房建外文翻译建筑材料混凝土与砂浆.docx

房建外文翻译建筑材料混凝土与砂浆.docx

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房建外文翻译建筑材料混凝土与砂浆

CONCRETEANDMORTAR

1.EarlyHistoryofCementandConcrete

Shelterfromtheverybeginningofman/existence,hasdemandedtheapplicationOfthebest,availabletechnologyofthecontemporaryera.Intheearliestages,structuresconsistedoframmedearth,orstoneblockslaidoneonanotherwithoutbenefitofanybondingorcementingmedium.Stabilityofthestonestructuresdependedontheregularsettingoftheheavystones,Theearliestmasonryprobablyconsistedofsun-driedclaybricks,setinregularcoursesinthinlayersofmoistmud.Whenthemoistmuddried,asolidclaywallresulted.Construction:

ofthiskindwascommoninthedrydesertareasoftheworld.

BurntgypsumasacementingmaterialwasdevelopedearlyintheEgyptianperiodandwasapparentlyusedinconstructionofsomeofthepyramids.LatertheGreeksandRomansdiscoveredmethodsofburninglimestonetoproducequicklimewhichwassubsequentlyslakedforuseinmakingmortar.BoththeGreeksandtheRomanslearnedthatcertainfinesoilorearth,whenmixedwiththelimeandthesand,producedasuperiorcementingmaterial.TheGreekmaterial,avolcanictufffromtheislandofSantorin,isstillusedinthatpartOftheworld.ThebestofthematerialsusedbytheRomanswasatufforashfromthevicinityofPozzuolinearMt.Vesuvius,hencethename“pozzolan”usedtoidentifyacertaintypeofmineraladmixtureusedinconcretetoday.

ThecementproducedbytheRomanswasahydrauliccement,thatis,ithadthecapabilityofhardeningunderwater.ManyoftheRomanstructureswereconstructedofaformofconcrete,usingthesematerials,andstonemasonrywasbondedwithamortarsimilarlycomposed.

DuringtheMiddleAgesofhistory,theartofmakinggoodmortarwasnearlylost,thelowpointhavingbeenreachedinaboutthellthcentury,whenmuchinferiormaterialwasused.Qualityofthelimestartedtoimproveatthistimeandinthe14thcenturyorlatertheuseofpozzolanswasagainpractised.

OneofthemostfamousprojectsofthecomparativelyrecentperiodwastheconstructionofthenewEddystoneLighthouseoffthecoastofEnglandin1757--59.JohnSmeaton,theengineeranddesignerofthestructure,investigatedmanymaterialsandmethodsofbondingthestonesforthebuilding.

Engineeringandscientificdevelopmentwasbeginningtomoverapidlyatthistime,andmanyresearchersinseveralcountrieswereinvestigatingcementingagentsmadefromgypsum,limestoneandothernaturalmaterials.Onediscoverywasamethodofmakingacementbyburninganaturallyoccurringmixtureoflimeandclay.propertiesofthenaturalcementwereveryerraticbecauseofvariationsintheproportionsinthenaturalmaterial,althoughuseofthisnaturalcementcontinuedformanyyears.

In1824JosephAspdin,abrickmasonofLeeds,England,tookoutapatentonamaterialhecalledPortlandcement,socalledbecauseconcretemadewithitwassupposedtoresemblethelimestonequarriednearPortland,England.Aspdinisgenerallycreditedwithinventingamethodofproportioninglimestoneandclay,burningthemixtureathightemperaturetoproduceclinkers,thengrindingtheclinkerstoproduceahydrauliccement.Hissmallkiln,producingabout16tonsofclinkeratatime,requiredseveraldays/oreachburn.Expansionanddevelopmentofcementmanufacturingwasslowforanumberofyears.About1850,however,theindustryhadbecomewellestablishednotonlyinEngland,butalsoinGermanyandBelgium.

ShipmentstotheUnitedStateswerestartedin1868andreachedapeakabout1895,atwhichtimeproductionwaswellunderwayintheUnitedStates.

MeanwhiletheUnitedStatesproductionofnaturalcementhadbeenstartedearlyinthe19thcenturyasaresultofthedemandforcementforconstructionoftheErieCanalandrelatedworks.Subsequentdevelopmentoftherotarykilnledtolargescaleproductionofcementthroughouttheworld.

Theuseofconcretewasexpandedbytheconstructionofrailroads,bridges,buildingsandstreetpavements.ResearchinreinforcingconcretewithsteelrodshadbeenstartedinFrance,andtheyear1875sawfirstuseofreinforcedconcreteintheUnitedStates.Much'oftheconcreteatthistimecontainedbarelyenoughwatertoenabletheconcretetoberammedintoplacebytheapplicationofmuchhandlabor.Therethenensuedaperiodofwetconcreteinwhichtheconcretewasflowedintoplace.Manyusersofconcrete,however,realizedthefollyofwetmixes,andabout1920DuffAbramsrevealedtheresultsofhisresearchandobservations.Hestatedthatthequalityofconcretewasdirectlyaffectedbytheamountofwaterinrelationtotheamountofcement;withinreasonablelimits,thequalityoftheconcretedecreasesasthewater-cementratiogoesup.Thishasbecomeoneofthebasiclawsofconcretetechnology.

