Properties of Concrete in Hardened State

1. Hardened ConcreteHardened Concrete

2. 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).).

3. Strength of ConcreteStrength of Concrete

4. 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)

5. 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.

6. Fracture and FailureFracture and Failure

7. The stages of cracking (fracture) in concreteThe stages of cracking (fracture) in concrete

8. Types of Concrete StrengthTypes 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. Compressive StrengthCompressive Strength

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. Compressive StrengthCompressive Strength

14. 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

15. 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

16. 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.

17. Tensile Strength of ConcreteTensile Strength of Concrete
• Split-Cylinder Test:Split-Cylinder Test:

18. Tensile Strength of ConcreteTensile Strength of Concrete
Split Cylinder TestSplit Cylinder Test

19. 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)

20. 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:

21. 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

22. Shear StrengthShear Strength

23. BondBond StrengthStrength

24. 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

25. Concrete StrengthConcrete Strength
FatigueFatigue StrengthStrength
TheThe strengthstrength ofof concreteconcrete againstagainst cycliccyclic oror repeatedrepeated
loadingloading isis calledcalled asas itsits fatiguefatigue strengthstrength

26. 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

27. 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”

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 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

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/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.

32. 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

33. Influence ofInfluence of AAggregate/ggregate/CCementement RRatioatio

34. 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.

35. 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.

36. Effect of Maximum size of AggregateEffect of Maximum size of Aggregate

37. 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.

38. Age ofAge of CConcreteoncrete

39. 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.

40. 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.

41. 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.

42. FatigueFatigue SStrength oftrength of CConcreteoncrete
• Modulus ofModulus of EElasticity,lasticity,
• CreepCreep
• Shrinkage of concreteShrinkage of concrete

43. 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.

44. 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

45. 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

46. Stress-Strain Plot of ConcreteStress-Strain Plot of Concrete

47. 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.

48. Determination ofDetermination of MModulus ofodulus of
EElasticitylasticity

49. 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

50. 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

51. 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

52. 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

53. 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.

54. 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.

55. 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.

56. CreepCreep

57. 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

58. 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.

59. CreepCreep

60. 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:

61. Stress Strain RatioStress Strain Ratio
Creep is linearly proportional to the stress: strengthCreep is linearly proportional to the stress: strength

62. 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

63. 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.

64. 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.

65. 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.

66. 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.

67. 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

68. DurabilityDurability

69. 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

70. 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.

71. ShrinkageShrinkage

72. 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

73. ShrinkageShrinkage

74. 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.

75. Plastic ShrinkagePlastic Shrinkage

76. 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

77. ShrinkageShrinkage

78. 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

79. 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.

80. 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..

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 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.

84. PermeabilityPermeability

85. 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.

86. PermeabilityPermeability

87. 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.

88. PermeabilityPermeability

89. 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

91. Thanks…Thanks…