Use of Modified Bituminous Binders in India - Current Imperatives

USEOFMODIFIEDBITUMINOUSBINDERSININDIA:CURRENT IMPERATIVES By Prof.PrithviSinghKandhal*andDr.M.P.Dhir**

[PublishedintheJournaloftheIndianRoadsCongress [PublishedintheJournaloftheIndian RoadsCongress,Volume72-3,Octob ,Volume72-3,OctobererDecember2011.Authors’respon December2011.Authors’responsestocommentsre sestocommentsreceivedonthispa ceivedonthispaperarealso perarealso givenattheend.] ABSTRACT

Bituminousbindersarepredominantly Bituminousbindersarepredominantlyusedinsurfacingthe usedinsurfacingthevastnetworkofroad vastnetworkofroadsin sin India.Inrecentyears,trafficloadsand India.Inrecentyears,trafficloadsandtyrepressuresha tyrepressureshaveincreased,w veincreased,whichhas hichhas createdasituationforwhichmodifiedbinde createdasituationforwhichmodifiedbinderswithenhance rswithenhancedperformanceare dperformanceareneeded. needed. However,currentspecificationsand However,currentspecificationsandguidelinesforselec guidelinesforselectionanduseofd tionanduseofdifferenttypes ifferenttypes ofmodifiedbinderssuchaspolymer ofmodifiedbinderssuchaspolymermodifiedbitumen(PMB)a modifiedbitumen(PMB)andcrumbrubber ndcrumbrubber modifiedbitumen(CRMB)areinadequate. Anattempthasbeenmadeinthispa Anattempthasbeenmadeinthispapertoevaluate pertoevaluatethecontemporary thecontemporarysituationin situationin regardtotheuseofmodifiedbindersinIn regardtotheuseofmodifiedbindersinIndia.Thedevelopm dia.Thedevelopmentanduseofmodifie entanduseofmodified d bituminousbindersinEuropeand bituminousbindersinE uropeandNorthAmericahasbe NorthAmericahasbeendescribedin endescribedindetail detail includingthefundamentalsofbitumenmod includingthefundamentalsofbitumenmodification.Thesew ification.Thesewerekeptinperspec erekeptinperspective tive whilemakingrecommendationsforuse whilemakingrecommendationsforuseofmodifiedbindersinIn ofmodifiedbindersinIndiaandidentifying diaandidentifying currentimperatives.

1. INTRODUCTION 1.1SurfacedroadsinIndiaareverypredominantly,ifnotentirely,constructedwith theuseofbituminousbinders.Thisislargelybecausethesebindershavebeenmost suit suited ed to the the majo major r impe impera rati tive ves s of road road deve develo lopm pmen ent: t: low low init initia ial l cost cost, , phas phased ed development,andreadyavailability.Withthesocio-economicprogressinIndia,the roadnetworkhastobeextendedtomoredifficultenvirons.Moreimportantly,traffic loadscarriedbythenetworkhavebeengrowingheavierandheavier.Thesesituations canbeexemplifiedasfollows: •

Heavy Heavy channe channeliz lized ed traffic traffic to be carrie carried d in tropic tropical al and sub-tr sub-tropi opica cal l locale locales s withhightemperatures;andhightyrepressuresintrucks(needabilitytoresist permanentdeformation/rutting).

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Higherpotentialfordevelopingfatiguecrackingduetorepeatedloads(need elasticityforfatigueresistance).

*AssociateDirectorEmeritus,NationalCen *AssociateDirectorEmeritus,NationalCenterforAsphaltTech terforAsphaltTechnology,Auburn nology,Auburn University,Alabama(currentlyinJaipur) University,Alabama(currentlyinJaipur)pkandhal@eng [email protected] .auburn.edu **FormerlyDirector,CentralRoadRese **FormerlyDirector,CentralRoadResearchInstitute,NewDe archInstitute,NewDelhi lhi [email protected]

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Higherpotentialforthermalcrackingatsiteswherepavementsaresubjected to subsub-ze zero ro temp temper erat atur ures es for for exte extend nded ed perio periods ds (nee (need d resi resist stan ance ce to ther therma mal l cracking).

Theref Therefore ore, , during during the last last two deca decades des, , highwa highway y engine engineers ers in India India have have becom become e increasinglyawarethattherewereindeedsituationsforwhichupgradedbituminous binderswereneeded. 1.2 Modi Modifi fied ed bind binder ers s are are thos those e bitu bitumi mino nous us bind binder ers s whos whose e prop proper ertie ties s have have been been 11,12 modifiedbythe modifiedbytheuseofadditive(s useofadditive(s).Bitumenbinde ).Bitumenbindershavebeenmodifie rshavebeenmodified d inorder to: • stiffenbindersandmixesathightemp stiffenbindersandmixesathightemperaturestominimizerutting eraturestominimizerutting • softenbindersatlowtemperaturestoimproverelaxationpropertiesandstrain tolerancethusminimizingnon-loadas tolerancethusminimizingnon-loadassociatedthermalcrac sociatedthermalcracking king improv improve e fatigu fatigue e resista resistance nce espec especial ially ly where where higher higher strain strains s are impose imposed d on • bituminousmixes. • improveaggregate-bitumenbonding improveaggregate-bitumenbondingtoreducestripping toreducestripping • improvebituminouspavementdurabilitywithaccompanyingnetreductionin lifecyclecosts permitthickerfilmsofbitumenonaggregateinspecialbituminousmixessuch • as open open grad graded ed asph asphal alt t fric frictio tion n cour course ses s (por (porou ous s asph asphal alt) t) and and ston stone e matri matrix x asphalt. 1.3 Howe Howeve ver, r, ther there e are are cond conditi ition onal aliti ities es for for the the prod produc uctio tion n and and use use of a modi modifi fied ed binder/mix binder/mixwithdifferent withdifferent modifierssince modifierssince the changesin changesin theproperties/perfo theproperties/performanc rmance e arenotthesame.Inotherwords,thereisneedtomatchtheroadsiteconditionswith appropria appropriatetypesofmodifier tetypesofmodifierandchoosethetypeanddosag andchoosethetypeanddosageofthe eofthemodifi modifiersothat ersothat life life cyc cycle costs osts are mini minimi mize zed d. Exerc xercis isin ing g of this this choic oice is predi redica cate ted d to the the availabilityofrelevantdecision-makingdata. 1.4 Useoflatexrubberinsouthe Useoflatexrubberinsouthernpartsofthecountr rnpartsofthecountrysomefour ysomefourdecades decadesbackmay backmay have have hera herald lded ed the the use use of modi modifi fied ed bind binder ers s in Indi India. a. The The past past deca decade de (200 (20011-10 10) ) howevermarkedamajorsurgeintheuseofmodifiedbitumenforroadsandairports, especiallytheuseofcrumbrubbermodifiedbitumen(CRMB)andpolymermodified bitumen(PMB).TheIndianRoad bitumen(PMB).TheIndianRoadsCongres sCongress(IRC)broughtoutaspecialpublic s(IRC)broughtoutaspecialpublication ation (SP:53)in1999toprovidetentativeguidelinesonthe (SP:53)in1999toprov idetentativeguidelinesontheuseofmodifiedbitumeninroa useofmodifiedbitumeninroad d 6 construction . Althou Although gh that that public publicati ation on had four four differ different ent specif specifica ication tions s for PMB (ela (elast stom omeer), r), PMB PMB (pla (plasstome tomer) r), , CRMB CRMB, , and natu natura ral l rub rubber ber modi modifi fied ed bitu bitume men n (NRM (NRMB B), it was was imp implie lied tha that the their perf perfo orman rmance ce was was equa qual in absen sence of any recommend recommendation ations s for their usefor use for specific specific traffic and/or and/or climatic climatic conditions conditions. . SP:53 wasrevisedin2010withonenotablefeatureinthatthespecificationsfordifferent type types s of modi modifi fied ed bind binder ers s were were unif unifie ied d into into one one spec specifi ifica catio tion n irre irresp spec ectiv tive e of the the 7 modifiertypeoritsconcentration . 1.5 Anattempthasbeenmadeinthispapertoevaluatethecontemporarysituationin regardtotheuseofmodifiedbituminousbindersinIndia.Presentedfirstisthepicture ondevelopmentanduseofmodifiedbindersinEuropeandNorthAmerica.Thisis followedbyasectiononcurrentuseofmodifiedbindersinIndiaandbyadiscussion

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astowhethertheprevailingsituationissatisfactoryortherearestrongimperativesfor change. 1.6Modifiedbindersaremeanttobeusedcarefullyforderivingduetechnicalandlife cyclecostadvantages.The cyclecostadvantages.Thepaperisesse paperisessentiallydirectedatthe ntiallydirectedatthefollowing: following:

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Doestheprevailingframeworkpermitexerc Doestheprevailingframeworkpermitexercisingofcorrectoptions? isingofcorrectoptions?

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Ifnot,whatissues(imperatives)need Ifnot,whatissues(imperatives)needtobeaddressedfo tobeaddressedforthefulfillmentofthis rthefulfillmentofthis objective.

1.7 Theimperatives,soidentified,concerntheIndianRoadsCongress(IRC),Bureau of Indian IndianStand Standards(BIS), ards(BIS), theroad the road authorities authorities (users),and (users),and thebusin the businessinterests essinterests of themodifiedbindersector.

2. DEVELOPMENTANDUSEOFMODIFIEDBINDERSINEUROPE ANDNORTHAMERICA

Itisconsideredprudenttogivethe Itisconsideredprudenttogivethehistoryofdevelopmenta historyofdevelopmentanduseofmod nduseofmodified ified bindersindevelopedcountriestopro bindersindevelopedcountriestoprovideproperpersp videproperperspectiveandbac ectiveandbackgroundfortheir kgroundfortheir useinIndia. 2.1EuropeanExperience 2.1.1Althoughpatentsformodifyingbitumenw Althoughpatentsformodifyingbitumenwithnaturalandsynthe ithnaturalandsyntheticpolymer ticpolymer weregrantedasearlyas1843,tes weregrantedasearlyas1843,testprojectsutilizingmodified tprojectsutilizingmodifiedbitumenwereplace bitumenwereplacedin din Europeinthe1930s.Neoprene Europeinthe1930s.Neoprenelatexwasintroduce latexwasintroducedinthe1950sin dinthe1950sinNorthAmerica NorthAmerica 11 andwasprimarilyusedinCanada andwasprimarilyusedinCanadaandthewesternU andthewesternUnitedStates nitedStates . 2.1.2Europeanswereclearlyahead EuropeanswereclearlyaheadoftheUSinthe1970 oftheUSinthe1970sindeveloping sindevelopingandusing andusing modifiedbitumenbinders.Thefollowingfa modifiedbitumenbinde rs.Thefollowingfactorsprovidedtheimp ctorsprovidedtheimpetusfor etusfor 11 developmentofmodifiedbitumenbinders developmentofmodifiedbitumenbindersduringthatperiod duringthatperiod . •

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Thecostofbitumenhadincrease Thecostofbitumenhadincreasedsubstantiallymaking dsubstantiallymakingthemodification themodification costsmoreattractiveandwithinreache costsmoreattractiveandwithinreachespeciallyinviewoflong speciallyinviewoflongterm term benefits. Europeanhighwayauthoritiesexpec Europeanhighwayauthoritiesexpectinnovationinbituminous tinnovationinbituminousroad road constructiontechnologyemanatingfro constructiontechnologyemanatingfromcontractorswhooften mcontractorswhooftenwarrantthe warrantthe performanceofbituminouspavements. performanceofbituminou spavements.Thesewarranties Thesewarrantiesprovided provided financialincentivetothecontractorsforus financialincentivetothecontractorsforusinghigherquality inghigherqualitymaterials materials whichreducelifecyclecosts.

2.1.3Duringthisperiodthehighwayautho DuringthisperiodthehighwayauthoritiesinEuropewereface ritiesinEuropewerefacedwiththetaskof dwiththetaskof upgradingandmaintaininganalready upgradingandmaintaininganalreadywelldeveloped welldevelopedhighwaynetwork.Itwa highwaynetwork.Itwas s deemednecessarytodevelop deemednecessarytodevelopeffectivetechn effectivetechniquesandmaterialsforre iquesandmaterialsforresurfacingand surfacingand strengtheningofexistinghighways strengtheningofexistinghighways.Whenanewidea .Whenanewideaisputforwardboththe isputforwardboththehighway highway authoritiesandcontractorsarewillingtosh authoritiesandcontractorsarewillingtosharethetechnology arethetechnologyandarewillingtotryit andarewillingtotryit withoutfearofcriticismincaseitfails.Inmanyc withoutfearofcriticisminca seitfails.Inmanycasesthenew asesthenewtechnologieswere technologieswere 14 patentedbythecontractors .

3

2.1.4Duringthisperiodmodifiedbitumentechno Duringthisperiodmodifiedbitumentechnologywasdev logywasdevelopedinFrance elopedinFranceand and otherEuropeancountries.Beside otherEuropeancountries.Besidesimprovingtheperforma simprovingtheperformanceanddura nceanddurabilityofhot bilityofhot mixasphalt(HMA),themodifiedbinderswe mixasphalt(HMA),themo difiedbinderswerehighlysuccessfu rehighlysuccessfulinthefollowing linthefollowing 14 applications . • • • • •

Durablechipseals(surfacedressing) ThinHMAwearingcourse Durableopengradedasphaltfrictionc Durableopengradedasphaltfrictioncourses(porousas ourses(porousasphalt) phalt) Asphaltwearingcourseforbridgedecks Durableslurryseals(microsurfacing)

2.2NorthAmericaExperience 2.2.1Inthemeantime,lowerinitialcostofunmodified Inthemeantime,lowerinitialcostofunmodified(neat)bitumenintheUSw (neat)bitumenintheUSwasa asa limitingfactorinacceptinghigherquality,relatively limitingfactorinacceptinghigherquality,relativelyexpensivemodifiedb expensivemodifiedbinders. inders. However,inearlyandmid1980s,the However,inearlyandmid1980s,theuseofpolymermo useofpolymermodifiedbitumen(PMB) difiedbitumen(PMB) proliferatedintheUSasnewerpolymersw proliferatedintheUSa snewerpolymersweredeveloped;Eu eredeveloped;Europeanbinderan ropeanbinderandmix dmix technologieswereintroduced;ruttingstarted technologieswereintroduced;ruttingstartedtobecomeama tobecomeamajorproblemduetohea jorproblemduetoheavy vy loadsandhightyrepressures;a loadsandhightyrepressures;andconceptoflowe ndconceptoflowerlifecyclecostsb rlifecyclecostsbecamebetter ecamebetter 1 understood . 2.2.2Differenttypesofmodified Differenttypesofmodifiedbitumencontaining bitumencontainingelastomersand elastomersandplastomerswere plastomerswere introducedandpromotedforuseby introducedandpromotedforusebythehighwayautho thehighwayauthoritiesintheUS.Many ritiesintheUS.Manyofthe ofthe productswerepatentedsotheirrea productswerepatentedsotheirrealcompositionwasno lcompositionwasnotknown.Nounified tknown.Nounified Europeanguidespecificationswere Europeanguidespecificationswereavailableforusein availableforuseintheUS.Thiscrea theUS.Thiscreated ted confusioninimplementingmodifiedbitumen confusioninimplementingmodifiedbitumentechnology.To technology.Toalleviatethecomplex alleviatethecomplex situation,TaskForce31wascrea situation,TaskForce31wascreatedtodevelopnationa tedtodevelopnationalguidespec lguidespecificationsfor ificationsfor differenttypesofpolymermodifiedbitumens.Th differenttypesofpolymermodifiedbitumens.Thistaskforcewas istaskforcewasajointeffortofthe ajointeffortofthe AmericanAssociationofStateHighways AmericanAssociationofStateHighwaysandTransportationO andTransportationOfficials(AASHTO), fficials(AASHTO), theAssociatedGeneralContractors theAssociatedGeneralContractors(AGC),andtheAmerican (AGC),andtheAmericanRoadand Roadand TransportationBuildersAssociation(ARTB TransportationBuildersAssociation(ARTBA).Sincepolymermod A).Sincepolymermodifiedbitumens ifiedbitumens wereofdifferenttypes(suchasela wereofdifferenttypes(suchaselastomersandplastomers stomersandplastomers)itwasneithertechnic )itwasneithertechnically ally possiblenordesirabletohavea possiblenordesirabletohaveacommonspecificationfora commonspecificationforalltypes.Putsimply, lltypes.Putsimply,apples apples cannotbecomparedwithorange cannotbecomparedwithoranges.Therefore,themod s.Therefore,themodifiedbinderswered ifiedbindersweredividedinto ividedinto differentclasses,eachclasswithitsown differentclasses,eachclasswithitsownspecification(AASH specification(AASHTO,1992).Three TO,1992).Three 1 separateguidespecifications weredevelopedin1992by weredevelopedin1992bytheAASHTO-AGCtheAASHTO-AGCARTBATaskForce31forPMB(ela ARTBATaskForce31forPMB(elastomer),PMB(elastomerlate stomer),PMB(elastomerlatex),andPMB x),andPMB (plastomer). 2.2.3Later,theAmericanSocietyforTesting Later,theAmericanSocietyforTestingandMaterials(ASTM)fo andMaterials(ASTM)followedsuit llowedsuit anddevelopedspecificationindividu anddevelopedspecificationindividuallyforeachclas allyforeachclassofmodifiedbitumendu sofmodifiedbitumenduring ring the1995-1997periodasshown the1995-1997periodasshowninTable1. inTable1. 2.2.4Inspiteofspecificationsavailableforea Inspiteofspecificationsavailableforeachtypeofpoly chtypeofpolymermodifiedbitumen, mermodifiedbitumen, thehighwayauthoritiesintheUShadd thehighwayauthoritiesintheUShaddifficulttimeselectingthea ifficulttimeselectingtheappropriatetype ppropriatetype becausetherewasalackofre becausetherewasalackofreliablecomparativefieldp liablecomparativefieldperformancedata erformancedataforalltypes. foralltypes. Moreover,theAASHTOandASTMspe Moreover,theAASHTOandASTMspecificationswereprimarily cificationswereprimarilybasedonempirica basedonempirical l testssuchassofteningpoint,pene testssuchassofteningpoint,penetration,Frassbreak tration,Frassbreakingpoint,andd ingpoint,andductilitysimilarto uctilitysimilarto

