Optimization of technical measures for improving

high-temperatureperformanceofasphalt–rubbermixture

ChuanXiao•TianqingLing•YanjunQiu

Received:1July2013/Revised:8October2013/Accepted:9October2013/Publishedonline:26October2013ÓTheAuthor(s)2013.ThisarticleispublishedwithopenaccessatSpringerlink.com

AbstractAsphalt–rubberpavementsoftenbecomedam-agedinhigh-temperatureregionsandappearruttedorwavy,andexperienceslippage.Toimprovethehigh-tem-peratureperformanceoftheasphalt–rubbermixture,tech-nicalmeasurements,suchas,theoptimaladjustmentofgradation,techniqueofcompositemodification,andcon-trolofcompactionwereinvestigated.Anoptimaladjust-mentofaggregategradationbasedonstonematrixasphaltimprovesthehigh-temperaturestabilityoftheasphalt–rubbermixturesignificantly.Throughcompositemodifi-cation,theeffectofasphalt–rubbermodificationwasenhanced,andthedynamicstabilityandrelativedefor-mationindicesoftheasphalt–rubbermixturewereimprovedsignificantly.Furthermore,compactionparame-tershadasignificantinfluenceonthehigh-temperaturestabilityoftheasphalt–rubbermixture.Therollingtimesforcompactingtheasphalt–rubbermixtureshouldbecontrolledtowithin18–20round-tripsatamoldingtem-peratureat180°C;iftherollingtimeisa12round-trip,thecompactiontemperatureoftheasphalt–rubbermixtureshouldbecontrolledbetween180and190°C.

KeywordsRoadengineeringÁOptimizationÁLaboratorytestÁAsphalt–rubbermixtureÁHigh-temperatureperformance

1Introduction

Rapidgrowthofwastetiresisaseriousenvironmentalproblembecauseoftheirhighlyresistantchemical,bio-logical,andphysicalproperties.Manyapproacheshavebeenconsideredtoencouragethesustainabledevelopment.Usingcrumbrubberinasphalt,whichinitiatedwiththemotivationtoimprovethebinderproperties,isoneofthepracticalwaystotackletheincreasingwastetires.

Ingeneral,theapproachesusedtoincorporatecrumbrubbermodifier(CRM)inroadpavingmaterialsareclas-sifiedasthedrymethodandthewetmethod[2].WetmethodisappliedinmostoftherubberizedasphaltprojectsinChina,whichentailsaddingthecrumbrubbertothebinderbeforemixingitwithaggregate[3].Thebehaviorofasphalt–rubberwithwetmethoddependsonseveralfac-tors,suchas,theorigin,fabricationprocessandgrainsizedistributionofthecrumbrubber,thetypeofbaseasphaltbinderusedinthemixture,andthetemperatureandtimeofthemixingprocess.Andersonetal.[4]investigatedtherheologicalandphysicalpropertiesofbindersmodifiedwithrubber,forrubbercontentsbelow20%byweight.Huangetal.[5]andShenandAmirkhanian[6]suggestedtheoptimalpreparationofasphalt–rubberaccordingtocomparativetestsonmaterialpropertiesofasphaltbinder.Inpavementdestruction,asphalt–rubberhasbecomeincreasinglyattractiveintheapplications,suchas,opengradedfrictioncourse(OGFC),stressabsorptionmembraneinterlayer(SAMI),andsupersilentpavement(SSP)[2].Theasphalt–rubberpavementsexhibituniqueadvantagesinreducingpavementthickness,delayingreflectioncracking,anddecreasingtrafficnoise[7,8].However,anobviousproblemintheapplicationoftheasphalt–rubbermixtureisthelackofhigh-temperaturestabilityusedasstructurallayer,whichcouldcauseseriousruttingunderrecycled

C.Xiao(&)ÁY.Qiu

SchoolofCivilEngineering,SouthwestJiaotongUniversity,P.O.Box520,No.111FirstNorthSection,2ndRingRoad,Chengdu610031,Sichuan,Chinae-mail:xcaaa6666@sina.com

T.Ling

SchoolofCivilEngineeringandArchitecture,ChongqingJiaotongUniversity,Chongqing400074,China

123

274C.Xiaoetal.

vehicleloading.Theindices,suchas,viscosity,penetration,andsofteningpointshowthattheasphalt–rubbershowsexcellentperformanceathigh-temperature[9].However,becauseoftheinterferenceofasphalt–rubberandaggregateduringthecompactingprocessandthelowstiffnessmod-ulusanddeformationcharacteristicsoftheasphalt–rubbermixture[8,10],itisdifficulttomeetthedesireddemandswhenapplyingasphalt–rubberpavementinhigh-tempera-tureregions.Furthermore,thereisnounifiedtechnicalspecificationforasphalt–rubberinChinaresultinginsig-nificantdiscrepanciesinaggregategradation,asphaltcontent,andmineralfillercontentwhenpavingwithasphalt–rubbermixture[11–13].Improvementsinthehigh-temperatureperformanceofasphalt–rubberpavementsarecriticalwhentheyareappliedinhigh-temperatureregionsandunderheavytrafficconditionsinChina.

