Propiedades mecánicas de alta resistencia del concreto.pdf

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Adnan et al. ConcreteResearch Letters Vol. 1(1) 201

35

www.crl.issres.net Vol. 1 (1) March 2010

TheMechanical Properties of High Strength

Concretefor Box Girder BridgeDeck in Malaysia

Azlan Adnan1, Meldi Suhatril1c

and Ismail M. Tai 21 Dept. of Structures and Materials, Facultyof Civil Engineering

Universiti Teknologi Malaysia, MALAYSIA2 Structure and BridgeUnit, Public WorkDepartmen

Kuala Lumpur, MALAYSIA

Selected paper fromtheAsia Pacific Structural Engineering Conferenc , APSEC 2009

Abstrac

This paper presents an experimental investigation of the mechanical properties of highstrength concretefor box girder bridge deck in Malaysia. To study the Malaysia condition,high strength concrete samples were obtained from a Malaysian precast concr te factorythat provides precast and in-situ concrete for box girder bridge deck construction. Themixed design properties of this type of concrete mixture were investigated; including theslump test, compressive strength, flexural strength, static modulus elasticity and Poissonsratio. Stress-strain curve relationship was produced as well, to be used for non-linearbehaviour study.

Keywords: box girder; slump; compressive; flexural; static modulus elasticity; Poissonsrati .

1. I ntroduction

Thepurpos of this research is to providethe material properties of concretebox girder bridgedeck with respect to the types and strength of concrete used in Malaysia. For mixed designproportionof this high strengthconcrete, asuper plasticizer was used to all w the concretetoreachthe 90% of the 28 days concretestrength in a period of 7 days. In the investigations, the testing ofthespecimens was performed in accordancetoBritishStandards. Th Euro cod 2, ASSHTO LRFDBridge Design Specification and ACI codes areused as the results comparison. Furthermore in this

research, a stress-strain curve relationship was produced in order to be used for non-linearbehaviou study. These resultscan beused as an input of material properties for studyingthe linearandnon-linear concretebehaviou usingfinite elementmethod.

2. Mix Design

The concrete mix was obtained fromone of precast concretefactories in Malaysia. In the mix,the admixtureor a super plasticizer was used to allow the concreteto reachthe 90% f the 28 daysconcrete strength in a period of 7 days. Other tests have been made by Nguyen et al. [1]; the

c

CorrespondingAuthor: Meldi SuhatrilEmail: [email protected] -2012 All rightsreserved. ISSR J ournals


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TheMechanical Properties of High Strength Concretefor Box Girder BridgeDeck in Malaysia

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concretestrengthdevelops rapidly in early stages byusingsuperplastisizer. Compressive strengthat03 days is over 60% and at 07 days is over 85-90% of strength at 28 days. The super plasticizerused in mix is Might superplastisize . Based on supertilisize research by Hattori [2]; waterreductions up to 30% were achieved with the use of this supertilisizer called Might -150. Sincethen, it has c nsiderably contributed to produce the high-strength concrete. The proportion of mixcan beseen in Table 1.

TABLE 1: MIX DESIGN PROPORTION FOR CONCRETE BOX GIRDER BRIDGE DECK IN MAL AY SIA

Mix Proportion/ 1 M3 QuantitySand (Kg) 81Aggregate(20m ) 108Cement (Kg) 470.8Admixture(L) 6.Water (L) 42.2

Based on AASHTO LRFD Bridge Design Specification; the concrete sample is classified asClass P (High Performance Concrete) where the sum of Portland Cement and other cementitious

materials shall b specified nottoexceed 593 Kg/3

[3]. Theconcretemix characteristic for class Pcan beseen in Table 2.