4

Europeanspecifications.TheAST Europeanspecifications.TheASTMspecificationgive MspecificationgiveninTable1gen ninTable1generallystatethat erallystatethat theguidespecificationsarenotperforma theguidespecificationsarenotperformancebased;justpro ncebased;justprovideareference videareferencefor for specifyingpolymermodifiedbitumens;an specifyingpolymermodifiedbitumens;andreflecttheproperties dreflectthepropertiesofcurrently ofcurrently availablecommercialproducts. Table1.ASTMStandardSpecification Table1.ASTMStandardSpecificationsfordifferenttypesofmod sfordifferenttypesofmodifiedbitumens ifiedbitumens ASTM Name of Standard Designation D 5976 Type I Polym lymer Modified Asphalt D 5840 D 5841

Type II Polym lymer Modified Asphalt TypeII III Polym lymer Modified ied Asphalt

D 5892

TypeIV IV Polyme lymerr Modifie ified d Asphalt

D61 6114

Asph Asphaalt-R lt-Ru ubbe bberB rBind inder(c r(caalle lledCR dCRMB MB inIndia)

Modifier type SBS/SB Block Copolymer or similar SBS latex or similar Ethyl Vinyl nylA Acetate tate (EVA) or similar Non cross-link inked SBS Bloc lock Copolymerorsimilar Crumbrubberfromtyres

2.2.5Therewasaneedfordeve Therewasaneedfordevelopingperformanceba lopingperformancebasedspecifications sedspecificationsforallroad forallroad pavingbitumenbinders,whichsho pavingbitumenbinders,whichshouldbeblindtothety uldbeblindtothetypeofmodificationorrefining peofmodificationorrefining process.A50-milliondollar,5-yearStrateg process.A50-milliondollar,5-yearStrategicHighwayResearc icHighwayResearchProgram(SHRP) hProgram(SHRP) wasundertakenfrom1987to1992 wasundertakenfrom1987to1992todevelopap todevelopaperformancebased erformancebasedgradingsystem gradingsystem forbitumen,whichwasbasedon forbitumen,whichwasbasedonengineeringprinciples engineeringprinciplestoaddressco toaddresscommonasphalt mmonasphalt pavementdistressproblems.Thes pavementdistressproblems.Theso-calledSuperpa o-calledSuperpaveperformanceg veperformancegrading(PG) rading(PG) systemincludesnewbitumentestsa systemincludesnewbitumentestsandspecifications ndspecificationswiththefollowingsalient withthefollowingsalient 10 features :

1. Testsandspecificationsareinte Testsandspecificationsareintendedforbitumen“binde ndedforbitumen“binders”,whichinclud rs”,whichinclude e bothmodifiedandunmodifiedbitumens. 2. Thephysicalpropertiesmeasured ThephysicalpropertiesmeasuredbySuperpave bySuperpavebitumentestsaredirec bitumentestsaredirectly tly relatedtofieldperformancebyenginee relatedtofieldperformanc ebyengineeringprinciplesrathertha ringprinciplesratherthanjustthe njustthe experience. 3. Along-termbitumenag Along-termbitumenagingtest,whichsimula ingtest,whichsimulatesagingofbitumens tesagingofbitumensduring5during510yearsinservice,wasdeve 10yearsinservice,wasdevelopedandinclude lopedandincludedforthefirsttime. dforthefirsttime. 4. Testsandspecificationsared Testsandspecificationsaredesignedtoeliminateor esignedtoeliminateorminimizethreespecific minimizethreespecific typesofasphaltpavementdistresse typesofasphaltpavementdistresses:rutting,fatiguecrack s:rutting,fatiguecracking,andthermal ing,andthermal cracking.Ruttingtypicallyoccursa cracking.Ruttingtypicallyoccursathightemperatures,fatigu thightemperatures,fatiguecrackingat ecrackingat intermediatetemperatures,andthermalc intermediatetemperatures,andthermalcrackingatlowtempera rackingatlowtemperatures. tures. 5. Theentirerangeofpavementtempe Theentirerangeofpavementtemperaturesexperienc raturesexperiencedattheprojec edattheprojectsiteis tsiteis considered.Newtestingequipments considered.Newtestingequipmentsweredeveloped weredeveloped/adoptedfortesting /adoptedfortesting bitumensforthispurpose.Arotationalvisc bitumensforthispurpo se.Arotationalviscometerisusedtome ometerisusedtomeasurethe asurethe bitumenviscosityat135C.Adyna bitumenviscosityat135C.Adynamicshearrheometer(D micshearrheometer(DSR)isusedto SR)isusedto measuretheviscoelasticproperties measuretheviscoelasticpropertiesofthebitumenattwotemp ofthebitumenattwotemperatures:high eratures:high temperaturecorrespondingtothemaximum7 temperaturecorrespondingtothemaximum7-daypaveme -daypavementtemperature nttemperature duringsummerattheprojectsite,andinte duringsummerattheprojectsite,andintermediatetemperaturec rmediatetemperaturecorresponding orresponding totheaverageannualtemperature totheaverageannualtemperatureofthepavementatthe ofthepavementattheprojectsite.A projectsite.A bendingbeamrheometeranda bendingbeamrheometerandadirecttensiontesterare directtensiontesterareusedtomeasu usedtomeasurethe rethe

5

rheologicalpropertiesofthebitumenatthe rheologicalpropertiesofthebitumenatthelowestpaveme lowestpavementtemperature nttemperature duringwinterattheprojectsite. 2.2.6TheSuperpaveperformancegra TheSuperpaveperformancegrade(PG)bitumenisbas de(PG)bitumenisbasedonclimate.Fo edonclimate.For r example,PG64-22bitumenissuitable example,PG64-22bitumenissuitableforaprojectlocation foraprojectlocation,wheretheaverag ,wheretheaverage7-day e7-day maximumpavementtemperatureisas maximumpavementtemperatureisasmuchas64C,a muchas64C,andtheminimumpave ndtheminimumpavement ment temperatureis–22C. 2.2.7Thehightemperaturegradesare ThehightemperaturegradesarePG52,PG58,PG6 PG52,PG58,PG64,PG70,PG76, 4,PG70,PG76,andPG andPG 82.Thelowtemperaturegradesare 82.Thelowtemperaturegradesare–4,–10,-16, –4,–10,-16,-22,-28,-34and -22,-28,-34andsoforth.Bothhigh soforth.Bothhigh andlowtemperaturegradesareinincre andlowtemperaturegradesareinincrementsof6Celsiusde mentsof6Celsiusdegrees.The grees.TheSuperpavePG SuperpavePG gradingsystemhasbeenimpleme gradingsystemhasbeenimplementedbymoststates ntedbymoststatesintheUS. intheUS. 2.2.8Althoughtheuseofmodifiedbitumenha Althoughtheuseofmodifiedbitumenhadincreasedinthe dincreasedintheUSpriorto USpriorto Superpavetechnology,itincrea Superpavetechnology,itincreasedsignificantlyafterthe sedsignificantlyafterthePGgradingsystemwa PGgradingsystemwas s adopted.Thatisbecausesome adopted.ThatisbecausesomePGgradesw PGgradeswithawiderangeofma ithawiderangeofmaximumand ximumand minimumtemperaturescannotbemade minimumtemperaturesc annotbemadewithunmodified(neat)b withunmodified(neat)bitumen.PG64-22 itumen.PG64-22 (equivalenttoIndia’sVG-20bitumengrade)is (equivalenttoIndia’sVG-20bitumengrade)isthemostcommonly themostcommonlyusedpaving usedpaving bitumeninlargepartsoftheUS.Howev bitumeninlargepartsoftheUS.However,thisgradeis“b er,thisgradeis“bumpedup”two umpedup”twogradesfor gradesfor useonheavilytraffickedroads.T useonheavilytraffickedroads.Thatis,PG64-22isbump hatis,PG64-22isbumpeduptoPG76-2 eduptoPG76-22which 2which canbeproducedonlywithmodification canbeproducedonlywithmodification.PG76-22isalsos .PG76-22isalsosuitedforuseonI uitedforuseonIndia’s ndia’s heavilytraffickedroads.Table2give heavilytraffickedroads.Table2givestheUSSpecification stheUSSpecificationforPG76-22whichisa forPG76-22whichisa polymermodifiedbinder.

Table2.USSpecificationforPG76-22ModifiedBinder S. No.  Te Test property Specified value 1 Viscosity at 135 C, Pa.s, max. 3 2 DSR: G*/sin delta at 76 C, kPa, min. 1.00 3 RTFO Residue: 2.20 DSR:G*/sindeltaat76C,kPa,min. 4 PAV Residue: 5,000 DSR:G*sindeltaat31C,kPa,max. 5 Creep stif tiffness S att-12C, C, MPa, max. 300 m-valueat-12C,min. 0.300 6 Direct tension failure strain at -12 C, %, min. 1.0 Note:PG76-22modifiedbinderissuitable Note:PG76-22modifiedbinderissuitableforheavytraffickedroa forheavytraffickedroadsinhotclimate dsinhotclimate ofIndia.ItisbeingusedintheMiddleEast.

2.2.9However,itwasrealizedthatSHRPrese However,itwasrealizedthatSHRPresearchwasco archwasconductedonunmod nductedonunmodified ified bitumenonlyandthereforeSuperpa bitumenonlyandthereforeSuperpavePGspecificationsmay vePGspecificationsmaynotcompletely notcompletelycover cover therequirementsdesiredfrommodifiedbinde therequirementsdesiredfrommodifiedbinders.Therefore,many rs.Therefore,manystatesintheUS statesintheUS adoptedtheso-called“PGPlus”s adoptedtheso-called“PGPlus”specificationsformodified pecificationsformodifiedbitumenbinders.In bitumenbinders.In conventionalPGspecifications,dy conventionalPGspecifications,dynamicshearrheome namicshearrheometer(DSR)isusedtomea ter(DSR)isusedtomeasure sure thecomplexmodulusG*andph thecomplexmodulusG*andphaseanglede aseangledelta.WhereasG*isa lta.WhereasG*isanalogoustototal nalogoustototal stiffnessmodulusofthebinder,pha stiffnessmodulusofthebinder,phaseangleindicates seangleindicatestheamountofelastic theamountofelastic componentinG*.Neatbitumenhas componentinG*.Neatbitumenhasaphaseang aphaseanglecloseto90deg lecloseto90degrees.Lowerthe rees.Lowerthe phaseangle,themorethebitumenb phaseangle,themorethebitumenbinderiselastic.I inderiselastic.InPGPlusspecifications nPGPlusspecificationssome some statesrequirethatthephaseangle statesrequirethatthephaseangleshouldnotbemore shouldnotbemorethan75degree than75degreesjusttoensure sjusttoensure

6

thatthemodifiedbitumendoeshaveadequateamounto thatthemodifiedbitumendoeshave adequateamountofpolymer(mostlikely fpolymer(mostlikely elastomer).Somestatesrequireempiricalte elastomer).Somestatesrequireempiricaltestssuchasela stssuchaselasticrecoveryinduc sticrecoveryinductilitytest tilitytest andtorsionrecoverytoachieve andtorsionrecoverytoachievethesameobjec thesameobjectiveinPGPlusspecifica tiveinPGPlusspecifications. tions. 2.2.10Besideswearingcoursesmodifiedb Besideswearingcoursesmodifiedbindersarealsoge indersarealsogenerallyusedin nerallyusedin bituminousbindercourses(whichare bituminousbindercourses(whicharewithinabout100mmfromthe withinabout100mmfromtheroadsurface)o roadsurface)on n heavilytraffickedroadsintheUS.Thisis heavilytraffickedroadsintheUS.Thisisbecausemos becausemostfieldstudieshave tfieldstudieshaveshownthat shownthat ruttingwithinthebituminouspavementusua ruttingwithinthebituminousp avementusuallyoccurstothede llyoccurstothedepthofabout100mm pthofabout100mm fromtheroadsurface. 2.2.11Theresilientmodulusofasphaltpav Theresilientmodulusofasphaltpavementcontaining ementcontainingPMBis“generally” PMBis“generally” higherthanthatforasphaltpavementc higherthanthatforasphaltpavementcontainingunmodified ontainingunmodifiedbinder.However, binder.However,the the rangeofresilientmoduliinbothcases rangeofresilientmoduliinbothcasesisverywidedueto isverywideduetomanyfactorssuch manyfactorssuchas as differentaggregatetypes,gradation,v differentaggregatetypes,gradation,voidparametersand oidparametersandconstructionvariability. constructionvariability. Thatis,thereistoomuchoverlapbe Thatis,thereistoomuchoverlapbetweenthemoduliofas tweenthemoduliofasphaltpavemen phaltpavementswithand tswithand withoutmodifiedbinders.Therefore,sofa withoutmodifiedbinders .Therefore,sofar,moststatesintheUSha r,moststatesintheUShavenotreduce venotreduced d thethicknessofbituminouslayerswh thethicknessofbituminouslayerswhenPMBisusedin enPMBisusedinlieuofunmodifiedbinde lieuofunmodifiedbinder. r. 2.2.12Itwouldbeprudentnowtodiscuss Itwouldbeprudentnowtodiscussthevarioustyp thevarioustypesofpolymersuse esofpolymersusedinthe dinthe USformanufacturingmodifiedbinders;theirc USformanufacturingmodifiedbinders;theircompatibilitywithbitumen;their ompatibilitywithbitumen;their storagestability;andtestproceduresu storagestability;andtestproceduresusedfortheircharac sedfortheircharacterization.Crumbrubber terization.Crumbrubber modifiedbitumen(CRMB)whichiscalled“a modifiedbitumen(CRMB )whichiscalled“asphalt-rubberbinder” sphalt-rubberbinder”intheUS,will intheUS,will alsobediscussed. 2.3TypesofPolymers 2.3.1Theterm“polymer”simplyreferstoa Theterm“polymer”simplyreferstoaverylargemolecu verylargemoleculemadebychemica lemadebychemically lly reactingmany(poly)smallermolecules reactingmany(poly)smallermolecules(monomers)toonea (monomers)tooneanothereitherinlong nothereitherinlong chainsorclusters.Thesequen chainsorclusters.Thesequenceandche ceandchemicalstructureofthemono micalstructureofthemonomersfromwhich mersfromwhich itismadedeterminesthephysicalprop itismadedeterminesthephysicalpropertiesofaspecificp ertiesofaspecificpolymer.Whenpolyme olymer.Whenpolymers rs areincorporatedintobitumen,theprope areincorporatedintobitumen,thepropertiesofthemodifiedbitumen rtiesofthemodifiedbitumendependonthe dependonthe 11 polymersystemusedandtheco polymersystemusedandthecompatibilityofthepolymerwiththe mpatibilityofthepolymerwiththebitumen bitumen . 2.3.2Polymersmostoftenusedinmodifying Polymersmostoftenusedinmodifyingbitumencanbe bitumencanbegroupedintwogene groupedintwogeneral ral categories:elastomersandplastomers categories:elastomersandplastomers.Asthenameimplies .Asthenameimplies,elastomersca ,elastomerscanbe nbe stretchedlikearubberbandandre stretchedlikearubberbandandrecovertheirshapew covertheirshapewhenthestretchingfo henthestretchingforceis rceis released.Elastomersaddonlya released.Elastomersaddonlyalittlestrengthtothebitumenu littlestrengthtothebitumenuntiltheyarestretche ntiltheyarestretched d whentheyreallygetstronger.Plastomers whentheyreallygetstronger.Plastomersformatough,rigid,three formatough,rigid,threedimensional dimensional networkswithinthebitumen.Thesep networkswithinthebitumen.Theseplastomersgivehigh lastomersgivehighinitialstrengthtothe initialstrengthtothe 11 bitumentoresistheavyloads.How bitumentoresistheavyloads.However,plastomersmay ever,plastomersmaycrackathighstrains crackathighstrains . 2.3.3Polymerdropletscanalsobee Polymerdropletscanalsobeemulsifiedinwater;thiswaterba mulsifiedinwater;thiswaterbasedemulsionis sedemulsionis calledlatex(exampleSBRLatex).Itise calledlatex(exampleSBRLatex).Itiseasytoincorporate asytoincorporatethewaterbased thewaterbasedlatexinto latexinto waterbasedasphaltemulsions.Th waterbasedasphaltemulsions.Thatiswhy;surfaced atiswhy;surfacedressing(chipsea ressing(chipseals)andslurry ls)andslurry sealswerethefirstpavingapplications sealswerethefirstpavingapplications,whichtookadv ,whichtookadvantageofpolyme antageofpolymermodified rmodified 11 bitumen . 2.3.4Iftwoormoredifferentmon Iftwoormoredifferentmonomersareused omersareusedtomakepolymers, tomakepolymers,theresulting theresulting polymersarecalledrandomorblockc polymersarecalledrandomorblockcopolymers.Forma opolymers.Formanufacturingblock nufacturingblock copolymers,apolymerofonemon copolymers,apolymerofonemonomerischemically omerischemicallyreactedtoablock reactedtoablockofanother ofanother

