外文翻译低热硅酸盐水泥混凝土的抗裂性能.docx

外文翻译低热硅酸盐水泥混凝土的抗裂性能.docx

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外文翻译低热硅酸盐水泥混凝土的抗裂性能

外文翻译

Anti-CrackPerformanceofLow-Heat

PortlandCementConcrete

Abstract:

Thepropertiesoflow-heatPortlandcementconcrete（LHC）werestudiedindetail.TheexperimentalresultsshowthattheLHCconcretehascharacteristicsofahigherphysicalmechanicalbehavior,deformationanddurability.Comparedwithmoderate-heatPortlandcement（MHC）,theaveragehydrationheatofLHCconcreteisreducedbyabout17.5%.Undersamemixingproportion,theadiabatictemperatureriseofLHCconcretewasreducedby2℃-3℃,andthelimitstensionofLHCconcretewasincreasedby10×10-6-15×10-6thanthatofMHC.Moreover,itisindicatedthatLHCconcretehasabetteranti-crackbehaviorthanMHCconcrete.

Keywords:

low-heatportlandcement;massconcrete;highcrackresistance;moderate-heatportlandcement

1Introduction

Theinvestigationoncrackofmassconcreteisahotproblemtowhichattentionhasbeenpaidforalongtime.Thecracksoftheconcreteareformedbymulti-factors,buttheyaremainlycausedbythermaldisplacementsinmassconcrete[1-3].Sothekeytechnologyonmassconcreteishowtoreducethermaldisplacementsandenhancethecrackresistanceofconcrete.

Aswellknown,thehydrationheatofbondingmaterialsisthemainreasonthatresultsinthetemperaturedifferencebetweenoutsideandinsideofmassconcrete[4,5].Inordertoreducetheinnertemperatureofhydroelectricconcrete,severalmethodshavebeenproposedinmixproportiondesign.Theseincludeusingmoderate-heatportlandcement（MHC）,reducingthecontentofcement,andincreasingthePortlandcement（OPC）,MHChasadvantagessuchaslowheatofhydration,highgrowthrateoflong-termstrength,etc[6,7].SoitismorereasonabletouseMHCinapplicationofmassconcrete.

Low-heatportlandcement（LHC）,namelyhighbelitecementiscurrentlyattractingagreatdealofinterestworldwide.ThisislargelyduetoitslowerenergyconsumptionandCO2emissioninmanufacturethanconventionalPortlandcements.LHChasalotofnoticeableproperties,suchaslowheatofhydrationexcellentdurability,

etc,sothefurtherstudycontinuestobeimportant[8-10].Thelong-termstrengthofC2ScanapproachtoorevenexceedthatofC3S[11].Inaddition,C2ShasaseriesofcharacteristicssuperiortoC3S.TheseincludethelowcontentofCaO,lowhydrationheat,goodtoughness,compacthydrationproducts,excellentresistancestochemicalcorrosion,littledryshrinkage,etc[12,13].

Forhydroelectricconcrete,thedesignrequirementshavesomecharacteristics,suchaslongdesignage,lowdesignstrength,lowhydrationtemperaturerise,andlowtemperaturegradient[14].AlltheserequirementsagreewiththecharacteristicsofLHC.Furthermore,LHChasahighhydrationactivityatlaterages,theeffectofwhichcanimprovetheinnermicro-crack.Basedonabove-mentionedanalyses,thepropertiesoflow-heatPortlandcementconcretewerestudiedindetailinthispaper.Comparedwiththemoderate-heatPortlandcement（MHC）concrete,theanti-crackbehaviorofLHCconcretewasanalyzed.

2Experimental

MHCwasproducedinGezhoubaHoldingCompanyCementPlant,China;andLHCwasproducedinHunanShimenSpecialCementCo.Ltd.,China.ThechemicalcompositionsandmineralcompositionsofcementarelistedinTable1andTable2respectively,andthephysicalandmechanicalpropertiesofcementarelistedinTable3.

Inspiteofalittledifferenceinchemicalcompositions,thereisanobviousdissimilaritybetweenthemineralcomponentofLHCandthatofMHCbecauseofthedifferentburningschedule.TheC3S（Alite）contentofMHCishigherthanthatofLHC,andtheC2S（Belite）contentofLHCishigherthanthatofMHC.Aliteisformedattemperaturesofabout1450℃,whileBeliteisformedataround1200℃.Therefore,LHCcanbemanufacturedatlowerkilntemperaturesthanMHC.AndtheamountofenergytheoreticallyrequiredtomanufactureLHCislowerthanthatofMHC.

Belitehydratescomparativelyslowly,andtheearlycompressivestrengthsofpastes,mortars,andconcretescontainingLHCaregenerallylowerasaresult.Thelong-termstrengthanddurabilityofconcretemadefromLHCcanpotentiallyexceedthoseofMHC.TheresultsfromTable3showthattheearlystrengthofLHCpastesislowerthanthatofMHCpastes,andthatthestrengthgrowthrateofLHCishigherthanthatofMHC.

