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Hardened Concrete

The document discusses factors that affect the strength of concrete, including water-cement ratio, aggregate-cement ratio, maximum aggregate size, and degree of compaction. It states that concrete strength is inversely proportional to water-cement ratio according to Abrams' law. A lower water-cement ratio and higher degree of compaction produce stronger concrete by reducing porosity. A leaner aggregate-cement ratio also increases strength by absorbing water and reducing shrinkage. Larger aggregate size can reduce water needs but may decrease strength by lowering surface area for bond development.

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Hardened ConcreteHardened Concrete
Strength of ConcreteStrength of Concrete • StrengthStrength ofof concreteconcrete isis commonlycommonly consideredconsidered itsits mostmost valuablevaluable property,property, althoughalthough inin manymany practicalpractical cases,cases, otherother characteristics,characteristics, suchsuch asas durabilitydurability andand permeabilitypermeability maymay inin factfact bebe moremore important.important. • StrengthStrength usuallyusually givesgives anan overalloverall picturepicture ofof thethe qualityquality ofof concreteconcrete becausebecause strengthstrength isis directlydirectly relatedrelated toto thethe structurestructure ofof thethe hydratedhydrated cementcement paste.paste. • StrengthStrength ofof concreteconcrete couldcould bebe defineddefined asas thethe ultimateultimate loadload thatthat causescauses failurefailure (or(or isis itsits resistanceresistance toto rupture)rupture) andand itsits unitsunits areare forceforce unitsunits divideddivided byby areaarea (N/mm(N/mm22).).
Strength of ConcreteStrength of Concrete
Strength of ConcreteStrength of Concrete • CharacteristicCharacteristic strengthstrength -- Compressive, TensileCompressive, Tensile andand FlexureFlexure strengthstrength • Modulus of ElasticityModulus of Elasticity • Creep and shrinkage of concreteCreep and shrinkage of concrete THE THREE S-WORDSTHE THREE S-WORDS Stress:Stress: a weight or load applieda weight or load applied to the concrete (in N)to the concrete (in N) Strength:Strength: the concrete’s abilitythe concrete’s ability toto carrycarry thethe weightweight oror loadload (in(in NN perper squaresquare mm)mm) Strain:Strain: howhow muchmuch thethe concreteconcrete stretchesstretches oror compressescompresses (deforms)(deforms) whenwhen carryingcarrying aa loadload (in(in inchesinches perper mm)mm)
Fracture andFracture and FFailureailure • ConcreteConcrete specimensspecimens subjectedsubjected toto anyany statestate ofof stressstress cancan anyanysupportsupport loadsloads ofof upup toto 40–60%40–60% ofof ultimateultimate withoutwithout apparentapparent signssigns ofof distress.distress. •BelowBelow thisthis level,level, anyany sustainedsustained loadload resultsresults inin creepcreep strainstrain whichwhich isis proportionaproportionall toto thethe appliedapplied stressstress andand cancan bebe defineddefined inin termsterms ofof specificspecific creepcreep (i.e.(i.e. creepcreep strainstrain perper unitunit stress)stress) •AsAs thethe loadload isis increasedincreased aboveabove thisthis level,level, softsoft butbut distinctdistinct noisesnoises ofof internalinternal disruptiondisruption cancan bebe heardheard until,until, atat aboutabout 70– 90%70– 90% ofof ultimate,ultimate, smallsmall fissuresfissures oror crackscracks appearappear onon thethe surface.surface. •AtAt ultimateultimate loadload andand beyond;beyond; thethe specimensspecimens areare increasinglyincreasingly disrupteddisrupted andand eventuallyeventually fracturedfractured intointo aa largelarge numbernumber ofof separateseparate pieces.pieces.
Fracture and FailureFracture and Failure
The stages of cracking (fracture) in concreteThe stages of cracking (fracture) in concrete
Types of Concrete StrengthTypes of Concrete Strength • CompressiveCompressive SStrengthtrength • TensileTensile SStrengthtrength • ShearShear SStrengthtrength • BondBond SStrengthtrength • ImpactImpact SStrengthtrength • FatigueFatigue SStrengthtrength
Compressive StrengthCompressive Strength • The compressive strength of concrete is defined as theThe compressive strength of concrete is defined as the strength of 28strength of 28 daysdays oldold specimensspecimens testedtested underunder monotonicmonotonic uniaxialuniaxial compressivecompressive load.load. • TestingTesting ofof cylindricalcylindrical samplessamples withwith 1515 cmcm diameterdiameter andand 3030 cmcm heightheight isis standard.standard. • CubeCube specimensspecimens ofof1515 cmcm ×× 15cm15cm ×× 1515 cmcm areare alsoalso beingbeing used.used. • Normally,Normally, thethe compressivecompressive strengthstrength ofof concreteconcrete isis determineddetermined byby testing,testing, andand thethe tensiletensile strengthstrength andand modulusmodulus ofof elasticityelasticity areare expressedexpressed inin termsterms ofof thethe compressivecompressive strength.strength.
Compressive StrengthCompressive Strength
Compressive StrengthCompressive Strength • ThereThere areare threethree failurefailure modesmodes forfor cylinderscylinders.. • UnderUnder axialaxial compressioncompression concreteconcrete failsfails inin shearshear.. • TheThe separationseparation ofof thethe specimenspecimen intointo columnarcolumnar piecespieces byby whatwhat isis knownknown asas splittingsplitting oror columnarcolumnar fracture.fracture. • CombinationCombination ofof shearshear andand splittingsplitting failure.failure.
Compressive StrengthCompressive Strength • The compressive strength of concrete is defined asThe compressive strength of concrete is defined as the strength of 28the strength of 28 daysdays oldold specimensspecimens testedtested underunder monotonicmonotonic uniaxialuniaxial compressivecompressive load.load. • TestingTesting ofof cylindricalcylindrical samplessamples withwith 1515 cmcm diameterdiameter andand 3030 cmcm heightheight isis standard.standard. • CubeCube specimensspecimens ofof1515 cmcm ×× 1515 cmcm ×× 1515 cmcm areare alsoalso beingbeing usedused • Normally,Normally, thethe compressivecompressive strengthstrength ofof concreteconcrete isis determineddetermined byby testingtesting,, andand thethe tensiletensile strengthstrength andand modulusmodulus ofof elasticityelasticity areare expressedexpressed inin termsterms ofof thethe compressivecompressive strength.strength.
Compressive StrengthCompressive Strength
Tensile Strength of ConcreteTensile Strength of Concrete • TheThe tensiletensile strengthstrength ofof concreteconcrete isis muchmuch lowerlower thanthan thethe compressivecompressive strength,strength, largelylargely becausebecause ofof thethe easeease withwith whichwhich crackscracks cancan propagatepropagate underunder tensiletensile loadsloads • TheThe tensiletensile strengthstrength ofof concreteconcrete isis measuredmeasured inin threethree ways:ways: directdirect tension,tension, splittingsplitting tension,tension, andand flexuralflexural tensiontension
Tensile Strength of ConcreteTensile Strength of Concrete • ItIt isis difficultdifficult toto testtest concreteconcrete inin directdirect (uniaxial)(uniaxial) tensiontension becausebecause ofof thethe problemproblem ofof grippinggripping thethe specimenspecimen satisfactorilysatisfactorily andand becausebecause therethere mustmust bebe nono eccentricityeccentricity ofof thethe appliedapplied load.load. Therefore,Therefore, directdirect tensiletensile testtest isis notnot standardizedstandardized andand rarelyrarely usedused • ModulusModulus ofof rupturerupture testtest andand splittingsplitting testtest areare commonlycommonly usedused toto determinedetermine thethe tensiletensile strengthstrength ofof concreteconcrete
Tensile Strength of ConcreteTensile Strength of Concrete • Direct-Tension TestDirect-Tension Test:: • The most direct way of measuring the tensileThe most direct way of measuring the tensile strength.strength. • Not a practical test.Not a practical test.
Tensile Strength of ConcreteTensile Strength of Concrete • Split-Cylinder Test:Split-Cylinder Test:
Tensile Strength of ConcreteTensile Strength of Concrete Split Cylinder TestSplit Cylinder Test
Tensile Strength of ConcreteTensile Strength of Concrete Modulus of Rupture Test:Modulus of Rupture Test: Four-point bending (two-point loading)Four-point bending (two-point loading) Three-point bending (third point loading)Three-point bending (third point loading)
Relationship Between Compressive andRelationship Between Compressive and Tensile Strength of ConcreteTensile Strength of Concrete • TensileTensile strengthstrength ofof concreteconcrete isis proportionalproportional toto thethe square-square- rootroot ofof thethe compressivecompressive strength.strength. • TheThe proportionalityproportionality constantconstant dependsdepends onon manymany factors,factors, suchsuch asas thethe concreteconcrete strengthstrength andand thethe testtest methodmethod usedused toto determinedetermine thethe tensiletensile strength.strength. • TheThe followingfollowing relationsrelations cancan bebe usedused asas aa rulerule ofof thumb:thumb:
Concrete StrengthConcrete Strength ShearShear StrengthStrength ShearShear strengthstrength ofof concreteconcrete isis takentaken approximatelyapproximately equalequal toto 2020 %% itsits compressivecompressive strengthstrength BondBond StrengthStrength •TheThe strengthstrength ofof bondbond betweenbetween steelsteel reinforcementreinforcement andand concreteconcrete isis calledcalled asas bondbond strengthstrength ofof concreteconcrete •BondBond strengthstrength developsdevelops primarilyprimarily duedue toto frictionfriction andand adhesionadhesion betweenbetween steelsteel reinforcementreinforcement andand concreteconcrete •InIn general,general, bondbond strengthstrength isis approximatelyapproximately proportionalproportional toto compressivecompressive strengthstrength ofof concreteconcrete upup toto aboutabout 2020 MPaMPa
Shear StrengthShear Strength
BondBond StrengthStrength
Concrete StrengthConcrete Strength ImpactImpact StrengthStrength ImpactImpact strengthstrength ofof concreteconcrete isis ofof importanceimportance inin drivingdriving concreteconcrete piles,piles, inin foundationsfoundations forfor machinesmachines exertingexerting impulsiveimpulsive loading,loading, andand alsoalso whenwhen accidentalaccidental impactimpact isis possible,possible, e.g.e.g. whenwhen handlinghandling precastprecast concreteconcrete membersmembers •ThereThere isis nono uniqueunique relationrelation betweenbetween impactimpact strengthstrength anotheranother strengthsstrengths ofof concrete.concrete. •However,However, somesome researchersresearchers havehave foundfound thatthat impactimpact isis relatedrelated toto thethe compressivecompressive strength,strength, andand itit hashas beenbeen suggestedsuggested thatthat thethe impactimpact strengthstrength variesvaries fromfrom 0.500.50 toto 0.750.75 ofof thethe compressivecompressive cubecube strengthstrength
Concrete StrengthConcrete Strength FatigueFatigue StrengthStrength TheThe strengthstrength ofof concreteconcrete againstagainst cycliccyclic oror repeatedrepeated loadingloading isis calledcalled asas itsits fatiguefatigue strengthstrength
Factors affecting strength of concreteFactors affecting strength of concrete • Water/cement ratio and degree of compactionWater/cement ratio and degree of compaction • Ratio of cement to aggregateRatio of cement to aggregate Grading, surface texture, shape,Grading, surface texture, shape, aggregate particlesaggregate particles Maximum size of aggregate.Maximum size of aggregate. SSstrengthstrength andandstiffnessstiffness ofof
Water/cement ratio and degree ofWater/cement ratio and degree of compactioncompaction • Strength of concrete primarily depends upon theStrength of concrete primarily depends upon the strength of cement paste.strength of cement paste. • The strength of cement paste depends upon theThe strength of cement paste depends upon the dilution of paste or in other words,dilution of paste or in other words, the strength of pastethe strength of paste increases with cement content and decreases with air and waterincreases with cement content and decreases with air and water content.content. • In 1918; Abrams’ law states thatIn 1918; Abrams’ law states that “assuming full“assuming full compaction, and at a given age and normalcompaction, and at a given age and normal temperature, strength of concrete can be taken to betemperature, strength of concrete can be taken to be inversely proportional to the water/cement ratio”inversely proportional to the water/cement ratio”
Abrams’ lawAbrams’ law where:where: •A, BA, B •w/c is the mass ratio of water tow/c is the mass ratio of water to cementcement
Water/cement ratio and degree ofWater/cement ratio and degree of compactioncompaction Water/Cement Ratio:Water/Cement Ratio: Typically: 0.35 – 0.45Typically: 0.35 – 0.45 Smaller w/c ratio → stronger concreteSmaller w/c ratio → stronger concrete
Gel/Space RatioGel/Space Ratio • Since concrete is a brittle material, its porositySince concrete is a brittle material, its porosity primarily governs its strength.primarily governs its strength. The compressive strength isThe compressive strength is found to be severely decreasing with increase in the porosity.found to be severely decreasing with increase in the porosity. • The porosity of concrete which governsThe porosity of concrete which governs the strengththe strength of concrete is affected by the gel/space ratio in concrete.of concrete is affected by the gel/space ratio in concrete. • TheThe gel/space ratio is the ratio of the solid products ofgel/space ratio is the ratio of the solid products of hydration to the space availablehydration to the space available for these hydration products.for these hydration products. • A higher gel/space ratio reducesA higher gel/space ratio reduces the porosity andthe porosity and therefore increases the strength of concrete.therefore increases the strength of concrete.