7

monomer.Forexample,SBS(styrene monomer.Forexample,SBS(styrene-butadiene-styrene)is -butadiene-styrene)ismadeupofabloc madeupofablockof kof polystyrenechemicallycombinedwitha polystyrenechemicallycombinedwithablockofpolybuta blockofpolybutadieneandan dieneandanotherblockof otherblockof polystyrene.Incaseofrandompoly polystyrene.Incaseofrandompolymer,themonomersa mer,themonomersarerandomlymixedinthe rerandomlymixedinthe polymerchain.SBR(styrene-butadie polymerchain.SBR(styrene-butadienerubber)isanexamp nerubber)isanexampleofarandompo leofarandompolymer. lymer. AlthoughSBRiscomposedofsame AlthoughSBRiscomposedofsamemonomerasSBSb monomerasSBSbutitsrandomorientation utitsrandomorientation 11 givesitdifferentphysicalproperties . 2.3.5Specificbinderandasphaltmixproperties Specificbinderandasphaltmixpropertiescanbeach canbeachievedbyse ievedbyselectingaright lectingaright typeofpolymerandensuringitisco typeofpolymerandensuringitiscompatiblewiththebitumen. mpatiblewiththebitumen.Generally,elastome Generally,elastomers rs arechosentogiveamoreresilien arechosentogiveamoreresilient,flexiblepavementwhe t,flexiblepavementwhereasplastomersare reasplastomersarechosen chosen toobtainhighstabilityorstiffnessmodulus.B toobtainhighstabilityorstiffnessmodulus.Bothelastomersa othelastomersandplastomersare ndplastomersare complexsystemswhosecharac complexsystemswhosecharacteristicsaredepende teristicsaredependentuponsomany ntuponsomanyfactorssuchas factorssuchas concentration;themolecularweight;thec concentration;themolecularweight;thechemicalcomposition;andth hemicalcomposition;andthemolecular emolecular orientationofaparticularpolymeraswella orientationofaparticu larpolymeraswellasthecrudesourc sthecrudesource,therefiningproces e,therefiningprocess, s, 11 andthegradeofthebitumenused . 2.3.6Elastomers:Elastomericpolymershave Elastomers:Elastomericpolymershavetheabilitytoresistperma theabilitytoresistpermanent nent deformationandcohesivefailureinthe deformationandcohesivefailureinthebituminousmixbystre bituminousmixbystretchingandthen tchingandthen recoveringtheirshapewhenthede recoveringtheirshapewhenthedeformingforceisremove formingforceisremoved.Similartoarubber d.Similartoarubber band,anelastomerexhibitslittlestrength band,anelastomerexhibitslittlestrengthatlowtensilestrains.Tha atlowtensilestrains.Thatiswhy;ifthe tiswhy;ifthe stiffnessofabituminousmixismeasured stiffnessofabituminou smixismeasuredasresilientmodulus(a asresilientmodulus(anon-destructivelow non-destructivelow straintest)itmaybesimilartothemixmadewithun straintest)itmaybesimilartothemixmadewithunmodifiedbaseb modifiedbasebitumen.Sincethe itumen.Sincethe tensilestrengthofanelastomerincreas tensilestrengthofanelastomerincreaseswithelongation, eswithelongation,dynamictestswhich dynamictestswhich measureaccumulatedshearstra measureaccumulatedshearstrainoveranumber inoveranumberofcyclesshould ofcyclesshouldbeusedtofully beusedtofully understandthevalueofelastomeric understandthevalueofelastomericmodificationofthebituminous modificationofthebituminousmix. mix.

Severaldifferenttypesofelastomericpolyme Severaldifferenttypesofelastomericpolymersareusedformod rsareusedformodifyingbitumen. ifyingbitumen. Examplesare:styrene-butadiene-s Examplesare:styrene-butadiene-styrene(SBS)blockco tyrene(SBS)blockcopolymer;styrene-butadie polymer;styrene-butadiene ne rubber;styreneisoprenestyrene(SIS);a rubber;styreneisoprenestyrene(SIS);andethyleneterpo ndethyleneterpolymer(ETP). lymer(ETP). 2.3.7Plastomers:Asmentionedearlier,therigid,thre Plastomers:Asmentionedearlier,therigid,threedimensionaln edimensionalnetworksof etworksof plastomersimpartquickearlytensilestreng plastomersimpartquic kearlytensilestrengthtothebituminousmixunde thtothebituminousmixunderheavy rheavy loads.Thesebituminousmixesalsoe loads.Thesebituminousmixesalsoexhibithighmoduliinlowstrain xhibithighmoduliinlowstraintestssucha testssuchas s resilientmodulus.However,despite resilientmodulus.How ever,despitehighearlystrengththe highearlystrengththesemixeshavelow semixeshavelowerstrain erstrain tolerance.Athighpavementstrainssu tolerance.Athighpavementstrainssuchasthoseoc chasthoseoccurringinbituminouso curringinbituminousoverlay verlay overconcretejoints,suchmixescra overconcretejoints,suchmixescrackinformoffatigue ckinformoffatiguecrackingorreflection crackingorreflection 11 cracking .

Plastomersusedformodifyingbitumenfo Plastomersusedformodifyingbitumenforflexiblepavementcon rflexiblepavementconstructionare structionare generallypolyolefinssuchaspo generallypolyolefinssuchaspolyethylene,polypropy lyethylene,polypropyleneorcopolymers leneorcopolymersof of polyolefins.Polyolefinsaretypicallyinco polyolefins.Polyolefinsaretypicallyincompatiblewithbitumenands mpatiblewithbitumenandseparatequickly eparatequickly inheatedstorage.However,so inheatedstorage.However,somenovelchemica menovelchemicalsystemshaveb lsystemshavebeendeveloped eendevelopedto to stabilizepolyethyleneinbitumen. Examplesofplastomersformodifyingbitume Examplesofplastomersformodifyingbitumenare:ethylene nare:ethylenevinylacetate(EVA); vinylacetate(EVA); ethylenebutylacrylate(EBA);polyethyle ethylenebutylacrylate(EBA);polyethylene;andethylene-me ne;andethylene-methyl-acrylate(EMA) thyl-acrylate(EMA) copolymer.

8

2.4CompatibilityofPolymerswithBitumen 2.4.1Itshouldberecognizedthatthere Itshouldberecognizedthatthereisacomplexrelationship isacomplexrelationshipbetweenthe betweenthe chemicalcompositionofbitumens,theirco chemicalcompositionofbitumens,theircolloidalstructure,and lloidalstructure,andtheirphysicaland theirphysicaland rheologicalproperties.Anythingsuch rheologicalproperties.Anythingsuchasapolymerwhich asapolymerwhichmodifiesthechemical modifiesthechemical compositionofbitumendefinitelymodifiesitsstructure compositionofbitumen definitelymodifiesitsstructureand,conse and,consequently,its quently,its 3 properties . 2.4.2Ifathermoplasticpolymerismixedhotwithbitumen Ifathermoplasticpolymerismixedhotwithbitumenwithoutanyspe withoutanyspecial cial 3 precautions,oneofthefollowingthree precautions,oneofthefollowingthreesituationsoccurs situationsoccurs : •

•

•

Themostlikelyresultisthatthemixisheterog Themostlikelyresultisthatthemixisheterogeneousbec eneousbecausethepolyme ausethepolymer r andbitumenarenotcompatible;thec andbitumenarenotcompatible;theconstituentsofthemixsep onstituentsofthemixseparate;andthe arate;andthe mixdoesnotpossessthecha mixdoesnotpossessthecharacteristicsofatyp racteristicsofatypicalbitumen. icalbitumen. Infrequently,themixistotallyhomogenou Infrequently,themixistotallyhomogenousevenatthemolec sevenatthemolecularleveland ularleveland thereforethepolymeriscompatiblewithbitumen thereforethepolymeriscompatiblewithbitumen.Theoilsinthebitume .Theoilsinthebitumen n solvatethepolymerperfectlyandthe solvatethepolymerperfectlyandtheresultingbinderissta resultingbinderisstable.However,the ble.However,the improvementintheservicequalityofbind improvementintheservicequalityofbinderisveryslight;only erisveryslight;onlyitsviscosity itsviscosity increases.Therefore,thisisnotthede increases.Therefore,thisisnotthedesiredresult. siredresult. Themixismicroheterogeneousa Themixismicroheterogeneousandconsistsoftwod ndconsistsoftwodistinctfinelyinterlocked istinctfinelyinterlocked phases.Thisisthecompatibilityw phases.Thisisthecompatibilitywhichisdesiredand hichisdesiredandwhichgivesthe whichgivesthebitumen bitumen genuinelymodifiedproperties.Thec genuinelymodifiedproperties.Thecompatiblepolymerab ompatiblepolymerabsorbssomeofthe sorbssomeofthe oilyfractionsand“swells”toformap oilyfractionsand“swells”toformapolymerphasedistinctfromthe olymerphasedistinctfromtheresidual residual bitumenphasecomprisingofhea bitumenphasecomprisingofheavyfractionsofthebind vyfractionsofthebinder(asphaltenes er(asphaltenes,resins ,resins andrestoftheoils).

2.4.3Thethirddesirablesituationmentioneda Thethirddesirablesituationmentionedabovetypically bovetypicallyoccurswhenthe occurswhenthe polymercontentislow(lessthanab polymercontentislow(lessthanabout4percent)where out4percent)whereinthebitumenisthe inthebitumenisthe continuousphaseofthesy continuousphaseofthesystemandthepolymerph stemandthepolymerphaseisdisperse aseisdispersedthroughoutthe dthroughoutthe bitumenmatrix.Thebitumenphaseh bitumenmatrix.Thebitu menphasehasarelativelyhighe asarelativelyhigherasphalteneco rasphaltenecontent ntent (becausesomeofitsoilhasbe (becausesomeofitsoilhasbeenabsorbedby enabsorbedbythepolymer)which thepolymer)whichincreasesits increasesits cohesionandelasticity.Athighse cohesionandelasticity.Athighservicetemperatures(a rvicetemperatures(about60C),highstiffness bout60C),highstiffness modulusofthepolymerphasee modulusofthepolymerphaseenhancesthe nhancesthemechanicalperformanc mechanicalperformanceofthemodified eofthemodified binder.Atlowservicetemperatures,the binder.Atlowservicetemperatures,thestiffnessmodulusofthed stiffnessmodulusofthedispersedpolyme ispersedpolymer r 3 phaseislowerthanthatofthebitumen phaseislowerthanthatofthebitumenmatrix,whichreduce matrix,whichreducesitsbrittleness sitsbrittleness . 2.5StorageStability

Thestoragestabilityofmodifiedbindersisv Thestoragestabilityofmodifiedbindersisveryimportantduringac eryimportantduringactualuse.Since tualuse.Since themodifiedbindershavetwodistinctpha themodifiedbindershavetwodistinctphasesasmentione sesasmentionedearlier,thereisalway dearlier,thereisalwaysa sa potentialforseparationorsedimentationunle potentialforseparationorsedimentationunlessthepolymera ssthepolymerandbitumenare ndbitumenare chemicallycross-linkedlikesomere chemicallycross-linkedlikesomereactiveterpolymers,whic activeterpolymers,whichhavebetterstorag hhavebetterstorage e stability.Thepotentialforseparationincreas stability.Thepotentialforseparationincreaseswhen(a)thed eswhen(a)thedifferenceindensity ifferenceindensity betweenthetwophasesincrea betweenthetwophasesincreasesand(b)thevisc sesand(b)theviscosityofthecontinu osityofthecontinuousphase ousphase 3 decreases .

