly related to the duration of Viscoelastic Theory: speed is directly related to the duration of loading

Elastic Theory: resilient modulus of each paving material should be selected proportional to vehicle speedshould be selected proportional to vehicle speed.


Environment66

The environmental factors that influence pavement pdesign include

temperature and

i i i precipitation.

Different standards of pavement design consider the effects of these factors in various wayseffects of these factors in various ways.


Temperatures67

The effect of temperature on asphalt pavements is p p pdifferent from that on concrete pavements.

Temperature affects the resilient modulus of bituminous layers and creates thermal stresses in cement concrete slabs.

I ld li t th ili t d l f t ili d In cold climates, the resilient modulus of unsterilized materials also varies with free-thaw cycles.

The elastic and viscoelastic properties of bituminous The elastic and viscoelastic properties of bituminous materials are affected significantly by pavement temperature.


p

Temperatures68

When the temperature is low, the bituminous layer p , ybecomes rigid and has less fatigue life.

The stiffness is also influenced by the condition of the mix and the hardness of the binder used.

To minimize thermal contraction cracking at low t t l ti l ft bi d d hi h bi d temperature a relatively soft binder and high binder content would be used,

whereas for hot conditions the hardness of the whereas for hot conditions the hardness of the binder would be increased and the binder content reduced to minimized plastic flow in the material.


p

Temperatures69

The warping stresses in rigid pavements are p g g pgenerated principally by temperature changes.

Warping stresses sometimes of the year or the day are additive to the traffic stresses and can influence the slab thickness requirements.

Sh t i th l b l th d th ff t f th Shortening the slab length reduces the effect of these stresses.


Temperatures70

Another effect of temperature on pavement design in ld li i h f i hi h l icold climate is the frost penetration which results in a

frost heave and stronger subgrade in the winter but a much weaker sub grade in the spring. g p gFrost heave causes differential settlements and pavement roughness. The most detrimental effect of frost penetration occurs The most detrimental effect of frost penetration occurs during the spring period when the ice melts and the sub grade is in saturated condition. It is desirable to protect the subgrade by using non-frost-susceptible materials or the design should take into account the weakening of the sub grade.


g g

Temperatures71

Softens AC in warm weather and hardens in cold weather (cold reduced strains but shorter fatigue lives).

Temperature gradient in PCC slabs affects curling and slab-soil contact area.

F t t tiFrost penetration

- Frost Heave differential settlements and roughnessroughness.

- Spring thaw saturated subgrade becomes weak (most detrimental state)


(most detrimental state).

Precipitation72

Precipitation is important in the design, construction p p g ,and performance of roads in three main aspects:

The construction of earth works

S h f Strength of pavement structure

Surface water drainage


Precipitation73

The construction of earthworks: -fThe specification of earthworks is normally defined either directly or in terms of a standard compaction test.

h d i i h ld h hThe design engineer should ensure that the contractor meets the requirements of such specification.

In dry areas such as in arid regions transporting water In dry areas, such as in arid regions, transporting water can considerably increase the construction cost.

In areas where excess rainfall over evaporation falls and cause difficulty for earthworks, and attaining the specification will only be possible in few dry months.


Precipitation74

Strength of pavement structure: -h l i f h il d i h The natural moisture content of the soil determines the

sub grade strength to be used in the design of the pavement structure. It i th ibilit f th d i i t ti t It is the responsibility of the design engineer to estimate that natural moisture content and the corresponding strength of the subgrade and insure that this moisture content is maintained throughout the service life of the content is maintained throughout the service life of the pavement structure. Furthermore, if the surface of a pavement is pervious, water in the form of rainfall percolates easily and can water in the form of rainfall percolates easily and can degrade the structural performance of each layer of the pavement structure.


Precipitation75

Surface water drainage: -f gThe maximum intensity of rainfall is required for the design of the surface water drainage system of the

d road.

This may include from open side ditches to crossing structures like culverts and bridges structures like culverts and bridges.

Minimum grades of roads are also decided based on the criterion of pavement drainage.

The link between rainfall and surface drainage is also important in the design and construction of roads.


Precipitation76

Affects quantity of water infiltrating into subgradeq y g gand location of groundwater table.

Weakens layers.

Shorter drainage time less HMA moisture damage.

Drainage layers are used in may areas to solve precipitation problems.