Gel/Space RatioGel/Space Ratio TheThegel/spacegel/space ratio,ratio, whichwhich governs the porositygoverns the porosity of concrete affectingof concrete affecting its strength, is affected byits strength, is affected by the water/cement ratiothe water/cement ratio ofof concreteconcrete A higher water/cementA higher water/cement ratio decreases theratio decreases the gel/space ratiogel/space ratio increasingincreasing the porosity therebythe porosity thereby decreasing the strength ofdecreasing the strength of concrete.concrete.
Influence ofInfluence of AAggregate/ggregate/CCementement RRatioatio • The aggregate/cement ratio, is only a secondary factor in theThe aggregate/cement ratio, is only a secondary factor in the strength of concrete but it has been found thatstrength of concrete but it has been found that, for a constant, for a constant water/cement ratio, a leaner mix leads to a higher strength.water/cement ratio, a leaner mix leads to a higher strength. • Some water may be absorbed by the aggregate: a larger amountSome water may be absorbed by the aggregate: a larger amount of aggregate absorbs a greater quantity of water,of aggregate absorbs a greater quantity of water, the effectivethe effective water/cement ratio being thus reduced.water/cement ratio being thus reduced. • A higher aggregate content would lead to lower shrinkage and lowerA higher aggregate content would lead to lower shrinkage and lower bleeding, and therefore to less damagebleeding, and therefore to less damage to the bond between theeto the bond between thee aggregate and the cement pasteaggregate and the cement paste • As a result, in a leaner mix,As a result, in a leaner mix, the voids form a smaller fraction off thethe voids form a smaller fraction off the total volume of concrete, and it is these voids that havetotal volume of concrete, and it is these voids that have an adverse effect on strengthan adverse effect on strength
Influence ofInfluence of AAggregate/ggregate/CCementement RRatioatio
Effect of Maximum size of AggregateEffect of Maximum size of Aggregate • The larger the aggregate the lower is the total surfaceThe larger the aggregate the lower is the total surface area and, thereforearea and, therefore, the lower is the requirement of water, the lower is the requirement of water for the given workability.for the given workability. • The use of larger size aggregate did not contribute toThe use of larger size aggregate did not contribute to higher strength as expected fromhigher strength as expected from the theoreticalthe theoretical considerations due to the following reasons.considerations due to the following reasons. • The larger maximum size aggregate gives lower surfaceThe larger maximum size aggregate gives lower surface area for developmentsarea for developments of gel bonds which is responsibleof gel bonds which is responsible for the lower strength of the concrete.for the lower strength of the concrete. • Secondly bigger aggregate size causes a more heterogeneitySecondly bigger aggregate size causes a more heterogeneity in the concretein the concrete which will prevent the uniform distributionwhich will prevent the uniform distribution ofof load when stressed.load when stressed.
Effect of Maximum size of AggregateEffect of Maximum size of Aggregate • When large size aggregate is used, due to internalWhen large size aggregate is used, due to internal bleeding,bleeding, the transition zone will become muchthe transition zone will become much weaker due to the development of micro cracks whichweaker due to the development of micro cracks which result in lower compressive strength.result in lower compressive strength.
Effect of Maximum size of AggregateEffect of Maximum size of Aggregate
Age ofAge of CConcreteoncrete • With an increase in age, the degree of hydrationWith an increase in age, the degree of hydration generally increasesgenerally increases the gel/space ratio so that strengththe gel/space ratio so that strength increasesincreases • Increase in the strength of concreteIncrease in the strength of concrete (at same w/c ratio)(at same w/c ratio) with increase in early age (from 1 to 28 days) of concrete.with increase in early age (from 1 to 28 days) of concrete.
Age ofAge of CConcreteoncrete
Influence ofInfluence of PProperties ofroperties of CCoarseoarse AAggregateggregate • The relation between the flexural and compressive strengthsThe relation between the flexural and compressive strengths depends on the type of coarse aggregate because the propertiesdepends on the type of coarse aggregate because the properties of aggregate, especiallyof aggregate, especially its shape and surface texture, affect theits shape and surface texture, affect the ultimate strength in compression very much less than the strength inultimate strength in compression very much less than the strength in tension or the cracking load in compression.tension or the cracking load in compression. • In experimental concrete, entirely smooth coarse aggregate led to aIn experimental concrete, entirely smooth coarse aggregate led to a lower compressive strengthlower compressive strength, typically by 10 per cent, than when, typically by 10 per cent, than when roughened.roughened. • The influence of the type of coarse aggregate on the strength ofThe influence of the type of coarse aggregate on the strength of concrete varies in magnitudeconcrete varies in magnitude and depends on the water/cementand depends on the water/cement ratio of the mix.ratio of the mix.
Influence ofInfluence of PProperties ofroperties of CCoarseoarse AAggregateggregate For water/cement ratios below 0.4, the use ofFor water/cement ratios below 0.4, the use of crushed aggregate has resultedcrushed aggregate has resulted in strengths up to 38 perin strengths up to 38 per cent higher than when gravel is used.cent higher than when gravel is used. With anWith an influenceinfluence strengthstrength increase in the water/cement ratio to 0.5increase in the water/cement ratio to 0.5,, thethe of aggregate falls offof aggregate falls off, presumably because, presumably because the of the hydrated cement paste itselfthe of the hydrated cement paste itself becomesbecomes paramount and, at a water/cement ratio of 0.65paramount and, at a water/cement ratio of 0.65, no, no difference in the strengths of concretes made with crusheddifference in the strengths of concretes made with crushed rock and gravel has observed.rock and gravel has observed.
Influence ofInfluence of TTemperature onemperature on SStrengthtrength • TheThe riserise inin thethe curingcuring temperaturetemperature speedsspeeds upup thethe chemicalchemical reactionsreactions ofof hydrationhydration andand thusthus affectsaffects beneficiallybeneficially thethe earlyearly strengthstrength ofof concreteconcrete withoutwithout anyany ill-effectsill-effects onon thethe laterlater strength.strength. • RapidRapid initialinitial hydrationhydration appearsappears toto formform productsproducts ofof aa poorerpoorer physicalphysical structure,structure, probablyprobably moremore porous,porous, soso thatthat aa proportionproportion ofof thethe porespores willwill alwaysalways remainremain unfilled.unfilled. • TheThe gel//spacegel//space ratioratio rulerule thatthat thisthis willwill leadlead toto aa lowerlower strengthstrength comparedcompared withwith aa lessless porous,porous, thoughthough slowlyslowly hydrating,hydrating, cementcement pastepaste inin whichwhich aa highhigh gel//spacegel//space ratioratio willwill eventuallyeventually bebe reached.reached.
FatigueFatigue SStrength oftrength of CConcreteoncrete • Modulus ofModulus of EElasticity,lasticity, • CreepCreep • Shrinkage of concreteShrinkage of concrete
Stress-Strain Plot of ConcreteStress-Strain Plot of Concrete • At stress below 30% of ultimate strength, the transitionAt stress below 30% of ultimate strength, the transition zone cracks remain stable. The stress-strain plot remainszone cracks remain stable. The stress-strain plot remains linearlinear.. • At stress betweenAt stress between 30% and 50% of ultimate strength,30% and 50% of ultimate strength, the transition zone micro-cracks begin to increase in length,the transition zone micro-cracks begin to increase in length, width and numbers. The stress-strain plot becomes non-linear.width and numbers. The stress-strain plot becomes non-linear. • At 50 to 60% of the ultimate stress, cracks begin toAt 50 to 60% of the ultimate stress, cracks begin to form in the matrix.form in the matrix. With further increase to about 75% of theWith further increase to about 75% of the ultimate stress, the cracks in the transition become unstable,ultimate stress, the cracks in the transition become unstable, and crack propagation in the matrix will increase. The stress-and crack propagation in the matrix will increase. The stress- strain curve bends towards the horizontal.strain curve bends towards the horizontal.
