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道路工程路桥毕业设计外文文献翻译
外文文献翻译
原文:
AsphaltMixtures-Applications,TheoryandPrinciples
1.Applications
Asphaltmaterialsfindwideusageintheconstructionindustry.Theuseofasphaltasacementingagentinpavementsisthemostcommonofitsapplications,however,andtheonethatwillbeconsideredhere.
Asphaltproductsareusedtoproduceflexiblepavementsforhighwaysandairports.Theterm“xible”isusedtodistinguishthesepavementsfromthosemadewithPortlandcement,whichareclassifiedasrigidpavements,thatis,havingbeamstrength.Thisdistinctionisimportantbecauseitprovidestheykeytothedesignapproachwhichmustbeusedforsuccessfulflexiblepavementstructures.
Theflexiblepavementclassificationmaybefurtherbrokendownintohighandlowtypes,thetypeusuallydependingonwhetherasolidorliquidasphaltproductisused.Thelowtypesofpavementaremadewiththecutback,oremulsion‘liquidproductsandareverywidelyusedthroughoutthiscountry.Descriptiveterminologyhasbeendevelopedinvarioussectionsofthecountrytotheextentthatonepavementtypemayhaveseveralnames.However,thegeneralprocessfollowedinconstructionissimilarformostlow-typepavementsandcanbe
describedasoneinwhichtheaggregateandtheasphaltproductareusuallyappliedtotheroadbedseparatelyandtheremixedorallowedtomix,formingthepavement.
Thehightypeofasphaltpavementsismadewithasphaltcementsofsomeselectedpenetrationgrade.
Fig.?
Amodernasphaltconcretehighway.Shoulderstripingisusedasasafelyfeature.
Fig.?
AsphaltconcreteattheSanFranciscoInternationalAirport.
Theyareusedwhenhighwheelloadsandhighvolumesoftrafficoccurandare,therefore,oftendesignedforaparticularinstallation.
2.Theoryofasphaltconcretemixdesign
Hightypesofflexiblepavementareconstructedbycombininganasphaltcement,ofteninthepenetrationgradeof85to100,withaggregatesthatareusuallydividedintothreegroups,basedonsize.Thethreegroupsarecoarseaggregates,fineaggregates,andmineralfiller.Thesewillbediscussedindetailinlaterchapter.
Eachoftheconstituentpartsmentionedhasaparticularfunctionintheasphaltmixture,andmixproportioningordesignistheprocessofensuringthatnofunctionisneglected.
Beforetheseindividualfunctionsareexamined,however,thecriteriaforpavementsuccessandfailureshouldbeconsideredsothatdesignobjectivescanbeestablished.
Asuccessfulflexiblepavementmusthaveseveralparticularproperties.First,itmustbestable,thatistoresistanttopermanentdisplacementunderload.Deformationofanasphaltpavementcanoccurinthreeways,twounsatisfactoryandonedesirable.Plasticdeformation
ofapavementfailureandwhichistobeavoidedifpossible.Compressivedeformationofthepavementresultsinadimensionalchangeinthepavement,andwiththischangecomealoss
ofresiliencyandusuallyadegreeofroughness.Thisdeformationislessseriousthantheonejustdescribed,butit,too,leadstopavementfailure.Thedesirabletypeofdeformationisanelasticone,whichactuallyisbeneficialtoflexiblepavementsandisnecessarytotheirlonglife.
Thepavementshouldbedurableandshouldofferprotectiontothesubgrade.Asphaltcementisnotimpervioustotheeffectsofweathering,andsothedesignmustminimizeweathersusceptibility.Adurablepavementthatdoesnotcrackorravelwillprobablyalsoprotecttheroadbed.Itmustberememberedthatflexiblepavementstransmitloadstothesubgradewithoutsignificantbridgingaction,andsoadryfirmbaseisabsolutelyessential.
Rapidlymovingvehiclesdependonthetire-pavementfrictionfactorforcontrolandsafety.Thetextureofthepavementsurfacesmustbesuchthatanadequateskidresistanceisdevelopedorunsafeconditionsresult.Thedesignprocedureshouldbeusedtoselecttheasphaltmaterialandaggregatescombinationwhichprovidesaskidresistantroadway.
Designprocedureswhichyieldpavingmixturesembodyingallthesepropertiesarenotavailable.Soundpavementsareconstructedwherematerialsandmethodsareselectedbyusingtime-testedtestsandspecificationsandengineeringjudgmentsalongwithaso-called
designmethod.
Thefinalrequirementforanypavementisoneofeconomy.Economy,again,cannotbemeasureddirectly,sincetrueeconomyonlybeginswithconstructioncostandisnotfullydeterminableuntilthefullusefullifeofthepavementhasbeenrecorded.If,however,the
requirementsforastable,durable,andsafepavementaremetwithareasonablesafetyfactor,thenthebestinterestsofeconomyhaveprobablybeenservedaswell.
