Guidelines for Long Lasting Bituminous Pavements in India

GUIDELINESFORLONGLASTINGBITUMINOUSPAVEMENTS ININDIA By PROF.PRITHVISINGHKANDHAL*, PROF.A.VEERARAGAVAN**&R.K.JAIN*** [ThispaperwaspublishedasPaperNo.564intheJournaloftheIndianRoads Congress,Volume71-3,October-December2010.Authors’responsesto commentsreceivedonthispaperarealsogivenattheend.] ABSTRACT TheMORTHSpecifications(2001)forproducingandplacingdense-graded bituminouspavingmixeshavebeenreviewedindetailandrecommendations made.Therecommendationsbasedonthecurrentstate-of-the-arttechnologies pertainto:selectionofviscositygradebitumen;amountofnaturalsandinfine aggregate;MarshallmixdesignproceduresinthelatestAsphaltInstituteMS-2; mixingandcompactiontemperaturesbasedonviscositygradedbitumen; minimummatcompactiondensitybasedontheoreticalmaximumspecific gravityofloosemix;andqualityacceptancecriteria.Ithasbeenrecommended tohaveonlyonespecificationeachforalldensegradedbituminousmixesusedin basecourse,bindercourse,andwearingcourse.Together,allrecommendations formguidelinesforobtaininglonglastingpavementsinIndia. 1.INTRODUCTIONANDBACKGROUND Atthepresenttimebituminouspavingmixesaregenerallyproducedandplaced inIndiaasspecifiedinMORTHPublication,“SpecificationsforRoadand 30 BridgeWorks”,FourthEdition2001 .Thereisaproliferationofbituminous pavingmixesinIndia.Eightmixes(twogradingseachofBM,DBM,SDBCand BC)arespecifiedintheMORTHspecifications.Acasewasmadeondetailed 10 technicalgroundsinarecentIndianRoadsCongresspaper byKandhal,Sinha andVeeraragavantoessentiallyhaveonlyfourdensegradedmixesofdifferent nominalmaximumaggregatesize(NMAS)inthespecifications,asisthecasein mostcountriesoftheworld.Thefollowingfourdensegradedmixeswere proposedalongwiththeirrecommendedrutresistantgradationsasgivenin Table1: 25mmNMASDenseBituminousMacadam(DBM)BaseCourse 19mmNMASBituminousConcrete(BC)BinderCourse 12.5mmNMASBituminousConcrete(BC)WearingCourseGrading1 (forheavytraffic) 9.5mmNMASBituminousConcrete(BC)WearingCourseGrading2 (forlighttomediumtraffic,urbanareas,andthinapplication) ---------------------------------------------------------------------------------------------- *AssociateDirectorEmeritus,NationalCenterforAsphaltTechnology(NCAT),Auburn University,USA(currentlyJaipur)<[email protected]> **ProfessorofCivilEngineering,IndianInstituteofTechnology,Chennai ***FormerChiefEngineer,HaryanaPWD 1

TABLE1.PROPOSEDFOURDENSEGRADEDMIXESFORINDIA Grading Proposed ProposedBC ProposedBC DBMBase BinderCourse WearingCourse Course Grading1 →

ProposedBC WearingCourse Grading2

Nominal Aggregate Size

25mm

19mm

12.5mm

9.5mm

Lift Thickness

75-100mm

50-75mm

30-50mm

25-40mm

SieveSize, mm

Percent Passing -

-

37.5

100

-

26.5

90-100

100

-

-

19

71-95

90-100

100

-

13.2

56-80

66-86

90-100

100

9.5

-

55-75

70-88

90-100

4.75

38-54

35-55

53-71

55-75

2.36

28-42

28-44

38-54

40-55

1.18

-

20-34

24-38

29-44

0.6

-

15-27

17-29

21-33

0.3

7-21

10-20

12-22

14-25

0.15

-

5-13

7-15

7-15

0.075

4-7

4-7

4-7

4-7

Bitumen Content

4.0-5.5

4.0-5.5

5.0-7.0

5.2-7.5

Note:Wearingcoursegrading1isrecommendedforheavytrafficroads(morethan1500 commercialvehiclesperday).Wearingcoursegrading2isrecommendedforlighttomedium trafficroads,inurbanareas,andforthin(25mm)applications

Itwasalsorecommendedtodeletetheopengraded,highlyporousBituminous Macadam(BM)andtheSemiDenseBituminousConcrete(SDBC)mixesfrom theMORTHspecificationsbecausebothofthesemixeshaveserioustechnical flawsandarenotcosteffective.Adetailedtechnicalandeconomicalcomparison 10 ofBMwithDBMwasmadeinthepaper intermsofpermeability,structural strength,useasPCC(profilecorrectivecourse),costconsiderations,traffic conditions,andgeneralstatements.Itwasconcludedwithtechnicaljustifications thatdensegradedDBMshouldbeusedinlieuofhighlyporous,opengraded, undrainedBMespeciallytoobtainlonglastingpavements.However,despite manyfundamental,technicalflawsassociatedwithBMasmentionedinthe paper,someengineersstilladvocatetoretainitinthespecifications.Thisis probablyduetothefollowingmisconceptions:

