土木工程材料第四章.ppt

Ch4ConcreteandMortar 4 1Propertiesoffreshconcrete 新拌砼 4 2Mixing拌合 Placing浇筑andCuring养护4 3PropertiesofHardenedConcrete4 4Mixproportioninganddesign ADefinitionofPortlandCementConcrete PCC Amixtureof PortlandCementFineAggregateCoarseAggregateWaterAirCementandwatercombine changingfromamoist plasticconsistencytoastrong durablerock likeconstructionmaterialbymeansofachemicalreactioncalled hydration VolumetricproportionsofconstituentsofPCC Basedonapparentdensity Basedonapparentdensity concretecanbedividedinto Normalweightconcrete 2350 2500kg m3 Lightweightconcrete upto1900kg m3 Heavyweightconcrete upto3200kg m3 4 1Propertiesoffreshconcrete 4 1 1Propertiesoffreshconcrete4 1 2FactorsaffectingConsistency 稠度 andWorkability 和易性 4 1 3Segregation 离析 andBleeding 泌水 4 1 1Propertiesoffreshconcrete Workability 和易性 Consistency 稠度 Slump 坍落度 Workability 和易性 Workabilitycanbedefinedastheeasewithwhichafresh concretemixcanbehandledfromthemixertothefinalstructure ExpressedbythreecharacteristicsConsistency稠度Mobility流动性Compatibility相容性 保水性和易性是指新拌混凝土易于各工序施工操作 搅拌 运输 浇灌 捣实等 并能获得质量均匀 成型密实的性能 影响和易性的主要因素 1 水泥浆的数量 与流动性以及粘聚性相关2 水泥浆的稠度 3 砂率此外水泥品种 骨料种类 粒形和级配 外加剂 时间 温度等 都对混凝土拌和物的和易性有一定影响 ConsistencyandSlump 稠度 坍落度 Consistencyisameasureofconcrete swetnessorfluidity anddependsonthemixproportionsandpropertiesofingredients MeasuredbySlumptest坍落度试验 Slumptest Slumptest Mold slumpcone坍落度筒Bottomdiameterof200mmtopdiameterof100mmheightof300mm ProcedureofSlumptest a Filltheconeusingstandardprocedure b Strikeoffexcess c Raisethemoldandmeasurethedisplacementoftheoriginalcenterofthespecimen Slump Intheslumptest thenumberofmmtheoriginalcenteroftheconesinksorsettlesuniformlyismeasuredtothenearest5mm Themeasurementiscalledslump E g slumpcanbe75 80 85mm etc Typesofslump Near zeroslumpVerydrymixNormalslumpProperlyproportionedconcreteShearslumpConcretelacksplasticityandcohesionCollapseslumpLean harshorextremelywetconcrete Recommendedslumpsforvarioustypeofconstruction 4 1 2FactorsaffectingConsistencyandWorkability InternalFactorsCementpropertiesProportionofcement Typesofcement FinenessAggregatepropertiesSurfaceareaofaggregate shape gradation maximumsizeofaggregateWatercontentWater to Cementratio水灰比AdmixturesWater reducingadmixture air entrainingadmixture减水剂 引气剂 4 1 2FactorsaffectingConsistencyandWorkability ExternalFactorsEnvironmentTemperature humidity windspeedTimeDelayinplacing Therelationshipofslumpandtemperature Therelationshipofslumpandtime 4 1 3SegregationandBleeding Segregation离析andBleeding泌水resultsinNonhomogeneity不均匀性Excessivebleeding Weaktoplayer Segregation Segregationisthetendencyforseparationbetweenlargeandfineparticlesoffreshconcrete SegregationresultsinRockpocket honeycomb蜂窝Sandstreaks砂条痕Crazing龟裂Surfacescaling表面剥落 Segregation ReasonsofsegregationVerywetmixtures lackoffineparticles highslumpconcrete OvervibrationControllingsegregationAir entainmentFinelydividedmaterialsDroppedvertically Bleeding Bleeding Aconcretemixthatdoesnotpossessproperconsistencyisunabletoholdthemixwater whichslowlygetsdisplacedandthenrisestothetopoftheform ReasonsofExcessivebleedingOvervibration o