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RETROFIT OF CONCRETE IN PIER STRUCTURES Sumargo1*, Ariyadi Basuki2, Raja Nasrul Fuad3, Meri Sri Wahyuni3

1Civil Engineering Department, Bandung State Polytechnic, Bandung Indonesia 2Center for Material and Technical Product, The Ministry of Industry

3Medan Institute of Technology, Medan *Corresponding author. Tel : +62 812 219 8097, Fax : +62 22 2013889

E-mail address : sumargo2004@yahoo.com (Sumargo)

Keywords: FRP, moment capacity, patching, grouting, injection.

ABSTRACT

Composite construction involving relatively new material system is used at pier of Jetty I PT. Petrokimia Gresik, where damages occur due to tides, corrosive environments, and the addition of the load on the pier that cause cracks. Additional loads on the structure of pier also accelerate the occurrence of cracks on pier structures such as beams, cross beams, and pier head. Cracks bring adverse effects to the structure in the form of corrosion of reinforcing the structure, where improvements can be made in the form of patching, grouting, injection, and strengthening with Fiber Reinforced Polymer material. Structural analysis showed that the 500 mm x 1200 mm beams need additional strengthening of 2 layers Mbrace CF 230/4900 as to increase the moment capacity of 68%, for 450 mm x 1550 mm beams need 1 layer CF 230/4900 to obtain additional moment capacity of 64%, for 500 mm x 1400 mm beams need 1 layer Mbrace CF 230/4900 for increase moment capacity of 62%, and for 1000 mm x 1200 mm beams need 1 layer Fiber Reinforced Polymer Laminate Mbrace 165/2500 as to increase the moment capacity of 69%.

INTRODUCTION

The port of PT. Petrokimia Gresik, East Java is a special port that supports the

company's activities so that port is only reserved for loading and unloading

items. It has a pier with a length of 620 meters and 36 meters wide and can

accommodate ships weighing 40,000 to 60,000 DWT and capability of loading

and unloading ships 185,800 tons/day. Cracks, spalling, and reinforcement

corrosion are occurred mostly due to the aggressive environment to the

structural material. This paper shows that the performance of the pier can be

improved without disturbing daily operational by repairing and strengthening with

advanced material technology.

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METHODOLOGY

Stages were done for the preparation of this study such as (a) visual observation

and inventory of failures, (b) secondary data collection and a series of inspection

and testing activities, (c) analysis for the reconditioned and strengthening of the

structures, followed by (d) apply of proposed analysis. The first two steps is

given ini Figure 1.

STRUCTURALDAMAGEINVESTIGATION

REINFORCED CONCRETE

PRELIMINARYINVESTIGATION

SELECTION (RANDOM)ELEMENTSTRUCTURE

REGISTRATION DATA FORCONCRETEBLANKETDETERMINE

WITHR-METER

DETERMINATION OF LOCATIONCONCRETE STEEL

REINFORCEMENT WITH R-METER

TESTING FOR CORROSION RATECHIPPING WITHPOTENTIALMETER

CORROSION RATEOF RECORDINGDATA REINFORCEMENT

CHIPPING FOR VISUALINSPECTIONOF DAMAGES SUSPECTED

DIAMETER MEASUREMENT REINFORCEMENT

MEASUREMENT OF CONCRETE BLANKET

DETERMINATION OFCORROSION

ON CONCRETESTEEL REINFORCEMENT

EXAMINATION OF QUALITY CONCRETE

CONCRETECORE SAMPLE(COREDRILLED)

POWERFULTESTPRESS

TEST CHLORIDECONTENT

SELECTION POSITIONCONCRETECORE SAMPLING

DETERMINATION OF LOCATION

CONCRETE REINFORCEMENT

HAMMER TEST

CONCRETECORE SAMPLING

CONC

LUSI

ONDA

TAAN

ALYS

ISAN

DRE

PORT

ING

DOCUMENTATION

FOLLOW-UPRETROFITTING IMPROVEMENT

SPRAYING PHENOLPTHALEIN&

MEASUREMENT SOLUTIONS LEVEL CARBONATION PUNCHT

Figure1. Inspection And Testing Activities Series

LITERATURE REVIEW

Strengthening with Fiber Reinforced Polymer (FRP)

The main advantages of composites are complementary elements of the

property. For example, glass fiber with a high tensile strength is very susceptible

to bending and failure due to the environment. It is equipped with polymer which

is weak against stress, but the fiber is easily formed and can protect the fiber

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surface. Composite Fiber Reinforced Polymer (FRP) consisting of three essential

elements of fiber, polymers, and additives. A high ratio of strength and stiffness

to weight and high energy absorption is an important properties of the composite

to increase load on the structure service life. Good corrosion resistance and

fatigue resistance of FRP composites has the advantage on the life-cycle cost of

structures. Carbon fiber composites are ideally suited to add strength, stiffness,

and energy absorption. Unlike glass and aramid fiber, carbon fiber shows no

corrosion or rupture due to failure at room temperature. [1]