2

•

•

 DensegradedDBMisnotflexiblee  DensegradedDBMisnotflexibleenoughtobeplace noughtobeplaceddirectlyonWMM ddirectlyonWMM  andthereforea“flexible”BMcours  andthereforea“flexible”BMcourseisnecessa eisnecessarybetweenthe rybetweentheWMMand WMMand  DBM.IftheDBMwasnotflexibleitwouldnotrutatall.Butthatisnot thecase.Ifthereisunevensettlement/consolidationofWMM,theDBM isflexibleenoughtodeformandadjustsimilartoBMifthatiswhatis desired.Itisacommonpracticeinmostcountriesoftheworldtoplace DBMtypebituminousbasecoursedirectlyoncrushedstonebasecourse (wecallitWMM).Thatpracticehasresultedindurablelonglasting pavementswithoutanyproblems.  BMischeaperthanDBMandthatiswhy  BMischeaperthanDBMandthatiswhyitisgoodfora itisgoodforadevelopingco developingcountry untry likeIndia.Adetailed,comparativecostanalysisgiveninthepapershows thattheDBMischeaperthantheBMby15to21%iftherelative structuralstrengthsareconsidered.OnlywhentheBMisusedasPCCto correctcamber/superelevationitischeaperthantheDBM.Butthe problemstillremainsthattheundrainedBMPCCwouldtrap moisture/watercreatinga“bathtub”withinthepavementandthuswill bepotentiallydetrimentaltothepavement.

SomeengineershavesuggestedretainingtheBMbutprovidingoutletforthe watertrappedintheopengradedBM.Todothis,theBMhastobeextendedall thewaytotheedgeoftheembankment(thatis,daylighted)orpavementedge drainshavetobeconstructedtodraintheBM.Bothofthesesolutionsarevery expensivepropositions. IfBMisusedasPCCforcorrectingcamber,itmaynotbepossibletodrainthe BMwedge(triangle)especiallyifitistowardsaraisedmedian.Moreover, rainwaterfallingintheraisedmedianmayalsoentersidewaysintotheporous BMwedgeandcausestrippingandpotholes.Suchacasehasbeenobservedona nationalhighwayinIndia. Asmentionedinthatpaper,itistimetomoveonfromopengraded“cheaper” mixestodensegraded,durablemixesiftheobjectiveistohavelonglasting pavementsbothforlow-volumeandhigh-volumeroads. Ifthedensegraded9.5mmNMASwearingcourseasrecommendedinTable1is adopted,thereisnoneedforthe“semi-dense”SDBC,whichistechnicallyflawed duetopessimumvoidsasexplainedintheIRCpaper.Therecommendeddense gradedmix(whichcanalsobeusedinthin25mmapplications)willbemore durableandcosteffectivethantheSDBC,becausetheformerisonlyabout5% costlierthanthelatter. Somediscussionofhowtherecommendedbasecourse,bindercourse,and wearingcoursemixes(Table1)shouldbeusedinnewpavementsaswellasin overlaysfollows. Basecoursemixes,whichuserelativelylargersizeaggregate,arenotonly stiff/stablebutalsoareeconomicalbecausetheyuserelativelylowerbitumen contents.Surfaceorwearingcoursemixeswithsmalleraggregateontheother handhaverelativelyhigherbitumencontents,whichnotonlyimparthigh 3

flexibilitybutalsoincreasetheirdurability.Thebinder(intermediate)course mixservesasatransitionbetweenthebasecourseandwearingcourse.Several 3,30,34 studies haveshownthatpermanentdeformation(rutting)withinflexible pavementisusuallyconfinedtothetop100to150mmofthepavement.This meansboththebinderandwearingcoursemixesshouldbedesignedtobe resistanttorutting.Thatiswhyinextremecasesofheavytrafficloadsandhigh tyrepressures,itisconsideredprudenttouseStoneMatrixAsphalt(SMA)mix inwhichduetostone-on-stonecontacttheloadiscarrieddirectlybythecoarse aggregateskeleton. Itisnotnecessarytouseallthreebituminouscourses(base,binder,andwearing) in a new new flex flexib ible le pave paveme ment nt un unle less ss the the traf traffi fic c is very very high high. . For For exam exampl ple, e, the the followin following g combin combinatio ations ns can be used used depend depending ing upon upon the total total thickne thickness ss of the bituminouscourse(s)requiredasperstructuraldesignbasedonIRC:37. • • •

WMM+DBMBaseCourse+BCBindercourse+BCWearingCourse WMM+BCBinderCourse+BCWearingCourse WMM+BCWearingCourseonly