TABLE 2: CONCRETE MIX CHARACTERISTIC

Class of concrete P (HPC)MinimumCementContent (K g/ 3) 33MaximumW/C ratio (Kg/K g) 0.49CoarseAggregate (mm) 4.75- 25

3. Test For Fresh Concret

The main purpose of this test is to determine the workability of fresh concrete. Freshconcrete is a mixture of water, cement, aggregate and cementitious cement. After mixing,operationssuch as transportation, placing, compactingand finishing of fresh concretecan affect theproperties of the hardened concrete. The ease with which a concrete mix can be handled from amixturetoitsfinal compacted shapeis termed as workability.

There are three main characteristics of workability that is consistency, mobility andcompactibility. Thetests commonly used for measuring workability do not measuretheseindividualcharacteristicsof workability. In this study, thetypeof test used was slump test.

Thedetermination f slump was carried out in accordancewithBS 1881: part 102 (1983) [ ].The test was conducted by using the standard size of metal mould, as prescribed in the standard.There are three types of slump that may result after the test. The test is only valid if it yields a true

slump where the concrete specimen remains substantially intact and symmetric. If the concretespecimens result is in shear type or collapses, the test should be repeated with another concretesample.

The mould for the slump test is a f ustum of a con , with 305 mm high. The base of themould with 203 mm diameter is placed on a smooth surfacewhile the smaller opening of 102 mmdiameter at the top. The container is filled with concrete in three layers. Each layer is tamped 25times with a standard 16 mm diameter steel rod. Rounded at the end, and the top surfaceis struckoff by means of a screeding and rolling motionof the tamping rod. The mould must be held firmlyagainst its base duringthe entireoperation. This is facilitated by handles or foot rests brazed to themould.

Immediately after filling, the cone is slowly lifted, and the unsupported concrete slumps -

hencethe nameof thetest. Thetest is widely conducted onsitealthough it is virtually impossibletolift theconevertically at theend of thetest. Ideally, all slump result should betrueslump. Thereare


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three types of slumps to be observed; true, shear and collapse. Based on the site test, the type ofslump is trueslump. Theslump test measurement onsitecan beseen in Figure1.

Figure1. Theprocess of Slump test measuremen

. Test for Hardened Concret

The most important property of hardening concrete is the compressive strength which iscommonly used for specification and quality control. Compressivestrengthof concreteis defined asthe maximumcompressiveload it can carry per unit area and is determined by using standard cube(100 x 100 x 100m ) or cylinders(150 mmdiameter x 300mmlength).

In general, the other properties of concrete such as Flexural strength, modulus elasticity andPoisson ratio were also tested in this report. Factors such as constituent materials, method ofpreparation, curingandtestconditioncan influencetheconcretestrength.

In order to obtain good concrete, the curing in suitable environment during early stages ofhardening should follow the placing of an appropriate mix. Curing is used for promoting thehydration of cement and consists of controlling the temperature and moisture movement from andinto theconcrete. Curingmay influencethe strength of concretebothfromthepoint of view of time

for which it is applied and the effectiveness of the method used. In strength terms, for example,poor curingwill beless damaging tothemass concretethan thin sections, whichcould dry out morequickly.

The curing process was conducted in Structural and Material Laboratory of UniversitiTeknologi Malaysiafor 28 days. Thesamples for hardened testing concretear shown in Figure2.

Figure2. Hardened concreteafter openingthemould for 2 hours

.1. CompressiveStrength Test

The compressive strength of normal concrete was obtained by crushing 100 x 100 x 100mmcubes at 28 days as shown in Figure 3. The mean value obtained fromthe three cubes wasthen taken as cube compressive strength for each normal concrete mix. The tests were

performed in accordance with BS 1881: Part 116 (1983) [5]. The compressive strength at theageof 7 and 28 dayswerealso carried out for the purpose of studying the strengthdevelopment


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of concrete. The co pressive strength of normal weight cubes was calculated by dividing themaximum load (P) (attained from the test) by the cross sectional area of the cube (A). Thecompressivestrengthis given bytheequation 1.

=P/A (1)It is assumed that for fully compacted concrete the compressive strength depends only

uponthewater/ cement ratio for agiven typeof cement, age, methodof testingand curing.