Inthispaper,weinvestigatethehigh-temperaturesta-bilityofanasphalt–rubbermixturebasedoninternalandexternalfactors.Atfirst,theoptimalgradationwasadjus-tedintheruttingtestswithdynamicstabilityandrelativedeformationasevaluationindices.Then,theschemeofcompoundmodificationandoptimizationofthecompac-tionparameterswereanalyzedtoimprovethehigh-tem-peraturestabilityoftheasphalt–rubbermixture.Toobtainareasonableschemeofcompoundmodification,compar-ativetestsofhigh-temperatureperformancewerecon-ductedbetweendifferentbindersandmixtures.Theeffectsofrollingtimeandmoldingtemperatureonairvoidvolumeandthedynamicstability(DS)wereinvestigatedtodetermineoptimalcompactionparameters.

2.2Materialpropertiesofaggregateandfiller

Thetestmethodsfollowed‘‘TestMethodsofAggregateforHighwayEngineering’’(JTGE42-2005)andthemainindicesoftheaggregateandmineralfillerintheasphalt–rubbermixturesarelistedinTables2and3,respectively.

3Testmethodandanalysis

3.1Optimizationofaggregategradation3.1.1Gradation-typeselection

Basedonthebroadoverviewofatypicalgradationtypeforanasphalt–rubbermixture,AR-AC-13(basedonArizonastandards[2,12]),SMA-13(traditionalstonematrixasphalt[15]),andAC-13(dense-gradedasphaltmixture[15])werechosenasresearchmaterialsonwhichtocon-ducttheruttingtests.Figure1showstheaggregategra-dationsofdifferentmixtures.

Theruttingtestsonthedifferentasphaltmixturesfol-lowed‘‘StandardTestMethodsofBitumenandBituminousMixturesforHighwayEngineering’’(JTGE20-2011)withparameterslistedinTable4.

TheruttingtestresultsforthedifferentasphaltmixturesaregiveninTable5.

Table5showsthatthepreferentialorderofthethreekindsofmixturesbasedonhigh-temperatureperformanceis:SMA-13[AR-AC-13[AC-13.Thisoccursbecauseofthedifferentcharacteristicsofthemixtures.

BecauseAC-13isa‘‘suspend-dense’’structuremixture,thereisinterferencebetweentheasphalt–rubberbinderandtheaggregateduringcompaction.Thistypeofmixtureisdifficulttocompactcompletelywithasphalt–rubber.Thismostlikelyexplainswhythehigh-temperatureperfor-manceindicesofAC-13aretheworstamongthethreekindsofasphaltmixtures.

AR-AC-13hasanaggregategradationbasedontheAri-zonastandardwithobviousgapgradationcharacteristics.Byenhancingthehighviscositybinderdosageandreducingtheamountoffineaggregate,especiallythefiller,morevoidsappearinthemineralaggregateofAR-AC-13andmore

2Testmaterials

2.1Materialpropertiesofasphalt–rubber

SK70#baseasphaltandcrumbrubber(30meshsize)wereusedtoproduceasphalt–rubberforcomparativetestsofasphalt–rubberperformance.Thetestmethodsfollowed‘‘StandardTestMethodsofBitumenandBituminousMixturesforHighwayEngineering’’fromtheindustrystandardofChina(JTGE20-2011)[14]withmainper-formanceindiceslistedinTable1.