Stress-Strain Plot of ConcreteStress-Strain Plot of Concrete • At 75 to 80% of the ultimate stress, the stress reachesAt 75 to 80% of the ultimate stress, the stress reaches a critical stress level for spontaneous crack growtha critical stress level for spontaneous crack growth under a sustained stress.under a sustained stress. Cracks propagate rapidly in bothCracks propagate rapidly in both the matrix and the transition zone.the matrix and the transition zone. Failure occurs whenFailure occurs when the cracks join together and become continuous.the cracks join together and become continuous. Concrete isConcrete is not a trulynot a truly elastic materialelastic material, as evident, as evident from thefrom the nonlinear stress-nonlinear stress- strain curvestrain curve for concrete,for concrete, shown in the figshown in the fig
Stress-Strain Plot of ConcreteStress-Strain Plot of Concrete • TheThe “initial tangent“initial tangent modulus” ismodulus” is givengiven byby thethe slopeslope ofof aa lineline drawndrawn tangenttangent toto thethe stress-strainstress-strain curvecurve atat thethe originorigin • TheThe “tangent modulus” is“tangent modulus” is givengiven byby thethe slopeslope ofof aa lineline drawn tangentdrawn tangent toto thethe stress-strainstress-strain curvecurve atat anyany pointpoint onon thethe curvecurve • TheThe “secant modulus” is“secant modulus” is givengiven byby thethe slopeslope ofof aa lineline drawndrawn fromfrom thethe originorigin toto aa pointpoint onon thethe curvecurve correspondingcorresponding toto aa 40%40% stressstress ofof thethe failurefailure stressstress • TheThe “secant modulus” is“secant modulus” is givengiven byby thethe slopeslope ofof aa lineline drawndrawn fromfrom thethe originorigin toto aa pointpoint onon thethe curvecurve correspondingcorresponding toto aa 40%40% stressstress ofof thethe failurefailure stressstress
Stress-Strain Plot of ConcreteStress-Strain Plot of Concrete
Determination of modulus of elasticity ofDetermination of modulus of elasticity of ConcreteConcrete • TestingTesting ofof cubecube oror cylindercylinder inin uni-axialuni-axial compressioncompression test.test. • MeasureMeasure loadload andand thethe correspondingcorresponding deformationdeformation asas thethe loadload isis increased.increased. DrawDraw thethe stressstress strainstrain curve.curve. • StrainStrain =Dial=Dial gaugegauge reading/gaugereading/gauge lengthlength == dl/Ldl/L • StressStress == Load/CrossLoad/Cross sectionalsectional area=area= P/AP/A • UseUse CompressometerCompressometer andand ExtensometerExtensometer toto measuremeasure deformations.deformations. DrawDraw stressstress strainstrain diagramdiagram andand determinedetermine thethe requiredrequired modulusmodulus.. • Deflection:Deflection: EE cancan bebe determineddetermined fromfrom testingtesting ofof beambeam also.also.
Determination ofDetermination of MModulus ofodulus of EElasticitylasticity
Determination of modulus of elasticityDetermination of modulus of elasticity • The test uses a 150 X 300 mm cylindrical specimen, whichThe test uses a 150 X 300 mm cylindrical specimen, which is loaded in compression.is loaded in compression. A compress meter is used toA compress meter is used to measure the longitudinal strains, and an extensometer is usedmeasure the longitudinal strains, and an extensometer is used to measure the transverse strains on the specimen.to measure the transverse strains on the specimen. • The chord modulus (E) is calculated as:The chord modulus (E) is calculated as:  wherewhere SS22 = stress corresponding to 40% of ultimate strength= stress corresponding to 40% of ultimate strength  SS11 = stress corresponding to a strain of 50 X 10= stress corresponding to a strain of 50 X 10-6-6  ΕΕ22 = longitudinal strain produced by stress S= longitudinal strain produced by stress S22
Poisson’s ratio (Static Method)Poisson’s ratio (Static Method) • When a material is compressed in one direction, itWhen a material is compressed in one direction, it usually tends to expand in the other two directionsusually tends to expand in the other two directions perpendicular to the direction of compression. Thisperpendicular to the direction of compression. This phenomenon is called the Poisson effect.phenomenon is called the Poisson effect. • The Poisson ratio is the ratio of the fraction (or percent)The Poisson ratio is the ratio of the fraction (or percent) of expansion divided by the fraction (or percent) ofof expansion divided by the fraction (or percent) of compression, for small values of these changes. μ = 0.15 - 0.20compression, for small values of these changes. μ = 0.15 - 0.20 – Actual value to be found from strain measurements on– Actual value to be found from strain measurements on concrete cylinder using extensometer.concrete cylinder using extensometer. where εwhere εt2t2,ε,εt1t1= transverse strains produced by S= transverse strains produced by S22& S& S11,, respectivelyrespectively
Relation between Modulus of Elasticity andRelation between Modulus of Elasticity and StrengthStrength • Modulus of elasticity of concrete increases approximatelyModulus of elasticity of concrete increases approximately with the square root of the strength.with the square root of the strength. The IS 456 of 2000The IS 456 of 2000 gives the Modulus of elasticity asgives the Modulus of elasticity as
Factors Affecting Modulus of Elasticity ofFactors Affecting Modulus of Elasticity of ConcreteConcrete • Effects of moisture conditionEffects of moisture condition • Specimens tested in dry condition show about 15%Specimens tested in dry condition show about 15% decrease in elastic modulus as compared to the wetdecrease in elastic modulus as compared to the wet specimensspecimens. This is explained by the fact that drying. This is explained by the fact that drying produces more micro-cracks in the transition zone, whichproduces more micro-cracks in the transition zone, which affects the stress-strain behavior of the concrete.affects the stress-strain behavior of the concrete. • This is opposite to its effects on compressive strength.This is opposite to its effects on compressive strength. The compressive strength is increased by about 15%The compressive strength is increased by about 15% when tested dry as compared with the wet specimenswhen tested dry as compared with the wet specimens
Factors Affecting Modulus of Elasticity ofFactors Affecting Modulus of Elasticity of ConcreteConcrete • Effects ofEffects of Aggregate propertiesAggregate properties • Porosity of aggregate has the most effect on thePorosity of aggregate has the most effect on the elastic modulus of concrete.elastic modulus of concrete. An aggregates with a lowAn aggregates with a low porosity has a high modulus of elasticity.porosity has a high modulus of elasticity. • The elastic modulus of concrete is affected by theThe elastic modulus of concrete is affected by the volume fraction of the aggregatevolume fraction of the aggregate as well as the elasticas well as the elastic modulus of the aggregate.modulus of the aggregate.
Factors Affecting Modulus of Elasticity ofFactors Affecting Modulus of Elasticity of ConcreteConcrete • Effects of cement matrixEffects of cement matrix • TheThe lowerlower thethe porosityporosity ofof thethe cementcement paste, thepaste, the higherhigher the elastic modulus of the cement paste.the elastic modulus of the cement paste. • The higher the elastic modulus of the cement paste, the higher theThe higher the elastic modulus of the cement paste, the higher the elastic modulus of the concrete.elastic modulus of the concrete. • Effects of transition zoneEffects of transition zone • The void spaces and and the micro cracksThe void spaces and and the micro cracks in the transition play a majorin the transition play a major role in affecting the stress-strain behavior of concrete.role in affecting the stress-strain behavior of concrete. • The transition zone characteristics affectThe transition zone characteristics affect the elastic modulus more thanthe elastic modulus more than it affects the compressive strength of concrete.it affects the compressive strength of concrete.
CreepCreep The ability of concrete to creep imparts a degree of ductilityThe ability of concrete to creep imparts a degree of ductility to concrete that enables it to tolerateto concrete that enables it to tolerate the normal range ofthe normal range of structural deformations encountered in practice.structural deformations encountered in practice. Creep provides a structure with the ability to redistributeCreep provides a structure with the ability to redistribute excessive stresses.excessive stresses. Without the ability to creep, concrete would simply be tooWithout the ability to creep, concrete would simply be too brittle for use in the majority of structuresbrittle for use in the majority of structures. However, creep. However, creep also may have detrimental effectsalso may have detrimental effects such as increased deflectionsuch as increased deflection resulting in cracking, loss of prestress, and buckling ofresulting in cracking, loss of prestress, and buckling of slender columns.slender columns. It isIt is therefore important that the designer takes the necessarytherefore important that the designer takes the necessary steps to allow for creep in the design of concrete structures.steps to allow for creep in the design of concrete structures.
CreepCreep
DefinitionDefinition Creep is defined as the increase in strainCreep is defined as the increase in strain (deformation) under a sustained stress (load).(deformation) under a sustained stress (load). WhenWhen loaded, concrete experiences an instantaneous elasticloaded, concrete experiences an instantaneous elastic strain, which is recoverable.strain, which is recoverable. In addition, an inelasticIn addition, an inelastic creep strain takes place that is only partiallycreep strain takes place that is only partially recoverablerecoverable
CreepCreep Test methodsTest methods Creep is usually determined by measuring theCreep is usually determined by measuring the change in strainchange in strain with time of a specimen subjected to awith time of a specimen subjected to a constant stress and stored under appropriate conditions.constant stress and stored under appropriate conditions.
CreepCreep
Factors Influencing CreepFactors Influencing Creep Factors Influencing creepFactors Influencing creep Creep of concrete is load induced, and is influenced by factorsCreep of concrete is load induced, and is influenced by factors associated with the applicationassociated with the application of load and the ability of theof load and the ability of the concrete to withstand the load.concrete to withstand the load. The potential of the concrete to creep is determined by mixThe potential of the concrete to creep is determined by mix materials and proportions of the concrete.materials and proportions of the concrete. The cement pasteThe cement paste creeps, and the role of the aggregate is to:creeps, and the role of the aggregate is to:
Stress Strain RatioStress Strain Ratio Creep is linearly proportional to the stress: strengthCreep is linearly proportional to the stress: strength
Cement Paste ContentCement Paste Content Cement paste content Hardened ConcreteCement paste content Hardened Concrete A 1% increase in cement paste by volume will result inA 1% increase in cement paste by volume will result in approximately a 5% increase in creep.approximately a 5% increase in creep. This is applicable forThis is applicable for concretes with a cement paste volume of 28% to 40%.concretes with a cement paste volume of 28% to 40%. The cement paste volume is influenced by the aggregateThe cement paste volume is influenced by the aggregate content of the mix:content of the mix: the greater the aggregate content, the lowerthe greater the aggregate content, the lower the cement paste contentthe cement paste content
Cement TypeCement Type Cement TypeCement Type The type of cement influences the strengthThe type of cement influences the strength development of concrete.development of concrete. A high stress : strain ratioA high stress : strain ratio could potentially result if the concrete is loaded at ancould potentially result if the concrete is loaded at an early age and the cement has a slow rate of strengthearly age and the cement has a slow rate of strength development.development.
DurabilityDurability The durability of a structure may be definedThe durability of a structure may be defined as the time for which the structure can fulfillas the time for which the structure can fulfill the function for which it was designed and constructed.the function for which it was designed and constructed.
DurabilityDurability • Defined as its resistance to deteriorationDefined as its resistance to deterioration processes that may occur as a result of interactionprocesses that may occur as a result of interaction with its environment (external)with its environment (external) or between theor between the constituent materials or their reaction withconstituent materials or their reaction with contaminants present (internal).contaminants present (internal). • Ability to with stand the damaging effectsAbility to with stand the damaging effects of theof the environment over a long period of time.environment over a long period of time. • The absence of durability maybe caused either byThe absence of durability maybe caused either by the environment to whichthe environment to which the concrete is exposedthe concrete is exposed i.e. external or internal causes.i.e. external or internal causes.