For low-volu low-volume me roads roads only a granula granular r base and a bitumin bituminous ous wearing wearing course course maysufficebasedonstructuralrequirements. Some Some exam exampl ples es are are give given n belo below w for for sugg sugges este ted d bitu bitum minou inous s cour course ses s for for tota total l required bituminous ous laye ayer thick ickness cons onside idering ing the recomm ommended lift ift thicknessesforthefourmixes(giveninTable1): Required Total Bituminous LayerThickness Less than 50 mm 75 mm – 125 mm 150 mm or more

Use BC Wearing Course only (Grading 1 or 2) BC Binder Course + BC Wearing course DBM Base Course + BC Binder Course + BC WearingCourse

Ifthetotaldesignbituminouslayerthicknessfallsbetween50mmand75mm,or between125mmand150mm,usethehigherthickness. IthasbeensurmisedbysomethataBCwearingcourseistoostiffandwillcrack ifplaceddirectlyover ifplaceddirectlyoverWMM.Thisisnotcor WMM.Thisisnotcorrectbecau rectbecausetheBCwearin setheBCwearingcourse gcourse hasrelative hasrelativelylowerstiff lylowerstiffnes nessdueto sdueto itslowerNMAS(12. itslowerNMAS(12.5or 5or 9.5mm)andhigh bitume bitumen n conten content. t. This This combin combinatio ation n is being being used used in other other countr countries ies includi including ng Austr ustral alia ia and and Sout South h Afric frica. a. Sim Similar ilarly ly, , a bitum itumin inou ous s over overla lay y requ requir ired ed for for strengtheningflexib strengtheningflexiblepavemen lepavementcanconsistofthefollowingdependi tcanconsistofthefollowingdependinguponthe nguponthe requiredthicknessasperIRC:81: BCBinderCourse+BCWearingCourse • BCWearingCourseonly • Unlike Unlike most most develop developed edcoun countri tries, es, overload overloading ing is a major major concern concern in India. India. On veryheavilytraffickedroadwithsevereoverloadingproblem,itisrecommended 4

tomodifytheBCwearingcourseandBCbindercourse(th tomodifytheBCwearingcourseandBCbin dercourse(thatis,thetop100mm atis,thetop100mm ofthepavementonly,whichislikelytorut)asfollows: •

• •

Ensure Ensu re to use use visc viscos osit ity y grad graded ed VG-30 -30 grad grade e bitu bitum men as per per late latest st 4 IS73:2006 , which which is signi signific fican antl tly y more more rut rut resist resistan ant t than than the the old 60/70 60/70 penetrationbitumen. Usepolymermodifiedbitumen(PMB) Use Use Stone Stone Matri Matrix x Asph Asphalt alt (SMA (SMA) ) as per per IRC Sp Spec ecifi ifica catio tions ns appro approved ved recently

Criticalreviewofthebituminouspavingmixesandtheirspecificationsis warrantedconsideringlessthanexpecteddurabilityofbituminousmixesin Indiaespeciallyaftermonsoonrains.Thispapercanbeconsideredasa continuationoftheIRCpaperreferredabove,whichreviewedtheproliferation ofbituminousmixesinIndiaandrecommendeddesirablemixesalongwiththeir gradations.Thispaperreviewsthespecificationsforproducingandplacingthe selectedfourdensegradedbituminousmixestoobtainlonglastingbituminous pavements.Bothreviewsareexpectedtobehelpfultothecontractorswhoare currentlydesigningtheirownprojects(includingbituminousmixselection) underthePublic-Private-Partnership(PPP)programme. RevisionstothecurrentMORTHspecificationshavebeensuggestedasfollows intermsofmaterials;designofmix;constructionoperations;andqualitycontrol andacceptance.OnlythesuggestedchangestotheMORTHspecificationshave beengiveninthispaper.Ithasbeenrecommendedtohaveonlyonespecification foralldensegradedbituminousmixesusedinbasecourse,bindercourse,and wearingcourse.

2.MATERIALS 2.1Bitumen 3 IndianStandardSpecificationforPavingBitumenIS:73:2006 mustnowbe usedforallbituminousmixes.ThisrevisedstandardissuedinJuly2006specifies viscositygradedbitumenonlysuchasVG-30andVG-10.Itreplacedpenetration gradedbitumensuchas60/70and80/100.Thenewviscositygraded(VG) bitumens,whichwillprovideconsistentresistancetoruttingathighpavement temperaturesmustbespecifiedinMORTHspecificationbyissuinga corrigendum,andimplementedassoonaspossiblesothattheuseofsubstandard penetrationgradedbitumenisdiscontinued. Tables2,3,and4givethestandardviscositygrades(VG),theirgeneral applications,andselectioncriteria.Theviscositygradesarereadilyavailable nowinIndiawithnoextracost.ThecontractorsespeciallythosewithPPPor BOTprojectsmustuseVGgradesonlytoensureadequaterutresistanceand durabilityoftheirprojects. Sincealltypesofmodifiedbitumen(Table4)arenotconsideredequalin performance,thetypeofmodifiershouldbespecifiedforeachcontract.Polymer 5

modifiedbitumenissuitableforhighly-traffickedroads.Testingofmodified bitumenatthepointofdeliveryshouldbespecifiedinthecontractsincephase separationduringtransportisquitecommon.Polymercanalsobeaddedatthe hotmixplantsitetoavoidphaseseparationand/ordegradation.However,itis necessarytohaveappropriateblendingequipmentandatestinglaboratoryto conductalltestsrequiredinthespecification. TABLE2.VISCOSITYGRADED(VG)BITUMENSANDTHEIRGENERAL APPLICATIONS