Figure3. Hardened cubeconcretefor 7 and 28 dayscuring

The process of compression strength test in Structural and material laboratory UniversitiTeknologi Malaysia can be seen in Figure . The failure cube samples after compressive testingis shown in Figure5.

Figure4. Theprocess of Compressivestrengthtes

Thecompressivestrength result at theageof 7 and 28 days can beseen in Tabl s 3 and. Theresultsshowthat theconcretestrengthat 7 daysachieved 90 % of 28 daysconcrete

strength. It is because, theconcretebox girder ridgedeck requires early strengthfoprestressingpurposes on site.


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Figure5. Failurecubeafter compressivetestingin structurela

TABLE 3: RESULT OF COMPRESSIVE TEST FOR 7 DAYS STRENGTH

SampleNo.

Weight(Kg) Area(m 2) Load (N) Strength (N/m 2)

1 2.46 100 517.63 51.7

2 2.48 100 515.672 51.567

3 2.46 100 528.45 52.84

TABLE : RESULT OF COMPRESSIVE TEST FOR 2 DAYS STRENGTH

SampleNo.

Weight (K g) Area (mm2) L oad (N) Strength(N/mm2)

Mean Cubestrength

1 2.51 1000 517.639 55.2

2 2.48 1000 515.672 57.626

3 2.51 1000 528.455 55.154

56.01

.2. Flexural Strength Test

The determination of the flexural tensile strength was obtained by testing in flexure; aset of three moulded prismspecimens of 100 x 100 x 500 mmat 28 days (Figure6). Themeanvalue obtained from the tests was taken as the flexural tensile strength of concrete. The testswerecarried out in accordancewithBS 1881: Part 118 (1983) [6]. Figure7 showsth process offlexural tensile test. The flexural tensile strength of the test prism was calculated by thefollowingequation:

2bd

PLfb (2)

wherefb is the flexural strength (N/m2), P is the breaking load (N), L is the distance between

the supporting rollers (mm), b is the width of the cross section and d is the depth (mm). The

flexural strength test results are shown in Table 5. Figure 8 shows the conditions of prissample after thetest.

Figur 6. Hardened prismfor flexural testingafter curingfor 28 days


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TABLE 5: FLEXURAL STRENGTH TEST RESULTS

No Fb(n/mm2)

Averag

1 6.2122 7.1312

3 6.6

6.6478

The values reported by various investigators for the modulus of rupture of normalweight high-strength concretes fall in the range of 7.5fc to 12fc where both the modulus ofruptureand the compressive strengthareexpressed in psi. Theequation 3 was recommended fortheprediction of thetensilestrengthof normal weightconcrete.

cr ff 9.0 MPa (3)

For 21 MPa cf


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WhereE is the modulus elasticity, F is the forceapplied to the object, A0 is the originalcross-sectional area through which the force is applied, L is the amount by whichthelength ofthe object changes, and L is the original length of the object. The modulus of elasticity ofconcrete and its corresponding compressive strength are required in all calculations for thedesign of concrete structures. The modulus of elasticity can be determined by measuring thecompressivestrain when asample is subjected toacompressivestress.

Figure 9 shows the concrete cylinder samples fo modulus of elasticity test. The staticmodulus of elasticity test is depicted in Figure 10. The crushed sample after modulus ofelasticity test can beseen in Figure11. Therelationship between stress and vertical strain can beseen in Figure12.

Fi ure9. Hardened cylinder concretesamples

Figure10. Stress strain relationship tes

Figure11. Static modulus of elasticity tes


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Figure12. Stress versus vertical strain

Many investigators have reported values for the modulus of elasticity of high-strengthconcrete of the order of 31-45 MPa, depending mostly on the method of determining themodulus [7]. Fromthe sample test, the modulus elasticity for concretebox girder bridgedeck isabout 33 GPa. Table 6 shows th comparison of modulus of elasticity empirical formula basedonEuro codeand ASHTO LRFD bridgedesign specification.