9

2.6CrumbRubberModifiedBitumen(CRMB) 2.6.1Duringthetimeperiodw Duringthetimeperiodwhenhighway henhighwayengineersintheU engineersintheUSweretryingto Sweretryingto understandcomplexpolymermodified understandcomplexpolymermodifiedbitumen(PMB)systems bitumen(PMB)systemsaspreviously aspreviously discussed,cameanotherfarmo discussed,cameanotherfarmorecomplexandlea recomplexandleastunderstoodmodified stunderstoodmodifiedbinder: binder: crumbrubbermodifiedbitumen(CRMB).IntheUS,CRMB crumbrubbermodifiedbitumen(CRMB).IntheUS,CRMBissimplycalled issimplycalledAsphaltAsphaltRubber(AR)binder.Rubberfromdiscarde Rubber(AR)binder.Rubberfromdiscardedtyresisgroundtoa dtyresisgroundtoaparticulateorcrumb particulateorcrumb priortoaddingittobitumentoproduceCRMB. 2.6.2CharlesMcDonald,whowasa CharlesMcDonald,whowasanengineerwithCityofPho nengineerwithCityofPhoenix,Arizona,US, enix,Arizona,US, developedtheARtechnologyinthe developedtheARtechnologyintheearly1960s.The early1960s.TheuseofARorCRMB useofARorCRMBwas was sporadicintheUSuntil1991,when sporadicintheUSuntil1991,whentheUSCongress theUSCongressmandateditsuse mandateditsuseinall50states inall50states throughcentrallegislation.Thiswasdon throughcentrallegislation.Thiswasdoneinspiteofthefac einspiteofthefactthattheperformance tthattheperformanceof of 13 bituminouspavementswithCRMBwasmixed bituminouspavementswithCRMBwasmixedintheUSinthep intheUSinthepast ast .Whereasin someprojectstheCRMBenhance someprojectstheCRMBenhancedtheperformance dtheperformanceofthebituminouspave ofthebituminouspavement, ment, therewasnosignificantimprovementino therewasnosignificantimprovementinotherprojects.Thispo therprojects.Thispoliticaldecisionbythe liticaldecisionbythe USCongress,whichwasnotbas USCongress,whichwasnotbasedonsound edonsoundengineeringprinciple engineeringprinciples,wasopposed s,wasopposed 9 bothbytheasphaltindustryand bothbytheasphaltindustryandthestatehighwayde thestatehighwaydepartments’officialsatthattime partments’officialsatthattime . 2.6.3Sincemostofthestatesdidnothav Sincemostofthestatesdidnothaveanyexperien eanyexperienceinusingCRMB,the ceinusingCRMB,theUS US FederalHighwayAdministration(FHWA)undertook FederalHighwayAdministration(FHWA)undertookanambitiousprac anambitiouspracticaltraining ticaltraining 8 programmeforstatehighwayengineers programmeforstatehighwayengineers.Thetrainingman .Thetrainingmanual ual emphasizedthe importanceofstringentqualitycontrolrequire importanceofstringentqualitycontrolrequirementsrightfromtheprod mentsrightfromtheproductionofthe uctionofthe CRMBatorincloseproximityofhotmixasph CRMBatorincloseproximityofhotmixasphaltplant;transportationofCRMB altplant;transportationofCRMB fromproductionsitetoasphaltmixplant;storag fromproductionsitetoa sphaltmixplant;storageofCRMBincontrac eofCRMBincontractor’splant;and tor’splant;and finaltestingofCRMBjustpriortoaddingittoaggreg finaltestingofCRMBjustprior toaddingittoaggregatesinasphaltpla atesinasphaltplantpugmillor ntpugmillor drum. 2.6.4Duringthemandateall50statesinthe Duringthemandateall50statesintheUSusedCRMBin USusedCRMBinnumerousbituminous numerousbituminous pavingprojectsfrom1991until1995whe pavingprojectsfrom1991until1995whenthemanda nthemandatewasrepealed. tewasrepealed.Thereafter, Thereafter, moststatesdiscontinuedtheroutineu moststatesdiscontinuedtheroutineuseofCRMBinbituminousp seofCRMBinbituminouspavingmixtures. avingmixtures. Therearethreeprimaryreasonsforthis. 2.6.5First,theuseofCRMBrequiresdevelopm First,theuseofCRMBrequiresdevelopmentofastatewide entofastatewideinfrastructure infrastructure consistingofstrategicallyplacedblen consistingofstrategicallyplacedblendingterminalsoron-siteble dingterminalsoron-siteblendingunits.Thisis ndingunits.Thisis requiredbecauseCRMBmustbeus requiredbecauseCRMBmustbeusedassoona edassoonaspossiblebec spossiblebecauseitsqualitycan auseitsqualitycanstart start todeteriorateasearlyas6hoursafterproduction. 2.6.6Second,thequalitycontrolrequire Second,thequalitycontrolrequirementsrightfromtheproduc mentsrightfromtheproductiontotheend tiontotheend useofCRMBaretoocumbersomeb useofCRMBaretoocumbersomebecauseoftwoissu ecauseoftwoissues:(a)crumbrubber es:(a)crumbrubbertendsto tendsto separateandsettledowninthebitume separateandsettledowninthebitumenand(b)crumbru nand(b)crumbrubberispronetode bberispronetodegradation gradation (devulcanizationanddepolyme (devulcanizationanddepolymerization)ifitsuseisdelay rization)ifitsuseisdelayedtherebylosing edtherebylosingitsvital itsvital propertiesincludingviscosity. 2.6.7Third,manystatessuchasArka Third,manystatessuchasArkansas,Georgia,K nsas,Georgia,Kansas,Minnes ansas,Minnesota,Nevada, ota,Nevada, Washington,andWisconsin havereportedmixedperformanceofbituminous pavementsconstructedwithCRMBand pavementsconstructedwithCRMBandthecosteffective thecosteffectivenessofCRMBwasfo nessofCRMBwasfoundto undto 9 benonetomarginal .

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2.6.8Atthepresenttime,CRMBisusedona Atthepresenttime,CRMBisusedonaroutinebasisonly routinebasisonlyinfourstatesinthe infourstatesinthe US:Arizona,California,Florida,andTexas US:Arizona,California,F lorida,andTexas.Theremaining .Theremaining46statesdono 46statesdonotappearto tappearto havemuchinterestindevelopingthe havemuchinterestindevelopingthenecessaryinfras necessaryinfrastructureandimplementing tructureandimplementingthe the necessaryqualitycontrolprogramme necessaryqualitycontrolprogrammetoensureeffectiveus toensureeffectiveuseofCRMB. eofCRMB. 2.6.9ProductionofCRMB:CRMB ProductionofCRMB:CRMBisproduced isproducedbytheso-calledwe bytheso-calledwetprocessinwhich tprocessinwhich crumbrubberisaddedtohotbitumena crumbrubberisaddedtohotbitumenandthemixtureisagita ndthemixtureisagitatedmechanicallyu tedmechanicallyuntil ntil thereisa“reaction”betweenthe thereisa“reaction”betweenthebitumenandcrumbrub bitumenandcrumbrubber.The“reac ber.The“reaction”isnota tion”isnota chemicalprocessbutratheradiffus chemicalprocessbutratheradiffusionprocessthatinclud ionprocessthatincludesthephys esthephysicalabsorption icalabsorption ofaromaticoilsfromthebitumenintothepoly ofaromaticoilsfromthe bitumenintothepolymerchainoftherubbe merchainoftherubber.Therubber r.Therubber particlesswellastheyabsorboils,whic particlesswellastheyabsorboils,whichcausethev hcausetheviscosityoftheCRMBtoincre iscosityoftheCRMBtoincrease ase duringthefirsthourorso.Afterthe“reaction” duringthefirsthouror so.Afterthe“reaction”andassocia andassociatedswellingisover,the tedswellingisover,the viscosityoftheblendlevelsoff. 2.6.10IftheCRMBismainta IftheCRMBismaintainedathightempe inedathightemperatureforaprolongedp ratureforaprolongedperiodoftime eriodoftime (aslittleas6hours),thecrumbrubberbeg (aslittleas6hours),thecrumbrubberbeginstodegrade(de instodegrade(devulcanizeand vulcanizeand depolymerize)causingtheCRMBvisc depolymerize)causingtheCRMBviscositytodecrease ositytodecreasefromitsplateaulevel(also fromitsplateaulevel(also calledthetargetviscosity).Physica calledthetargetviscosity).Physicalandchemicalprope landchemicalpropertiesofCRMBareinfluenc rtiesofCRMBareinfluenced ed bythefollowingfactors.

a. BitumenCrudeSourceandMethodo BitumenCrudeSourceandMethodofRefining:Theche fRefining:Thechemical mical compositionofbitumenvariesfromonep compositionofbitumen variesfromonepetroleumcrudesou etroleumcrudesourceto rceto another,fromwhichitisrefined.Notwocru another,fromwhichitisrefined.Notwocrudesourcesare desourcesarethesame. thesame. Themethodofrefiningalsoaffectsbitume Themethodofrefiningalsoaffectsbitumen’schemicalcomp n’schemicalcompositionin ositionin termsofasphaltenesandmaltenes termsofasphaltenesandmaltenescontents.Since contents.Sincebitumenisa bitumenisa hydrocarbonandcrumbrubbera hydrocarbonandcrumbrubberalsocontainssub lsocontainssubstantialamountsof stantialamountsof hydrocarbons,theirmutualchemica hydrocarbons,theirmutualchemicalcompatibilityaffectsthep lcompatibilityaffectsthephysical hysical andchemicalpropertiesofCRMB.Th andchemicalpropertiesofCRMB.Thetypeandamo etypeandamountofoilreadily untofoilreadily availableinbitumenforabsorptionby availableinbitumenforabsorptionbycrumbrubberalsoa crumbrubberalsoaffectsthese ffectsthese properties.Bitumenslowinaromaticoilstend properties.BitumenslowinaromaticoilstendtoproduceCRMB toproduceCRMBwith with 5 pooradhesiveproperties . b. SourceofCrumbRubber:Crumbrubber SourceofCrumbRubber:Crumbrubbercanbeobtained canbeobtainedfromtruck fromtruck tyresorautomobiletyresorboth.Wholetruc tyresorautomobiletyresorboth.Wholetrucktyrecontains18 ktyrecontains18percent percent naturalrubbercomparedto9perce naturalrubbercomparedto9percentinanautomobilety ntinanautomobiletyreand2 reand2 percentintyretreads.Theamoun percentintyretreads.Theamountofnaturalrubberhas tofnaturalrubberhasshownto shownto affectthepropertiesofCRMBsignificantly.Eac affectthepropertiesofCRMBsignificantly.Eachlotofcrumbrubbe hlotofcrumbrubber r mayhavedifferentchemicalcompos mayhavedifferentchemicalcompositiondepending itiondependingonthesource onthesource (trucktyresorautomobiletyresormixtureofbo (trucktyresorautomobiletyresormixtureofboth)and,therefore, th)and,therefore, whencombinedwiththesameso whencombinedwiththesamesourceofbitumenmay urceofbitumenmaygivedifferent givedifferent properties.  c. MethodofProducingCrumbRubber:Crumbru MethodofProducingCrumbRubber:Crumbrubberisproduc bberisproducedfrom edfrom discardedtyresbytwomethods:(a discardedtyresbytwomethods:(a)grindingatambienttempe )grindingatambienttemperatures ratures and(b)grindingcryogenicallycooled and(b)grindingcryogenicallycooledtyrerubber.Theg tyrerubber.Thegrinding rinding methodaffectsthecrumbrubberparticle methodaffectsthecrumbrubberparticlemorphology,which morphology,whichinturn inturn affectstherateofreactionandpropertiesofCRMB. d. AmountandSizeofCrumbRubber:Bo AmountandSizeofCrumbRubber:Boththeamountands ththeamountandsizeof izeof crumbrubberparticlesaffectthepropertiesofCRMB.

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2.6.11TransportationofCRMB:Evenafterthecrumbrubberhas“reacted” withbitumen,ithasatendencytose withbitumen,ithasate ndencytoseparatefrombitumenpartia paratefrombitumenpartiallyandsettledown llyandsettledown duringtransportationandstorageatthe duringtransportationa ndstorageatthecontractor’splantuntilCRMBisus contractor’splantuntilCRMBisused. ed. Therefore,itisessentialthatthetrucktankers Therefore,itisessentialthatthetrucktankerscarryingCRMBaree carryingCRMBareequippedwith quippedwith heavy-dutyrecirculationdevicesor heavy-dutyrecirculationdevicesormechanicalagitatorstok mechanicalagitatorstokeepthecrumb eepthecrumbrubber rubber insuspension. 2.6.12CRMBUseintheUS:Eventhen,thefewstatesintheUS,w :Eventhen,thefewstatesintheUS,whichuse hichuse CRMBonaroutinebasisattheprese CRMBonaroutinebasisatthepresenttime,requirethattheCRMB nttime,requirethattheCRMBshouldbe shouldbe usedwithinaspecifiednumberofho usedwithinaspecifiednumberofhoursafterproduction.For ursafterproduction.Forexample,California, example,California, Kansas,andArizonaspecifythatthe Kansas,andArizonaspecifythattheCRMBmustbeus CRMBmustbeusedwithin4,6,an edwithin4,6,and10 d10 5 hours,respectively .ThiskindofrequirementdoesnotallowtheCRMBtobe producedatoilrefineries,whicharege producedatoilrefineries,whicharegenerallyfarawayfromas nerallyfarawayfromasphaltmixplants. phaltmixplants. Thatiswhy;aninfrastructureofnumerous Thatiswhy;aninfrastructureofnumerousblendingterminalsoro blendingterminalsoron-siteblending n-siteblending unitsarenecessarywithinastate.

Atthepresenttime,onlyfourstatesintheUS Atthepresenttime,onlyfourstatesintheUSuseCRMBonaro useCRMBonaroutinebasis utinebasis besidesPMB;somewereforcedtou besidesPMB;somewereforcedtouseitbecauseofsta seitbecauseofstatelegislation.Threeo telegislation.Threeof f thesefourstatesalsousePerforman thesefourstatesalsousePerformanceGradesPG76-22 ceGradesPG76-22forheavilytrafficked forheavilytrafficked roads.However,theyhavedifferents roads.However,theyhavedifferentspecificationforCRMB(called pecificationforCRMB(calledasphaltasphaltrubberintheUS)andPMBsbecaus rubberintheUS)andPMBsbecausetheCRMBcann etheCRMBcannotmeetPG76-22 otmeetPG76-22 specificationrequirements.Onheavilytra specificationrequirements.Onheavilytraffickedroadsthey ffickedroadstheypreferandspecify preferandspecifyPG PG 76-22madewithpolymers(commonlyela 76-22madewithpolymers(commonlyelastomers).Floridauses stomers).FloridausesCRMBonlyin CRMBonlyin frictioncourses. NotonlyCRMBandPMBsaredifferentmaterialsa NotonlyCRMBandPMBsaredifferentmaterialsandthereforeneed ndthereforeneeddifferent different specifications;itisalsonotpossibletouse specifications;itisalso notpossibletousethedynamicsh thedynamicshearrheometer(DSR) earrheometer(DSR) fortestingCRMBbecauseithasdiscre fortestingCRMBbecauseithasdiscreetrubberparticles. etrubberparticles. SinceCRMBandPMBaredifferentmaterialsw SinceCRMBandPMBaredifferentmaterialswithdifferentfieldperformance ithdifferentfieldperformance, , thefourstatesspecifythebindertype thefourstatesspecifythebindertypetobeusedonsp tobeusedonspecificprojectsco ecificprojectsconsidering nsidering thetrafficandmixtype. A“nextgeneration”ofasphalt-rubbe A“nextgeneration”ofasphalt-rubber(CRMB)isbeingexamined r(CRMB)isbeingexaminedinFlorida, inFlorida, Texas,andArizona,whichca Texas,andArizona,whichcanpotentiallymeetPG76 npotentiallymeetPG76-22requirements.Itis -22requirements.Itis calledterminalblendasphalt–rubber, calledterminalblendasphalt–rubber,whichismanufac whichismanufacturedbyblendingdige turedbyblendingdigested sted groundtyrerubberwithsomeSBSpolyme groundtyrerubberwithsomeSBSpolymer.However,useo r.However,useofCRMBinroad fCRMBinroad pavingapplicationsisnotthaturgen pavingapplicationsisnotthaturgentnowintheUSbec tnowintheUSbecauseotheruse auseotherusesof sof discardedtyresarenowinvogue discardedtyresarenowinvoguesuchasproduc suchasproducingelectricenergy, ingelectricenergy,useasfuelin useasfuelin limeandcementkilns,andrecyc limeandcementkilns,andrecyclingtomakedifferentproduc lingtomakedifferentproductsfromtyres. tsfromtyres.

2.7TestProceduresSpecifictoModifiedBinders 2.7.1Severaltestproceduresspecifictomod Severaltestproceduresspecifictomodifiedbindershav ifiedbindershavebeenadapted ebeenadaptedor or developedtoidentifyandmeasure developedtoidentifyandmeasuretheirimprovedproperties theirimprovedpropertiesandtodifferentiate andtodifferentiate themfromunmodifiedbinders.These themfromunmodifiedbind ers.Thesetestproceduresa testproceduresandcriteriaareincluded ndcriteriaareincludedin in 11 thespecificationsformodifiedbinders .