Beam flexural capacity is based on ultimate strength limit, which is

determined by limit compressive strength of concrete, reinforcing steel yield

stress, and effective stress of FRP, Figure 2. The flexural strength required given

as [3]: (1)

The required Carbon Fiber Reinforced Polymer (CFRP) is determined by using

environmental reduction factor ( of 0.95. Calculating FRP stress through

(2)

in which,

= environmental reduction factor and = ultimate tensile strength

Calculate FRP strain as (3)

in which = ultimate rupture strain

The area of FRP is calculated using (4)

in which, = number of layers = thickness of layers = length of layers

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hd

d’

gnc

d-ch-c

bfe bi

s

s ‘

cu = 0,003

a

fsAs

Ffe = Ef fe

C1

Cc

Ts

Tfe = Af Ef fe

Fs’

0,85Fc’½ a

½ a

Af = ntfc f

(a) section (b) distributionstrain

(c) Distribution voltageequivalent

(d) coupling force

Figure 2. The Stress-Strain Diagram of Beams with FRP Reinforcement

The neutral axis depth (c) is determined by the equilibrium equation:

(5)

To protect the bonding ability of FRP, use the following bonding coefficient

For ≤ 180000; (6a)

For > 180000 (6b)

By giving the assumption that the ultimate strain in concrete for 0003, the FRP

effective strain can be calculated by (7)

in which, = strain of concrete = depth of beam

= depth of neutral Axis = strain of concrete with FRP = strain of FRP

Nominal flexural moment capacity of strengthened beam using FRP can be

calculated by: (8)

in which, = reinforcement area = reinforcement stress = reduction factor = 0.85 = area of FRP = effective Stress of FRP; = elastic modulus of FRP

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RESULTS OF THE OBSERVATION

Inspection performed on pier head structural elements, such as beams, cross

beams, the beam path cranes, plate on area Jetty I. In general, failure occurs in

the form of spalling which preceded the occurrence of cracks in concrete

surfaces. Triggers cracks can be categorized into two causes. First, cracks due

to corrosion caused by the swelling volume of reinforcement in concrete that

stressing concrete covers out and become cracked. Second, spalling and cracks

expanded into structural caused by an excessive stress (related to the loading)

or unanticipated design load or due to insufficient compressive strength of

concrete.

a. Slab and Pier Head

The pier head experiences some concrete surface spalling. It is triggered by the

presence of cracks due to corrosion processes that occur in the reinforcement,

Figure 3. The failure is categorized as light failure at new or repaired concrete as

much as 24.76%, light failure at old concrete of 9.52%, moderate at new or

repaired concrete of 7.62%, moderate at old concrete of 4.76% of the total

number of pier head in the structure.

Figure 3. Spalling and Triggered Corrosion Cracks at Slab and Cross Beam

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b. Cross Beam

There are delaminations of new concrete layer at the bottom surface. The failure

is categorized as light failure in new concrete material 19.07%, light in old

concrete 19.7%, moderate in new concrete material 25.76%, moderate in old

concrete 25.76%, and heavy in new concrete 3.03% of the total cross beams in

Jetty I.

c. Beam Element Structure

The bottom part of beams show flaking and cracks, even in some places are

found failures in the former repair or strengthening, Gambar 4. The failure is light

in new concrete repair 21.4%, light in old concrete 7.95%, moderate in new

concrete repair 15.6%, moderate old concrete 3.98%, and heavy in new

concrete repair 0.61% of the total number of beams in Jetty I.

Figure 4. Spalling and Crack at Beam

TESTING RESULTS

Concrete compressive strength of structural elements in Jetty I ranges 265-322

kg/cm2. Such values are comparable with the original compressive strength

design of 27 MPa 275.3 kg/cm2.

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DATA STRUCTURES AND ANALYSIS

Pier of Jetty I was modeled as a 3 dimensional structure with longitudinal and

transverse beams in accordance with drawings, Figure 5. It has a total length of

282 meters and 24.5 meters wide.

Figure 5. Three Dimensional View of Jetty I

There are four concrete beams with the dimension: 1000mm x 1200mm as cross

beam, 450mm x 1550mm as a crane beam, 500mm x 1400mm as longitudinal

beam 1, and 500mm x 1200mm as an longitudinal beam 2.