ViscosityGradeGeneralApplications (VG)

VG-40Useinhighlystressedareassuchasthoseinintersections,neartoll (40-60penetration)booths,andtruckparkinglotsinlieuofold30/40penetrationgrade

VG-3 VG-30 0     Us Usef efor orp pavi aving ngi inm nmos ost tof ofIn Indi dia ain inl lieu ieuof ofo old ld6 60/7 0/70 0pen penetr etrati ation ong grad rade e (50-70penetration)

VG-2 VG-20 0     Us Use efo for rpa pavi ving ngi in nco cold ldc cli lim matic atic, ,hi high gha alt ltit itud ude ere regi gion ons sof ofN Nor orth thI Ind ndia ia (60-80penetration)

VG-10Useinsprayingapplicationsandforpavinginverycoldclimatein (80-100penetration)lieuofold80/100penetrationgrade

TABLE3.SELECTIONCRITERIAFORVISCOSITY-GRADED(VG)PAVINGBITUMENS BASEDONCLIMATICCONDITIONS 0                         Hig Highest hestDa Daily ilyMea MeanA nAirT irTemp emperat erature, ure, C 0 0 0 LowestDailyMean Lessthan20 C 20to30 C Morethan30 C AirTemperature,C 0

Morethan–10 C 0

-10 Corlower

VG-10

VG-20

VG-30

VG-10

VG-10

VG-20

TABLE4.SELECTIONCRITERIAFORGRADEOFMODIFIEDBITUMEN 0

Highest Daily Mean Air Temperature, C 0 0 0 Lessthan20 C 20to30 C Morethan30 C LowestDaily MeanAir 0 Temperature, C

 GradeofModified Bitumen

GradeofModified Bitumen

6

GradeofModified Bitumen

Morethan-10 C 0

0

-10 Corlower

PMB/NRMB120 CRMB50

PMB/NRMB70 CRMB55

PMB/NRMB40 CRMB60

PMB/NRMB120 CRMB50

PMB/NRMB120 CRMB50

PMB/NRMB70 CRMB55

PMB=PolymermodifiedbitumenNRMB=Naturalrubbermodifiedbitumen CRMB=Crumbrubbermodifiedbitumen

2.2CoarseAggregate ThestrippingtestIS:6241hasbeenspecifiedforcoarseaggregateinthepresent MORTHspecifications.Thistest,whichisconductedoncoarseaggregate only,  only,is antiquatedandproventobeinadequatebasedonresearchconductedinthepast. Mostmixturespassthiseasystatic-immersiontestand,thereforeantistripping agentsarenotusedwhenactuallyneededresultinginstrippingproblems.In manycases,thefineaggregateishydrophilicandcausesstripping,whichcanbe worsethanthatfromthecoarseaggregate.Manyofthestrippingproblems (especiallypotholesaftermonsoons)inIndiaarepotentiallyduetorelianceon thisantiquatedtest.ThereisaneedtousetheWaterSensitivityorMoisture SusceptibilityTestAASHTOT283,whichisconductedonthewholebituminous mix.Thistest,whichismostcommonlycalledMoistureSusceptibilityTest,is alsousedintheSuperpavemixdesign.ThistestisalreadyintheMORTH specificationsSection800asa“watersensitivity”testandthereforeitis recommendedtomakeitmandatorytobeconductedonallbituminousmixesat thetimeofmixdesignandonceaweekduringmixproduction.IS6241canbe retainedonlyasascreeningtestforthecoarseaggregate. Therecommendedrevisedphysicalpropertiesofcoarseaggregatearegivenin Table5. TABLE5.PHYSICALPROPERTIESOFCOARSEAGGREGATE Property

Test

Requirement

Testmethod

Cleanliness

Grainsizeanalysis

Max.5%passing0.075mm

IS2386PartI

Particle Shape

FlakinessandElongation Index(combined) Heavytraffic(morethan 1500commercial vehicles/day) Lighttraffic(lessthan 1500commercial vehicles/day)

