专业英语9-10

Lesson12BituminousSurfaceCoursesThebituminoussurfacecoursehastoprovideresistance(抵抗)totheeffectsofrepeatedloadingbytyres（轮胎）andtotheeffectsoftheenvironment.Inaddition,itmustofferadequateskidresistance（抗滑能力）inwetweatheraswellascomfortablevehicleride.Itmustalsoberesistanttorutting（车辙）andtocracking（裂缝）.Itisalsodesirablethatsurfacecourseisimpermeable（不渗水的）,exceptinthecaseofporousasphalt(多空隙沥青面层).Hotrolledasphalt(HRA)（热压沥青混凝土）isagapgraded（间断级配）materialwithlesscoarseaggregate（粗集料）.Infactitisessentiallyabitumen/fineaggregate（细集料）/filler（填料）mortar（胶浆）intowhichsomecoarseaggregateisplaced.Themechanicalpropertiesaredominatedbythoseofthemortar.ThismaterialhasbeenextensivelyusedasthewearingcourseonmajorroadintheUK,thoughitsusehasrecentlydeclinedasnewmaterialshavebeenintroduced.Itprovidesadurable（耐久的、耐用的）layerwithgoodresistancetocrackingandonewhichisrelativelyeasytocompact（压实）.Thecoarseaggregatecontentislow(typically30%)whichresultsinthecompactedmixturehavingasmoothsurface.Accordingly（因此）,theskidresistanceisinadequateandprecoated（预浇）chippings（石屑）arerolledintothesurfaceatthetimeoflayingtocorrectthisdeficiency（不足）.InScotland,HRAwearingcourseremainsthepreferredwearingcourseontrunkroads（干线道路）includingmotorway（高速公路、汽车专用公路）but，since1999thinsurfacingshavebeenthepreferredoptioninEnglandandWales.Since1999inNorthernIreland,HRAwearingcourseandthinsurfacingsarethepreferredpermittedoptions.Porousasphalt(PA)isauniformlygraded（单一级配）materialwhichisdesignedtoprovidelargeairvoids（空隙率）sothatwatercandraintotheverges（路肩、边缘）withinthelayerthickness.Ifthewearingcourseistobeeffective,thebasecourse（基层）belowmustbewaterproof（防水的）andthePAmusthavetheabilitytoretainitsopentextured（构造、纹理）propertieswithtime.Thickbinderfilms（吸附沥青膜）arerequiredtoresistwaterdamage（水损害）andageing（老化）ofthebinder.Inuse,thismaterialminimizesvehiclespray（水雾）,providesaquietrideandlowerrollingresistancetotrafficthandensemixtures（密级配混合料）.BituminousSurfaceCoursesItisoftenspecified（指定）forenvironmentalreasonsbutstonemasticasphalt(SMA)(沥青玛蹄脂碎石)andspeciallythinsurfacingsaregenerallyfavouredincurrentUKpractice.TherehavebeenhighprofileinstanceswhereaPAwearingcoursehasfailedearlyinitslife.TheHighwaysAgency（公路局）doesnotrecommendtheuseofaPAattrafficlevelsabove6000commercialvehicles（载重车）perday.Asphalticconcrete（沥青混凝土）anddensebitumenmacadam(DBM)（密级配沥青碎石）arecontinuouslygradedmixtures（连续级配混合料）similarinprincipletotheDBMsusedinroadbases(基层)andbasecoursesbutwithsmallermaximumparticlesizes（最大粒径）.Asphalticconcretetendstohaveaslightly（稍微）densergradingandisusedforroadsurfacesthroughouttheworldwiththeexceptingoftheUK.ItismoredifficulttomeetUKskidresistanceStandards（抗滑标准）withDBMsthanHRA,SMAorPA.ThisproblemcanberesolvesbyprovidingaseparatesurfacetreatmentbutdoingsogenerallymakesDBMeconomicallyunattractive.Stonemasticasphalt(SMA)materialwaspioneered（开辟、开路）inGermanyandScandinaviaandisnowwidelyusedintheUK.SMAhasacoarse,aggregrateskeleton（碎石骨架）,likePA,butthevoidsarefilledwithafineaggregate/filler（填料）/bitumenmortar.Inmixturesusingpenetrationgradebitumen（石油沥青）,fibres（纤维）areaddedtohold（吸收、吸附）thebitumenwithinthemixture(toprevent“binderdrainage”).Bitumenoilbitumen(earthoil)naturalbitumenTarWhereapolymermodifiedbitumen（聚合物改性沥青）isused,thereisgenerallynoneedforfibres.SMAisagap-gradedmaterialwithgoodresistancetoruttingandhighdurability（耐久性）.modifiedbitumenSBSSBRPE\EVAItdiffersfromHRAinthatthemortarisdesignedtojustfillthevoidsinthecoarseaggregatewhereas,inHRA,coarseaggregateisintroducedintothemortaranddoesnotprovideacontinousstonematrix（矿质骨架）.ThehigherstonecontentHRAs,however,arerathersimilartoSMAbutarenotwideusedaswearingcoursesintheUK,beingpreferredforroadbaseandbasecourseconstruction.Avarietyofthinandwhatwerecalledultra（超的、极端的）thinsurfacings(nowadays,thetendencyistousetheterm‘thinsurfacings’forboththinandultrathinsurfacings)havebeenintroducedinrecentyears,principallyasaresultofdevelopmentworkconcentrated（集中）inFrance.Thesematerialsvaryintheirdetailedconstituents（成分、要素、组成部分）butusuallyhaveanaggregategradingsimilartoSMAandoftenincorporate(联合、结合、加入)apolymermodifiedbitumen.Theymaybeusedoverahighstiffnessroadbaseandbasecourseorusedforresurfacing（翻修路面）ofexistingpavements.Forheavydutypavements(i.ethosedesignedtohaveausefullifeoffortyyears),themaintenancephilosophy（哲学、哲理）isoneofminimumlaneoccupancy（占用）,whichonlyallowstimeforreplacement（替换）ofthewearingcoursetothese‘longlife’pavementstructures.Thenewgenerationofthinsurfacingsallowsthistobeconvenientlyachieved.Thevariousgeneric（种类的）mixturetypesdescribedabovecanbecomparedwithrespecttotheirmechanicalpropertiesanddurabilitycharacteristicsbyreference（参考）toFig.12.1.Thisshows,inprinciple,howlowstonecontentHRA,asphalticconcrete,SMAandPAmixturesmobilizeresistance(流动阻力)toloadingbytraffic.Asphalticconcrete(Fig.12.1a))presentssomethingofacompromise（和解、折衷方案）whenwelldesigned,sincethedenseaggregategradingcanoffergoodresistancetotheshearstresses（剪切应力）whichcauserutting,whileanadequatebindercontentwillprovidereasonableresistancetothetensilestresses（拉应力）whichcausecracking.Ingenera