《拌砼和易性》PPT课件

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1、第四章新拌砼的性质Freshconcreteisamixtureofwater,cement,aggregateandadmixture(ifany).Aftermixing,operationssuchastransporting,placing,compactingandfinishingoffreshconcretecanallconsiderablyaffectthepropertiesofhardenedconcrete.第一节——和易性一、砼的和易性定义二、和易性的测定三、影响和易性的因素四、调整和易性的措施Thecharact

2、eristicsoffreshconcrete(新拌混凝土)whichaffectfullcompactionareitsconsistency（稠度）,mobility（流动性）andcompactability（易密性）.Inconcretepracticetheseareoftencollectivelyknownasworkability（工作性，和易性）.Theabilityofconcretetomaintainitsuniformityisgovernedbyitsstability（稳定性）,whichdependsonit

3、sconsistencyanditscohesiveness（粘聚性）..Forpracticalpurposesworkabilitygenerallyimpliestheeasewithwhichaconcretemixcanbehandledfromthemixertoitsfinallycompactedshape.Thethreemaincharacteristicsofthepropertyareconsistency,mobilityandcompactability.Consistencyisameasureofwetnes

4、sorfluidity.Mobilitydefinestheeasewithwhichamixcanflowintoandcompletelyfilltheformworkormould.Compactabilityistheeasewithwhichagivenmixcanbefullycompacted,allthetrappedairbeingremoved.一砼和易性的定义：指砼拌和物易于施工操作（拌和、运输、浇灌、捣实）并能保证质量均匀、成型密实的性能。它包括流动性(mobility)、粘聚性(cohesiveness)和保水性(

5、waterretentivity)三方面的含义。和易性包括三个方面：1、流动性指砼拌和物在自重或施工机械振捣的作用下，能够流动并均匀密实地填满模板的性能。2、粘聚性保持整体均匀，不发生分层离析现象。3、保水性保持水分不使之泌出。Threetestswidelyusedformeasuringworkabilityaretheslump,compactingfactorandV-Bconsistometertests.SlumptestwasdevelopedbyChapmanintheUnitedStatesin1913.A300mmhig

6、hconcretecone,preparedunderstandardconditions(BS1881:part2)isallowedtosubsideandtheslumpofreductioninheightoftheconeistakentobeameasureofworkability.混凝土分层离析外分层内分层新拌混凝土泌水示意图二、和易性的测定方法砼拌和物坍落度试验维勃稠度试验扩展度试验二、砼拌和物坍落度的测定Thethreetypesofslumpusuallyobservedaretrueslump,shearslumpa

7、ndcollapseslump,asillustratedinfigure13.2.Atrueslumpisobservedwithcohesiveandrichmixesforwhichtheslumpisgenerallysensitivetovariationsinworkability.Acollapseslumpisusuallyassociatedwithverywetmixesandisgenerallyindicativeofpoorqualityconcreteandmostfrequentlyresultsfromseg

8、regationofitsconstituentmaterials.Shearslumpoccursmoreofteninleanermixesthaninrichonesand