Strength*

LosAngelesAbrasion Value

IS2386PartI

Max.35% Max.40%

Binderandwearingcourse: Max.30%

IS2386PartIV

Basecourse:35% AggregateImpactValue

Binderandwearingcourse: Max.24% 7

IS2386PartIV

Basecourse:27%

Polishing**

PolishedStoneValue

Min.55

IS2386PartIV

Durability

Soundness(eitherSodium orMagnesiumSulphate)– 5cycles Max.12%

IS2386PartV

Max.18%

IS2386PartV

WaterAbsorption

Max.2%

IS2386PartIII

CoatingandStrippingof BitumenAggregate Mixtures

Min.RetainedCoating95%

IS:6241

SodiumSulphate

MagnesiumSulphate Water Absorption Stripping***

Notes: *Theaggregatemaysatisfyeitherofthetwotests. **Onlyforwearingcourses ***Thistestshallbeconductedasascreeningtestforcoarseaggregateonly.Itismandatoryto conductAASHTOT283(AnnexureI),whichisconductedonthewholebituminousmixas specifiedinTable6.

ConsiderationshouldbegiventoincreasethemaximumLosAnglesabrasion valuesby5%becausethepresentlyspecifiedvaluesaretoostringentandmay necessitatetransportofaggregatesoverlongdistancesathighcosts.TheStateof GeorgiaintheUShasthebestroadsintheUS.Ithasgraniteasthepredominant 6 aggregatetypewithhighLAabrasionvalues.Georgiaspecifies maximumLA abrasionof50%forgraniteaggregate.Whereas,veryhighLAvaluesbeyonda thresholdvaluearenotdesirable,verylowvaluesdonotnecessarilymeanitisa 16 betteraggregate . ConsiderationshouldalsobegiventodeletetheAggregateImpactValue(AIV) testbecausetheLAAbrasiontestsubjectstheaggregatetobothimpactand abrasion(fromsteelballsandaggregatetoaggregatecontactwhenthedrumis rotated).UnlikeAIV,LAAbrasionsimulatestheprocessingofaggregateina drierdrum.MostcountriesintheworldincludingtheUSspecifyLAAbrasion testonly. NotalltestsspecifiedinTable5needtobeconductedveryfrequently.Testssuch asPolishedStoneValueandSoundnessneedtobeconductedatthetimeof source(quarry)approvalandlessfrequentlythereafter. 16,17,23

7

Kandhaletal andothers haveconductedresearchandreportedonseveral newtestmethodsfortestingandcharacterizingcoarseaggregatesfor bituminousmixes.Thenewtestmethodspertaintoparticleshape,angularity 8

andsurfacetexture(suchasuncompactedvoidcontent)andsoundness& durability(suchasMicro-Devaltest).Thenewimprovedtestmethodshavebeen adoptedbyAASHTOandneedtobeconsideredbytheBureauofIndian Standards(BIS),IRC,andMORTHtoenhancethequalityofbituminousmixes inIndia. 2.3FineAggregate Fineaggregateisdefinedasmaterialpassingeither4.75mmor2.36mmsieve. Rightnow,theMORTHspecificationisnotclearintermsofcrushedsand versusnaturalsandusedasafineaggregate.Onecanuse100percentnatural sand(whichtendstocontainroundedparticles)inallbituminouscourses,which increasesthepotentialforruttingproblems.Manyagenciesintheworldlimitthe amountofnaturalsandto50percentintheDBMtypebasecoursesand10 percentintheBCbinderandwearingcourses(layerswithin100mmoftheroad surface)tominimizeruttingproblem.Thisrequirementshouldalsobeincluded intheMORTHspecifications. 15,16,17,21,25

8

Kandhaletal andothers havealsoresearchedandreportedonnew improvedtestmethodsfortestingandcharacterizingfineaggregatesfor bituminousmixes.Thenewtestmethodspertaintoparticleshape(suchasfine aggregateangularityorFAAtest)andplasticfines(suchasMethyleneBluetest). ThesenewtestmethodshavebeenadoptedbyAASHTOandneedtobe consideredbyBIS,IRCandMORTH. 2.4Filler ManyhighwayengineersinIndialiketospecifyaddingmineralfillertothe bituminousmixevenifthereisnodeficiencyoffinesintheaggregatesused.This isnotjustified.AllasphaltplantsinIndiaarerequiredtohavebaghousesto collectthefinesfromthedryer.These“baghousefines”shouldbeincorporated backintothemixinacontrolledmannerthroughascrewconveyer.Many 9,16 studies intheUShaveshownthatthebaghousefines(whicharesameasstone dustormineraldustresultingfromtheaggregatecrushingoperation)aregood mineralfillers.Portlandcementdoesnothaveanyadvantageoverstonedust andthereforeitsuseisnotcosteffective.However,ifthedesignedmixfailsthe MoistureSusceptibilitytest(AASHTOT283)thenadditionof1-2%hydrated limeisdesirable.Hydratedlimeisnotonlyagood antistrippingagent,itcanalsoretardtheoxidationoragingofthebitumen duringservice. InregionsofIndiawherehydrophilicaggregatessuchasquartziteandgranite areusedinmixes,itshouldbemademandatorytoaddhydratedlimeinevery tonofhotmixproducedinthewholeregion.Forexample,inandaroundJaipur onlyquartziteaggregateisusedinbituminousmixesand,therefore,this requirementifimplementedwillbeveryhelpful. Unfortunately,thereisnoIndianstandardforhydratedlimetobeusedin bituminousmix(thereisforbuildinglime).Therefore,areferenceneedstobe madetoAASHTOM303,“LimeforAsphaltMixtures”,whichspecifiesactive limecontent(CaOH2+CaO)above90percent. 9

