土木工程專(zhuān)業(yè)英語(yǔ) 課件 2.1 Materials for Concrete and Mix Proportions

2.1MaterialsforConcreteandMixProportionsConstituentsofconcreteMixtureofaggregateandpastePaste(30to40%)Portlandcement(7%to15%byVol.)Water(14%to21%byVol.)Aggregates60%to70%CoarseaggregatesFineaggregatesAdmixturesThe10-20-30-40Rule

Theessentialingredientsofconcrete.

Atypicalconcretebatch,byvolume,contains

10%cement

20%waterandair

30%sand

40%gravelCement,Water,FineandCoarseAggregatesAdmixture(Chemicals)CementGelStone-likeMaterialMixtureReaction(Water+Cement)Hydration(ExothermicReaction)ProducingSignificantHeatBondingfineandcoarseaggregatesPortlandCementDrypowderofveryfineparticlesFormsapastewhenmixedwithwaterChemicalreaction-HydrationGelPastecoatsalltheaggregatestogetherHardensandformsasolidmassWaterNeededfortwopurposes:chemicalreactionwithcementworkabilityOnly1/3ofthewaterisneededforchemicalreactionMorewater(twicethanasneededforreactionwithcement)areaddedforworkabilityExtrawaterremainsinporesandholesresultsinporosityGoodforpreventingplasticshrinkagecrackingandworkabilityBadforpermeability,strength,durability.AggregatesCheapfillersHardmaterialProvideforvolumestabilityPreventvolumechangesProvideabrasionresistanceAdmixturesSetretardingadmixtures緩凝劑Setacceleratingadmixtures速凝劑Waterreducingadmixtures減水劑Superplasticizers

高效減水劑Airentrainingadmixtures加氣劑Mineralflyash（粉煤灰）silicafume（硅灰）slags(礦渣）DesirablepropertyofplasticconcreteWorkability:workintoallpartsofcontainingformseaseofplacementresistancetosegregationhomogeneousmassSlumptestConsistencyAbilitytoflowDesirablepropertyofhardenedconcreteStrengthStronginCompressionweakintensiontensilestrength~1/10ofcompressionstrengthsteelisusedtoreinforceconcreteDurability:abrasionresistancetoughnessWater-tightnessStrengthofConcreteaffectedby:Water/Cementratio(seeFigurenext)Curingconditions(moistorair,Figurenext)Durability:weather,suchascycleoffreezingandthawing(high-strength,airentrainedconcrete)seawaterordeicingsalt(sulfatesdeteriorateconcrete;solution:TypesIIorV)VariationofCompressivestrengthwithwater/cementratioTheEffectofCuringonCompressiveStrengthPlainconcreteafterpreparation[7prepE5reiFEn]

配制andplacement澆筑needscuringtoattainstrengthplasticconcreteshouldnotbetransportedoverlongdistanceswithoutproperagitation.TransitMixTruck(Ready-MixTruck)PlacementToday-DirectFromtheTransitMixerCuringofconcreteProcessofmaintainingenoughmoistureinconcretetomaintaintherateofhydrationduringitsearlystagesThemostimportantsinglestepindevelopingconcretestrength,afterpropermixdesign-Ifnotproperlycarriedout,affectsitsstrength,watertightnessanddurabilityMethodsofcuringPondingorimmersion;sprayingorfogging;wetcoveringsImperviouspaper;plasticsheets;membrane-formingcuringcompound;steamcuring3.2.3ProportioningConcreteMixturesMethods:trial-batchmethodabsolute-volumemethodFactorsdeterminingmixproportionW/CratioType&sizeofaggregateAirornonair-entrainedSlumpofmixSliceofair-entrainedconcreteWaterStrength,durability,watertightness,andwearresistanceiscontrolledbytheamountofwaterused.AggregatecodeMaximumsizeofaggregatecanbenolargerthan:1/5ofnarrowestdimensionbetweenformboards3/4ofclearspacingofrebarrods1.DescribeingredientsusedforconcretePortlandcement(binder)WaterExplaintheinfluenceofW/Conconcreteproperty？Lesswater,stronger,moredurable&watertighttheconcreteToomuchwater,weak&porousAggregate（filler,coarse(gravel,stone)&fine(sand)aggregate)ExplaintheinfluenceofaggregateonconcretepropertyAggregatephysicalproperty:elasticitySoft,porousaggregatecanresultinweakconcretewithlowwearresistanceHardaggregatescanmakestrongconcretewithahighresistancetoabrasion.Aggregatechemicalproperty:chemicalreactivity(determinedbythealkali-aggregatereaction),bondAggregatesizegrade,shape,surfacetexture,Admixture(optional)Whyareadmixtureusedinconcrete?toaccelerateorretardtheinitialset,improveworkability,reducewaterrequirements,increasestrength,improvedurability,de