2.AdvantagesandDisadvantagesofConcreteandItsWater-CementRatio

ConcreteisamixtureofPortlandcement,water,sand,andcrushedgravelorstone.Thewaterandcementformacementpasteinwhichthesandandstoneorgravelaremixed.Thesandandstoneorgraveltogethermakeuptheaggregateofaconcretemixture.Theaggregateservesnostructuralfunction.Itismerely,afillerthataddslow-costbulktothecementpaste;itusuallymakesupabout75percentofagivenmassofconcrete,byvolume,althoughapooraggregatecanreducethestrengthofabatchofconcreteconsiderably,goodaggregateaddsonlyslightlytothestrengthofthecement.

Thetwoprincipaladvantagesofconcreteasaconstructionmaterialareitsrelativecheapnessandtheeasewithwhichitcanbehandledandplacedwhileitisintheplasticstate.

Theprincipalstructuraladvantagesofconcreteareitsgreatcompressivestrengthanditsdurability,Concretecanwithstandveryhighcompressiveloads.Thisiswhatmakesconcretesosuitableforthefoundations,walls,andcolumnsofbuildings,andfordrivewaysandwalksaswell.

Theprincipalstructuraldisadvantageofconcreteisitspoortensilestrength.Thatis,itcannotwithstandpullingorbendingloadswithoutcrackingorbreaking.Forthisreason,steelrods,orreinforcementsteel,areoftenembeddedinconcrete,thereinforcementsteelprovidingthetensilestrengththeconcretelacks.Concretewithreinforcementsteelembeddedinitisreinforcedconcrete.

Inadditiontoitspoortensilestrength,concrete,likemostconstructionmaterials,expandsinhotweatherandwhenwetandcontractsincoldweatherandasitdriesout.Unlessthesemovementsareallowedforduringconstruction,theconcretewillcrack.

And,contrarytocommonbelief,solidconcreteisnotimpervioustowater.Somemoisturewillmigrateintothebest-madeconcrete.Butiftheconcreteshouldbeexcessivelyporous,whichcanhappeniftoomuchwaterhasbeenusedinmixingit,moisturecaneasilyentertheconcreteafterithascured.Ifthismoistureshouldbepresentwithintheconcretewhencoldweathercomes,themoisturemayfreeze,whichmayresultinseriousfrostdamagetothestructure.

Despitetheselimitations,concreteisaninherentlystronganddurableconstructionmaterial.Iftheproportionsofwater,cement,andaggregatearecarefullycalculatedandiftheconcreteisplacedandallowedtocureaccordingtosimplebutdefiniterules,itispossibletoobtainfromtheconcreteallthestrengthanddurabilitythatisinherentinit.

Theratioofwatertocementinabatchofconcreteistheprincipaldeterminantoftheconcrete'sfinalstrength.Atonetimetheinstructionsforpreparingabatchofconcretewouldhavecontainedproportionssuchas1:

2:

4,indicatingthat1partofPortlandcementto2partsofsandto4partsofgravelbyvolumeweretobemixedtogether,afterwhichsufficientwaterwastobeaddedtoobtainaworkablemixture.Thisprocedureignoredentirelytheimportanceofthewater-cementratio.Italsoresultedveryofteninthepreparationoraveryweakconcrete,sincethenaturaltendencyistoaddenoughwatertomakeplacementoftheconcreteaseasyaspossible-thesloppierthebetter,asfarastheworkmenareconcerned.Thismannerofspecifyingtheproportionsofconcreteisobsoleteandshouldneverbefollowed.

Intheory,ittakesonly3galofwatertohydratecompletely1cuftofcement.（Asackofcementcontains1cuftexactly,andthesackweighs94lb）.Butthiswater-cementratioproducesamixturethatistoostifftobeworked.Inpractice,therefore,additionalwater,between4and8galpersackofcement,isusedtoobtainaworkablemixture.

Butthegreatertheproportionofwaterinawater-cementratio,theweakerthefinalconcretewillbe.Theadditionalwaterthatisnecessarytoachieveaworkablebatchwillonlyevaporatefromtheconcreteastheconcretesets,anditwillleavebehindintheconcreteinnumerablevoids.Thisisthereasontherewillalwaysbesomeporosityinconcrete.Whenanexcessiveamountofwaterhasbeenused,therewillbeanexcessivenumberofvoids,whichmaycausetheconcretetoleakbadly.Ifthesevoidsshouldbefilledwithmoisturewhencoldweathercomes,theywillcausethefrostdamagealludedtoabove.

Asageneralrule,therefore,6galofwaterpersackofcementshouldbethemaximumamountusedformakingconcrete;andthelesstheamountofwaterthatisused,thestrongertheconcretewillbe.Alsoincludedinthe6galiswhateversurfacemoistureiscontainedinthesandthatispartoftheaggregate.

3.Mortar

Mortarisamixtureofacementitiousmaterial（whichmaybeportlandcementorlimeorboth）andsand.Whenwaterisaddedtotheseingredients,theresultisaplasticsubstancethatisusedtobindtogetherbricks,tiles,concreteblocks,andotherkindsofmaso