Withtheserequirementsinmind,thefunctionsoftheconstituentpartscanbeexaminedwithconsiderationgivetohoweachpartcontributestonow-establishedobjectivesorrequirements.Thefunctionsoftheaggregatesistocarrytheloadimposedonthepavement,andthisisaccomplishedbyfrictionalresistanceandinterlockingbetweentheindividual
piecesofaggregates.Thecarryingcapacityoftheasphaltpavementis,then,relatedtothesurfacetexture(particularlythatofthefineaggregate)andthedensity,or“compa
theaggregates.Surfacetexturevarieswithdifferentaggregates,andwhilearoughsurface
textureisdesired,thismaynotbeavailableinsomelocalities.Densemixturesareobtainedbyusingaggregatesthatareeithernaturallyorartificiallyed”.Thismea“nswthealltgtrhaedfine
aggregateservestofillthevoidsinthecoarseraggregates.Inadditiontoaffectingdensityandthereforestrengthcharacteristics,thegradingalsoinfluencesworkability.Whenanexcessofcoarseaggregateisused,themixbecomesharshandhardtowork.Whenanexcessofmineralfillerisused,themixesbecomegummyanddifficulttomanage.
Theasphaltcementintheflexiblepavementisusedtobindtheaggregateparticlestogetherandtowaterproofthepavements.Obtainingtheproperasphaltcontentisextremelyimportantandbearsasignificantinfluenceonalltheitemsmarkingasuccessfulpavement.Achiefobjectiveofallthedesignmethodswhichhavebeendevelopedistoarriveatthebestasphaltcontentforaparticularcombinationofaggregates.
3.Mixdesignprinciples
Certainfundamentalprinciplesunderliethedesignproceduresthathavebeendeveloped.Beforetheseprocedurescanbeproperlystudiedorapplied,someconsiderationoftheseprinciplesisnecessary.
Asphaltpavementsarecomposedofaggregates,asphaltcement,andvoids.Consideringtheaggregatealone,allthespacebetweenparticlesisvoidspace.Thevolumeofaggregatevoidsdependsongradingandcanvarywidely.Whentheasphaltcementisadded,aportionoftheseaggregatevoidsisfilledandafinalair-voidvolumeisretained.Theretentionofthisair-voidvolumeisveryimportanttothecharacteristicsofthemixture.Thetermair-voidvolumeisused,sincethesevoidsareweightlessandareusuallyexpressedasapercentageofthetotalvolumeofthecompactedmixture.
Anasphaltpavementcarriestheappliedloadbyparticlefrictionandinterlock.Iftheparticlesarepushedapartforanyreason,thenthepavementstabilityisdestroyed.Thisfactorindicatesthatcertainlynomoreasphaltshouldbeaddedthantheaggregatevoidscanreadilyhold.However,asphaltcementissusceptibletovolumechangeandthepavementissubjecttofurthercompactionunderuse.Ifthepavementhasnoairvoidswhenplaced,orifitlosesthemundertraffic,thentheexpandingasphaltwilloverflowinaconditionknownas
bleeding.Thelossofasphaltcementthroughbleedingweakensthepavementandalsoreducessurfacefriction,makingtheroadwayhazardous.
CoarseandHne
Asphallcernenlandveryfinecgqregole
Airvoid
Fig.?
3Crosssectionofanasphaltconcretepavementshowingtheaggregateframeworkboundtogetherbyasphaltcement.
Theneedforaminimumair-voidvolume(usually2or3percent)hasbeenestablished.
Inaddition,amaximumair-voidvolumeof5to7percentshouldnotbeexceed.Anexcessofairvoidspromotesravelingofthepavementandalsopermitswatertoenterandspeedupthedeterioratingprocesses.Also,inthepreseneeofexcessairtheasphaltcementhardensandageswithanaccompanyinglossofdurabilityandresiliency.
Theair-voidvolumeofthemixisdeterminedbythedegreeofcompactionaswellasbytheasphaltcontent.Foragivenasphaltcontent,alightlycompactedmixwillhavealargevoidsvolumeandalowerdensityandagreaterstrengthwillresult.Inthelaboratory,thecompactioniscontrolledbyusingaspecifiedhammerandregulatingthenumberofblows
andtheenergyperblow.Inthefield,thecompactionandtheairvoidsaremoredifficulttocontrolandtestsmustbemadenospecimenstakenfromthecompactedpavementtocheekonthedegreeofcompactionbeingobtained.Trafficfurthercompactthepavement,andallowaneemustbemadeforthisinthedesign.Asystematiccheckingofthepavementoveranextendedperiodisneededtogivenfactualinformationforaparticularmix.Achangeindensityofseveralpercentisnotunusual,however.
Asphaltcontenthasbeendiscussedinconnectionwithvariousfacetsoftheixdesignproblem.Itisaveryimportantfactorinthemixdesignandhasabearinganallthecharacteristicsldasuccessfulpavement:
stability,skidresistanee,durability,andeconomy.Ashasbeenmentioned,thevariousdesignproceduresareintendedtoprovideameansforselectingtheasphaltcontent.Thesetestswillbeconsi