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2.7.2Softeningpoint(ringa Softeningpoint(ringandball)hasbeen ndball)hasbeenusedformodifiedbind usedformodifiedbindersto ersto measuretheirresistancetoflowathighte measuretheirresistancetoflowathightemperatures.Thistestiswid mperatures.Thistestiswidelyusedin elyusedin Europeforpavingbitumensasan Europeforpavingbitumensasanindicatorofresistance indicatorofresistancetoruttingduringhot toruttingduringhot summer.Penetrationtesthasbeenu summer.Penetrationtesthasbeenusedasanindica sedasanindicatorofbinderstiffnessa torofbinderstiffnessat t intermediatetemperatureof25C. 2.7.3Toughnessandtenacitytes ToughnessandtenacitytestwasusedintheUSto twasusedintheUStomeasuretensile measuretensilestrength strength 15 duringelongationofneoprenemodifiedbitumenbinders .Itisstillusedinsome states.Aforceductilitytestwasalsode states.Aforceductilitytestwasalsodevelopedtomeas velopedtomeasuretensilepropertiesby uretensilepropertiesby usinganinexpensiveforcea usinganinexpensiveforceadapterinthestandardd dapterinthestandardductilitymachine. uctilitymachine. 2.7.4Elastomermodifiedbitumen Elastomermodifiedbitumenshavetheu shavetheuniqueabilitytoelas niqueabilitytoelasticallyrecover ticallyrecover fromdeformationwhichisadesirableproperty fromdeformationwhichisa desirablepropertyforpavingbinders. forpavingbinders.Atorsion Atorsion recoverytestwasdevelopedinthe recoverytestwasdevelopedintheUSasafieldtesttoide USasafieldtesttoidentifypresenceof ntifypresenceof elastomersinmodifiedbitumens.Thistestiss elastomersinmodified bitumens.ThistestisspecifiedinCaliforniab pecifiedinCaliforniabesidesother esidesother states.Anelasticrecoveryafterductilitytest,a states.Anelasticrecoveryafterductilitytest,alsoincludedinthe lsoincludedintheTaskforce31 Taskforce31 1 Specification ,hasbeenwidelyaccepte ,hasbeenwidelyacceptedandusedintheU dandusedintheUSandEurope SandEuropefor for elastomermodifiedbitumens. 2.7.5Unfortunately,mostofthe Unfortunately,mostofthetestsusedformodified testsusedformodifiedbindersareemp bindersareempiricaland iricaland notperformancebased.Rather,thes notperformancebased.Rather,thesetestsidentifythep etestsidentifythepresenceofcertainty resenceofcertaintypesof pesof modifiers.Itistheperformancewhichshou modifiers.Itistheperformanc ewhichshouldbemeasured ldbemeasuredtogainthemost togainthemost 11 benefitfromthemodification . 2.7.6Asmentionedearlier,someoftheSHRP Asmentionedearlier,someoftheSHRPSuperpavetests Superpavetests(seeTable2) (seeTable2) describedinSection2.2.5areno describedinSection2.2.5arenotadequatetofullyc tadequatetofullycharacterizemodifiedbinde haracterizemodifiedbinders. rs. NationalCooperativeHighwayResea NationalCooperativeHighwayResearchProgram(NCHRP)Project9 rchProgram(NCHRP)Project9-10, -10, “CharacterizationofModifiedAsphaltBinders “CharacterizationofM odifiedAsphaltBindersinSuperpave inSuperpaveMixDesign”was MixDesign”was 2 undertakentoaddressthatproblem.I undertakentoaddressthatproblem.Itsrecommendations tsrecommendations arestillbeing examined. 2.7.7SomecountrieslikeAustraliahave SomecountrieslikeAustraliahaveadoptedmorerationa adoptedmorerationaltestmethodsfor ltestmethodsfor measuringconsistencyandstiffness measuringconsistencyandstiffnessofmodifiedbindersinlieu ofmodifiedbindersinlieuofsofteningpoint ofsofteningpoint andpenetration(Table3).Specialelas andpenetration(Table3).Specialelastometerconsistingofc tometerconsistingofconcentriccylindersis oncentriccylindersis used.Thiscanbeconsidere used.Thiscanbeconsideredasasteptow dasasteptowardstheperformance ardstheperformancebased based specificationwhichisbasedonra specificationwhichisbasedonrationaltestmethods. tionaltestmethods.

Table3.AustralianSpecificationforPMBClassA15E S. No. Test property Specified value 1 Consistency at 60 C (Pa.s) min. 8,000 2 Stiffness at 25 C, (kPa), max. 30 3 Viscosity at 165 C (Pa.s) max. 0.9 4 Torsional recovery at 25 C, 30 s, %, min. 58 5 Softening point C, min. 82 Note:PMBClassA15Eissuitableforhe Note:PMBClassA15Eissuitableforheavytraffickedroad avytraffickedroadsinhotclimateofIndia. sinhotclimateofIndia.

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2.8FieldPerformanceofPavementswithPolymerModifiedBitumen

Polymermodifiedbitumensespeciallythosewithelastomersa Polymermodifiedbitumensespeciallytho sewithelastomersareroutinelyused reroutinelyused todayintheUSinflexiblepavements todayintheUSin flexiblepavementstructuresoroverlaysca tructuresoroverlayscarryinghighvolumes rryinghighvolumes oftraffic.Althoughtherehavebeennu oftraffic.Althoughthereha vebeennumerouslaboratorya merouslaboratoryandfieldstudies ndfieldstudies comparingtheperformanceofPMBmo comparingtheperfo rmanceofPMBmodifiedandunmodifiedbitumen difiedandunmodifiedbitumenmixes, mixes, therehadnotbeenaconcerted therehadnotb eenaconcertedeffortuntil2007toquan effortuntil2007toquantifythebenefitsofusing tifythebenefitsofusing PMBmixesortodevelopguidance PMBmixesortodeve lopguidanceonwhentheuse onwhentheuseofPMBmixiscost-effec ofPMBmixiscost-effective. tive. 16 VonQuintusetal conducte conductedanextensive danextensiveinvestigationofover35 investigationofover35real-world real-world pavementsectionsinNorthAmericato pavementse ctionsinNorthAmericatoquantifythebene quantifythebenefitsofusingPMB fitsofusingPMB modifiedmixes.Thetestsectionsuse modifiedmixes.Thete stsectionsusedinperformance dinperformancecomparisonsinclude comparisonsincludedboth dboth roadwayandacceleratedpave roadwayanda cceleratedpavementtestsections menttestsections.Performancedata .Performancedataforthetest forthetest sectionswerederivedfrompublishedliterature sectionswere derivedfrompublishedliteratureorotherpublicsou orotherpublicsourcessuchasthe rcessuchasthe Long-TermPavementPerformanceor Long-TermPave mentPerformanceortheNationalCenterforAs theNationalCenterforAsphalt phalt Technology(NCAT)databases.O Technology(N CAT)databases.Onthebasisofthepe nthebasisoftheperformancecomparison rformancecomparisons s madebetweenPMBmodifiedandun madebetween PMBmodifiedandunmodifiedbitumensec modifiedbitumensections,itwasfoundthat tions,itwasfoundthat PMBmixessignificantlyenhancenoto PMBmixessignifican tlyenhancenotonlytheruttingperformanc nlytheruttingperformanceofflexible eofflexible pavementsbutalsotheirfatigueand pavementsbu talsotheirfatigueandfractureperformance.T fractureperformance.Theexamplesuse heexamplesusedin din this2007studyshowanextende this2007study showanextendedservicelifefordee dservicelifefordeep-strengthasphaltpa p-strengthasphaltpavements vements of5to10yearsthroughtheuseo of5to10years throughtheuseofPMBmixesontheba fPMBmixesonthebasisoftheperformanc sisoftheperformance e observationsfromthecompanionunmo observationsfromthe companionunmodifiedtestsections. difiedtestsections.[Sincetheaverag [Sincetheaveragelife elife ofbituminoussurfacingintheUSisabou ofbituminoussurfacin gintheUSisabout8-10years,thismea t8-10years,thismeanstheincrease nstheincreasein in serviceliferangingfromabout50to100p serviceliferanging fromabout50to100percent.]According ercent.]Accordingtotheresearchers, totheresearchers,a a definitebiasexistsbetweenthepred definitebiasexistsbe tweenthepredictedandmeasured ictedandmeasureddistressvalues distressvaluesforthe forthe sectionswithPMBmixtureswhenusingc sectionswithPMBmixture swhenusingcurrentmechanistic–e urrentmechanistic–empiricaldistress mpiricaldistress predictionmodels.Thisfindingsugge predictionmodels.T hisfindingsuggestsaneedfordifferen stsaneedfordifferentcalibrationfactorsin tcalibrationfactorsin PMBmixes(duetotheirenhancedpe PMBmixes(duetothe irenhancedperformance)foruseinru rformance)foruseinruttingandfatigue ttingandfatigue crackingpredictionequations.

3.HISTORICAL USEOFMODIFIEDBINDERSININDIA. 3.1Initiation 3.1.1Useoflatexrubbersomefourdec Useoflatexrubbersomefourdecadesagomay adesagomaybesaidtohave besaidtohavemarkedthe markedthe introductoryuseofmodifiedbindersinIndia introductoryuseofmodifiedbindersinIndia.Atthattimethereweres .Atthattimethereweresharp harp fluctuationsinthedemand-supplypo fluctuationsinthedemand-supplypositionofrubberinsouthe sitionofrubberinsouthernIndia.Therefore, rnIndia.Therefore,  thoughtwasgiventoincorporatela thoughtwasgiventoincorporatelatexrubberintobitumen.Some texrubberintobitumen.Someroadtestsec roadtestsections tions werelaidwithrubberlatexmodifiedbinder.Fu werelaidwithrubberlatexmodifiedbinder.Fullerbenefitwouldhave llerbenefitwouldhavebeenavailable beenavailable ifatthattimethebindertechnologyknowle ifatthattimethebindertec hnologyknowledgelevelwash dgelevelwashighenougha ighenoughandthe ndthe necessaryequipmenthadthe necessaryequipmenthadtherequisitecapabilities.Ev requisitecapabilities.Evennow,one ennow,onerefineryonthe refineryonthe southwestcoastproducesabou southwestcoastproducesabout20,000tonnes t20,000tonnesperyearoflatexrubb peryearoflatexrubbermodified ermodified bitumen. 3.1.2Inflowofinformationfromintern Inflowofinformationfrominternationalsourceson ationalsourcesonpotentialbenefitsof potentialbenefitsof modifiedbitumenbindersandlaying modifiedbitumenbinde rsandlayingoftestsectionsstartedc oftestsectionsstartedcatchingtheinteres atchingtheinterestof tof somesectionsofIndianroadco somesectionsofIndianroadcommunityduringthe198 mmunityduringthe1980sandthe19 0sandthe1990s.Many 90s.Many peopleknowledgeableinmodifiedbind peopleknowledgeableinmodifiedbindertechnology ertechnologyandcommercialinteres andcommercialinterestsplayed tsplayed akeyroleintheintroductionofmodifiedbinde akeyroleintheintroductionofmodifiedbindersonIndianroa rsonIndianroadsduringthat dsduringthat period.Thesupplierssetupoffice period.Thesupplierssetupofficesandplants,andu sandplants,andusheredinmarke sheredinmarketingefforts. tingefforts.

14

Currently,therearesuppliersforavarietyo Currently,therearesuppliersforavarietyofmodifiedbinderssuc fmodifiedbinderssuchaslatexrubber, haslatexrubber, crumbrubber,elastomeric,andplas crumbrubber,elastomeric,andplastomericthermosettingpoly tomericthermosettingpolymers. mers. 3.2Guidelines 6

3.2.1Astheinterestwaspickingup,the Astheinterestwaspickingup,theIndianRoadsCon IndianRoadsCongressbroughto gressbroughtout ut aspecial publication(SP:53)in1999titled,“Tentative publication(SP:53)in19 99titled,“TentativeGuidelinesonUse GuidelinesonUseofPolymerand ofPolymerand RubberModifiedBinders”.Thisdocu RubberModifiedBinders”.Thisdocumentcontained,intera mentcontained,interalia,separaterequire lia,separaterequirements ments fordifferentgradesofelastomericandplas fordifferentgradesofelastomericandplastomericthermoplasticmodifiers tomericthermoplasticmodifiers,andlatex ,andlatex andcrumbrubbermodifiers.Indicatived andcrumbrubbermodifiers.Indicativedosageswerea osageswerealsogivenalongwithg lsogivenalongwithgrade rade selectioncriteriabasedonmaximumand selectioncriteriabasedonmaximumandminimumatmosphe minimumatmospherictemperaturesa rictemperaturesatthe tthe site.Requirementsofsofteningpointan site.Requirementsofsofteningpointandelasticrecovery delasticrecoveryweredifferentfordifferent weredifferentfordifferent typesandgradesofmodifications. typesandgradesofmodifications.However,therewas However,therewasnoguidancea noguidanceastowhich stowhich modifiedbinderwassuitablebased modifiedbinderwassuitablebasedontrafficlevelandintens ontrafficlevelandintensity.TheBureauof ity.TheBureauof IndianStandards(BIS)alsodevelope IndianStandards(BIS)alsodevelopedsimilarseparates dsimilarseparatespecificationsfordifferent pecificationsfordifferent 4 modifiedbindersin2002 . 3.2.2Recently,theIndianRoadsCong Recently,theIndianRoadsCongresshasissue resshasissuedthe2010ve dthe2010versionofSP:53 rsionofSP:53 7 whereinthespecificationsfordifferenttype whereinthespecificationsfordifferenttypesofmodifiershavebe sofmodifiershavebeenunified enunified . Obviously,toaccommodatetheCRM Obviously,toaccommodatetheCRMBtheminimumelasticre Btheminimumelasticrecovery covery requirementwasreducedforallmodifiedb requirementwasreducedforallmodifiedbindersincludingPMB indersincludingPMBwithelastomer, withelastomer,

3.3Usage 3.3.1Duringthepastdecade(2001 Duringthepastdecade(2001-2010),useofmodified -2010),useofmodifiedbitumenhaspicke bitumenhaspickedup dup impressively,crossing0.5milliontonnesp impressively,crossing0.5milliontonnesperyearmark.Cu eryearmark.Currently,itmaybeinthe rrently,itmaybeinthe rangeof12-15percentofthetotalbitumen rangeof12-15percentofthetotalbitumenconsumedo consumedonroads.Nearly8 nroads.Nearly80percentof 0percentof thisconsumptionisinrespectofcrumb thisconsumptionisinre spectofcrumbrubbermodifiedbitumen rubbermodifiedbitumen.Latexrubberis .Latexrubberis usedonlytotheextentof15,000– usedonlytotheextentof15,000–20,000tonnes 20,000tonnesperyear,con peryear,consumedmostlyinan sumedmostlyinand d aroundthestateofKerala.Theremain aroundthestateofKerala.Theremaining20percentissh ing20percentissharedbetween aredbetweenelastomeric elastomeric andplastomericthermoplasticpolymersb andplastomericthermoplasticpolymersbroadlyintheratioof2:1, roadlyintheratioof2:1,respectively. respectively. 3.3.2Increasingconsiderationisbeing Increasingconsiderationisbeinggiventotheuseo giventotheuseofmodifiedbindersin fmodifiedbindersin importantairportpavementprojects.Airportsa importantairportpave mentprojects.AirportsatDelhi,Hyderabada tDelhi,HyderabadandBangalore ndBangalore maybecitedasexamplesofthe maybecitedasexamplesoftheirsubstantialuse.An irsubstantialuse.Anotableaspectistha otableaspectisthatSP:53- tSP:53- 2010provisionsarenotbeingfollowe 2010provisionsarenotbeingfollowedintoto.Therequ dintoto.Therequirementsinrespectof irementsinrespectof softeningpoint,elasticrecovery,e softeningpoint,elasticrecovery,etc,arebeingenhan tc,arebeingenhancedvis-à-visthose cedvis-à-visthoseofSP:53- ofSP:53- 2010.Inotherwords,PMBswithelastome 2010.Inotherwords,PMBswithelastomerswhichmeetthe rswhichmeettheenhancedrequire enhancedrequirements ments arebeinglargelyused. 3.3.3Costwise,crumbrubbermodifiedbitumen Costwise,crumbrubbermodifiedbitumenisbeingquoted isbeingquotedatthelowestrate, atthelowestrate, onlyuptoabout10percenthigh onlyuptoabout10percenthigherthanthepriceofunmo erthanthepriceofunmodifiedbitumen.The difiedbitumen.Thecostliest costliest modificationisthatwithSBStypepolymers modificationisthatwithSB Stypepolymers–about30perce –about30percentcostincreasew ntcostincreasewith ith 3%SBSand50%increasewith5%S 3%SBSand50%increasewith5%SBS.Higherinitialcostdoe BS.Higherinitialcostdoesnotnecessa snotnecessarily rily meanthatSBSmodifiedbinderislessa meanthatSBSmodifiedbinderislessadvantageouson dvantageousonlifecyclecostba lifecyclecostbasis.Choice sis.Choice istobemadeineachcaseo istobemadeineachcaseonthebasisoflow nthebasisoflowestlifecyclecost. estlifecyclecost. 3.3.4TheIRCguidelinesinSP:53doesno TheIRCguidelinesinSP:53doesnotthrowtherequisite tthrowtherequisitelightastohowcho lightastohowchoice ice istobemadeofthemodifieranditsdos istobemadeofthemodifieranditsdosageinsurfaceco ageinsurfacecourseofabituminous urseofabituminous

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pavement.Theexercisingofc pavement.Theexercisingofchoicerequires,intera hoicerequires,interalia,gooddatao lia,gooddataonrelative nrelative quantitativeimprovementsinperformance quantitativeimprovem entsinperformanceforasetofconditions.Ifs forasetofconditions.Ifsuchdataareno uchdataarenot t availableadequately,thenone availableadequately,thenonehastoguess hastoguessthebasisbeing thebasisbeingusedfordeciding usedfordecidingonthe onthe typeandconcentrationofthemodifiers typeandconcentrationofthemodifiers.Consideringthep .Consideringthepresentusagerates resentusageratesof of differentmodifiedbindersmentionedearlier,o differentmodifiedbindersme ntionedearlier,oneisledtothinkthatthec neisledtothinkthatthechoicesare hoicesare probablybeingmadeontheba probablybeingmadeonthebasisoflowestinitialcost,w sisoflowestinitialcost,whichisnotdesirable. hichisnotdesirable. 3.4Perfo 3.4Performance rmanceandEc andEconomic onomics s 3.4.1 There Thereis is gross grossina inadeq dequac uacy yof ofpub publish lisheddata eddata in India India on relati relative ve perfor performan mance ce withandwithoutdifferentbindermodificationsundertypicalconditionsofloading, climat climate, e, and and their their combin combinati ations ons. . Intera Interacti ctions ons with with users users and other other knowle knowledge dgeab able le peoplebringouta peoplebringouta picturewhichislessthanreassu picturewhichislessthanreassuring. ring.Someof Someof thenotablesinthis thenotablesinthis regardfollow.