The leg of the pier are steel pipe of 322 MPa of yield stress, concrete filled with a

diameter of 1270 mm with of thick 12.7 mm.

STRUCTURE ANALYSIS

a. Pier Loading

The analysis covers all the possible loadings such as self weight, conveyor,

pipeline, live load, crawlers, trailers, trucks, cranes, earthquake loads, and load

the ship docked.

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b. Structure Analysis

Beams have concrete cover of 40 mm and 29 mm diameter of reinforcement.

Properties of FRP are: thickness of layers = 0.17 mm, ultimate tensile

strength = 4.9 kN/mm2, ultimate rupture strain = 0.021 mm/mm, and

elastic modulus = 230 000 N/mm2.

The computed moments are: ultimate moment = 2244.46 kN-m and service

moment = 1549.65 kN-m. Structural analysis shows that φ 578.157 kN-

m < kN-m. So the 500/1200 beam require strengthening structures

using FRP. Two layers of FRP may increase the capacity of the beam as φ

kN-m > kN-m. The resume of analysis is given in Table 1.

Table 1. Beams Nominal Moment

Ultimate Moment Service Moment Nominal Moment (fMn) Nominal Moment ( fMn)

(Mu) (Ms) without FRP with FRP

2244.46 kNm 1549.65 kNm 578.157 kNm 3076.622 kNm 2 layer1316.004 kNm 963.017 kNm 755.308 kNm 3411.12 kNm 1 layer1192.16 kNm 914.096 kNm 578.157 kNm 2447.735 kNm 1 layer3009.9 kNm 2191 kNm 585.258 kNm 3186.263 kNm 1 layer

450 mm x 1550 mm500 mm x 1400 mm

1000 mm x 1200 mm

Number of Layer FRPBeam Size

500 mm x 1200 mm

PIER REPAIR

Cracked, spalled, and chipped were occurred in pier structure of PT. Petrokimia

Gresik.

a. Cracking and Spalling

Cracking occurs at the plate, beam, pier head and pier. This repair method aims

to fill the cracked concrete with Emaco Nanocrete R4 and Resin material

Concresive 2525, Figure 6 and 7.

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Figure 6. Injection Process Figure 7. Chipped on the beam Figure 8. Grouting Process

b. Chipped

This repair method aims to improve the chipped concrete elements by grouting

with Special cement MASTERFLOW 830[2] and Resin material Concresive

2525[2], Figure 8.

c. Wrapping Beams with FRP

The beam dimensions 450x1550, 500x1200, 500x1400 were strengthened

using CFRP Mbrace CF 230/4900 [2], while for the beam with 100x1200 were

improved with FRP Mbrace Laminates 165/2500 [2] after 2525 Concresive resin

material is applied.

QUALITY CONTROL

Quality control (QC) is intended to see whether the implementation of repair and

retrofitting is in conformity with existing standards. Without applying

standardized QC will result in dispute among owner, consultant, and applicator.

Equipment such as Ultra Sonic Pulse Velocity meters/UPV and core drill are

usually used for patching, grouting, and injection. While pull-off test is the QC

for the coherence between 2525 Concresive resin material used to bond FRP.

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CONCLUSION AND STUDY IMPACT

a. The results of visual observations revealed structural deterioration as shown

in Table 2.

Table 2: Percentage Rate of Structure Damage

Mild Medium Weight Mild Medium Weight

19.70% 25.76% 3.03%

Structure ElementOld Concrete New Concrete

Plate - - - - - -

Beam 7.95% 3.98% - 21.40% 15.60% 0.61%

Pier Head 9.52% 4.76% - 24.76% 7.62% -

Cross Beam 19.70% 25.76% -

b. Most of the beams on the structure has been cracked, but the capacity of

cross-section is still above the ultimate moment, meaning that the condition

of the structure is no longer elastic.

c. Advanced material technology has proven its ability in strengthening

concrete structures without major disturbance to the daily operational of the

pier. This can contribute to the acceleration of economic development in a

region with port infrastructures such as North Sumatra. However, with more

than 90% of local content of this material but still high price, is a challenge

for future research.

REFERENCES

1. Vijay, P.V., Hota Gangarao, Narendra Taly. Reinforced Concrete Design With FRP Composites. CRC Press. New York. 2006.

2. PT. BASF Indonesia. Product Selection Guide Building Systems. Jakarta. 2011.

3. SNI 03-2847-2002 Tata Cara Perhitungan Struktur Beton untuk Bangunan Gedung

4. Bank, L.C. (2005). Mechanically-Fastened FRP (MF-FRP) – A Viable Alternative fo Strengthening RC Member, FRP Composites in Civil Engineering – CICE 2004 – Seracino (ed), pp. 3-14.