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1、第二课沥青及沥青混合料Asphalt$MixAsphaltText:Asphalt&AsphaltPavingMaterials1AsphaltDefinedTheblackcementingagentknownasasphalthasbeenusedforroadconstructionforcenturies.Althoughtherearenaturaldepositsofasphalt,orrockasphalt,mostusedtodayisproducedduringtherefiningofcrudeoil.Asphaltisaconstitu
2、entofmostpetroleumsandisisolatedthroughtherefiningprocess.Asphaltiscalledabituminousmaterialbecauseitcontainsbitumen,ahydrocarbonmaterialsolubleincarbondisulfate.Thetarobtainedfromthedestructivedistillationofsoftcoalalsocontainsbitumen.Bothpetroleumasphaltandcoaltararereferredtoasb
3、ituminousmaterials.Becausetheirpropertiesdiffergreatly,petroleumasphaltshouldnotbeconfusedwithcoaltar.Petroleumasphaltiscomposedalmostentirelyofbitumenwhilethebitumencontentincoaltarisrelativelylow.Thetwomaterialsshouldbetreatedasseparateentities.Oneofthecharacteristicsandadvantage
4、sofasphaltasanengineeringconstructionandmaintenancematerialsisitsversatility.Althoughasemi-solidatordinarytemperratures,asphaltmaybeliquefiedbyapplyingheat,dissolvingitinsolvents,oremulsifyingit.Asphaltisastrongcementthatisreadilyadhesiveandhighlywaterproofanddurable,makingitpartic
5、ularlyusefulinroadbuilding.Itisalsohighlyresistanttotheactionsofmostacids,alkalis,andsalts.1.1AsphaltBinderAsphaltisproducedinavarietyoftypesandgradesrangingfromhard-brittlesolidstonearwater-thinliquids.Thesemi-solidformknownasasphaltbinderisthebasicmaterialusedinHot-MixAsphalt(HMA
6、)pavements.Liquidasphaltisproducedwhenasphaltbinderisblendedor“cutback”withpetroleumdistillatesoremulsifiedwithwaterandanemulsifyingagent.Atambientairtemperatures,asphalitbinderisablack,sticky,highlyviscousmaterial.Itisastronganddurablebinderwithexcellentadhesiveandwaterproofingcha
7、racteristics.Applyingheat,whichfacilitatesmixingwithmineralaggregatestoproduceHMA,canreadilyliquefyasphaltbinders.ThelargestuseofasphaltbinderisforHMA.Aftercompactingandcoolingtoairtemperature,HMAisaverystrongmaterialwiththeabilitytosustainheavytrafficloadswhileremainingflexibleeno
8、ughtowithstandambientenvir