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XX大学学生毕业设计外文文献翻译原文：AsphaltMixtures-Applications,TheoryandPrinciples1.ApplicationsAsphaltmaterialsfindwideusageintheconstructionindustry.Theuseofasphaltasacementingagentinpavementsisthemostcommonofitsapplications,however,andtheonethatwillbeconsideredhere.Asphaltproductsareusedtoproduceflexiblepavementsforhighwaysandairports.Theterm“flexible”isusedtodistinguishthesepavementsfromthosemadewithPortlandcement,whichareclassifiedasrigidpavements,thatis,havingbeamstrength.Thisdistinctionisimportantbecauseitprovidestheykeytothedesignapproachwhichmustbeusedforsuccessfulflexiblepavementstructures.Theflexiblepavementclassificationmaybefurtherbrokendownintohighandlowtypes,thetypeusuallydependingonwhetherasolidorliquidasphaltproductisused.Thelowtypesofpavementaremadewiththecutback,oremulsion,liquidproductsandareverywidelyusedthroughoutthiscountry.Descriptiveterminologyhasbeendevelopedinvarioussectionsofthecountrytotheextentthatonepavementtypemayhaveseveralnames.However,thegeneralprocessfollowedinconstructionissimilarformostlow-typepavementsandcanbedescribedasoneinwhichtheaggregateandtheasphaltproductareusuallyappliedtotheroadbedseparatelyandtheremixedorallowedtomix,formingthepavement.Thehightypeofasphaltpavementsismadewithasphaltcementsofsomeselectedpenetrationgrade.第1页共12页XX大学学生毕业设计Fig.·1Amodernasphaltconcretehighway.Shoulderstripingisusedasasafelyfeature.Fig.·2AsphaltconcreteattheSanFranciscoInternationalAirport.Theyareusedwhenhighwheelloadsandhighvolumesoftrafficoccurandare,therefore,oftendesignedforaparticularinstallation.2.TheoryofasphaltconcretemixdesignHightypesofflexiblepavementareconstructedbycombininganasphaltcement,ofteninthepenetrationgradeof85to100,withaggregatesthatareusuallydividedintothreegroups,basedonsize.Thethreegroupsarecoarseaggregates,fineaggregates,andmineralfiller.Thesewillbediscussedindetailinlaterchapter.Eachoftheconstituentpartsmentionedhasaparticularfunctionintheasphaltmixture,andmixproportioningordesignistheprocessofensuringthatnofunctionisneglected.Beforetheseindividualfunctionsareexamined,however,thecriteriaforpavementsuccessandfailureshouldbeconsideredsothatdesignobjectivescanbeestablished.Asuccessfulflexiblepavementmusthaveseveralparticularproperties.First,itmustbestable,thatistoresistanttopermanentdisplacementunderload.Deformationofanasphalt第2页共12页XX大学学生毕业设计pavementcanoccurinthreeways,twounsatisfactoryandonedesirable.Plasticdeformationofapavementfailureandwhichistobeavoidedifpossible.Compressivedeformationofthepavementresultsinadimensionalchangeinthepavement,andwiththischangecomealossofresiliencyandusuallyadegreeofroughness.Thisdeformationislessseriousthantheonejustdescribed,butit,too,leadstopavementfailure.Thedesirabletypeofdeformationisanelasticone,whichactuallyisbeneficialtoflexiblepavementsandisnecessarytotheirlonglife.Thepavementshouldbedurableandshouldofferprotectiontothesubgrade.Asphaltcementisnotimpervioustotheeffectsofweathering,andsothedesignmustminimizeweathersusceptibility.Adurablepavementthatdoesnotcrackorravelwillprobablyalsoprotecttheroadbed.Itmustberememberedthatflexiblepavementstransmitloadstothesubgradewithoutsignificantbridgingaction,andsoadryfirmbaseisabsolutelyessential.Rapidlymovingvehiclesdependonthetire-pavementfrictionfactorforcontrolandsafety.Thetextureofthepavementsurfacesmustbesuchthatanadequateskidresistanceisdevelopedorunsafeconditionsresult.Thedesignprocedureshouldbeusedtoselecttheasphaltmaterialandaggregatescombinationwhichprovidesaskidresistantroadway.Designprocedureswhichyieldpavingmixturesembodyingallthesepropertiesarenotavailable.Soundpavementsareconstructedwherematerialsandmethodsareselectedbyusingtime-testedtestsandspecificationsandengineeringjudgmentsalongwithaso-calleddesignmethod.Thefinalrequirementforanypavementisoneofeconomy.Economy,again,cannotbemeasureddirectly,sincetrueeconomyonlybeginswithconstructioncostandisnotfullydeterminableuntilthefullusefullifeofthepavementhasbeenrecorded.If,however,therequirementsforastable,durable,andsafepavementaremetwithareasonablesafetyfactor,thenthebestinterestsofeconomyhaveprobablybeenservedaswell.Withtheserequirementsinmind,thefunctionsoftheconstituentpartscanbeexaminedwithconsiderationgivetohoweachpartcontributestonow-establishedobjectivesorrequirements.Thefunctionsoftheaggregatesistocarrytheloadimposedonthepavement,andthisisaccomplishedbyfrictionalresistanceandinterlockingbetweentheindividualpiecesofaggregates.Thecarryingcapacityoftheasphaltpavementis,then,第3页共12页XX大学学生毕业设计relatedtothesurfacetexture(particularlythatofthefineaggregate)andthedensity,or“compactness,”,oftheaggregates.Surfacetexturevarieswithdifferentaggregates,andwhilearoughsurfacetextureisdesired,thismaynotbeavailableinsomelocalities.Densemixturesareobtainedbyusingaggregatesthatareeithernaturallyorartificially“wellgraded”.Thismeansthatthefineaggregateservestofillthevoidsinthecoarseraggregates.Inadditiontoaffectingdensityandthereforestrengthcharacteristics,thegradingalsoinfluencesworkability.Whenanexcessofcoarseaggregateisused,themixbecomesharsha