(a) Unlike Unlike in devel develope oped d countr countries ies, , whene whenever ver modifie modified d binde binders rs are used used short short test test secti sections ons using using unmod unmodifie ified d bitumen bitumen are not built built in India India for evalua evaluation tion of relati relative ve fieldperformance. (b)Systematicexercisesaregenerallynotunde (b)Systematicexercisesaregenerallynotundertakenatthepavemen rtakenatthepavementdesignstagefor tdesignstagefor objectivelychoosingthemodifierand objectivelychoosingthemodifieranditsconcentration.Thatd itsconcentration.Thatdecisioniseitheragiven ecisioniseitheragiven oneaspartoftheprojectdesign oneaspartoftheprojectdesignordecidedotherwise ordecidedotherwisesubjectively. subjectively. (c)Qualitychecksareprescribedbutproperimplementationisyettobecomeanorm. Therehavebeencaseso Therehavebeencasesofseparationinmodified fseparationinmodifiedbinder,leadingtopo binder,leadingtopoorresults. orresults. (d)Gooddataonactualbenefits/economiesrealizedfromtheuseofmodifiedbinders isratherscarceandthedecision isratherscarceandthedecisionprocesscurrently processcurrentlybeingadoptedla beingadoptedlacksrigour. cksrigour. 3.4.2Untilrelativefieldperforma Untilrelativefieldperformancedataisobtained ncedataisobtainedinIndia,thereisnoo inIndia,thereisnoother ther recoursebuttorelyonsimilardataore recoursebuttorelyonsimilardataorexperienceinthede xperienceinthedevelopedcountries. velopedcountries.A A comparativefieldperformancestudyof comparativefieldperformancestudyofdifferentmodifiedbindersha differentmodifiedbindershasbeen sbeen undertakenbyIITMadrasrecen undertakenbyIITMadrasrecently.Thisstudyhasbe tly.Thisstudyhasbeensponsore ensponsoredbyMORTH.More dbyMORTH.More suchstudiesshouldbeunde suchstudiesshouldbeundertakenacrossI rtakenacrossIndiatoobtainfieldperforma ndiatoobtainfieldperformancedataunde ncedataunder r differenttrafficandclimaticconditions.

4. RECOMMENDATIONSFORUSEOFMODIFIEDBINDERSIN INDIA 4.1Thereisanurgentneedtocollateallavailablegoodperformancedataondifferent modifierstoidentifythegaps,andtoinstitutesystematicstudiesforfillingthosegaps. Intheinterim,thehistoryofdevelopment,use,andexperiencewithmodifiedbinders indevelopedcountriesshouldbehelpfulinmakingrecommendationsfortheirusein India.Ithasbeenwellestablishedthatmodifiedbindersmadewithdifferentpolymers (elastomersandplastomers)anddifferentmod (elastomersandplastomers)anddifferentmodifiers(crumbrubberandn ifiers(crumbrubberandnaturalrubber) aturalrubber) are are comp comple lex x syst system ems s with with vast vastly ly diffe differe rent nt physi physica cal l and and chem chemic ical al char charac acte teri rist stic ics. s. Ther Theref efor ore, e, ther there e cann cannot ot be a comm common on spec specif ific icat atio ion n for for thes these e diff differ eren ent t type types s of modi modifie fied d bind binder ers. s. Each Each type type must must have have its own own sepa separa rate te spec specifi ifica catio tion n simil similar ar to AASHTOandASTM.IncaseofacommonspecificationlikeinIRC:SP:53-2010,the follo followi wing ng cons conseq eque uenc nces es are are expe expect cted ed: : (a) (a) lowe lowerin ring g the the requ require ireme ment nts s to the the leve level l where here a wea weak mod modifie ifier r lik like crumb rumb rubb rubbeer can can also lso quali ualify fy, , would ould lowe lower r the the perfo performa rmance nce standa standard rd for all modifie modifiers; rs; (b) supplie suppliers rs of better better and more more expen expensiv sive e prod produc ucts ts will will tend tend to down downgr grad ade e the the qual qualit ity y of thei their r prod produc ucts ts so as to be more more

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competitivepricewiseifthatisthecriterionfordecisionmaking;and(c)loweringthe qualitywillcomeinthewayofproducingstillbetterproductsthushavinganegative effectonfurtherR&Dactivities.

4.2 Polymermodifiedbitume Polymermodifiedbitumen(PMB)withelastomersismos n(PMB)withelastomersismostcommonlyuse tcommonlyusedwith dwith successonmajorhighwaysinthe successonmajorhighwaysinthedevelopedc developedcountriesbecause ountriesbecauseelasticityinthis elasticityinthis PMBprovidesresistancetobothruttingan PMBprovidesresistancetobothruttingandfatiguecracking. dfatiguecracking.SuchPMBsarea SuchPMBsarealso lso relativelymorestableandmaintaintheirintegritybe relativelymorestableandmaintaintheirintegritybettercomparedtoPMBsw ttercomparedtoPMBswith ith plastomers,CRMB,andNRMB(naturalrubber plastomers,CRMB,andNRMB(naturalrubbermodifiedbitumen).Supe modifiedbitumen).Superpave rpave performancegradeshavebeen performancegradeshavebeenmadesucce madesuccessfullywiththesePMBs. ssfullywiththesePMBs.PMBswith PMBswith elastomersarethereforerecommended elastomersarethereforerecommendedforheavilytraffickedroa forheavilytraffickedroadsinIndia. dsinIndia. 4.3 Polymermodifiedbitume Polymermodifiedbitumenwithplastomersareh nwithplastomersarehardlyusedinflexiblep ardlyusedinflexiblepavements avements inthedevelopedcountriesbeca inthedevelopedcountriesbecausealthoughthey usealthoughtheyprovidehigherstreng providehigherstrengthinitially, thinitially, theyarepronetocrackingathighs theyarepronetocrackingathighstrainsanddonotre trainsanddonotreboundafterdeforming boundafterdeformingforce force isremoved.Therefore,thereisnonee isremoved.Therefore,thereisnoneedtohaveasp dtohaveaspecificationinIndiaforPMBs ecificationinIndiaforPMBs withplastomerstoavoiditsunnecess withplastomerstoavo iditsunnecessaryandimproperu aryandimproperuse,untilpropertechnic se,untilpropertechnical al  justificationisprovided.  4.4 Aseparatespecificationmaybeco Aseparatespecificationmaybeconsideredifdesiredfo nsideredifdesiredfornaturalrubbermodified rnaturalrubbermodified bitumen(NRMB)foritslimiteduseinIndiatosupportthelocalindustryin southernIndia.Itshouldnotbeused southernIndia.Itshouldnotbeusedonheavilytraffickedro onheavilytraffickedroadswhereonly adswhereonlyPMBs PMBs withelastomersshouldbeuseda withelastomersshouldbeusedasmentionedearlier.Ho smentionedearlier.However,NRMBshouldbe wever,NRMBshouldbe usedwithcautionbecauselikeCRMB usedwithcautionbecauselikeCRMBithasdegradation ithasdegradationproblemsifkeptathigh problemsifkeptathigh temperaturefortoolong. 4.5 IthasbeenestablishedthatCRMBismu IthasbeenestablishedthatCRMBismuchmorecomplexa chmorecomplexandleastunde ndleastunderstood rstood comparedtoPMBswithelastomers.Beca comparedtoPMBswithelastomers.Becauseofthecomp useofthecomplexandvarying lexandvarying chemicalcompositionofcrumbrubberob chemicalcompositionofcrumbrubberobtainedfromtread/sidew tainedfromtread/sidewalloftruck alloftruck and/orcartyres,itscompatibilitywithbitumenisalway and/orcartyres,itscompatibilitywithbitumenisalwaysquestionable. squestionable.Thatis Thatis why;CRMBhasgivenmixedperforman why;CRMBhasgivenmixedperformanceintheUS.Nohig ceintheUS.Nohighperformancegra hperformancegrade de PGgradesuchasPG76-22ca PGgradesuchasPG76-22canbemadewithCRMB nbemadewithCRMBbecauseitlac becauseitlacksadequate ksadequate elasticcomponent.IfIndiaweretoadop elasticcomponent.IfIndiaweretoadoptPGgradingtoday, tPGgradingtoday,PG76-22wouldbe PG76-22wouldbe recommendedforheavilytraffickedroa recommendedforheavilytraffickedroads.Therefore,CRMBisn ds.Therefore,CRMBisnotrecommended otrecommended foruseinIndiaonheavilytraffickedroads. 4.6 IfCRMBisconsidered IfCRMBisconsideredforuseonmediumtra foruseonmediumtraffickedroads,itshould ffickedroads,itshouldhaveitsown haveitsown separatespecificationandshouldbe separatespecificationandshouldbespecifiedas specifiedassuchforspecificp suchforspecificprojects.Thisis rojects.Thisis becauseitselasticrecoveryisc becauseitselasticrecoveryisconsiderablylowerthan onsiderablylowerthanthatofPMBswith thatofPMBswith elastomers.Someofthetestsspecified elastomers.SomeofthetestsspecifiedintheSuperpave intheSuperpavePGgradingsyste PGgradingsystemsuch msuch asdynamicshearrheometer(DSR)ca asdynamicshearrheometer(DSR)cannotbeconducte nnotbeconductedonCRMBsamp donCRMBsamples les becauseithasdiscreetrubberpa becauseithasdiscreetrubberparticles.Thatmeans,itisno rticles.Thatmeans,itisnotpossibletospe tpossibletospecify cify maximumphaseangledelta(which maximumphaseangledelta(whichisobtainedwithDSR)toens isobtainedwithDSR)toensuresome uresome elasticityintheCRMB.Rather,elasticrecov elasticityintheCRMB. Rather,elasticrecoverytestwithductilitymachineh erytestwithductilitymachinehasto asto bemaintainedandcontinuedatthepresenttime. 4.7 IfCRMBisspecifiedformed IfCRMBisspecifiedformediumtraffickedroads,itsho iumtraffickedroads,itshouldbeblended uldbeblendedonsitein onsitein closeproximityofhotmixplantssothatitcan closeproximityofhotmixplantssothatitcanbeusedwithin6-8h beusedwithin6-8hoursafter oursafter production.Claimsthattheso-called“c production.Claimsthatt heso-called“chemicallymodified”CRMB hemicallymodified”CRMBinIndiadoes inIndiadoes

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nothavesettlementand/ordegradation nothavesettlementand/ordegradationproblemshaveno problemshavenotbeenvalidated tbeenvalidatedasyet asyet withanyreportedmeaningfulfieldtestdata.T withanyreportedmeaningfulfieldtestdata.ThenumberofCRMB henumberofCRMBmanufactures manufactures isgrowinginIndia;manydonothave isgrowinginIndia;ma nydonothavequalifiedtechnicals qualifiedtechnicalstaffwhounderstands taffwhounderstands thiscomplex,unpredictablebinderma thiscomplex,unpredictablebindermaterial.Obviously,ifon-site terial.Obviously,ifon-siteblendingis blendingis done,afullyequippedtestinglabo done,afullyequippedtestinglaboratorystaffedwithqualifiedtec ratorystaffedwithqualifiedtechniciansshould hniciansshould bemandatoryattheblendingterminal. 4.8 Useofanymodifiedbinderinbituminousmixo Useofanymodifiedbinderinbituminousmixonlowvolumerura nlowvolumeruralroadssuchas lroadssuchas PMGSYisdetrimentaltotheirdurability.Thecurrentpra PMGSYisdetrimentaltotheird urability.ThecurrentpracticeofusingCRMBin cticeofusingCRMBin suchapplicationsshouldbedisc suchapplicationsshouldbediscontinueduntilprope ontinueduntilpropertechnicaljustificationis rtechnicaljustificationis provided. 4.9 Pendingtheavailabilityofnationallyacce Pendingtheavailabilityofnationallyacceptedperformance ptedperformancedatafromIndianroad datafromIndianroad projects,itwouldbeagoodideaforbothroadusersandroadbusinessinterestsifthe supplierofmodifiedbitumenortheconstructioncontractorwarrantyitsperformance onaspecificproject.

5

CURRENTIMPERATIVES

Basedonthedetailedrecommend Basedonthedetailedrecommendationsmadeforuse ationsmadeforuseofmodifiedbitumenb ofmodifiedbitumenbindersin indersin IndiainprecedingSection4,thefollowing IndiainprecedingSection4,thefollowingcurrentimperativesha currentimperativeshavebeenidentified: vebeenidentified: 1. IRC:SP:53-2010,“GuidelinesonUseo IRC:SP:53-2010,“GuidelinesonUseofModifiedBitumeninRoad fModifiedBitumeninRoad Construction”mustberevisedimmediate Construction”mustberevisedimmediatelybydeletingthe lybydeletingthecommon common specificationtableforalltypesofpolymers specificationtableforalltypesofpolymersandmodifierssothats andmodifierssothatsubstandard ubstandard PMBisnotusedinIndia.Thereis PMBisnotusedinIndia.Thereisnoneedtohav noneedtohaveanyspecification eanyspecificationtablefor tablefor modifiedbindersinthispublication.Rather, modifiedbindersinthis publication.Rather,referenceshou referenceshouldbemadeto ldbemadeto currenteditionIS15462,“Polymerand currenteditionIS15462,“PolymerandRubberModifiedBitume RubberModifiedBitumen– n– Specification”.IRC:SP:53shouldremainon Specification”.IRC:SP:53shouldremainonlyaguide(asthe lyaguide(asthenameimplies) nameimplies) forusingmodifiedbinders.Historically,theB forusingmodifiedbinders.Historically,theBureauofIndianStand ureauofIndianStandards(BIS) ards(BIS) hastheresponsibilityofmaintainingsta hastheresponsibilityofmaintainingstandardsforallroadpa ndardsforallroadpavingbinders. vingbinders. 2. TheIndianRoadsCongresssh TheIndianRoadsCongressshouldrequestthe ouldrequesttheBIStodeleteIS1546 BIStodeleteIS15462and 2and developthreeseparatestandard developthreeseparatestandardsoneeachfor soneeachforPMB(elastomer),CRMB,and PMB(elastomer),CRMB,and NRMBwithdifferentISdesignationssimilartoASTMstand NRMBwithdifferentISdesig nationssimilartoASTMstandardsmentioned ardsmentioned earlier.Thiswouldfacilitateselectingan earlier.Thiswouldfacilitateselectingandspecifyingapprop dspecifyingappropriatemodified riatemodified bitumenbytheengineerforaspec bitumenbytheengineerforaspecificprojectdepending ificprojectdependingontraffic. ontraffic. 3. RevisedIRC:SP:53mu RevisedIRC:SP:53muststateonlyPMB ststateonlyPMB(elastomer)shouldbe (elastomer)shouldbeusedfor usedfor heavilytraffickedroads.Norecomme heavilytraffickedroads.Norecommendationshouldbema ndationshouldbemadeforPMB deforPMB (plastomer),itsuseisnotadvisedforflexiblep (plastomer),itsuseisnotadvisedforflexiblepavementsinIn avementsinIndia. dia. 4. RevisedIRC:SP:53mu RevisedIRC:SP:53muststateCRMBca ststateCRMBcanbeusedonme nbeusedonmediumtraffickedroads diumtraffickedroads only.Itsuseonlowvolumeroads only.Itsuseonlowvolumeroadsshouldbeba shouldbebanned.CRMBmustbe nned.CRMBmustbeblended blended onsitesothatitcanbeusedwithin6-8 onsitesothatitcanbeusedwithin6-8hoursofproduction. hoursofproduction.Afullyequipped Afullyequipped testinglaboratorystaffedwithqualifiedtechnic testinglaboratorystaffedwithqualifiedtechniciansmustberequire iansmustberequiredatthe datthe blendingterminal. 5. Indiashouldcollectandcollateda Indiashouldcollectandcollatedataonrelativeperforma taonrelativeperformanceobtainableunde nceobtainableunder r differentsetsofsiteconditionswithdifferenttypesa differentsetsofsiteconditionswithdifferenttypesandlevelsofbitume ndlevelsofbitumen n modification.Pendingtheavailabilityofthese modification.Pendingtheavailabilityofthesefindings,modifiedbinde findings,modifiedbinder r

18

suppliersandconstructioncontrac suppliersandconstructioncontractorsshouldprovidew torsshouldprovidewarrantiesonfield arrantiesonfield performance.