Factors Influencing DurabilityFactors Influencing Durability The following factors are of equal importance inThe following factors are of equal importance in influencing the durability of a concrete structure:influencing the durability of a concrete structure: •• The achievement of structural durability requiresThe achievement of structural durability requires rigorous attention to detail by the designer,rigorous attention to detail by the designer, contractor, supervisory engineer and materialscontractor, supervisory engineer and materials engineer.engineer. Even if the highest possible grades of concreteEven if the highest possible grades of concrete are supplied, the structure will only be durable if goodare supplied, the structure will only be durable if good practice prevails in all phases of the building project.practice prevails in all phases of the building project.
Factors Influencing DurabilityFactors Influencing Durability • To accurately predict cracking, concrete properties such asTo accurately predict cracking, concrete properties such as shrinkageshrinkage creep are consideredcreep are considered • Member Shapes complicating concrete compaction andMember Shapes complicating concrete compaction and thin concretethin concrete section are avoidedsection are avoided • Ponding of water is prevented,Ponding of water is prevented, Rain and sea water drainedRain and sea water drained away from structure.away from structure. • No ingress of water canNo ingress of water can occur into joints.occur into joints. • Correct curing time and methodsCorrect curing time and methods are specifiedare specified
DurabilityDurability
Durability is Achieved ByDurability is Achieved By • Well Compacted ConcreteWell Compacted Concrete • Good workmanship reduced porosityGood workmanship reduced porosity • Use of aluminosulphate resisting cement ,Use of aluminosulphate resisting cement , Portland blast furnace slag, or PortlandPortland blast furnace slag, or Portland pozzolana cement.pozzolana cement. • Sufficient cover over reinforcementSufficient cover over reinforcement • Use of low water cement RatioUse of low water cement Ratio
ShrinkageShrinkage Shrinkage cracks in concreteShrinkage cracks in concrete occur due to change inoccur due to change in moisture of concrete. Most of the building materialsmoisture of concrete. Most of the building materials like concrete, mortar, burnt clay bricks are porouslike concrete, mortar, burnt clay bricks are porous inin their structure in the form of inter-molecular space.their structure in the form of inter-molecular space. They expand when they absorb the moisture andThey expand when they absorb the moisture and shrink when they dry. This is the main cause theshrink when they dry. This is the main cause the concrete shrinks on drying. Shrinkage of concrete isconcrete shrinks on drying. Shrinkage of concrete is an irreversible process.an irreversible process.
ShrinkageShrinkage
ShrinkageShrinkage Concrete shrinkageConcrete shrinkage can become problematic whencan become problematic when doing any type of construction, but especially whendoing any type of construction, but especially when dealing with floorsdealing with floors. Concrete shrinkage is the. Concrete shrinkage is the contracting of the concrete due to the watercontracting of the concrete due to the water evaporatingevaporating from the mixture. This evaporation will cause thefrom the mixture. This evaporation will cause the concrete to weaken. This can lead to cracks, internalconcrete to weaken. This can lead to cracks, internal warping and external deflectionwarping and external deflection
ShrinkageShrinkage
ShrinkageShrinkage Types of Concrete ShrinkageTypes of Concrete Shrinkage There are numerousThere are numerous types of concrete shrinkagetypes of concrete shrinkage including plastic shrinkage, drying shrinkage,including plastic shrinkage, drying shrinkage, autogenous shrinkage, and carbonation shrinkage.autogenous shrinkage, and carbonation shrinkage. Plastic shrinkagePlastic shrinkage happens soon after the concrete ishappens soon after the concrete is poured in the forms. The water evaporates andpoured in the forms. The water evaporates and results in a reduction of volumeresults in a reduction of volume, this causes the, this causes the concrete on the surface to collapse. It can be reduced byconcrete on the surface to collapse. It can be reduced by covering the surfacecovering the surface with polyethylene sheetingwith polyethylene sheeting immediately after it is poured.immediately after it is poured.
Plastic ShrinkagePlastic Shrinkage
ShrinkageShrinkage Drying shrinkageDrying shrinkage is the ever lasting process for concrete withinis the ever lasting process for concrete within drying conditions.drying conditions. The loss of water within the gel pores of theThe loss of water within the gel pores of the concrete is what causes the concrete to shrink.concrete is what causes the concrete to shrink. TheThe finer the gelfiner the gel within the pores, the more shrinkage there is.within the pores, the more shrinkage there is. Autogenous shrinkageAutogenous shrinkage is most prevalent within the concrete inis most prevalent within the concrete in the interior of a dam.the interior of a dam. When the temperature is constantWhen the temperature is constant shrinkage may occur, especially when there is no moistureshrinkage may occur, especially when there is no moisture movementmovement Carbonation shrinkageCarbonation shrinkage is where carbon dioxide penetratesis where carbon dioxide penetrates beyond the surface of the concrete.beyond the surface of the concrete. This also depends on theThis also depends on the moisture content and the humidity levels. Carbonationmoisture content and the humidity levels. Carbonation shrinkage is caused by the disbanding of calcium hydroxideshrinkage is caused by the disbanding of calcium hydroxide crystals and the evidence of calcium carbonatecrystals and the evidence of calcium carbonate
ShrinkageShrinkage
ShrinkageShrinkage Factors Affecting ShrinkageFactors Affecting Shrinkage There are soThere are so many factorsmany factors that affect the shrinkage of concrete.that affect the shrinkage of concrete. The most important factor is theThe most important factor is the drying conditiondrying condition or theor the humidity in the atmosphere.humidity in the atmosphere. No shrinkage will occur if theNo shrinkage will occur if the concrete is placed in one hundred percent relative humidity.concrete is placed in one hundred percent relative humidity. The shrinkage rate will decrease rapidly with time. It hasThe shrinkage rate will decrease rapidly with time. It has been documented that fourteen to thirty-four percent of thebeen documented that fourteen to thirty-four percent of the twenty year shrinkage will occur within two weeks of it beingtwenty year shrinkage will occur within two weeks of it being poured.poured. Within one year of the concrete being poured, shrinkageWithin one year of the concrete being poured, shrinkage will be about sixty-six to eighty-five percent of the twenty yearwill be about sixty-six to eighty-five percent of the twenty year shrinkageshrinkage
ShrinkageShrinkage The water toThe water to cement ratiocement ratio will influence thewill influence the amount of shrinkage that occurs.amount of shrinkage that occurs. TheThe concrete’s richnessconcrete’s richness also affects thealso affects the shrinkage. The process of swelling and thenshrinkage. The process of swelling and then drying affects the concrete’s integrity and thedrying affects the concrete’s integrity and the shrinkage.shrinkage.
ShrinkageShrinkage Factors affecting shrinkage are:Factors affecting shrinkage are: 1. Aggregate -Concrete with higher aggregate1. Aggregate -Concrete with higher aggregate content exhibits smaller shrinkage.content exhibits smaller shrinkage. Concrete withConcrete with aggregates of higher modulus of elasticity or ofaggregates of higher modulus of elasticity or of rougher surfaces is more resistant to the shrinkagerougher surfaces is more resistant to the shrinkage process.process. 2. Water-cement ratio - The higher the W/C ratio2. Water-cement ratio - The higher the W/C ratio is, the higher the shrinkage.is, the higher the shrinkage. As W/C increases, pasteAs W/C increases, paste strength and stiffness decrease; and as water contentstrength and stiffness decrease; and as water content increases, shrinkage potential increasesincreases, shrinkage potential increases..
ShrinkageShrinkage 3. Member size - Shrinkage decrease with an3. Member size - Shrinkage decrease with an increase in the volume of the concrete memberincrease in the volume of the concrete member However,However, the duration of shrinkage is longer forthe duration of shrinkage is longer for larger members since more time is needed forlarger members since more time is needed for shrinkage effects to reach the interior regionsshrinkage effects to reach the interior regions.. 4. Medium ambient conditions - The rate of4. Medium ambient conditions - The rate of shrinkage isshrinkage is lower at higher values of relativelower at higher values of relative humidity. Shrinkage becomes stabilized at lowhumidity. Shrinkage becomes stabilized at low temperaturestemperatures..
ShrinkageShrinkage 5. Admixtures - effect varies from admixture to5. Admixtures - effect varies from admixture to admixture.admixture. Any material which substantially changesAny material which substantially changes the pore structure of the paste will affect thethe pore structure of the paste will affect the shrinkage characteristics of the concreteshrinkage characteristics of the concrete. In general,. In general, as pore refinement is enhanced, shrinkage is increased.as pore refinement is enhanced, shrinkage is increased.
PermeabilityPermeability • Concrete has a tendency to be porous due to theConcrete has a tendency to be porous due to the presence of voids formed during or after placingpresence of voids formed during or after placing.. • Penetration by substance may adversely affectPenetration by substance may adversely affect durabilitydurability e.g. Ca(OH)e.g. Ca(OH)22 leaches out.leaches out. • Ingress of air and moisture resultingIngress of air and moisture resulting in corrosion.in corrosion. • Important with regards to water tightnessImportant with regards to water tightness ofof • liquid retaining structure.liquid retaining structure.
PermeabilityPermeability
PermeabilityPermeability To produce concrete of low permeability, fullTo produce concrete of low permeability, full compaction & proper curingcompaction & proper curing is essential.is essential. Low permeability is important in increasingLow permeability is important in increasing resistantresistant to frost action and chemical attack andto frost action and chemical attack and in protecting embedded steel against corrosion.in protecting embedded steel against corrosion.
PermeabilityPermeability
PermeabilityPermeability The permeability of cement paste varies with the ageThe permeability of cement paste varies with the age of concrete or with progress of hydrationof concrete or with progress of hydration.. •With age, the permeability decreases because gelWith age, the permeability decreases because gel gradually fillgradually fill the original water filled space.the original water filled space. •For the same w/c ratio, the permeability of pasteFor the same w/c ratio, the permeability of paste with coarser cement particleswith coarser cement particles is higher than those withis higher than those with finer cement.finer cement. •In general, the higher the strength of cement paste,In general, the higher the strength of cement paste, the lowerthe lower will the permeability.will the permeability.
PermeabilityPermeability
PermeabilityPermeability Factors influencing permeability are:Factors influencing permeability are: i. W/C Ratioi. W/C Ratio ii. Curingii. Curing iii. Method of compactioniii. Method of compaction iv. Workabilityiv. Workability v. Soundness & porosity of the aggregatev. Soundness & porosity of the aggregate vi. Age (permeability decrease with age)vi. Age (permeability decrease with age) vii. Grading of aggregatevii. Grading of aggregate viii.Type of structureviii.Type of structure
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Hardened Concrete

  • 1.
  • 2.