Table1Propertiesofasphalt–rubberPerformanceindex

180°Crotationviscosity(Pas)Softeningpoint(°C)Penetration(0.1mm)Elasticrecovery(%)

Value2.867.650.478.0

Technicalstandard[9]2.5–5.0[6530–70C60

TestmethodT0625T0606T0604T0662

NoteThecodeoftestmethodfollowedJTGE20-2011[14]

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High-temperatureperformanceofasphalt–rubbermixtureTable2PropertiesofaggregateAggregatetype10–15mmgravel5–10mmgravelStonechip

Apparentdensity(gÁcm-3)2.9282.9122.725

Bulkdensity(gÁcm-3)2.8342.8262.725

Crushedstonevalue(%)11.211.6–

Water-washingmethod

\\0.075mm(%)0.20.2–

Flatandelongatedparticleincoarseaggregate(%)7.87.1–

Waterabsorption(%)1.841.88–

Sturdiness(%)0.30.31.2

275

Sand

equivalent(%)––78.4

Table3PropertiesoffillerApparentdensity(gÁcm-3)2.710

Hydrophiliccoefficient0.6

Plasticityindex(%)2.2

Water

content(%)0.43

HeatingstabilityColordidnotchangeat200°C

Passpercentage(%)

\\0.6mm\\0.3mm\\0.15mm\\0.075mm100.0

99.9

97.2

91.8

100Passing percentage (%)8060402001613.29..752.361.180.6AR-AC-13SMA-13AC-130.30.150.08Sieve size (mm)Fig.1Comparisonofaggregategradationsignificantfeaturesappearintheframeworkstructure.However,ruttingtestresultsshowthatthetypical‘‘S’’gra-dationtypedidnotreachtheexpectedtarget.Onefactorthatcontributestotheproblemmaybethatwithareductioninfiller,theasphaltmortarstiffnessisreducedmakingthemixturepronetodeformation.ItisthereforedifficulttoachievecohesionandstabilityintheAR-AC-13mixture.SMA-13isalsoagapgradationmixture,butcomparedwithAR-AC-13,theasphalt–rubbermixturebasedontra-ditionalSMA-13hasmorefineaggregateandlessasphaltbinderproportion,andthedeficienciesinAR-AC-13canbeovercome.

3.1.2Gradationoptimization

TheruttingtestresultsofSMA-13withtheasphalt–rubberwereunabletomeetheavytrafficdemands[11].WethereforeselectedSMA-13(AR-SMA-13)forfurtheradjustmentofaggregategradation.Theoptimaladjustmentofthepassingpercentagesthroughcrucialsieveswasstudiedtoimprovethehigh-temperatureperformanceofAR-SMA-13.Thekeysievesforaggregategradationwereselectedbecause:(1)theaggregategradationshouldformaframeworkstructurewithexcellentstrength;(2)crumbrubberiscoarsecomparedwithconventionalmodifiersand

Table4RuttingtestparametersTestparametersMoldingmethodSpecimensizeTesttemperaturePressureLoadingdistanceLoadingspeed

ValueWheelmolding3009300950mm60±1°C0.7±0.05MPa230±10mm42±1timesmin-1Table5RuttingtestresultsfordifferentasphaltmixturesMixturetypeAR-AC-13SMA-13AC-13

Asphaltcontent(%)7.05.84.3

Dynamicstability(timesmm-1)1,7213,2191,480

Relativedeformation(%)4.32.95.2

NoteDynamicstabilityisdefinedastheaxleloadingtimewhenthemixturespecimengeneratesa1-mmdeformation.Relativedeformationisdefinedastheratiobetweenfinaldeformationandoriginalmixturespecimenheight[11]

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276C.Xiaoetal.

itisnecessarytodecreasethefillerproportionofAR-SMA-13andincreasevoidsinthemineralaggregate(VMA)sothatthereisenoughfillingspacefortheasphalt–rubberbinderintheasphalt–rubbermixture;and(3)2.36mmisanimportantsievesizeforaggregategradation.Thevariationinthe2.36-mmpassingpercentagewouldnotinfluencethemixturevolumeparameterssignificantly.Itisthereforehelpfultoreducetheinfluencecausedbyvari-abilityintheothervolumeparameters.

Asdiscussedabove,thepassingpercentagesthroughthe0.075-and2.36-mmsievesizeswereselectedascrucialsievesuponwhichtomakeadjustments.ThechangesinpasspercentageareshowninTable6.

HotmixasphaltwasdesignedaccordingtotheMarshalltest[15]withresultsgiveninTable7(whereVVisthevolumeofairvoidsandVFAisvoidsfilledwithasphalt).Ruttingtests[14]wereconductedtodeterminetheoptimalgradationtypeforAR-SMA-13.TheDSandrel-ativedeformationwerechosenasevaluationindices.Table8showsthedifferencesamongthethreetypesofmixturesfromtheruttingtests.