5.ACKNOWLEDGEMENT

AnumberofexpertsandusersinIn AnumberofexpertsandusersinIndiawerecontacted diawerecontactedforexchangeo forexchangeofviewson fviewson currentpracticesofusingmodifiedbinders currentpracticesofusingmodifiedbinders.Usefuldiscussions .UsefuldiscussionswithDr.P.K.Jainof withDr.P.K.Jainof CRRIandMr.B.R.TyagiofOomsPoly CRRIandMr.B.R.TyagiofOomsPolymerModifiedBitumenPvtLtda merModifiedBitumenPvtLtdarethankfully rethankfully acknowledged. 6.REFERENCES

1. AASHTO-AGC-ARTBAJointCommittee,“Guide AASHTO-AGC-ARTBAJointCommittee,“GuideSpecificationsforPolyme SpecificationsforPolymer r ModifiedAsphalt”,TaskForce31 ModifiedAsphalt”,TaskForce31Report,1992. Report,1992. 2. Bahia,H.U.etal,“CharacterizationofMo Bahia,H.U.etal,“CharacterizationofModifiedAsphaltBinders difiedAsphaltBindersinSuperpave inSuperpave MixDesign”,TransportationResearc MixDesign”,TransportationResearchBoard,NCHRPRepo hBoard,NCHRPReport459,2001. rt459,2001. 3. Brule,B.,“Polymer–ModifiedAsphaltCe Brule,B.,“Polymer–ModifiedAsphaltCementsusedinRoa mentsusedinRoadConstruction dConstruction Industry:BasicPrinciples”,Transpo Industry:BasicPrinciples”,TransportationResearchBo rtationResearchBoard,Transportation ard,Transportation ResearchRecord1535,1996. 4. BureauofIndianStandards.IS154 BureauofIndianStandards.IS15462:2004,“Polyme 62:2004,“PolymerandRubberMo randRubberModified dified Bitumen–Specification,2004. 5. Hanson,D.I.,J.A.EppsandR.G. Hanson,D.I.,J.A.EppsandR.G.Hicks,“Construc Hicks,“ConstructionGuidelinesforCrumb tionGuidelinesforCrumb RubberModifiedHotMixAsphalt”,Fede RubberModifiedHotMixAsphalt”,FederalHighwayAdministration ralHighwayAdministrationReport Report DTFH61-94-C-00035,August1996. 6. IndianRoadsCongressPublica IndianRoadsCongressPublicationSP:53,“TentativeG tionSP:53,“TentativeGuidelinesonUse uidelinesonUseof of PolymerandRubberModifiedBitumeninRo PolymerandRubberModifiedBitumeninRoadConstruction”,De adConstruction”,December cember 1999. 7. IndianRoadsCongressPublica IndianRoadsCongressPublicationSP:53,“Guidelines tionSP:53,“GuidelinesonUseModified onUseModified BitumeninRoadConstruction”,Sec BitumeninRoadConstruction”,SecondRevision,201 ondRevision,2010. 0. 8. Kandhal,P.S.andD.I.Hanson Kandhal,P.S.andD.I.Hanson,“CrumbRubberMod ,“CrumbRubberModifierTechnologies” ifierTechnologies”, , FederalHighwayAdministration,CrumbRubbe FederalHighwayAdministration,CrumbRubberModifierWorkshopMa rModifierWorkshopManual, nual, March1993. 9. Kandhal,P.S.,“QualityControlRequirem Kandhal,P.S.,“QualityControlRequirementsforUsingCrum entsforUsingCrumbRubber bRubber ModifiedBitumen(CRMB)inBituminousmixtures”, ModifiedBitumen(CRMB )inBituminousmixtures”,JournaloftheIndia JournaloftheIndian n RoadsCongress,Volume67-1,2006. 10. Kandhal,P.S.,“AnOverviewofVisc Kandhal,P.S.,“AnOverviewofViscosityGradingSyste osityGradingSystemAdoptedinIndia mAdoptedinIndia forPavingBitumen”,IndianRoadsCon forPavingBitumen”,IndianRoadsCongress,IndianHig gress,IndianHighways,April2007. hways,April2007. 11. King,Gayle,H.King,R.D.Pavlovich, King,Gayle,H.King,R.D.Pavlovich,A.L.Epps,and A.L.Epps,andPrithviKandhal, PrithviKandhal, “AdditivesinAsphalt”,AssociationofA “AdditivesinAsphalt”,AssociationofAsphaltPavingTe sphaltPavingTechnologists,Journ chnologists,Journal al ofAsphaltPavingTechnology, ofAsphaltPavingTechnology,Volume68A,1999. Volume68A,1999. 12. Roberts,F.L.,P.S.Kandhal,E.R.B Roberts,F.L.,P.S.Kandhal,E.R.Brown,D.Y.Leea rown,D.Y.LeeandT.W.Kennedy ndT.W.Kennedy,“Hot ,“Hot MixAsphaltPavingMaterials,MixtureDesig MixAsphaltPavingMaterials,MixtureDesignandConstruction” nandConstruction”Textbook Textbook publishedbyUSNationalAsphaltPa publishedbyUSNationalAsphaltPavementAssoc vementAssociation,SecondEd iation,SecondEdition, ition, 1996. 13. Shuler,T.S.,R.D.Pavlovich,J.A.Epp Shuler,T.S.,R.D.Pavlovich,J.A.EppsandC.K.Ada sandC.K.Adams,“Investiga ms,“Investigationsof tionsof MaterialsandStructuralPropertiesofAsph MaterialsandStructuralPropertiesofAsphalt-RubberPavingMixtures– alt-RubberPavingMixtures– Volume1”,TexasTransportationI Volume1”,TexasTransportationInstituteReportFHWA/RD-86/027 nstituteReportFHWA/RD-86/027,1986. ,1986.

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14. Terrel,R.L.andJ.L.Walter,“ModifiedA Terrel,R.L.andJ.L.Walter,“ModifiedAsphaltPavementMa sphaltPavementMaterials–The terials–The EuropeanExperience”,Proce EuropeanExperience”,Proceedings,theAsso edings,theAssociationofAsphaltPaving ciationofAsphaltPaving Technologists,Volume55,1986. 15. Thompson,D.C.andJ.F.Hag Thompson,D.C.andJ.F.Hagman,“TheModification man,“TheModificationofAsphaltwith ofAsphaltwith Neoprene”,Proceedings,theA Neoprene”,Proceedings,theAssociationofAsph ssociationofAsphaltPavingTech altPavingTechnologists, nologists, Volume27,1958. 16. VonQuintus,H.,J.MallelaandM.S.Buncher,“ VonQuintus,H.,J.MallelaandM.S.Buncher,“QuantificationofEffectof QuantificationofEffectof Polymer-ModifiedAsphaltonFlexiblePaveme Polymer-ModifiedAspha ltonFlexiblePavementPerformance” ntPerformance”. . TransportationResearchBoard, TransportationRe searchBoard,TransportationResea TransportationResearchRecord200 rchRecord2001,2007. 1,2007. *****************************************

Authors’ResponsestoCommentsonPaperNo.573 ,“UseofModified BituminousBindersinIndia:CurrentImperatives”by Prof.P.S.Kandhal andDr.M.P.Dhir ShriBhaskarGhosh

WhyareyouinsistingtoproduceCRMBimpregnatedhotmatrixatsite?Whatisthe harmif harmif weproduceitinconven weproduceitinconventiona tionalStationa lStationaryhotMixPlantandbring ryhotMixPlantandbringit it tositein tippertruck?Isthereanymaximumtimeperiod tippertruck?Isthereanymaximumtimeperiodbetweenitsprodu betweenitsproductionandlaying? ctionandlaying? Prof.P.K.Sikdar

IRC:53-2010mustbeimmediatelywithdraw IRC:53-2010mustbeimmediatelywithdrawn.Thereisnose n.Thereisnosenseofconsidering nseofconsideringall all typesofmodifiedbitumentobejustonetype. To crea reate conve onven nienc ience e for for fie field engin nginee eers rs (in (in contra ntracct etc) tc) by rem removin oving g the the requirementofexercisingchoiceisjustadisaster.Howapolymermodifiedbinder withdifferentmodifierscanbesameinitsqua withdifferentmodifiersca nbesameinitsqualityandperformance lityandperformance? ? There There is plenty plenty of experi experienc ence e of using using modifie modified d bitume bitumen n in the count country ry and and many many researches are also lso availa ilable. Jus Just one specifi ificatio tion for all typ types is a very unprofessionalandcrudeway unprofessionalandcrudewayofhandlingtherivalryo ofhandlingtherivalryofmodifiedbinderproduce fmodifiedbinderproducers. rs. ShriA.V.Sinha 1. The conclu nclussion ion of the the author thor is tha that for for hig high perfor rforma manc ncee roa roads only nly elastomericpolymermodifiedbindershouldbeusedandplastomericpolymer andCRMBshouldnotbeused. -

The experi experienc ence e on some some projec projects ts (e.g. (e.g. DelhiDelhi-Gur Gurga gaon) on) does does not supportthisview.

2. IRC: IRC:SP SP:5 :53: 3:20 2010 10 is stat stated ed to have have made made comp comprom romis ises es on elas elastic tic reco recove very ry propertyandhence,byimplication,n propertyandhence,byimplication,notdesirable. otdesirable. -

Poly Polyme mer r (Ela (Elast stom omer er) ) cann cannot ot dict dictat ate e the the benc benchm hmar arki king ng of data data recovery,itwillbeunfairtoothermodifiers.

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3. Use Use of modi modifi fied ed bitu bitume men n shou should ld not not be base based d on cost cost alon alone, e, but but cost cost plus plus performance. -

Theuserwillchooseonethatisappropriate.

ShriJitenderKumar

1. Besi Beside des s rest restor orin ing g the the elas elasti tic c reco recove very ry requ requir irem emen ent t from from 60 to 70 % for for elast lastom omeeric ric PMB PMB, do you reco recomm mmeend any furt furth her upg upgrad radation tion for for this this material? 2. Doyourecommendanyfurtherupg Doyourecommendanyfurtherupgradationofspecifica radationofspecificationforCRMB? tionforCRMB? 3. Whenwearegoingforhighersofteningpointofmodifiedbinders,whyelastic 0 recoveryshouldbemeasuredat15 Conlyandwhynotathigheroperating 0 temps.Like60 C? 4. We really really never never had plasto plastomer meric ic specif specifica icatio tions. ns. It is actua actually lly a higher higher end end elastomericandlowerendelastomericspecification. 5. CRMBismoreofgoodwastemanage CRMBismoreofgoodwastemanagementthanseriousb mentthanseriousbitumenmodification. itumenmodification. ShriKaushikBandopadhyay

Wouldyoupleaseclarifytheroleof(a)Ex-planttransitatthepointofexecutionand (b)Qualitycontrol&workmanshipwithrespec (b)Qualitycontrol&workma nshipwithrespecttothepopularuse ttothepopularuseofPMB&CRMB ofPMB&CRMB ShriB.C.Ghosh

“CRMBmustbeblendedatsiteforwhichawell-equippedlaboratoryshouldbethere atsite”.Myquestionisthatwhatarethe atsite”.Myquestionisthatwhataretheteststobeco teststobeconductedatsite? nductedatsite? Dr.SunilBose

Superpavespecificationsweredesignedforneatbinders.Theyareinappropriatefor polymer polymermodif modified iedbitum bitumen. en. Infact different differentasph asphaltsbehavedifferent altsbehavedifferently ly even even when theyhavethesameperformancegrade. - Natura Natural l rubber rubber improv improves es rutting rutting but is sensit sensitive ive to decomp decomposi ositio tion n and often often has compatibilityproblem. - Use Use of tyre tyre rubb rubber er as asph asphal alt t modi modifi fier er is envi enviro ronm nmen enta tall lly y good good and and resu result lts s in redu reduce ced d rutti rutting ng and and refle reflect ctio ion n crac cracki king ng but but spec specia ial l conc conclu lusi sion on like like high high mixin mixing g temperatureandlongdigestiontimenee temperatureandlongdigestiontimeneedtobemaintained dtobemaintained. . - SBS SBS increa increase ses s asphal asphalt t elasti elasticity city and SBS modifie modified d aspha asphalt lt can can berecycled berecycled. . SBS modifiedbinderperformsbetteratlowertemperature.

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Envelop lope avoids ids problem lems of separatio tion during ing stora torag ge, tran ransportat tation and application.Itincreasespavementmoistureresistanceandresultsinmodifiedasphalt performingbetterinhightemperatureDSRtests.Assuchplastomerscannotberuled out. The elastic recovery very tes test has shown to be a good measure urement of polym lymer contributiontobinderperformance,althoughnorelationshipappearstoexistbetween rut rut res resista istan nce and elast lastic ic rec recovery very. . Elas lastic tic rec recovery very and othe other r conve onven ntion tionaal measureme measurementsare ntsareincon inconsisten sistent tinranking inranking polymermodifiedbinder polymermodifiedbinder performanc performanceand eand only only measur measure e whethe whether r or not a modifie modifier r is presen present t in the aspha asphalt lt specim specimen en, , not not its contributiontotheasphaltperformance. ShriR.K.Panigrahi

For For pave paveme ment nt dete deteri rior orati ation on stud study y how how this this modi modifie fied d bitu bitumin minou ous s bind binder er help helps s to convincetheclienttoutilizethismaterialinlargerextent?Costofthematerialis veryusefulornotforconventionalorothermaterials. Yoursuggestionandinputsforfutureo Yoursuggestionandinputsforfutureofthismaterialmodifiedbinder. fthismaterialmodifiedbinder.