    Strength of ConcreteStrengthof Concrete • StrengthStrength ofof concreteconcrete isis commonlycommonly consideredconsidered itsits mostmost valuablevaluable property,property, althoughalthough inin manymany practicalpractical cases,cases, otherother characteristics,characteristics, suchsuch asas durabilitydurability andand permeabilitypermeability maymay inin factfact bebe moremore important.important. • StrengthStrength usuallyusually givesgives anan overalloverall picturepicture ofof thethe qualityquality ofof concreteconcrete becausebecause strengthstrength isis directlydirectly relatedrelated toto thethe structurestructure ofof thethe hydratedhydrated cementcement paste.paste. • StrengthStrength ofof concreteconcrete couldcould bebe defineddefined asas thethe ultimateultimate loadload thatthat causescauses failurefailure (or(or isis itsits resistanceresistance toto rupture)rupture) andand itsits unitsunits areare forceforce unitsunits divideddivided byby areaarea (N/mm(N/mm22).).
  • 3.
  • 4.
    Strength of ConcreteStrengthof Concrete • CharacteristicCharacteristic strengthstrength -- Compressive, TensileCompressive, Tensile andand FlexureFlexure strengthstrength • Modulus of ElasticityModulus of Elasticity • Creep and shrinkage of concreteCreep and shrinkage of concrete THE THREE S-WORDSTHE THREE S-WORDS Stress:Stress: a weight or load applieda weight or load applied to the concrete (in N)to the concrete (in N) Strength:Strength: the concrete’s abilitythe concrete’s ability toto carrycarry thethe weightweight oror loadload (in(in NN perper squaresquare mm)mm) Strain:Strain: howhow muchmuch thethe concreteconcrete stretchesstretches oror compressescompresses (deforms)(deforms) whenwhen carryingcarrying aa loadload (in(in inchesinches perper mm)mm)
  • 5.
    Fracture andFracture andFFailureailure • ConcreteConcrete specimensspecimens subjectedsubjected toto anyany statestate ofof stressstress cancan anyanysupportsupport loadsloads ofof upup toto 40–60%40–60% ofof ultimateultimate withoutwithout apparentapparent signssigns ofof distress.distress. •BelowBelow thisthis level,level, anyany sustainedsustained loadload resultsresults inin creepcreep strainstrain whichwhich isis proportionaproportionall toto thethe appliedapplied stressstress andand cancan bebe defineddefined inin termsterms ofof specificspecific creepcreep (i.e.(i.e. creepcreep strainstrain perper unitunit stress)stress) •AsAs thethe loadload isis increasedincreased aboveabove thisthis level,level, softsoft butbut distinctdistinct noisesnoises ofof internalinternal disruptiondisruption cancan bebe heardheard until,until, atat aboutabout 70– 90%70– 90% ofof ultimate,ultimate, smallsmall fissuresfissures oror crackscracks appearappear onon thethe surface.surface. •AtAt ultimateultimate loadload andand beyond;beyond; thethe specimensspecimens areare increasinglyincreasingly disrupteddisrupted andand eventuallyeventually fracturedfractured intointo aa largelarge numbernumber ofof separateseparate pieces.pieces.
  • 6.
  • 7.
    The stages ofcracking (fracture) in concreteThe stages of cracking (fracture) in concrete
  • 8.
    Types of ConcreteStrengthTypes of Concrete Strength • CompressiveCompressive SStrengthtrength • TensileTensile SStrengthtrength • ShearShear SStrengthtrength • BondBond SStrengthtrength • ImpactImpact SStrengthtrength • FatigueFatigue SStrengthtrength
  • 9.
    Compressive StrengthCompressive Strength •The compressive strength of concrete is defined as theThe compressive strength of concrete is defined as the strength of 28strength of 28 daysdays oldold specimensspecimens testedtested underunder monotonicmonotonic uniaxialuniaxial compressivecompressive load.load. • TestingTesting ofof cylindricalcylindrical samplessamples withwith 1515 cmcm diameterdiameter andand 3030 cmcm heightheight isis standard.standard. • CubeCube specimensspecimens ofof1515 cmcm ×× 15cm15cm ×× 1515 cmcm areare alsoalso beingbeing used.used. • Normally,Normally, thethe compressivecompressive strengthstrength ofof concreteconcrete isis determineddetermined byby testing,testing, andand thethe tensiletensile strengthstrength andand modulusmodulus ofof elasticityelasticity areare expressedexpressed inin termsterms ofof thethe compressivecompressive strength.strength.
  • 10.
  • 11.
    Compressive StrengthCompressive Strength •ThereThere areare threethree failurefailure modesmodes forfor cylinderscylinders.. • UnderUnder axialaxial compressioncompression concreteconcrete failsfails inin shearshear.. • TheThe separationseparation ofof thethe specimenspecimen intointo columnarcolumnar piecespieces byby whatwhat isis knownknown asas splittingsplitting oror columnarcolumnar fracture.fracture. • CombinationCombination ofof shearshear andand splittingsplitting failure.failure.
  • 12.
    Compressive StrengthCompressive Strength •The compressive strength of concrete is defined asThe compressive strength of concrete is defined as the strength of 28the strength of 28 daysdays oldold specimensspecimens testedtested underunder monotonicmonotonic uniaxialuniaxial compressivecompressive load.load. • TestingTesting ofof cylindricalcylindrical samplessamples withwith 1515 cmcm diameterdiameter andand 3030 cmcm heightheight isis standard.standard. • CubeCube specimensspecimens ofof1515 cmcm ×× 1515 cmcm ×× 1515 cmcm areare alsoalso beingbeing usedused • Normally,Normally, thethe compressivecompressive strengthstrength ofof concreteconcrete isis determineddetermined byby testingtesting,, andand thethe tensiletensile strengthstrength andand modulusmodulus ofof elasticityelasticity areare expressedexpressed inin termsterms ofof thethe compressivecompressive strength.strength.
  • 13.
  • 14.
    Tensile Strength ofConcreteTensile Strength of Concrete • TheThe tensiletensile strengthstrength ofof concreteconcrete isis muchmuch lowerlower thanthan thethe compressivecompressive strength,strength, largelylargely becausebecause ofof thethe easeease withwith whichwhich crackscracks cancan propagatepropagate underunder tensiletensile loadsloads • TheThe tensiletensile strengthstrength ofof concreteconcrete isis measuredmeasured inin threethree ways:ways: directdirect tension,tension, splittingsplitting tension,tension, andand flexuralflexural tensiontension
  • 15.
    Tensile Strength ofConcreteTensile Strength of Concrete • ItIt isis difficultdifficult toto testtest concreteconcrete inin directdirect (uniaxial)(uniaxial) tensiontension becausebecause ofof thethe problemproblem ofof grippinggripping thethe specimenspecimen satisfactorilysatisfactorily andand becausebecause therethere mustmust bebe nono eccentricityeccentricity ofof thethe appliedapplied load.load. Therefore,Therefore, directdirect tensiletensile testtest isis notnot standardizedstandardized andand rarelyrarely usedused • ModulusModulus ofof rupturerupture testtest andand splittingsplitting testtest areare commonlycommonly usedused toto determinedetermine thethe tensiletensile strengthstrength ofof concreteconcrete
  • 16.
    Tensile Strength ofConcreteTensile Strength of Concrete • Direct-Tension TestDirect-Tension Test:: • The most direct way of measuring the tensileThe most direct way of measuring the tensile strength.strength. • Not a practical test.Not a practical test.
  • 17.
    Tensile Strength ofConcreteTensile Strength of Concrete • Split-Cylinder Test:Split-Cylinder Test:
  • 18.
    Tensile Strength ofConcreteTensile Strength of Concrete Split Cylinder TestSplit Cylinder Test
  • 19.
    Tensile Strength ofConcreteTensile Strength of Concrete Modulus of Rupture Test:Modulus of Rupture Test: Four-point bending (two-point loading)Four-point bending (two-point loading) Three-point bending (third point loading)Three-point bending (third point loading)
  • 20.
    Relationship Between CompressiveandRelationship Between Compressive and Tensile Strength of ConcreteTensile Strength of Concrete • TensileTensile strengthstrength ofof concreteconcrete isis proportionalproportional toto thethe square-square- rootroot ofof thethe compressivecompressive strength.strength. • TheThe proportionalityproportionality constantconstant dependsdepends onon manymany factors,factors, suchsuch asas thethe concreteconcrete strengthstrength andand thethe testtest methodmethod usedused toto determinedetermine thethe tensiletensile strength.strength. • TheThe followingfollowing relationsrelations cancan bebe usedused asas aa rulerule ofof thumb:thumb:
  • 21.
    Concrete StrengthConcrete Strength ShearShearStrengthStrength ShearShear strengthstrength ofof concreteconcrete isis takentaken approximatelyapproximately equalequal toto 2020 %% itsits compressivecompressive strengthstrength BondBond StrengthStrength •TheThe strengthstrength ofof bondbond betweenbetween steelsteel reinforcementreinforcement andand concreteconcrete isis calledcalled asas bondbond strengthstrength ofof concreteconcrete •BondBond strengthstrength developsdevelops primarilyprimarily duedue toto frictionfriction andand adhesionadhesion betweenbetween steelsteel reinforcementreinforcement andand concreteconcrete •InIn general,general, bondbond strengthstrength isis approximatelyapproximately proportionalproportional toto compressivecompressive strengthstrength ofof concreteconcrete upup toto aboutabout 2020 MPaMPa
  • 22.
  • 23.
  • 24.
    Concrete StrengthConcrete Strength ImpactImpactStrengthStrength ImpactImpact strengthstrength ofof concreteconcrete isis ofof importanceimportance inin drivingdriving concreteconcrete piles,piles, inin foundationsfoundations forfor machinesmachines exertingexerting impulsiveimpulsive loading,loading, andand alsoalso whenwhen accidentalaccidental impactimpact isis possible,possible, e.g.e.g. whenwhen handlinghandling precastprecast concreteconcrete membersmembers •ThereThere isis nono uniqueunique relationrelation betweenbetween impactimpact strengthstrength anotheranother strengthsstrengths ofof concrete.concrete. •However,However, somesome researchersresearchers havehave foundfound thatthat impactimpact isis relatedrelated toto thethe compressivecompressive strength,strength, andand itit hashas beenbeen suggestedsuggested thatthat thethe impactimpact strengthstrength variesvaries fromfrom 0.500.50 toto 0.750.75 ofof thethe compressivecompressive cubecube strengthstrength
  • 25.
    Concrete StrengthConcrete Strength FatigueFatigueStrengthStrength TheThe strengthstrength ofof concreteconcrete againstagainst cycliccyclic oror repeatedrepeated loadingloading isis calledcalled asas itsits fatiguefatigue strengthstrength
  • 26.
    Factors affecting strengthof concreteFactors affecting strength of concrete • Water/cement ratio and degree of compactionWater/cement ratio and degree of compaction • Ratio of cement to aggregateRatio of cement to aggregate Grading, surface texture, shape,Grading, surface texture, shape, aggregate particlesaggregate particles Maximum size of aggregate.Maximum size of aggregate. SSstrengthstrength andandstiffnessstiffness ofof
  • 27.