AsshowninTable8,thehigh-temperaturestabilityofAR-SMA-13Ireducedthefillerproportionfrom10%to8%,yieldedabettermixturethantheothertwotypes,andistheonlymixturethatmeetsthetechnicalstandards.Gradationadjustmenttooptimizethehigh-temperatureperformanceofAR-SMA-13isthereforefeasible.3.2Compoundmodification

3.2.1Preparationofcompound-modifiedsampleStyrene–butadieneblockcopolymer(SBS)andviscosity-reducingadditive(termedSAK)werechosenasmodifierstostudycompoundmodificationonasphalt–rubber.Based

Table6AdjustmentofaggregategradationGradationtype

Passpercentage(%)13.2mm

Standardgradation[15]GradationIGradationII

959595

9.5mm62.562.562.5

4.75mm272727

onthedifferentpropertiesofSBS[16,17]andSAK[18],differentpreparationprogramswereformulatedforthetwotypesofcompound-modifiedasphalt–rubber:(1)

SBS-Rubbercompound-modifiedasphalt(termedS-Rasphalt):(a)heatbaseasphaltto180°C,addSBS(2%)intobaseasphalt,andshearfor30minusinganemulsionshearapparatusat180°Cand3,500rpm;(b)swellanddevelopfor30minat150°Cbymanualmixing;(c)heatmodifiedasphaltto190–200°C,adddrycrumbrubberandthenshearanddevelopfor45–60minusinganemulsionshearapparatusat3,000rpm.

SAK-Rubbercompound-modifiedasphalt(termedK-Rasphalt):(a)heatbaseasphaltto150°C,addSAK(2.5%)intobaseasphalt,andmixbyhand;(b)heatmodifiedasphaltto190–200°C,adddrycrumbrubber,thenshearanddevelopfor45–60minat3,000rpm.

(2)

3.2.2Asphaltbindertests

Pureasphalt–rubber,SBSasphalt,S-Rasphalt,andK-Rasphaltwereselectedtoanalyzetheasphaltbinderprop-erties.Theevaluationindiceschosenwere180°Crotationviscosity,penetration,softeningpoint,andelasticrecoverywithresultsshowninFig.2.

Comparativetestresultsforthedifferentasphalt–rubbertypesshowthatthehigh-temperatureperformanceofallthreetypesofasphalt–rubber(pure,S-R,andK-R)wasbetterthanSBSasphalt.Intermsofcompoundmodifica-tion:(1)S-Rasphaltexhibitsabetterhigh-temperatureperformanceforallindicescomparedwithpureasphalt–rubber;the180°Crotationviscosity,softeningpoint,andelasticrecoveryincreasedby10.7,17.6,and3.8%,

2.36mm20.518.516.5

1.18mm191715

0.6mm161412

0.3mm13119

0.15mm12108

0.075mm1086

Table7ResultsfromtheMarshalltestGradationtypeStandardgradationGradationIGradationII

Asphaltcontent(%)5.86.06.1

Bulkdensity(gÁcm-3)2.4352.4442.437

VV(%)4.24.34.1

VMA(%)17.117.517.6

VFA(%)75.475.476.7

Marshallstability(kN)7.948.028.21

Flowvalue(mm)2.632.312.57

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High-temperatureperformanceofasphalt–rubbermixture

Table8Comparisonofdifferentmixturesforhigh-temperatureperformanceMixturetype

DynamicstabilityRelativedeformation(timesmm-1)(%)Testvalue

StandardTestvalueStandardAR-SMA-133,219C3,500

4.3B3.1

AR-SMA-13I3,6882.9AR-SMA-13II

3,275

5.2

respectively,whilethe25°Cpenetrationdecreasedby4.6%.(2)SAKaddition(viscosity-reducingadditive)resultedinaK-R180°Crotationviscosityreductionof60.7%comparedwithpureasphalt.Thishelpsenhancemixturecompactnessandprovidestructuralstrength.The25°CpenetrationoftheK-Rasphaltdecreasedby7.1%.Itssofteningpointandelasticrecoveryincreasedby28.3and1.3%,respectively.