Authors’ResponsestoComments

ThequestionfromShriBhaskarGho ThequestionfromShriBhaskarGhoshisnotclear.Whatdo shisnotclear.Whatdoeshemean eshemeanbyCRMB byCRMB impregnatedhotmatrix?Anyway,ShriG impregnatedhotmatrix?Anyway,ShriGhoshisreferredtoSec hoshisreferredtoSection2.6ofthepap tion2.6ofthepaper. er. Briefly,theauthorsmeantostatethatonc Briefly,theauthorsme antostatethatoncethecrumbrubbe ethecrumbrubberisblendedwithbitumen risblendedwithbitumen toproduceCRMBbinder,thelattermustbe toproduceCRMBbinder,thelattermustbeusedwithin6-8hou usedwithin6-8hourstoproduceh rstoproducehotmix otmix asphalt.Thisissobecausethe asphalt.ThisissobecausethequalityofCRMBasa qualityofCRMBasabindercanstarttod bindercanstarttodeteriorateas eteriorateas earlyassixhoursafterblendingrubberinbitumen. TheauthorsagreewithProf.P.K.Sikda TheauthorsagreewithProf.P.K.SikdarthatIRC:SP:53:2010mustbe rthatIRC:SP:53:2010mustbewithdrawn withdrawn immediatelybecauseashestate immediatelybecauseashestated(a)polymermodifiedbinde d(a)polymermodifiedbinderwithdifferent rwithdifferent modifierscannotbethesameinitsqu modifierscannotbethesameinitsqualityandperformance alityandperformance,and(b)havingon ,and(b)havingone e specificationforalltypesofmodifiedbinders specificationforalltypesofmodifiedbindersisaveryunprofess isaveryunprofessionalandcrude ionalandcrudeway way ofhandlingtherivalryofmodifiedbinderpro ofhandlingtherivalryofmodifiedbinderproducers.Theau ducers.Theauthorshavemades thorshavemadesimilar imilar recommendationsin“Section5Curre recommendationsin“Section5CurrentImperatives”ofthe ntImperatives”ofthepaperthat paperthat IRC:SP:53:2010mustberevisedimmediately IRC:SP:53:2010mustbe revisedimmediatelybydeletingthecommo bydeletingthecommonspecification nspecification table;ratherreferenceshouldbemade table;ratherreferenceshouldbemadetocurrenteditionofIS1 tocurrenteditionofIS15462,“Polymera 5462,“Polymerand nd RubberModifiedBitumen–Specifications”. Thefollowingitem-wiseresponsesaregiventocommentsma Thefollowingitem-wiseresponsesareg iventocommentsmadebyShriA.V.Sinh debyShriA.V.Sinha: a: 1. Itisacommonworldwidepracticeba Itisacommonworldwidepracticebasedonextensive sedonextensiveperformanceexpe performanceexperience rience thatonlyelastomericpolymermodifiedbind thatonlyelastomericpolymermodifiedbindersareusedforhe ersareusedforheavy-trafficked avy-trafficked roadsandairfieldrunways.Theau roadsandairfieldrunways.Theauthorshavenotse thorshavenotseenanydoc enanydocumented umented experienceonDelhi-Gurgaonroad. 2. Concerninghiscommentsthatelas Concerninghiscommentsthatelastomericpolymerca tomericpolymercannotdictatethe nnotdictatethe benchmarkofelasticrecoverybe benchmarkofelasticrecoverybecauseitwillbeunfairtoo causeitwillbeunfairtoothermodifiers, thermodifiers, pleaserefertocommentsmadeby pleaserefertocommentsmadebyProf.Sikdar.Heha Prof.Sikdar.Hehasstatedthatitis sstatedthatitis unprofessionalandcrudeway unprofessionalandcrudewayofhandlingrivalryofmod ofhandlingrivalryofmodifiedbinder ifiedbinder producers.Thereisnoquestione producers.Thereisnoquestionelastomericpolymers lastomericpolymershavebetterperformanc havebetterperformance e

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comparedtoCRMB.Therefore,weca comparedtoCRMB.Therefore,wecannotlowertheelas nnotlowertheelasticrecovery ticrecovery requirement(thatisthebenchmark)arb requirement(thatisthe benchmark)arbitrarilyjusttoaccommodate itrarilyjusttoaccommodateCRMBin CRMBin thecommonspecification.Itwillnotbeinnationalinterest. 3. Theauthorsagreethatuseofmo Theauthorsagreethatuseofmodifiedbitumenshouldn difiedbitumenshouldnotbebased otbebasedoncost oncost alonebutcostplusperformance alonebutcostplusperformance.However,thiscanno .However,thiscannotbeachieved tbeachievedunless unless thereare“separate”specifications thereare“separate”specificationstochoosefrom. tochoosefrom.

Item-wiseresponsestoShriJitenderKumar’s Item-wiseresponsestoShriJitenderKumar’squeriesareasfo queriesareasfollows: llows: 1. Theelasticrecoveryrequirementfor Theelasticrecoveryrequirementforelastomericpolymerss elastomericpolymersshouldatleastbe houldatleastbe restoredto75percent(andnot70pe restoredto75percent(andnot70percentasmentione rcentasmentionedbyShriKumar)as dbyShriKumar)as previouslyspecifiedforelastomericPMB previouslyspecifiedforelastomericPMBinIRC:SP:53:2002.Some inIRC:SP:53:2002.Some progressivestatesintheUShave progressivestatesintheUShave75percentminimume 75percentminimumelasticrecovery lasticrecovery requirementevenfortheRTFOTresidue requirementevenfortheRTFOTresidue,whichisevenmo ,whichisevenmorestringent. restringent. 2. AsmentionedinthepaperinSection AsmentionedinthepaperinSection2.6CrumbRubber 2.6CrumbRubberModifiedBitumen ModifiedBitumen andSection5.0Item4,furtherupgra andSection5.0Item4,furtherupgradationofCRMBspec dationofCRMBspecificationneedstobe ificationneedstobe madeasfollows:(a)UseCRMBinhotmixas madeasfollows:(a)UseCRMBinhotmixasphaltwithin6-8hours phaltwithin6-8hoursofits ofits productionbecauseitispronetod productionbecauseitispronetodegradation,(b)UntilCRMBisu egradation,(b)UntilCRMBisused,truck sed,truck tankerscarryingCRMBandcontractors tankerscarryingCRMBandcontractors’storagetankssho ’storagetanksshouldbeequippe uldbeequipped d withheavy-dutyrecirculationdevices withheavy-dutyrecirculationdevicesormechanicalag ormechanicalagitatorstokeepthe itatorstokeepthe crumbrubberinsuspension,an crumbrubberinsuspension,and(c)Afullyequippedte d(c)Afullyequippedtestinglaboratory stinglaboratory staffedwithqualifiedtechniciansmustbe staffedwithqualifiedtechniciansmustberequiredattheCRMBb requiredattheCRMBblending lending terminalinthevicinityofhotmixplant.Inadd terminalinthevicinityo fhotmixplant.Inaddition,minimumpercentage ition,minimumpercentageof of thecrumbrubberintheCRMBaswellas thecrumbrubberintheCRMBaswellasitsgradationshoulda itsgradationshouldalsobe lsobe specified. 3. Elasticrecoverytestisconducted Elasticrecoverytestisconductedafterthebinderthread afterthebinderthreadisstretchedfor10 isstretchedfor10 cm,cutatthecenter,andthena cm,cutatthecenter,andthenallowedtorecover.Sinc llowedtorecover.Sinceductilitytestcan eductilitytestcannot not beconductedathightempera beconductedathightemperaturessuchas6 turessuchas60Cbecause 0Cbecausebitumenbecomes bitumenbecomestoo too soft,ductilitytestisconductedat25C soft,ductilitytestiscon ductedat25Corlowertemperatures. orlowertemperatures.Moreover, Moreover, differencebetweenelasticrecove differencebetweenelasticrecoveryofdifferentbindersbec ryofdifferentbindersbecomemoredistinct omemoredistinct andsignificantatrelativelylowertesttempera andsignificantatrelativelylowertesttemperatures.Historically,elastic tures.Historically,elastic recoverytestshavebeenco recoverytestshavebeenconductedat15 nductedat15Cfororiginalmodifiedbindersan Cfororiginalmodifiedbindersand d at25CforTFOTorRTFOTresidueo at25CforTFOTorRTFOTresidueofmodifiedbinders. fmodifiedbinders. 4. TheauthorsagreewithShriKumarthatw TheauthorsagreewithShriKumarthatwedidnotreallyhav edidnotreallyhaveatrue eatrue plastomericPMBspecification,whichlike plastomericPMBspecification,whichlikeASTMD5841should ASTMD5841shouldnothaveany nothaveany elasticrecoveryrequirement.Itisnotun elasticrecoveryrequirement.Itisnotunderstoodastowhy derstoodastowhyIRC:SP:53:2002 IRC:SP:53:2002 hadelasticrecoveryrequirementfor hadelasticrecoveryrequirementforplastomericPMBspec plastomericPMBspecification. ification. 5. Aswementionedinthepaper(Sec Aswementionedinthepaper(Section2.6.12lastpa tion2.6.12lastparagraph),thereareo ragraph),thereareother ther usesofdiscardedtyressucha usesofdiscardedtyressuchasproducingele sproducingelectricalenergy;usea ctricalenergy;useasfuelinlime, sfuelinlime, brickandcementkilns(it’salreadybe brickandcementkilns(it’salreadybeingdoneinIndia);an ingdoneinIndia);andrecyclingto drecyclingto makedifferentrubberproductssuchasmats.

InresponsetoShriKaushikBando InresponsetoShriKaushikBandopadhyaybothPMB padhyaybothPMBandCRMBsho andCRMBshouldbe uldbe testedbytheproducersatthepointofma testedbytheproducersatthepointofmanufacture(qualityc nufacture(qualitycontrol)andbythe ontrol)andbythe users(contractorsorgovernment)atthe users(contractorsorgovernment)atthepointofdelivery(qua pointofdelivery(qualityassurance). lityassurance). QualitycontrolrequirementsaremorecriticalforCRMB.S Qualitycontrolrequireme ntsaremorecriticalforCRMB.ShriBandpadhyay hriBandpadhyayis is referredtothefollowingIRCpaper:

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Kandhal,P.S. QualityControlRequirementsforUsingCrumbRubberModified Bitumen(CRMB).JournaloftheIndianRoa Bitumen(CRMB).Journa loftheIndianRoadsCongress,Volume dsCongress,Volume67-1,April67-1,AprilJune2006. Thispapercanalsobeacce Thispapercanalsobeaccessedontheinte ssedontheinternetatthefollowinglink: rnetatthefollowinglink: http://www.scribd.com/doc/19383778/Quality-Control-Requirements-forUsing-Crumb-Rubber-Modified-Bitumen-CRMB

ShriB.Ghoshhasaskedwhichtes ShriB.Ghoshhasaskedwhichtestsshouldbecond tsshouldbeconductedonCRMB uctedonCRMBwhen when producedatsite.Alltestswhicharein producedatsite.AlltestswhichareinthespecificationsforCRMB thespecificationsforCRMB(Table5of (Table5of IRC:SP:53:2002)shouldbeconduc IRC:SP:53:2002)should beconductedsuchaspe tedsuchaspenetration,softeningp netration,softeningpoint,elastic oint,elastic recoveryoforiginalandTFOTresidue, recoveryoforiginalandTFOTresidue,andseparation. andseparation.

MostofthecommentswhichDr.Bose MostofthecommentswhichDr.Bosehasmadearea hasmadearealreadymentioned lreadymentionedinthe inthe paper.Hehasmerelyrepeated paper.Hehasmerelyrepeatedthem.Forexample,we them.Forexample,weagreeallSuperpa agreeallSuperpavetests vetests andspecificationrequirementsarenota andspecificationrequirementsarenotapplicabletopolymermo pplicabletopolymermodifiedbitumen. difiedbitumen. Thatiswhy;manystatesintheUSuse Thatiswhy;manystatesintheUSuse“PGPlus”spe “PGPlus”specificationsand cificationsandtestssuchas testssuchas elasticrecovery. AsmentionedinSection4.4ofthepa AsmentionedinSection4.4ofthepaper,theauthorsa per,theauthorsalsoagreethatna lsoagreethatnatural tural rubberissensitivetodegradation. TheauthorsalsoagreewithDr.Bose TheauthorsalsoagreewithDr.Bosethattheuseoftyrerub thattheuseoftyrerubberinproducing berinproducing CRMBisenvironmentallygood.Howev CRMBisenvironmentallygood.However,aspointedoutinthe er,aspointedoutinthepaper(Section paper(Section 2.6.6)specialprecautionsneed 2.6.6)specialprecautionsneedtobetakenwhe tobetakenwhenproducing,transp nproducing,transporting,and orting,and usingCRMB. TheauthorsalsoconcurwithDr.Bos TheauthorsalsoconcurwithDr.Bosethatelastomericpoly ethatelastomericpolymersincreaseas mersincreaseasphalt phalt elasticityandSBSmodifiedasphaltca elasticityandSBSmodifiedasphaltcanberecycled.Althou nberecycled.Althoughplastomersha ghplastomershave ve relativelyhigherstiffnessathightemperatures relativelyhigherstiffness athightemperatures(asshowninDSRtes (asshowninDSRtests), ts), elastomersarepreferredworldwideforuseo elastomersarepreferredworldwideforuseonhigh-traffickedroads nhigh-traffickedroadsandairfield andairfield runways(seeSection4.2ofpape runways(seeSection4.2ofpaper).Sincetheuseof r).Sincetheuseofplastomersisvery plastomersisverylimited limited (almostnegligibleonhighways)itisbettertode (almostnegligibleonhighways)itisbettertodeletethemtoavoidany letethemtoavoidanyconfusion confusion amongtheusers. TheauthorsagreewithDr.Bosethatthe TheauthorsagreewithDr.Bosethattheremaynotbed remaynotbedirectrelationshipbetwe irectrelationshipbetween en elasticrecoveryandrutresistance. elasticrecoveryandrutresistance.However,theelasticre However,theelasticrecoverytestdoe coverytestdoes s indicatethepresenceandamoun indicatethepresenceandamountofelastomerinthemod tofelastomerinthemodifiedbitumen.Since ifiedbitumen.Since performancebasedspecificationsha performancebasedspecificationshavenotbeen venotbeenimplementedinIndiaa implementedinIndiaasyet,there syet,there isnootheralternativethanrelyingonth isnootheralternativethanrelyingontheelasticrecoveryte eelasticrecoverytestlikeitisstillbeing stlikeitisstillbeing usedintheUSwith“PGPlus”spec usedintheUSwith“PGPlus”specifications.AnewRep ifications.AnewRepeatedStressCreep eatedStressCreep Recovery(RSCR)hasbeendev Recovery(RSCR)hasbeendevelopedrecentlyinthe elopedrecentlyintheUS,whichisfarbe US,whichisfarbetterthan tterthan theempiricaltestssuchaselasticre theempiricaltestssuchaselasticrecovery.However, covery.However,RSCRisyettobe RSCRisyettobe implementedevenintheUS. InresponsetoShriPanigrahi,modifiedbinde InresponsetoShriPanigrahi,modifiedbinders,althoughexpe rs,althoughexpensive,doprovide nsive,doprovide betterperformanceandlongerservice betterperformanceandlongerservicelifecomparedtounmod lifecomparedtounmodifiedbinderson ifiedbinderson

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heavy-traffickedroadsandairfieldrunways heavy-traffickedroadsandairfieldrunways.Therefore,theirlife-cyc .Therefore,theirlife-cyclecostis lecostis lowercomparedtounmodifiedbinders.Sug lowercomparedtounmodifiedbinders.Suggestionsabou gestionsabouttheuseofdifferent ttheuseofdifferent typesofmodifiedbindersaregivenin typesofmodifiedbindersaregivenin“Section4Recomme “Section4RecommendationsforUse ndationsforUseof of ModifiedBindersinIndia”ofthepaper. Authors’Closure

Itisquiteclearfromthepaperaswellassomestrongcomme Itisquiteclearfromthepaperaswellasso mestrongcommentsreportedherein ntsreportedherein thatIRC:SP:53:2010containinga“common thatIRC:SP:53:2010con taininga“common”specificationfora ”specificationforalltypesof lltypesof modifiedbitumenshouldbewithdrawnimmed modifiedbitumenshou ldbewithdrawnimmediatelyinnationalinteres iatelyinnationalinterestsothat tsothat substandardmodifiedbitumenisnotuse substandardmodifiedbitumenisnotusedonroadsan donroadsandairfieldpavements dairfieldpavementsin in India.AllrecommendationsgiveninSe India.AllrecommendationsgiveninSection4ofthepape ction4ofthepaperconcerningtheuse rconcerningtheuseof of variousmodifiedbindersshouldbeimpleme variousmodifiedbindersshouldbeimplementedassoon ntedassoonaspossible. aspossible. **********************************************

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