14,16

Kandhaletal havereportedonnewtestmethods(suchasRigdenvoids)for testingandcharacterizingmineralfillers,stonedust,andbaghousefines.BIS, IRCandMORTHshouldconsiderthesetestmethods. 2.5AggregateGradation AggregategradationsforDBMbasecourse,BCbindercourse,andtwoBC wearingcourseswerediscussedearlier.Thefinalrecommendedgradationsfor useinIndiaaregiveninTable1.Justificationforadoptingthesemixesandtheir 10 respectiverevisedgradationsisgivenindetailintheIRCpaper mentioned earlier. 3.DESIGNOFMIX Atthepresenttime,allbituminousmixesaredesignedwithMarshallMethod using75blowsregardlessoftraffic.MORTHspecificationshouldbeabletobe usedonalltypesofroads:NH,SH,MDR,andODR.So50-blowMarshall DesignmustbeusedforlowtomediumtrafficroadssuchasODR.Itisneither technicallycorrectnordesirabletodesignallroadswith75blowsasstipulatedin thepresentMORTHspecificationsbecauseitwillgiveundesirablylowbitumen contentsforlowtomediumtrafficroads,whichwillreducethedurabilityof suchroads.LowroaddurabilityisasevereprobleminIndia.Onlyhigh-volume roads(carryingmorethan1500commercialvehiclesperday)shoulduse75-blow 33 MarshallDesignlikeitisdoneinmostcountriesoftheworld .Eveninthe Superpavemixdesignthereare4levelsoflabcompactiondependingontraffic. InSuperpave,thereisacompactionlevelintermsofgyrations,whichis equivalentto50-blowMarshallandisusedonmostroadswithlighttomedium traffic.Continuingtouse75blowsforallroadsinIndiawillreducethedesign bitumencontentofroadswithlighttomediumtrafficbyasmuchas0.5percent resultinginlowerservicelife. Quiteoften,itisarguedthatthetrafficwillincreaseonexistinglowtomedium traffickedroadsinafewyears.However,bythattimethebitumenwouldget oxidizedandthereforegetstiffenedtocounteracttheeffectofslightlyhigher bitumencontent. MORTHmixdesignrequirementsforalldensegradedmixesneedtoberevised asshowninTable6.Theminimumstability,rangeofflow,andVFBvaluesfor both50and75blowMarshalldesignshavebeentakenfromthelatestsixth 2 edition oftheAsphaltInstituteMS-2,whichiswidelyusedsuccessfully worldwideandhasbeenreferredtoinMORTHspecificationatseveralplaces. ThesevalueshavebeenusedinveryhotclimateareassuchasinArizonainthe USandotherhot,tropicalcountriessuccessfully. Itshouldalsobeensuredthattheratiobyweightoffines(materialpassing0.075 mmsieve)andeffectivebitumencontent(fines/bitumenratio)inthebituminous mixisbetween0.6to1.2asincludedinTable6.Thiswaytherearesome minimumfinestostiffenthebitumenandnottoomuchfineswhichwillmakethe mortartoobrittle(dull)andlesscohesiveandwillalsoreducetheVMAmore thandesired. 10

SomevaluesinTable6arebasedonsomeresearchdoneinIndia.Ithadalso includedcriteriaforheavyrainfallareas.Thereisnosoundtechnicalreason whatsoeverforhavingadifferentMarshallstabilityandflowcriteriaforheavy rainfallareas.Itisthepavementtemperatureandnottheamountofrainfall, whichaffectstheseproperties.Therefore,rainfallhasnotbeenconsideredin Table6.Highrainfallcanpotentiallyincreasethemoisturedamageinthemix. ForthatAASHTOT283isenoughwith80%minimumretainedtensilestrength requirement.IthasworkedverywellinhotandheavyrainfallareaoftheUS (rainfallsignificantlymorethanIndia).SincethereisAASHTOT283whichhas beenspecifiednowanditrequires60Cwater-bathconditioning,thereisnoneed 0 tohaveRetainedMarshallstabilityafter24hoursinwaterat60 C,whichisless severethanAASHTOT283.