    Water/cement ratio anddegree ofWater/cement ratio and degree of compactioncompaction • Strength of concrete primarily depends upon theStrength of concrete primarily depends upon the strength of cement paste.strength of cement paste. • The strength of cement paste depends upon theThe strength of cement paste depends upon the dilution of paste or in other words,dilution of paste or in other words, the strength of pastethe strength of paste increases with cement content and decreases with air and waterincreases with cement content and decreases with air and water content.content. • In 1918; Abrams’ law states thatIn 1918; Abrams’ law states that “assuming full“assuming full compaction, and at a given age and normalcompaction, and at a given age and normal temperature, strength of concrete can be taken to betemperature, strength of concrete can be taken to be inversely proportional to the water/cement ratio”inversely proportional to the water/cement ratio”
  • 28.
    Abrams’ lawAbrams’ law where:where: •A,BA, B •w/c is the mass ratio of water tow/c is the mass ratio of water to cementcement
  • 29.
    Water/cement ratio anddegree ofWater/cement ratio and degree of compactioncompaction Water/Cement Ratio:Water/Cement Ratio: Typically: 0.35 – 0.45Typically: 0.35 – 0.45 Smaller w/c ratio → stronger concreteSmaller w/c ratio → stronger concrete
  • 30.
    Gel/Space RatioGel/Space Ratio •Since concrete is a brittle material, its porositySince concrete is a brittle material, its porosity primarily governs its strength.primarily governs its strength. The compressive strength isThe compressive strength is found to be severely decreasing with increase in the porosity.found to be severely decreasing with increase in the porosity. • The porosity of concrete which governsThe porosity of concrete which governs the strengththe strength of concrete is affected by the gel/space ratio in concrete.of concrete is affected by the gel/space ratio in concrete. • TheThe gel/space ratio is the ratio of the solid products ofgel/space ratio is the ratio of the solid products of hydration to the space availablehydration to the space available for these hydration products.for these hydration products. • A higher gel/space ratio reducesA higher gel/space ratio reduces the porosity andthe porosity and therefore increases the strength of concrete.therefore increases the strength of concrete.
  • 31.
    Gel/Space RatioGel/Space Ratio TheThegel/spacegel/spaceratio,ratio, whichwhich governs the porositygoverns the porosity of concrete affectingof concrete affecting its strength, is affected byits strength, is affected by the water/cement ratiothe water/cement ratio ofof concreteconcrete A higher water/cementA higher water/cement ratio decreases theratio decreases the gel/space ratiogel/space ratio increasingincreasing the porosity therebythe porosity thereby decreasing the strength ofdecreasing the strength of concrete.concrete.
  • 32.
    Influence ofInfluence ofAAggregate/ggregate/CCementement RRatioatio • The aggregate/cement ratio, is only a secondary factor in theThe aggregate/cement ratio, is only a secondary factor in the strength of concrete but it has been found thatstrength of concrete but it has been found that, for a constant, for a constant water/cement ratio, a leaner mix leads to a higher strength.water/cement ratio, a leaner mix leads to a higher strength. • Some water may be absorbed by the aggregate: a larger amountSome water may be absorbed by the aggregate: a larger amount of aggregate absorbs a greater quantity of water,of aggregate absorbs a greater quantity of water, the effectivethe effective water/cement ratio being thus reduced.water/cement ratio being thus reduced. • A higher aggregate content would lead to lower shrinkage and lowerA higher aggregate content would lead to lower shrinkage and lower bleeding, and therefore to less damagebleeding, and therefore to less damage to the bond between theeto the bond between thee aggregate and the cement pasteaggregate and the cement paste • As a result, in a leaner mix,As a result, in a leaner mix, the voids form a smaller fraction off thethe voids form a smaller fraction off the total volume of concrete, and it is these voids that havetotal volume of concrete, and it is these voids that have an adverse effect on strengthan adverse effect on strength
  • 33.
    Influence ofInfluence ofAAggregate/ggregate/CCementement RRatioatio
  • 34.
    Effect of Maximumsize of AggregateEffect of Maximum size of Aggregate • The larger the aggregate the lower is the total surfaceThe larger the aggregate the lower is the total surface area and, thereforearea and, therefore, the lower is the requirement of water, the lower is the requirement of water for the given workability.for the given workability. • The use of larger size aggregate did not contribute toThe use of larger size aggregate did not contribute to higher strength as expected fromhigher strength as expected from the theoreticalthe theoretical considerations due to the following reasons.considerations due to the following reasons. • The larger maximum size aggregate gives lower surfaceThe larger maximum size aggregate gives lower surface area for developmentsarea for developments of gel bonds which is responsibleof gel bonds which is responsible for the lower strength of the concrete.for the lower strength of the concrete. • Secondly bigger aggregate size causes a more heterogeneitySecondly bigger aggregate size causes a more heterogeneity in the concretein the concrete which will prevent the uniform distributionwhich will prevent the uniform distribution ofof load when stressed.load when stressed.
  • 35.
    Effect of Maximumsize of AggregateEffect of Maximum size of Aggregate • When large size aggregate is used, due to internalWhen large size aggregate is used, due to internal bleeding,bleeding, the transition zone will become muchthe transition zone will become much weaker due to the development of micro cracks whichweaker due to the development of micro cracks which result in lower compressive strength.result in lower compressive strength.
  • 36.
    Effect of Maximumsize of AggregateEffect of Maximum size of Aggregate
  • 37.
    Age ofAge ofCConcreteoncrete • With an increase in age, the degree of hydrationWith an increase in age, the degree of hydration generally increasesgenerally increases the gel/space ratio so that strengththe gel/space ratio so that strength increasesincreases • Increase in the strength of concreteIncrease in the strength of concrete (at same w/c ratio)(at same w/c ratio) with increase in early age (from 1 to 28 days) of concrete.with increase in early age (from 1 to 28 days) of concrete.
  • 38.
    Age ofAge ofCConcreteoncrete
  • 39.
    Influence ofInfluence ofPProperties ofroperties of CCoarseoarse AAggregateggregate • The relation between the flexural and compressive strengthsThe relation between the flexural and compressive strengths depends on the type of coarse aggregate because the propertiesdepends on the type of coarse aggregate because the properties of aggregate, especiallyof aggregate, especially its shape and surface texture, affect theits shape and surface texture, affect the ultimate strength in compression very much less than the strength inultimate strength in compression very much less than the strength in tension or the cracking load in compression.tension or the cracking load in compression. • In experimental concrete, entirely smooth coarse aggregate led to aIn experimental concrete, entirely smooth coarse aggregate led to a lower compressive strengthlower compressive strength, typically by 10 per cent, than when, typically by 10 per cent, than when roughened.roughened. • The influence of the type of coarse aggregate on the strength ofThe influence of the type of coarse aggregate on the strength of concrete varies in magnitudeconcrete varies in magnitude and depends on the water/cementand depends on the water/cement ratio of the mix.ratio of the mix.
  • 40.
    Influence ofInfluence ofPProperties ofroperties of CCoarseoarse AAggregateggregate For water/cement ratios below 0.4, the use ofFor water/cement ratios below 0.4, the use of crushed aggregate has resultedcrushed aggregate has resulted in strengths up to 38 perin strengths up to 38 per cent higher than when gravel is used.cent higher than when gravel is used. With anWith an influenceinfluence strengthstrength increase in the water/cement ratio to 0.5increase in the water/cement ratio to 0.5,, thethe of aggregate falls offof aggregate falls off, presumably because, presumably because the of the hydrated cement paste itselfthe of the hydrated cement paste itself becomesbecomes paramount and, at a water/cement ratio of 0.65paramount and, at a water/cement ratio of 0.65, no, no difference in the strengths of concretes made with crusheddifference in the strengths of concretes made with crushed rock and gravel has observed.rock and gravel has observed.
  • 41.
    Influence ofInfluence ofTTemperature onemperature on SStrengthtrength • TheThe riserise inin thethe curingcuring temperaturetemperature speedsspeeds upup thethe chemicalchemical reactionsreactions ofof hydrationhydration andand thusthus affectsaffects beneficiallybeneficially thethe earlyearly strengthstrength ofof concreteconcrete withoutwithout anyany ill-effectsill-effects onon thethe laterlater strength.strength. • RapidRapid initialinitial hydrationhydration appearsappears toto formform productsproducts ofof aa poorerpoorer physicalphysical structure,structure, probablyprobably moremore porous,porous, soso thatthat aa proportionproportion ofof thethe porespores willwill alwaysalways remainremain unfilled.unfilled. • TheThe gel//spacegel//space ratioratio rulerule thatthat thisthis willwill leadlead toto aa lowerlower strengthstrength comparedcompared withwith aa lessless porous,porous, thoughthough slowlyslowly hydrating,hydrating, cementcement pastepaste inin whichwhich aa highhigh gel//spacegel//space ratioratio willwill eventuallyeventually bebe reached.reached.
  • 42.
    FatigueFatigue SStrength oftrengthof CConcreteoncrete • Modulus ofModulus of EElasticity,lasticity, • CreepCreep • Shrinkage of concreteShrinkage of concrete
  • 43.
    Stress-Strain Plot ofConcreteStress-Strain Plot of Concrete • At stress below 30% of ultimate strength, the transitionAt stress below 30% of ultimate strength, the transition zone cracks remain stable. The stress-strain plot remainszone cracks remain stable. The stress-strain plot remains linearlinear.. • At stress betweenAt stress between 30% and 50% of ultimate strength,30% and 50% of ultimate strength, the transition zone micro-cracks begin to increase in length,the transition zone micro-cracks begin to increase in length, width and numbers. The stress-strain plot becomes non-linear.width and numbers. The stress-strain plot becomes non-linear. • At 50 to 60% of the ultimate stress, cracks begin toAt 50 to 60% of the ultimate stress, cracks begin to form in the matrix.form in the matrix. With further increase to about 75% of theWith further increase to about 75% of the ultimate stress, the cracks in the transition become unstable,ultimate stress, the cracks in the transition become unstable, and crack propagation in the matrix will increase. The stress-and crack propagation in the matrix will increase. The stress- strain curve bends towards the horizontal.strain curve bends towards the horizontal.
  • 44.
    Stress-Strain Plot ofConcreteStress-Strain Plot of Concrete • At 75 to 80% of the ultimate stress, the stress reachesAt 75 to 80% of the ultimate stress, the stress reaches a critical stress level for spontaneous crack growtha critical stress level for spontaneous crack growth under a sustained stress.under a sustained stress. Cracks propagate rapidly in bothCracks propagate rapidly in both the matrix and the transition zone.the matrix and the transition zone. Failure occurs whenFailure occurs when the cracks join together and become continuous.the cracks join together and become continuous. Concrete isConcrete is not a trulynot a truly elastic materialelastic material, as evident, as evident from thefrom the nonlinear stress-nonlinear stress- strain curvestrain curve for concrete,for concrete, shown in the figshown in the fig
  • 45.