TABLE 6: THE COMPARISON OF MODULUS ELASTICITY EMPIRICAL FORMULA BASED ONEUROCODE AND AASHTO LRFD BRIDGE DESIGN SPECIFICATION.

EUROCODE AASHTO

37,846 Mpa 37,08 Mpa

4.4. Poissons Rati

Poissons ratio is a ratio between the lateral and axial strains of an axially and/orflexurally loaded structural element. The normal method in determining Poissons ratio is by astatic test in which a specimen is subjected to compressive forces and simultaneousmeasurements of boththelongitudinal and lateral strains aremade. If the material does not obey

the Hookes law, and the stress strain relationship is curved, then static value of Poissons ratiowill depend onthe stress, unless the relationship of lateral strain to longitudinal stress is similartothat of longitudinal strain.

The design and analysis of some types of structures require the knowledge of Poiss nsratio. The ratio of the lateral strain accompanyingand an axial strain to the applied axial strain.

The sign of train is ignored. We usually interested in applied compression and therefore haveaxial contractionandlateral extension.

Based on AASHTO, if Poissons ratio is not determined by physical test, Poisson ratiomay assume as 0.2 [3]. It is also similar to Euro cod , Poissons ratio may be taken equal to0.2[8]. Based on the result obtained, the relationship stress and lateral strain can be se n inFigure 13. From the relationshi of stress, vertical and lateral strain (Figur s 5 and 6), the

Poissons ratio valueis about 0.26.


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Figure13. Stressversus horizontal strain

5. Conclusion

The mechanical properties of high strength concrete fo box girder bridge deckconstruction in Malaysia for a period of 28 days havebeen evaluated and the results arestill intherangeof previoushigh-strengthconcreteproperties studies. Thefollowingconclusions havebeen made:(1) The Normal compressiv strength (fcu) used for concretebox girder bridge deck is about

56 N/m 2.(2) TheNormal flexural strengthused for concretebox girder bridgedeck is 6.65 N/m 2.(3) The Normal static modulus of elasticity used for concretebox girder bridge d ck is about

33 GPa.( ) TheNormal Poissons ratio used for concretebox girder bridgedeck is about 0.26.(5) The stress strain curve relationship has been produced and can be used for nonlinear

behavior studyfor concretebox girder bridgedeck usingfiniteelementmethod.

References

[1] Nguyen Van huynh, Pha Vinh Nga, and Thai Hong Chuong. Research on Making High

Strength Concrete Using Silica Colloid Additiv . In 2008 Proceedings of th 3rd ACFInternational Conferenc -ACF/VCA 2008. 2008, Ho Chi Minh city, Vietnam.[2] Hattor , K, Experiences withMightySuperplasticizersin J apan, SP-62, 1979, p 37-66.[3] AASHTO, AASHTO LRFD BridgeDesign Specifications. ThirdEdition, American Association

of StateHighway and Transportation Officials, Washington, D.C, 2005, pp 5-1 5-16.[ ] British Standard Institution, Testing Concrete Part 102: Methods for Determination of Slum .

London: (BS1881: Part 102:1983), 1983, pp 1-3.[5] British Standard Institution, Testing Concrete Part 116: Methods for Deter ination of

CompressiveStrengthof ConcreteCubes. London: (BS1881: Part 116:1983), 1983, pp 1-3.[6] BritishStandard Institution, TestingConcretePart 118: Methods for Determination of Flexural

Strength. London: (BS1881: Part 118:1983), 1983, pp 2-5.


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[7] ACI Committe , State of the Art Report on High Strength Concret , (ACI 363R-92), 1997, pp5-1 5-3.

[8] Euro code 2, Design of Concrete Structures part 1-1. London: (BS EN 1992-1-1:200 ), 200 ,pp27-36.

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Propiedades mecánicas de alta resistencia del concreto.pdf