4)s·aP3(ytisosiv2noitator1C° 0810asphalt-rubberPure SBS asphhaltS-R asphaltK-R asphaltAsphalt type(a) 180°Crotationviscosity9080)C°70( gninetf60oS5040asphalt-rubberPure SBS asphhaltS-R asphaltK-R asphaltAsphalt type(c) Softening pointFig.2ComparisonofasphaltbindertestresultsJ.Mod.Transport.(2013)21(4):273–280

277

Compoundmodificationinasphaltbindertestsisthereforesignificantwiththecomprehensivehigh-temper-atureperformanceoftheS-Rasphaltbeingbetterthantheotherasphalttypes.3.2.3Asphaltmixturetests

RuttingtestswereconductedontheSBSasphaltmixturewithoutfiber(SBS-SMA-13),asphalt–rubbermixture(AR-SMA-13),SBS-ARcompound-modifiedmixture(SBS-AR-SMA-13),andSAK-ARcompound-modifiedmixture(SAK-AR-SMA-13)withresultsshowninFig.3.

Thefollowingisconcludedfromthegraphicalillustra-tionsinFig.3:(1)

BasedontheDSandrelativedeformation,thepreferen-tialorderofthefourkindsofmixtureswas:SBS-AR-SMA-13[SAK-AR-SMA-13&SBS-SMA-13[AR-SMA-13.

56)mm 1.520( no50itarten48ep C46 °524442asphalt-rubberPure SBS asphhaltS-R asphaltK-R asphaltAsphalt type(b)25°Cpenetration8280)%( yrevoc78er citsalE7674asphalt-rubberPure SBS asphhaltS-R asphaltK-R asphaltAsphalt type(d)Elasticrecovery123

278

7,0001)- m·ms6,000emit( yti5,000libats cim4,000anyD3,000 SBS- AR-SBS-AR-SAK-AR-SMA-13AMA-13SMA-13SMA-13Mixture type(a) Dynamic stabilities3.0)2.8%( noit2.6amrofed2.4 evitale2.2R2.0 SBS- AR-SBS-AR-SAK-AR-SMA-13AMA-13SMA-13SMA-13Mixture type(b) Relative deformationsFig.3Comparisonofruttingtestresults(2)

ComparedwithAR-SMA-13,theDSofSBS-AR-SMA-13increasedby66.3%andtherelativedeformationincreasedby30.0%.TheDSofSAK-AR-SMA-13increasedby15.5%anditsrelativedeformationincreasedby10.0%.Therefore,compoundmodificationcanimprovehigh-temperaturestability.(3)

Thehigh-temperatureviscosityofSBSasphaltwaslowerthanthatofpureasphalt–rubber,butSBS-SMA-13hadgoodruttingresistance.Therefore,fordifferenttypesofasphaltwithdifferentmechanisms,theviscosityindexisunilateralattimes.Wenowneedtointegratefactorscomprehensivelytoevaluatethehigh-temperatureperformanceofasphaltanditsmixtures.

3.3Effectofmoldingparameters

Duringtheruttingtest,themoldingtemperatureandrollingtimeswerecloselyrelatedtothecompactnessandstabilityofthemixture.Asdemonstratedinthecurrentstandard

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C.Xiaoetal.

(JTGE20-2011),12round-tripsarerecommendedfortherollingtimeformoldingruttingtestspecimens.Thecom-pactnessofthebaselineasphaltmixturemeetsthespeci-ficationdemandafter12round-tripsofwheel-rolling.Thestandardalsorecommendsatemperatureofapproximately140–170°Ctomoldruttingtestspecimens.Becauseofthepropertiesofhighviscosityasphalt–rubber,thecompact-nessandhigh-temperaturestabilityoftheasphalt–rubbermixturewithrecommendedmoldingparametersarefarbelowstandardvalues[19].

Weselectedrollingtimeandformingtemperatureasmoldingparameterstoanalyzethecompactioneffectonhigh-temperatureperformanceoftheasphalt–rubbermixture.

3.3.1Rollingtimesforcompaction

Differentrollingtimes(10,12,14,16,18,20,22,and24round-trips)wereselectedformoldingasphalt–rubbermixturespecimensatuniformtemperature(180°C).FromFig.4,weconcludethat:

987)%6( VV31012141618202224Rolling times (round-trip)(a) Volume of air voids4,5004,2001)- m3,900·msemit3,600( SD3,3003,0001012141618202224Rolling times (round-trip)(b) Dynamic stabilityFig.4RelationshipbetweenVVandDSwithrollingtimeJ.Mod.Transport.(2013)21(4):273–280

High-temperatureperformanceofasphalt–rubbermixture

1110)%( 9 VV87140150160170180190Molding temperature (°C)(a)4,0003,5001)- m3,000·msemi2,500t( SD2,0001,500140150160170180190Molding temperature (°C)(b)Fig.5RelationshipofVVandDSwithmoldingtemperature(1)

TheVVdecreaseswithincreaseinrollingtime,buttherateofchangedecreasesgradually.Iftheasphalt–rubbermixtureiscompactedwith12round-tripsbythewheel-rollingmethod,itsVVis7.7%(largerthantheobjectiveof3%–5%[11]).Thisoccursbecausetheviscosityoftheasphalt–rubberbinderishigh,thereisathickcoveringoftheaggregatewithasphaltmortar,andtheasphalt–rubbermixtureisthereforehardertocompact.

