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1、PropertiesofFreshConcreteEditedbyH.-J.WierigFreshconcreteisamixtureofwater,cement,aggregateandadmixture(ifany).Aftermixing,operationssuchastransporting,placing,compactingandfinishingoffreshconcretecanallconsiderablyaffectthepropertiesofhardenedconcrete.Itisimportantthatthe
2、constituentmaterialsremainuniformlydistributedwithintheconcretemassduringthevariousstagesofitshandlingandthatfullcompactionisachieved.Wheneitheroftheseconditionsisnotsatisfiedthepropertiesoftheresultinghardenedconcrete,forexample,strengthanddurability,areadverselyaffected.
3、Thecharacteristicsoffreshconcretewhichaffectfullcompactionareitsconsistency,mobilityandcompactability.Inconcretepracticetheseareoftencollectivelyknownasworkability.Theabilityofconcretetomaintainitsuniformityisgovernedbyitsstability,whichdependsonitsconsistencyanditscohesiv
4、eness.Sincethemethodsemployedforconveying,placingandconsolidatingdaconcretemix,aswellasthenatureofthesectiontobecast,mayvaryfromjobtojobitfollowsthatthecorrespondingworkabilityandstabilityrequirementswillalsovary.Theassessmentofthesuitabilityofafreshconcreteforaparticularj
5、obwillalwaystosomeextentremainamatterofpersonaljudgment.Inspiteofitsimportance,thebehaviourofplasticconcreteoftentendstobeoverlooked.Itisrecommendedthatstudentsshouldlearntoappreciatethesignificanceofthevariouscharacteristicsofconcreteinitsplasticstateandknowhowthesemayalt
6、erduringoperationsinvolvedincastingaconcretestructure.13.1WorkabilityWorkabilityofconcretehasneverbeenpreciselydefined.Forpracticalpurposesitgenerallyimpliestheeasewithwhichaconcretemixcanbehandledfromthemixertoitsfinallycompactedshape.Thethreemaincharacteristicsoftheprope
7、rtyareconsistency,mobilityandcompactability.Consistencyisameasureofwetnessorfluidity.Mobilitydefinestheeasewithwhichamixcanflowintoandcompletelyfilltheformworkormould.Compactabilityistheeasewithwhichagivenmixcanbefullycompacted,allthetrappedairbeingremoved.Inthiscontextthe
8、requiredworkabilityofamixdependsnotonlyonthecharacteristicsandrelativeproportionsofthecon
