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1、PropertiesofFreshConcreteEditedbyH.-J.WierigFreshconcreteisamixtureofwater,cement,aggregateandadmixture(ifany).Aftermixing,operationssuchastransporting,placing,compactingandfinishingoffreshconcretecanallconsiderablyaffectthepropertiesofhardenedconcrete.Itisimportantthatthecon
2、stituentmaterialsremainuniformlydistributedwithintheconcretemassduringthevariousstagesofitshandlingandthatfullcompactionisachieved.Wheneitheroftheseconditionsisnotsatisfiedthepropertiesoftheresultinghardenedconcrete,forexample,strengthanddurability,areadverselyaffected.Thecha
3、racteristicsoffreshconcretewhichaffectfullcompactionareitsconsistency,mobilityandcompactability.Inconcretepracticetheseareoftencollectivelyknownasworkability.Theabilityofconcretetomaintainitsuniformityisgovernedbyitsstability,whichdependsonitsconsistencyanditscohesiveness.Sin
4、cethemethodsemployedforconveying,placingandconsolidatingdaconcretemix,aswellasthenatureofthesectiontobecast,mayvaryfromjobtojobitfollowsthatthecorrespondingworkabilityandstabilityrequirementswillalsovary.Theassessmentofthesuitabilityofafreshconcreteforaparticularjobwillalways
5、tosomeextentremainamatterofpersonaljudgment.Inspiteofitsimportance,thebehaviourofplasticconcreteoftentendstobeoverlooked.Itisrecommendedthatstudentsshouldlearntoappreciatethesignificanceofthevariouscharacteristicsofconcreteinitsplasticstateandknowhowthesemayalterduringoperati
6、onsinvolvedincastingaconcretestructure.13.1WorkabilityWorkabilityofconcretehasneverbeenpreciselydefined.Forpracticalpurposesitgenerallyimpliestheeasewithwhichaconcretemixcanbehandledfromthemixertoitsfinallycompactedshape.Thethreemaincharacteristicsofthepropertyareconsistency,
7、mobilityandcompactability.Consistencyisameasureofwetnessorfluidity.Mobilitydefinestheeasewithwhichamixcanflowintoandcompletelyfilltheformworkormould.Compactabilityistheeasewithwhichagivenmixcanbefullycompacted,allthetrappedairbeingremoved.Inthiscontexttherequiredworkabilityof
8、amixdependsnotonlyonthecharacteristicsandrelativeproportionsofthecon