(2)

Thecompactnessoftheasphalt–rubbermixtureincreaseswithincreaseinrollingtimeandthereforetheDSincreasessignificantly.Fortheasphalt–rubbermixture,anincreaseinrollingtimecontributestobetterstructuralstrengthandstability.Toenhancemixturecompactnessandachievehigh-temperaturestability,therollingtimesoftheasphalt–rubbermixtureshouldbecontrolledstrictly.However,ifthecompactnessweretoohigh,itwouldresultininterferencebetweenthebinderandaggregateandbleedingintheasphaltpavement.SothatthemixtureVVreachesitsobjectivevalue(3%–5%[11])andsothatthereisnointerferenceincompaction,therolling

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279

timesformoldingasphalt–rubbermixturesshouldbecontrolledbetween18and20round-trips.3.3.2Moldingtemperature

Differentmoldingtemperatures(140,150,160,170,180,and190°C)werechosentomoldruttingspecimensatuniformrollingtimes(12round-trips).AsshowninFig.5,themoldingtemperaturewascloselyrelatedtotheVVandDS.TheVVdecreasedwithincreaseinmoldingtemper-ature.Asthemoldingtemperatureincreased,thehigh-temperaturestabilityoftheasphalt–rubbermixtureimprovedsignificantly.TheVVofthemixturemoldedat140°Cwas1.5timesthatmoldedat190°CandtheDSwas52.1%ofthosemoldedat190°C.Figure5bindicatesthatwithdeclineintemperature,thedowntrendoftheDSwasmoresignificant.Thecompactiontemperaturemustthereforebecontrolledstrictlytoensuregoodperformanceoftheasphalt–rubbermixture.Iftherollingtimetomoldruttingspecimensissetat12round-trips,thetemperaturemustbecontrolledat180–190°Ctomeettechnicalstan-dards(DSC3,500timesmm-1).

4Conclusion(1)

Thehigh-temperaturestabilityofthemixturesvariedas:AR-SMA-13[AR-AC-13[AC-13.Thehigh-temperatureperformanceofAR-SMA-13canbeimprovedbyadjustmentoftheSMA-13gradation.Thisresultsinadecreaseofthe0.075-mmpassingpercentagefrom10to8%andthatofthe2.36-mmpassingpercentagefrom20.5to18.5%.

(2)

Theeffectsofcompoundmodificationinasphalt–rubberaresignificant.Thecomprehensivehigh-tem-peratureperformanceofS-Rasphaltisbetterthantheothertypesofasphalt.Comparedwithpureasphalt–rubber,theK-RasphaltwithSAKimprovedthehigh-temperatureperformanceindices,suchas,thesoft-eningpoint,penetration,andelasticrecovery.Itsviscosityreducedsignificantlyandthereforeenhancesmixturecompactnesstoyieldstructuralstrength.(3)

Thehigh-temperatureperformanceofthefourmix-tureswas:SBS-AR-SMA-13[SAK-AR-SMA-13&SBS-SMA-13[AR-SMA-13.Thehigh-tem-peraturestabilitycanthereforebeimprovedbycompoundmodification,especiallySBScompoundmodificationinasphalt–rubber.

(4)

Compactionparameters,suchas,moldingtempera-tureandrollingtimeswerecloselyrelatedtothehigh-temperaturestabilityoftheasphalt–rubbermixture.Withincreaseinrollingtime,thecompactnessand

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280dynamicstabilityoftheasphalt–rubbermixturesincreasedgraduallyandtherollingtimesformoldingtheasphalt–rubbermixturesshouldbecontrolledfor18–20round-tripsatuniformtemperature(180°C).Withdecreaseincompactiontemperature,thecom-pactnessanddynamicstabilityoftheasphalt–rubbermixturedecreasedbydegrees.Ifsettingrollingtimesof12round-tripswereusedastheuniformcase(asfortheSBSasphaltmixture),thecompactiontem-peraturemustbecontrolledat180–190°Ctomeettechnicalstandards.

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