Materials77

Pavement materials include soils, aggregates, , gg g ,bituminous binders and cement.

The properties of these materials under traffic loading in a given environmental conditions is fundamental for the proper design of pavement structures structures.

Moreover, if economically constructed facilities are to be obtained locally available materials are to be to be obtained, locally available materials are to be used efficiently.


Materials Properties78

Stiffness - time, temperature, moisture effects (pre-failure properties) Poison Ratio (relatively small effect on pavement responses)responses)Strength - time, temperature, moisture effects (Failure properties: cracking, fatigue, permanent ( p p g, g , pdeformation)DurabilityPermeabilityThermal-Volumetric Properties


Materials Properties79

Types of Material BehaviorElastic - recoverable, time independentPlastic - non-recoverable, time independentViscous non recoverable time dependentViscous - non-recoverable, time dependentCombination Visco-elastic - recoverable, time dependent

Pavement Materials1. PCC2. Soils/Granular Materials

bili d il3. Stabilized Soils4. HMA5 Liquid Asphalts


5. Liquid Asphalts

Performance and Failure Criteria80

Pavements are normally designed and constructed to y gprovide, during the design life, a riding quality acceptable for both private and commercial vehicles

ith t bl i twith acceptable maintenance.



"Fatigue Cracking" is the progressive cracking of the h l f i bili d b l dasphalt surfacing or stabilized base layers due to

cumulative repeated traffic loading. This occurs as a result of tensile stresses and strains in This occurs as a result of tensile stresses and strains in the bottom zone and propagates upward to the top. On the pavement surface, it finally manifests as alligator cracks along the wheel trackscracks along the wheel tracks.Fatigue cracking is considered a major structural distress and is predominantly caused by traffic loading. Ingress of rainwater through the cracks can lead to structural failure of the underlying layers.



"Rutting" is defined as the permanent deformation of a pavement due to the progressive accumulation of visco-plastic vertical compressive strains under traffic loading. traffic loading. On the pavement surface, it manifests as longitudinal depressions in the wheel tracks.

i ifi i l d j lSignificant rutting can lead to major structural failures and hydroplaning potentials.Surface ruts may occur in the asphalt-surfacing layer Surface ruts may occur in the asphalt-surfacing layer under the action of heavy vehicle loading, particularly in areas of extreme high temperatures.



Distress Types in Flexible PavementsFatigue Cracking is based on the horizontal tensile strain at the bottom of HMA (relates to the allowable number of load repetitions).Rutting in surface layer is the permanent deformation or rut depth along the wheel paths.Rutting due to sub-surface layers is mainly due to decrease Rutting due to sub surface layers is mainly due to decrease in thickness of the component layers above the subgrade.Thermal cracking occurs in locations where winter temperature falls below –10 °F Pavement will crack when temperature falls below 10 F. Pavement will crack when thermal stress is greater than the fracture strength.Thermal fatigue cracking is caused by tensile strain in the asphalt layer due to daily temperature cycle


asphalt layer due to daily temperature cycle.


Distress Types in Rigid Pavementsyp g

Fatigue cracking is most likely caused by the edge stress at the mid-slab. Allowable load repetitions depend on the stress ratio between flexural tensile stress and the concrete modulus of rupture.

P i i i d b th ili t Pumping or erosion is caused by the resilient deformation under repeated wheel loads.

Faulting Spalling and Joint deterioration are Faulting, Spalling, and Joint deterioration are major types of distress in rigid pavement.



Gravel Roads defects include:Distress

Potholes

C iCorrugation

Rutting

RavelingRaveling

Erosion

Loss of wearing course material



Cracks in wheel tracks



Longitudinal and alligator cracking in the Wheel g g gpath.



Cracking observed on a narrow polder roadg p



reflective cracking in jointed concrete pavementg j p



Low temperature cracking observed on a highwayp g g y



Roughness due to potholes due to severe crackingg p g



Rutting in an asphalt pavementg p p


Distress Types in Flexible Pavements93

Different pavement design methods consider p gpavement failures as design criteria, but differently.

AASHTO method of pavement design uses a rating system known as Present Serviceability Index (PSI) is used to account for performance of pavements.

A h lt I tit t d Sh ll P d l t th Asphalt Institute and Shell Procedures relate the allowable number of load repetition to control fatigue cracking and permanent deformationsfatigue cracking and permanent deformations.


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HIGHWAY II

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