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1、Lecture3 Fundamentals June6 2003CVEN444 LectureGoals ConcretePropertiesSteelProperties ConcreteMixingandProportioning QualityWorkabilityEconomical Inthedesignofconcretemixes threeprincipalrequirementsforconcreteareofimportance ConcreteMixingandProportioning Qualityofconcreteismeasuredbyitsstrengthan
2、ddurability Theprincipalfactorsaffectingthestrengthofconcrete assumingasoundaggregates W Cratio andtheextenttowhichhydrationhasprogressed Durabilityofconcreteistheabilityoftheconcretetoresistdisintegrationduetofreezingandthawingandchemicalattack ConcreteMixingandProportioning Workabilityofconcretema
3、ybedefinedasacompositecharacteristicindicativeoftheeasewithwhichthemassofplasticmaterialmaydepositedinitsfinalplacewithoutsegregationduringplacement anditsabilitytoconformtofineformingdetail ConcreteMixingandProportioning Economicaltakesintoaccounteffectiveuseofmaterials effectiveoperation andeaseof
4、handling Thecostofproducinggoodqualityconcreteisanimportantconsiderationintheoverallcostoftheconstructionproject ConcreteMixingandProportioning Theinfluenceofingredientsonpropertiesofconcrete ConcreteMixingandProportioning 3 WorkabilityWorkabilitymeasuredbyslumptest Layer1 Fill1 3full 25stokesLayer2
5、 Fill2 3full 25stokesLayer3 Fillfull 25stokesLiftconeandmeasureslump typically2 6in ConcreteMixingandProportioning Slumptest Themeasurementoftheconsistencyofthemixisdonewiththeslump conetest Therecommendconsistencyforvariousclassesofconcretestructures ConcreteMixingandProportioning 4 AdmixturesAppli
6、cations ImproveworkabilityAccelerateorretardsettingandhardeningAidincuringImprovedurability ConcreteMixingandProportioning 4 AdmixturesAir Entrainment AddairvoidswithbubblesHelpwithfreeze thawcycles workability etc Decreasesdensity reducesstrength butalsodecreasesW CSuperplasticizers increaseworkabi
7、litybychemicallyreleasingwaterfromfineaggregates ConcreteMixingandProportioning 5 TypesofCementTypeI GeneralPurposeTypeII LowerheatofhydrationthanTypeITypeIII HighEarlyStrengthHigherheatofhydrationquickerstrength 7daysvs 28daysforTypeI ConcreteMixingandProportioning 5 TypesofCementTypeIV LowHeatofHy
8、drationGraduallyheatsup lessdistortion massivestructures TypeV SulfateResistingForfootings basements sewers etc exposedtosoilswithsulfates ConcreteMixingandProportioning FailureMechanismofConcrete ShrinkageMicrocracksaretheinitialshrinkagecracksduetocarbonationshrinkage hydrationshrinkage anddryings
9、hrinkage ConcreteMixingandProportioning FailureMechanismofConcrete BondMicrocracksareextensionsofshrinkagemicrocracks asthecompressionstressfieldincreases theshrinkagemicrocrackswidenbutdonotpropagatesintothematrix Occurat15 20 ultimatestrengthofconcrete ConcreteMixingandProportioning FailureMechani
10、smofConcrete MatrixMicrocracks aremicrocracksthatoccurinthematrix Thepropagatefrom20 fc Occurupto30 45 ultimatestrengthofconcrete Matrixmicrocracksstartbridgeoneanotherat75 Aggregatemicrocracksoccurjustbeforefailure 90 ConcreteProperties 1 UniaxialStressversusStrainBehaviorinCompression ConcreteProp
11、erties Thestandardstrengthtestgenerallyusesacylindricalsample Itistestedafter28daystotestforstrength fc TheconcretewillcontinuetohardenwithtimeandforanormalPortlandcementwillincreasewithtimeasfollows ConcreteProperties CompressiveStrength f cNormallyuse28 daystrengthfordesignstrengthPoisson sRatio n
12、n 0 15to0 20Usuallyusen 0 17 ConcreteProperties ModulusofElasticity EcCorrespondstosecantmodulusat0 45f cACI318 02 Sec 8 5 1 wherew unitweight pcf 90pcf wc 155pcfFornormalweightconcrete wc 145pcf ConcreteProperties ComputeEcforf c 4500psifornormalweight 145pcf concreteusingbothACIequations ConcreteP
13、roperties Cpressivestress oFortypical curvesincompression ovariesbetween0 0015 0 003Fornormalstrengthconcrete o 0 002 ConcreteProperties Maximumuseablestrain uACICode u 0 003Usedforflexuralandaxialcompression ConcreteProperties TypicalConcreteStress StrainCurvesinCompression ConcreteProperties Types
14、ofcompressionfailure Therearethreemodesoffailure a Underaxialcompressionconcretefailsinshear b theseparationofthespecimenintocolumnarpiecesbywhatisknownassplittingorcolumnarfracture c Combinationofshearandsplittingfailure ConcreteProperties 2 TensileStrengthTensilestrength 8 to15 off cModulusofRuptu
15、re frFordeflectioncalculations use Test ACIEq 9 10 ConcreteProperties 2 TensileStrength cont SplittingTensileStrength fctSplitCylinderTest ConcreteProperties 2 TensileStrength cont NotgiveninACICode ConcreteProperties 3 ShrinkageandCreepShrinkage Duetowaterlosstoatmosphere volumeloss Plasticshrinkag
16、eoccurswhileconcreteisstill wet hotday flatwork etc DryingshrinkageoccursafterconcretehassetMostshrinkageoccursinfirstfewmonths 80 withinoneyear Cyclesofshrinkingandswellingmayoccurasenvironmentchanges Reinforcementrestrainsthedevelopmentofshrinkage ConcreteProperties Fig 3 21 MacGregor 1997 ShrinkageofanUnloadedSpecimen 80 ofshrinkageoccursinfirstyear ConcreteProperties ShrinkageisafunctionofW Cratio highwatercontentreducesamountofaggregatewhichrestrainsshrinkage Aggregatetype content modulusof
