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Lecture3 Fundamentals June6 2003CVEN444 1 LectureGoals ConcretePropertiesSteelProperties 2 ConcreteMixingandProportioning QualityWorkabilityEconomical Inthedesignofconcretemixes threeprincipalrequirementsforconcreteareofimportance 3 ConcreteMixingandProportioning Qualityofconcreteismeasuredbyitsstrengthanddurability Theprincipalfactorsaffectingthestrengthofconcrete assumingasoundaggregates W Cratio andtheextenttowhichhydrationhasprogressed Durabilityofconcreteistheabilityoftheconcretetoresistdisintegrationduetofreezingandthawingandchemicalattack 4 ConcreteMixingandProportioning Workabilityofconcretemaybedefinedasacompositecharacteristicindicativeoftheeasewithwhichthemassofplasticmaterialmaydepositedinitsfinalplacewithoutsegregationduringplacement anditsabilitytoconformtofineformingdetail 5 ConcreteMixingandProportioning Economicaltakesintoaccounteffectiveuseofmaterials effectiveoperation andeaseofhandling Thecostofproducinggoodqualityconcreteisanimportantconsiderationintheoverallcostoftheconstructionproject 6 ConcreteMixingandProportioning Theinfluenceofingredientsonpropertiesofconcrete 7 ConcreteMixingandProportioning 3 WorkabilityWorkabilitymeasuredbyslumptest Layer1 Fill1 3full 25stokesLayer2 Fill2 3full 25stokesLayer3 Fillfull 25stokesLiftconeandmeasureslump typically2 6in 8 ConcreteMixingandProportioning Slumptest Themeasurementoftheconsistencyofthemixisdonewiththeslump conetest Therecommendconsistencyforvariousclassesofconcretestructures 9 ConcreteMixingandProportioning 4 AdmixturesApplications ImproveworkabilityAccelerateorretardsettingandhardeningAidincuringImprovedurability 10 ConcreteMixingandProportioning 4 AdmixturesAir Entrainment AddairvoidswithbubblesHelpwithfreeze thawcycles workability etc Decreasesdensity reducesstrength butalsodecreasesW CSuperplasticizers increaseworkabilitybychemicallyreleasingwaterfromfineaggregates 11 ConcreteMixingandProportioning 5 TypesofCementTypeI GeneralPurposeTypeII LowerheatofhydrationthanTypeITypeIII HighEarlyStrengthHigherheatofhydrationquickerstrength 7daysvs 28daysforTypeI 12 ConcreteMixingandProportioning 5 TypesofCementTypeIV LowHeatofHydrationGraduallyheatsup lessdistortion massivestructures TypeV SulfateResistingForfootings basements sewers etc exposedtosoilswithsulfates 13 ConcreteMixingandProportioning FailureMechanismofConcrete ShrinkageMicrocracksaretheinitialshrinkagecracksduetocarbonationshrinkage hydrationshrinkage anddryingshrinkage 14 ConcreteMixingandProportioning FailureMechanismofConcrete BondMicrocracksareextensionsofshrinkagemicrocracks asthecompressionstressfieldincreases theshrinkagemicrocrackswidenbutdonotpropagatesintothematrix Occurat15 20 ultimatestrengthofconcrete 15 ConcreteMixingandProportioning FailureMechanismofConcrete MatrixMicrocracks aremicrocracksthatoccurinthematrix Thepropagatefrom20 fc Occurupto30 45 ultimatestrengthofconcrete Matrixmicrocracksstartbridgeoneanotherat75 Aggregatemicrocracksoccurjustbeforefailure 90 16 ConcreteProperties 1 UniaxialStressversusStrainBehaviorinCompression 17 ConcreteProperties Thestandardstrengthtestgenerallyusesacylindricalsample Itistestedafter28daystotestforstrength fc TheconcretewillcontinuetohardenwithtimeandforanormalPortlandcementwillincreasewithtimeasfollows 18 ConcreteProperties CompressiveStrength f cNormallyuse28 daystrengthfordesignstrengthPoisson sRatio nn 0 15to0 20Usuallyusen 0 17 19 ConcreteProperties ModulusofElasticity EcCorrespondstosecantmodulusat0 45f cACI318 02 Sec 8 5 1 wherew unitweight pcf 90pcf wc 155pcfFornormalweightconcrete wc 145pcf 20 ConcreteProperties ComputeEcforf c 4500psifornormalweight 145pcf concreteusingbothACIequations 21 ConcreteProperties Cpressivestress oFortypical curvesincompression ovariesbetween0 0015 0 003Fornormalstrengthconcrete o 0 002 22 ConcreteProperties Maximumuseablestrain uACICode u 0 003Usedforflexuralandaxialcompression 23 ConcreteProperties TypicalConcreteStress StrainCurvesinCompression 24 ConcreteProperties Typesofcompressionfailure Therearethreemodesoffailure a Underaxialcompressionconcretefailsinshear b theseparationofthespecimenintocolumnarpiecesbywhatisknownassplittingorcolumnarfracture c Combinationofshearandsplittingfailure 25 ConcreteProperties 2 TensileStrengthTensilestrength 8 to15 off cModulusofRupture frFordeflectioncalculations use Test ACIEq 9 10 26 ConcreteProperties 2 TensileStrength cont SplittingTensileStrength fctSplitCylinderTest 27 ConcreteProperties 2 TensileStrength cont NotgiveninACICode 28 ConcreteProperties 3 ShrinkageandCreepShrinkage Duetowaterlosstoatmosphere volumeloss Plasticshrinkageoccurswhileconcreteisstill wet hotday flatwork etc DryingshrinkageoccursafterconcretehassetMostshrinkageoccursinfirstfewmonths 80 withinoneyear Cyclesofshrinkingandswellingmayoccurasenvironmentchanges Reinforcementrestrainsthedevelopmentofshrinkage 29 ConcreteProperties Fig 3 21 MacGregor 1997 ShrinkageofanUnloadedSpecimen 80 ofshrinkageoccursinfirstyear 30 ConcreteProperties ShrinkageisafunctionofW Cratio highwatercontentreducesamountofaggregatewhichrestrainsshrinkage Aggregatetype content modulusofElasticity Volume SurfaceRatio 31 ConcreteProperties ShrinkageisafunctionofTypeofcement finelyground AdmixturesRelativehumidity largestforrelativehumidityof40 orless Typicalmagnitudeofstrain 200to600 10 6or 200to600microstrain 32 ConcreteProperties CreepDeformations strains undersustainedloads Likeshrinkage creepisnotcompletelyreversible 33 ConcreteProperties Magnitudeofcreepstrainisafunctionofalltheabovethataffectshrinkage plusmagnitudeofstressageatloading 34 ConcreteProperties Creepstraindevelopsovertime AbsorbedwaterlayerstendtobecomethinnerbetweengelparticlesthataretransmittingcompressivestressesBondsformbetweengelparticlesintheirdeformedposition 35 ConcreteProperties Tri axialCompressionConfinedCylinderImprovedstrengthandductilityversusuniaxialcompressionExample spiralreinforcedwhere F1 longitudinalstressatfailureF3 lateralpressure 36 ConcreteProperties Tri axialCompression Fig 3 15 MacGregor 1997 37 SteelReinforcement 1 GeneralStandardReinforcingBarMarkings 38 SteelReinforcement 1 GeneralMostcommontypesfornon prestressedmembers hot rolleddeformedbarsweldedwirefabric 39 SteelReinforcement Areas Weights Dimensions 40 SteelReinforcement 2 T