Extensiveresearchhasshownthattheairvoidrangeof3to5percentappliesto 2 allcourses,whichisalsoreflectedinthelatestAsphaltInstituteMS-2 .Infact somestatesintheUSspecifyevenlowerairvoids2to4percentforthebase courses,whichdonotgetfurthercompactionfromtraffic.Thisisunlikepast practicewhenhigherairvoidswerespecifiedforbasecoursescomparedto binderandwearingcourses. TABLE6.REQUIREMENTOFTHEDENSEGRADEDBITUMINOUSMIX WHENUSINGUNMODIFIEDBITUMEN Specification Compactionlevel(Numberof blows) o

Minimumstability(kNat60 C) AASHTOT245

Requirements 75blowsoneachfaceofthespecimenforheavy trafficand50blowsoneachfaceforlightto mediumtraffic 9.0forheavytrafficroads*(75-blowMarshall specimen) 5.3forlighttomediumtrafficroads(50-blow Marshallspecimen) 2

Minimumflow(mm) AASHTOT245 Maximumflow(mm) 4 AASHTOT245 Ratiooffinestoeffectivebitumen 0.6–1.2 content %AirVoids(MS-2andASTM 3–5 D2041) %Voidsfilledwithbitumen 65–75forheavytraffic*(75-blowMarshall (VFB)AsphaltInstituteMS-2 specimen) 65-78forlighttomediumtraffic(50-blow Marshallspecimen) MarshallQuotient.kN/mm 2to5 (stability/flow) TensileStrengthRatio (minimum),%,AASHTOT283

80 11

(withfreeze&thawoption)(see AnnexureIfortheoutlineofthis testmethod)

%VoidsinMineralaggregateVMA

NominalMaximum Particlesize(mm)**

Min%VMArelatedtodesigned%airvoids***

9. 5

3 14

4 15

5 16

13.2

13

14

15

19.0

12

13

14

26.5 37.5

11 10

12 11

13 12

*Heavytrafficroadsarethoseroadscarryingmorethan1500commercial vehiclesperday(CVD). **Thenominalmaximumparticlesizeisonesizelargerthanthefirstsieve, whichretainsmorethan10%material. ***ForintermediatevalueofdesignedpercentageairvoidsinterpolatetheVMA.

AlthoughthelatestMS-2(sixtheditionatthepresenttime)shouldbeusedfor MarshallDesign,manycontractorsdonotfollowitcompletely.Forexample,the maximumspecificgravityofthebituminousmix(Gmm)shouldnotbecalculated byaformulafromthespecificgravityvaluesofindividualaggregatesand 39 bitumen.Rather,itshouldbemeasureddirectly byusingASTMD2041,which determinestheweightandvolumeofloose,voidlessmixtocalculatethe maximumspecificgravityofthemix.Volumeofthevoidlessmixisdetermined aftersubmergingitinwaterandremovingallairbubblesbyapplyingvacuum. AnoutlineofASTMD2041isgiveninAnnexureII.Also,thebulkspecific gravityofthecoarseaggregateandthefineaggregateshouldbemeasuredby usingASTMC127andASTMC128,respectively,ratherthantheIndian StandardsIS:2386(PartIII),whichareoutdatedandsuitableforconcrete mixturesonlyandnotforbituminousmixes.Theproceduresforobtainingthe saturatedsurfacedry(SSD)conditionofcoarseandfineaggregatesintheIndian Standardsarenotcorrectforbituminousmixes.BothASTMtestsgivespecific instructionstoobtainSSDconditionoftheaggregate.Forexample,incaseof fineaggregate(ASTMC128)sandconemethodshouldbeusedtoobtainSSD condition.Unlessthesethreetestmethods:ASTMD2041,C127andC128are used,thecalculatedvaluesofairvoidsandVMAcanbehighlyerroneous becausetheactualamountofbitumenabsorbedbytheaggregatewillnotbe obtainedandconsideredThesethreeASTMstandardsshouldbeincorporated intheMORTHspecifications. Inaccordancewiththelatest(sixthedition)oftheAsphaltInstituteManualMS12

2aswellasSuperpavemixdesignmethod,thedesignbitumencontentshouldbe selectedtocorrespondwith4.0percentairvoidsforalltypesofmixtures.The selectedbindercontentmustsatisfyallotherMarshallandvoidproperties.The currentpracticeofdeterminingtheoptimumbitumencontentbyaveragingthe bitumencontentscorrespondingtohigheststability,highestdensity,4%air voids,etc.shouldbediscontinued.Thisisbecause(a)someofthecurvesarenot welldefinedintermsoftheirpeakand(b)airvoidcontentisthemostimportant parameterforselectingthedesignbitumencontentasitaffectsbothrutand fatigueresistanceofthebituminousmixes. MinimumtensilestrengthratiousingAASHTOT283hasbeenspecifiedin Table6totestthedesignedmixformoisturesusceptibility.TheAASHTOT283 testmethodinvolves:preparationoftwosubsetsofMarshallspecimenswith6to 8%airvoids;testingonesubsetindryconditionforindirecttensilestrength (Marshalltestingmachinecanbeusedforthisinconjunctionwith12.5mmwide steelstripattopandbottom);conditioningtheothersubsetbyvacuum 0 saturatingwithwater,onefreeze&onethawcycle(in60 Cwaterbath)tocause potentialstrippingandthentestingforindirecttensilestrength;andcalculating theretainedtensilestrengthfromtestdataondryandconditionedsubsets. AASHTOT283hasworkedverywellinhotandheavyrainfallareasoftheUS (rainfallsignificantlymorethanIndia).ItisalsousedintheSuperpavemix design.AASHTOT283shouldreplacethepresentlyspecifiedASTMD1075, whichdeterminesretainedMarshallstability.AnoutlineofAASHTOT283is giveninAnnexureI. Wheremaximumnominalsizeoftheaggregateismorethan25mm,modified 19,26 MarshallmethoddevelopedbyKandhal using6-inchdiameterspecimenas describedintheAsphaltInstituteManualMS-2(SixthEdition)andASTMD 5581shouldbeused.Thistestmethodrequiresmodifiedequipment(whichis commerciallyavailable)andmodifiedprocedure.WhenthemodifiedMarshall testisused,thespecifiedminimumstabilityvaluesandthespecifiedflowvalues giveninTable6shouldbemultipliedby2.25and1.5,respectively. 20,22