Thehydrationheatofbondingmaterialswastested.ClassIflyashofbondingmaterialscamefromShandongZhouxianPowerPlant,China.TheexperimentalresultsshowninTable4indicatethatthehydrationheatofLHCismuchlowerthanthatofMHC.The1-day,3-dayand7-dayhydrationheatofLHCwithoutflyashis143kJ/kg,205kJ/kg,227kJ/kg,respectively.The1-day,3-dayand7-dayhydrationheatofMHCwithoutflyashis179kJ/kg,239kJ/kg,278kJ/kg,respectively.ComparedwithMHC,theaveragehydrationheatofLHCconcreteisreducedbyabout17.5%.Obviously,lowhydrationisofadvantagetoabatethepressuretotemperaturecontrol,andtoreducethecrackprobabilityduetothetemperaturegradients.TheadiabatictemperatureofLHCconcreteandMHCconcretewastested.Asaresult,theadiabatictemperatureriseofLHCconcreteislowerthanthatofMHCconcreteandthedifferentvaluerangesfrom2℃to3℃ingeneral.

Afteraddingflyash,allspecimensshowalowerhydrationheat,anditdecreaseswithincreasingflyashcontent.ForMHCwith30%flyash,the1d,3d,7daccumulativehydrationheatisreducedby14.5%,20.5%,21.9%,respectively;andforLHCwith30%flyash,the1d,3d,7daccumulativehydrationheatisreducedby21.7%,26.3%,23.3%,respectively.Obviously,theeffectofflyashonthehydrationheatofLHCismorethanthatofMHC.ItiswellknownthattheflyashactivationcouldbeactivatedbyCa（OH）2.LHChasalowercontentofC3SandahighercontentofC2SthanMHC,sotheCa（OH）2,namelytheexcitercontentinhydrationproductsofLHCpastesislower.Decreasingthehydrationactivationofflyashreducesthehydrationheatofbondingmaterials.

3ResultsandDiscussion

Inthisexperiment,ZB-1AtyperetardingsuperplasticizerandDH9air-entrainingagentwereused.ThedosageofZB-1was0.7%bytheweightoftheblending,andthedosageofDH9wasadjustedtogiveanair-containingof4.5%to6.0%.Theparametersthataffectedthedosageincludedthecompositionandthefinenessofthecementused,andwhethertheflyashwasused.Fourgradationsofaggregatewereused,

120mm-80mm:

80mm-40mm:

40mm-20mm:

20mm-5mm=30:

30:

20:

20.

Thetermwater-to-cementitiouswasusedinsteadofwater-to-cement,andthewater-to-cementitiousratiowasmaintainedat0.50foralltheblending.Theslumpofconcretewasmaintainedatabout40mm,andtheaircontentwasmaintainedatabout5.0%intheexperimental.Afterbeingdemoulded,allthespecimenswereinastandardcuringchamber.ThemixproportionparameterofconcreteislistedinTable5.

3.1Physicalandmechanicalproperties

Thephysicalandmechanicalpropertiesincludestrength,elasticmodulus,limitstension,andsoon.TheresultsofstrengthshowninTable6indicatetheearlystrength（7dcuringages）ofLHC（oddsamples）concreteincreasesslowly.Theratiobetween7dcompressivestrengthand28dcompressivestrengthofLHCconcreteisabout0.4,whileforMHCconcretetheratioisabout0.6.ComparedwithMHCconcrete,thegrowthrateofstrengthofLHCconcretebecomesfasterafter7dcuringages.Thecompressivestrengthfor28d,90d,180dcuringagesofLHCconcretecontaining20%offlyashis30.2MPa,43.8MPa,48.5MPa,respectively,whilethatofMHCconcretecontaining20%offlyashis28.3MPa,35.6MPa,39.8MPa,respectively.ThecontentofC2SinLHCishigherthanthatinMHC,whichresultsintheabove-mentioneddifference.

Table6showsthatthestrengthgrowthrateofconcretemadewithflyashblendedcementsishigherthanthatofblankspecimens;themorethedosageofflyash,thehigherthegrowthrate.Flyashhasaglassynature,whichcanreactwithCa（OH）2.SinceCa（OH）2isahydrationproductofcement,thereactionbetweenflyashandCa（OH）2,called“secondaryhydration”,willhappenatlatishages.ThemagnitudeofCa（OH）2isaffectedbysomefactors,suchasthewater-to-cementitious,thedosageofcement.

TheelasticmodulusandthelimitstensionofconcretearegiveninTable7.Undersamemixingproportion,theelasticmodulusofLHCconcreteisapproximatelyequaltothatofMHC;the28-daylimitstensionofLHCconcreteisincreasedby10×10-6to15×10-6thanthatofMHC,andthe90-daylimitstensionofLHCconcreteisincreasedby12×10-6thanthatofMHCconcrete.TheaboveresultsshowthattheuseofLHCimprovesthelimitstensionofconcrete.Increasingthelimitstensionofconcretewillbebenefittothecrackresistanceofconcrete.

3.2Deformationcharacteristics

Deformationcharacteristicsofconcreteincludedryingshrinkage,autogenousdeformation,creep,etc.ThedryingshrinkageofconcreteisshowninFig.1.Thedryingshrinkageincreaseswithage.Atearlyagesaupto90days,alltheLHCconcretespecimensshowalowerdryingshrinkage;anditdecreaseswithincreasingtheflyashcontent.Whencontaining30%offlyash,thedryingshrinkageofLHCconcreteis363×10-6at90days,whileforMHCconcretethevalueis408×10-6.Asaresult,thevolumestabilityofLHCconcreteisbetterthanthatofMHCconcreteindryingenvironment.

ExperimentresultsofautogenousdeformationofconcretearegiveninFig.2.ThereisanobviousdifferencebetweenthedevelopmentofautogenousdeformationofLHCconcreteandthatofMHCconcrete.TheautogenousdeformationofLHCconcretehasanexpansivetendency.Atearlyages