    Stress-Strain Plot ofConcreteStress-Strain Plot of Concrete • TheThe “initial tangent“initial tangent modulus” ismodulus” is givengiven byby thethe slopeslope ofof aa lineline drawndrawn tangenttangent toto thethe stress-strainstress-strain curvecurve atat thethe originorigin • TheThe “tangent modulus” is“tangent modulus” is givengiven byby thethe slopeslope ofof aa lineline drawn tangentdrawn tangent toto thethe stress-strainstress-strain curvecurve atat anyany pointpoint onon thethe curvecurve • TheThe “secant modulus” is“secant modulus” is givengiven byby thethe slopeslope ofof aa lineline drawndrawn fromfrom thethe originorigin toto aa pointpoint onon thethe curvecurve correspondingcorresponding toto aa 40%40% stressstress ofof thethe failurefailure stressstress • TheThe “secant modulus” is“secant modulus” is givengiven byby thethe slopeslope ofof aa lineline drawndrawn fromfrom thethe originorigin toto aa pointpoint onon thethe curvecurve correspondingcorresponding toto aa 40%40% stressstress ofof thethe failurefailure stressstress
  • 46.
    Stress-Strain Plot ofConcreteStress-Strain Plot of Concrete
  • 47.
    Determination of modulusof elasticity ofDetermination of modulus of elasticity of ConcreteConcrete • TestingTesting ofof cubecube oror cylindercylinder inin uni-axialuni-axial compressioncompression test.test. • MeasureMeasure loadload andand thethe correspondingcorresponding deformationdeformation asas thethe loadload isis increased.increased. DrawDraw thethe stressstress strainstrain curve.curve. • StrainStrain =Dial=Dial gaugegauge reading/gaugereading/gauge lengthlength == dl/Ldl/L • StressStress == Load/CrossLoad/Cross sectionalsectional area=area= P/AP/A • UseUse CompressometerCompressometer andand ExtensometerExtensometer toto measuremeasure deformations.deformations. DrawDraw stressstress strainstrain diagramdiagram andand determinedetermine thethe requiredrequired modulusmodulus.. • Deflection:Deflection: EE cancan bebe determineddetermined fromfrom testingtesting ofof beambeam also.also.
  • 48.
    Determination ofDetermination ofMModulus ofodulus of EElasticitylasticity
  • 49.
    Determination of modulusof elasticityDetermination of modulus of elasticity • The test uses a 150 X 300 mm cylindrical specimen, whichThe test uses a 150 X 300 mm cylindrical specimen, which is loaded in compression.is loaded in compression. A compress meter is used toA compress meter is used to measure the longitudinal strains, and an extensometer is usedmeasure the longitudinal strains, and an extensometer is used to measure the transverse strains on the specimen.to measure the transverse strains on the specimen. • The chord modulus (E) is calculated as:The chord modulus (E) is calculated as:  wherewhere SS22 = stress corresponding to 40% of ultimate strength= stress corresponding to 40% of ultimate strength  SS11 = stress corresponding to a strain of 50 X 10= stress corresponding to a strain of 50 X 10-6-6  ΕΕ22 = longitudinal strain produced by stress S= longitudinal strain produced by stress S22
  • 50.
    Poisson’s ratio (StaticMethod)Poisson’s ratio (Static Method) • When a material is compressed in one direction, itWhen a material is compressed in one direction, it usually tends to expand in the other two directionsusually tends to expand in the other two directions perpendicular to the direction of compression. Thisperpendicular to the direction of compression. This phenomenon is called the Poisson effect.phenomenon is called the Poisson effect. • The Poisson ratio is the ratio of the fraction (or percent)The Poisson ratio is the ratio of the fraction (or percent) of expansion divided by the fraction (or percent) ofof expansion divided by the fraction (or percent) of compression, for small values of these changes. μ = 0.15 - 0.20compression, for small values of these changes. μ = 0.15 - 0.20 – Actual value to be found from strain measurements on– Actual value to be found from strain measurements on concrete cylinder using extensometer.concrete cylinder using extensometer. where εwhere εt2t2,ε,εt1t1= transverse strains produced by S= transverse strains produced by S22& S& S11,, respectivelyrespectively
  • 51.
    Relation between Modulusof Elasticity andRelation between Modulus of Elasticity and StrengthStrength • Modulus of elasticity of concrete increases approximatelyModulus of elasticity of concrete increases approximately with the square root of the strength.with the square root of the strength. The IS 456 of 2000The IS 456 of 2000 gives the Modulus of elasticity asgives the Modulus of elasticity as
  • 52.
    Factors Affecting Modulusof Elasticity ofFactors Affecting Modulus of Elasticity of ConcreteConcrete • Effects of moisture conditionEffects of moisture condition • Specimens tested in dry condition show about 15%Specimens tested in dry condition show about 15% decrease in elastic modulus as compared to the wetdecrease in elastic modulus as compared to the wet specimensspecimens. This is explained by the fact that drying. This is explained by the fact that drying produces more micro-cracks in the transition zone, whichproduces more micro-cracks in the transition zone, which affects the stress-strain behavior of the concrete.affects the stress-strain behavior of the concrete. • This is opposite to its effects on compressive strength.This is opposite to its effects on compressive strength. The compressive strength is increased by about 15%The compressive strength is increased by about 15% when tested dry as compared with the wet specimenswhen tested dry as compared with the wet specimens
  • 53.
    Factors Affecting Modulusof Elasticity ofFactors Affecting Modulus of Elasticity of ConcreteConcrete • Effects ofEffects of Aggregate propertiesAggregate properties • Porosity of aggregate has the most effect on thePorosity of aggregate has the most effect on the elastic modulus of concrete.elastic modulus of concrete. An aggregates with a lowAn aggregates with a low porosity has a high modulus of elasticity.porosity has a high modulus of elasticity. • The elastic modulus of concrete is affected by theThe elastic modulus of concrete is affected by the volume fraction of the aggregatevolume fraction of the aggregate as well as the elasticas well as the elastic modulus of the aggregate.modulus of the aggregate.
  • 54.
    Factors Affecting Modulusof Elasticity ofFactors Affecting Modulus of Elasticity of ConcreteConcrete • Effects of cement matrixEffects of cement matrix • TheThe lowerlower thethe porosityporosity ofof thethe cementcement paste, thepaste, the higherhigher the elastic modulus of the cement paste.the elastic modulus of the cement paste. • The higher the elastic modulus of the cement paste, the higher theThe higher the elastic modulus of the cement paste, the higher the elastic modulus of the concrete.elastic modulus of the concrete. • Effects of transition zoneEffects of transition zone • The void spaces and and the micro cracksThe void spaces and and the micro cracks in the transition play a majorin the transition play a major role in affecting the stress-strain behavior of concrete.role in affecting the stress-strain behavior of concrete. • The transition zone characteristics affectThe transition zone characteristics affect the elastic modulus more thanthe elastic modulus more than it affects the compressive strength of concrete.it affects the compressive strength of concrete.
  • 55.
    CreepCreep The ability ofconcrete to creep imparts a degree of ductilityThe ability of concrete to creep imparts a degree of ductility to concrete that enables it to tolerateto concrete that enables it to tolerate the normal range ofthe normal range of structural deformations encountered in practice.structural deformations encountered in practice. Creep provides a structure with the ability to redistributeCreep provides a structure with the ability to redistribute excessive stresses.excessive stresses. Without the ability to creep, concrete would simply be tooWithout the ability to creep, concrete would simply be too brittle for use in the majority of structuresbrittle for use in the majority of structures. However, creep. However, creep also may have detrimental effectsalso may have detrimental effects such as increased deflectionsuch as increased deflection resulting in cracking, loss of prestress, and buckling ofresulting in cracking, loss of prestress, and buckling of slender columns.slender columns. It isIt is therefore important that the designer takes the necessarytherefore important that the designer takes the necessary steps to allow for creep in the design of concrete structures.steps to allow for creep in the design of concrete structures.
  • 56.
  • 57.
    DefinitionDefinition Creep is definedas the increase in strainCreep is defined as the increase in strain (deformation) under a sustained stress (load).(deformation) under a sustained stress (load). WhenWhen loaded, concrete experiences an instantaneous elasticloaded, concrete experiences an instantaneous elastic strain, which is recoverable.strain, which is recoverable. In addition, an inelasticIn addition, an inelastic creep strain takes place that is only partiallycreep strain takes place that is only partially recoverablerecoverable
  • 58.
    CreepCreep Test methodsTest methods Creepis usually determined by measuring theCreep is usually determined by measuring the change in strainchange in strain with time of a specimen subjected to awith time of a specimen subjected to a constant stress and stored under appropriate conditions.constant stress and stored under appropriate conditions.
  • 59.
  • 60.
    Factors Influencing CreepFactorsInfluencing Creep Factors Influencing creepFactors Influencing creep Creep of concrete is load induced, and is influenced by factorsCreep of concrete is load induced, and is influenced by factors associated with the applicationassociated with the application of load and the ability of theof load and the ability of the concrete to withstand the load.concrete to withstand the load. The potential of the concrete to creep is determined by mixThe potential of the concrete to creep is determined by mix materials and proportions of the concrete.materials and proportions of the concrete. The cement pasteThe cement paste creeps, and the role of the aggregate is to:creeps, and the role of the aggregate is to:
  • 61.
    Stress Strain RatioStressStrain Ratio Creep is linearly proportional to the stress: strengthCreep is linearly proportional to the stress: strength
  • 62.
    Cement Paste ContentCementPaste Content Cement paste content Hardened ConcreteCement paste content Hardened Concrete A 1% increase in cement paste by volume will result inA 1% increase in cement paste by volume will result in approximately a 5% increase in creep.approximately a 5% increase in creep. This is applicable forThis is applicable for concretes with a cement paste volume of 28% to 40%.concretes with a cement paste volume of 28% to 40%. The cement paste volume is influenced by the aggregateThe cement paste volume is influenced by the aggregate content of the mix:content of the mix: the greater the aggregate content, the lowerthe greater the aggregate content, the lower the cement paste contentthe cement paste content
  • 63.
    Cement TypeCement Type CementTypeCement Type The type of cement influences the strengthThe type of cement influences the strength development of concrete.development of concrete. A high stress : strain ratioA high stress : strain ratio could potentially result if the concrete is loaded at ancould potentially result if the concrete is loaded at an early age and the cement has a slow rate of strengthearly age and the cement has a slow rate of strength development.development.
  • 64.
    DurabilityDurability The durability ofa structure may be definedThe durability of a structure may be defined as the time for which the structure can fulfillas the time for which the structure can fulfill the function for which it was designed and constructed.the function for which it was designed and constructed.
  • 65.
    DurabilityDurability • Defined asits resistance to deteriorationDefined as its resistance to deterioration processes that may occur as a result of interactionprocesses that may occur as a result of interaction with its environment (external)with its environment (external) or between theor between the constituent materials or their reaction withconstituent materials or their reaction with contaminants present (internal).contaminants present (internal). • Ability to with stand the damaging effectsAbility to with stand the damaging effects of theof the environment over a long period of time.environment over a long period of time. • The absence of durability maybe caused either byThe absence of durability maybe caused either by the environment to whichthe environment to which the concrete is exposedthe concrete is exposed i.e. external or internal causes.i.e. external or internal causes.
  • 66.
    Factors Influencing DurabilityFactorsInfluencing Durability The following factors are of equal importance inThe following factors are of equal importance in influencing the durability of a concrete structure:influencing the durability of a concrete structure: •• The achievement of structural durability requiresThe achievement of structural durability requires rigorous attention to detail by the designer,rigorous attention to detail by the designer, contractor, supervisory engineer and materialscontractor, supervisory engineer and materials engineer.engineer. Even if the highest possible grades of concreteEven if the highest possible grades of concrete are supplied, the structure will only be durable if goodare supplied, the structure will only be durable if good practice prevails in all phases of the building project.practice prevails in all phases of the building project.
  • 67.
    Factors Influencing DurabilityFactorsInfluencing Durability • To accurately predict cracking, concrete properties such asTo accurately predict cracking, concrete properties such as shrinkageshrinkage creep are consideredcreep are considered • Member Shapes complicating concrete compaction andMember Shapes complicating concrete compaction and thin concretethin concrete section are avoidedsection are avoided • Ponding of water is prevented,Ponding of water is prevented, Rain and sea water drainedRain and sea water drained away from structure.away from structure. • No ingress of water canNo ingress of water can occur into joints.occur into joints. • Correct curing time and methodsCorrect curing time and methods are specifiedare specified
  • 68.
  • 69.
    Durability is AchievedByDurability is Achieved By • Well Compacted ConcreteWell Compacted Concrete • Good workmanship reduced porosityGood workmanship reduced porosity • Use of aluminosulphate resisting cement ,Use of aluminosulphate resisting cement , Portland blast furnace slag, or PortlandPortland blast furnace slag, or Portland pozzolana cement.pozzolana cement. • Sufficient cover over reinforcementSufficient cover over reinforcement • Use of low water cement RatioUse of low water cement Ratio
  • 70.
    ShrinkageShrinkage Shrinkage cracks inconcreteShrinkage cracks in concrete occur due to change inoccur due to change in moisture of concrete. Most of the building materialsmoisture of concrete. Most of the building materials like concrete, mortar, burnt clay bricks are porouslike concrete, mortar, burnt clay bricks are porous inin their structure in the form of inter-molecular space.their structure in the form of inter-molecular space. They expand when they absorb the moisture andThey expand when they absorb the moisture and shrink when they dry. This is the main cause theshrink when they dry. This is the main cause the concrete shrinks on drying. Shrinkage of concrete isconcrete shrinks on drying. Shrinkage of concrete is an irreversible process.an irreversible process.
  • 71.
  • 72.
    ShrinkageShrinkage Concrete shrinkageConcrete shrinkagecan become problematic whencan become problematic when doing any type of construction, but especially whendoing any type of construction, but especially when dealing with floorsdealing with floors. Concrete shrinkage is the. Concrete shrinkage is the contracting of the concrete due to the watercontracting of the concrete due to the water evaporatingevaporating from the mixture. This evaporation will cause thefrom the mixture. This evaporation will cause the concrete to weaken. This can lead to cracks, internalconcrete to weaken. This can lead to cracks, internal warping and external deflectionwarping and external deflection
  • 73.
  • 74.
    ShrinkageShrinkage Types of ConcreteShrinkageTypes of Concrete Shrinkage There are numerousThere are numerous types of concrete shrinkagetypes of concrete shrinkage including plastic shrinkage, drying shrinkage,including plastic shrinkage, drying shrinkage, autogenous shrinkage, and carbonation shrinkage.autogenous shrinkage, and carbonation shrinkage. Plastic shrinkagePlastic shrinkage happens soon after the concrete ishappens soon after the concrete is poured in the forms. The water evaporates andpoured in the forms. The water evaporates and results in a reduction of volumeresults in a reduction of volume, this causes the, this causes the concrete on the surface to collapse. It can be reduced byconcrete on the surface to collapse. It can be reduced by covering the surfacecovering the surface with polyethylene sheetingwith polyethylene sheeting immediately after it is poured.immediately after it is poured.
  • 75.
  • 76.
    ShrinkageShrinkage Drying shrinkageDrying shrinkageis the ever lasting process for concrete withinis the ever lasting process for concrete within drying conditions.drying conditions. The loss of water within the gel pores of theThe loss of water within the gel pores of the concrete is what causes the concrete to shrink.concrete is what causes the concrete to shrink. TheThe finer the gelfiner the gel within the pores, the more shrinkage there is.within the pores, the more shrinkage there is. Autogenous shrinkageAutogenous shrinkage is most prevalent within the concrete inis most prevalent within the concrete in the interior of a dam.the interior of a dam. When the temperature is constantWhen the temperature is constant shrinkage may occur, especially when there is no moistureshrinkage may occur, especially when there is no moisture movementmovement Carbonation shrinkageCarbonation shrinkage is where carbon dioxide penetratesis where carbon dioxide penetrates beyond the surface of the concrete.beyond the surface of the concrete. This also depends on theThis also depends on the moisture content and the humidity levels. Carbonationmoisture content and the humidity levels. Carbonation shrinkage is caused by the disbanding of calcium hydroxideshrinkage is caused by the disbanding of calcium hydroxide crystals and the evidence of calcium carbonatecrystals and the evidence of calcium carbonate
  • 77.
  • 78.
    ShrinkageShrinkage Factors Affecting ShrinkageFactorsAffecting Shrinkage There are soThere are so many factorsmany factors that affect the shrinkage of concrete.that affect the shrinkage of concrete. The most important factor is theThe most important factor is the drying conditiondrying condition or theor the humidity in the atmosphere.humidity in the atmosphere. No shrinkage will occur if theNo shrinkage will occur if the concrete is placed in one hundred percent relative humidity.concrete is placed in one hundred percent relative humidity. The shrinkage rate will decrease rapidly with time. It hasThe shrinkage rate will decrease rapidly with time. It has been documented that fourteen to thirty-four percent of thebeen documented that fourteen to thirty-four percent of the twenty year shrinkage will occur within two weeks of it beingtwenty year shrinkage will occur within two weeks of it being poured.poured. Within one year of the concrete being poured, shrinkageWithin one year of the concrete being poured, shrinkage will be about sixty-six to eighty-five percent of the twenty yearwill be about sixty-six to eighty-five percent of the twenty year shrinkageshrinkage
  • 79.
    ShrinkageShrinkage The water toThewater to cement ratiocement ratio will influence thewill influence the amount of shrinkage that occurs.amount of shrinkage that occurs. TheThe concrete’s richnessconcrete’s richness also affects thealso affects the shrinkage. The process of swelling and thenshrinkage. The process of swelling and then drying affects the concrete’s integrity and thedrying affects the concrete’s integrity and the shrinkage.shrinkage.
  • 80.
    ShrinkageShrinkage Factors affecting shrinkageare:Factors affecting shrinkage are: 1. Aggregate -Concrete with higher aggregate1. Aggregate -Concrete with higher aggregate content exhibits smaller shrinkage.content exhibits smaller shrinkage. Concrete withConcrete with aggregates of higher modulus of elasticity or ofaggregates of higher modulus of elasticity or of rougher surfaces is more resistant to the shrinkagerougher surfaces is more resistant to the shrinkage process.process. 2. Water-cement ratio - The higher the W/C ratio2. Water-cement ratio - The higher the W/C ratio is, the higher the shrinkage.is, the higher the shrinkage. As W/C increases, pasteAs W/C increases, paste strength and stiffness decrease; and as water contentstrength and stiffness decrease; and as water content increases, shrinkage potential increasesincreases, shrinkage potential increases..
  • 81.
    ShrinkageShrinkage 3. Member size- Shrinkage decrease with an3. Member size - Shrinkage decrease with an increase in the volume of the concrete memberincrease in the volume of the concrete member However,However, the duration of shrinkage is longer forthe duration of shrinkage is longer for larger members since more time is needed forlarger members since more time is needed for shrinkage effects to reach the interior regionsshrinkage effects to reach the interior regions.. 4. Medium ambient conditions - The rate of4. Medium ambient conditions - The rate of shrinkage isshrinkage is lower at higher values of relativelower at higher values of relative humidity. Shrinkage becomes stabilized at lowhumidity. Shrinkage becomes stabilized at low temperaturestemperatures..
  • 82.
    ShrinkageShrinkage 5. Admixtures -effect varies from admixture to5. Admixtures - effect varies from admixture to admixture.admixture. Any material which substantially changesAny material which substantially changes the pore structure of the paste will affect thethe pore structure of the paste will affect the shrinkage characteristics of the concreteshrinkage characteristics of the concrete. In general,. In general, as pore refinement is enhanced, shrinkage is increased.as pore refinement is enhanced, shrinkage is increased.
  • 83.
    PermeabilityPermeability • Concrete hasa tendency to be porous due to theConcrete has a tendency to be porous due to the presence of voids formed during or after placingpresence of voids formed during or after placing.. • Penetration by substance may adversely affectPenetration by substance may adversely affect durabilitydurability e.g. Ca(OH)e.g. Ca(OH)22 leaches out.leaches out. • Ingress of air and moisture resultingIngress of air and moisture resulting in corrosion.in corrosion. • Important with regards to water tightnessImportant with regards to water tightness ofof • liquid retaining structure.liquid retaining structure.
  • 84.
  • 85.
    PermeabilityPermeability To produce concreteof low permeability, fullTo produce concrete of low permeability, full compaction & proper curingcompaction & proper curing is essential.is essential. Low permeability is important in increasingLow permeability is important in increasing resistantresistant to frost action and chemical attack andto frost action and chemical attack and in protecting embedded steel against corrosion.in protecting embedded steel against corrosion.
  • 86.
  • 87.
    PermeabilityPermeability The permeability ofcement paste varies with the ageThe permeability of cement paste varies with the age of concrete or with progress of hydrationof concrete or with progress of hydration.. •With age, the permeability decreases because gelWith age, the permeability decreases because gel gradually fillgradually fill the original water filled space.the original water filled space. •For the same w/c ratio, the permeability of pasteFor the same w/c ratio, the permeability of paste with coarser cement particleswith coarser cement particles is higher than those withis higher than those with finer cement.finer cement. •In general, the higher the strength of cement paste,In general, the higher the strength of cement paste, the lowerthe lower will the permeability.will the permeability.
  • 88.
  • 89.
    PermeabilityPermeability Factors influencing permeabilityare:Factors influencing permeability are: i. W/C Ratioi. W/C Ratio ii. Curingii. Curing iii. Method of compactioniii. Method of compaction iv. Workabilityiv. Workability v. Soundness & porosity of the aggregatev. Soundness & porosity of the aggregate vi. Age (permeability decrease with age)vi. Age (permeability decrease with age) vii. Grading of aggregatevii. Grading of aggregate viii.Type of structureviii.Type of structure
  • 91.