Kandhaletal andothersobservedthatthebituminouspavementsintheUS wereachievingdensitiesunderheavytrucktrafficwithhightyrepressures significantlyhigherthanthoseobtainedinthelaboratoryusing75-blow Marshallcompactor.Inotherwords,thepavementdensityafter2-3years’ trafficwasgreaterthan75-blowMarshalllaboratorydesigndensity.Increasing thenumberofblowsabove75didnothelpbecauseitsimplycausedaggregate breakdown(degradation)undertheimpacttypeMarshallhammercompaction. Thatiswhy;Superpavegyratorycompactor(SGC)wasdevelopedandmade partoftheSuperpavemixdesignmethod. WhenabituminousmixneedstobedesignedinIndiaforveryheavytruck traffic,thefollowingoptionshouldbeconsideredinadecreasingorderof  preferenceformixdesign/adjustments: 1.Superpavemixdesign.ThismixdesignmethodisfullydevelopedintheUS andmanualssimilartoMS-2areavailableforSuperpave.Superpavemix designmethodcanbeadoptedinIndiaoratleastallowedformajor 13

projectswithminoradjustments.Itusesagyratorycompactor,whichcan providetheneededcompactioneffortbasedondesigntrafficwithout significantaggregatedegradation.Optimumbitumencontentisselected at4.0percentairvoidcontent. 2.UseaRotatingBase,SlantedFootMarshallHammer.Thisautomated, 20,22 mechanicalMarshallcompactorhasbeenusedintheUSeffectively to achievehighlaboratorydensityusing75blows.Itsfoothasa1-degree bevelorslant.Everytimethehammerislifted,thebasesupportingthe Marshallmouldrotatesautomaticallysothattheslantedfootfallsat differentplacesinthemouldcausingakneadingaction.Thisstandard mechanicalMarshallcompactorisavailablecommerciallyfromatleast threeequipmentsuppliersintheUSandifneeded,canbefabricatedin India.Again,designbitumencontentisselectedat4.0percentairvoid content. 3.UseaMarshallHammerwithHugoFoot.Prof.HugoofSouthAfrica developedtheHugofoot.Thisfootalsocausessomekneadingaction duringcompactionbecauseithasindentsonitsfaceandisalsorotated.It isnotknownwhetheritisavailablecommercially. 4.AdjustmenttoBitumenContent.ConducttheconventionalMarshallMix designwith75blowsanddeterminethebitumencontentat4.0percentair voidcontent.Reducethisbitumencontentby0.2to0.3percentandadopt thereducedbitumencontentinthejobmixformula.Thisadjustmentis basedonthefactthatthedesignbitumencontentobtainedbythe Superpavevolumetricmixdesignisgenerallylessthanthatobtainedby conventionalMarshalldesignby0.2to0.3percent. Theprecedingchangesinthemixdesignproceduresshouldatleastbepermitted tobeusedbyPPPorBOTcontractorstoensurerutresistantbituminous pavementssubjectedtoveryheavytrucktraffic. 32

Theconceptofrefusaldensityhasbeensuggestedbysomeresearchers . However,theincreasednumberofblows(suchas300or400)oneachsideofthe specimenusedinthistestcancausesignificantbreakdownoftheaggregatein themixwhilethemixisalsocoolingfast.Thedegradedmixinthelaboratoryhas noresemblancetotheactualmixusedontheroad,whichhardlydegradesunder rollersandtraffic.AsmentionedinMORTHManualforSupervisionof 31 BituminousConstruction ,anyconclusionsdrawnfromaseverelydegraded mixinthistestmaybecomeinvalid.Moreover,theextentofdegradationvaries fromaggregatetoaggregatedependingontheirtoughness,whichisanother variable. SincetheMarshallstabilitycannotbecompletelyreliedupontoensurearut resistantbituminousmix,itisrecommendedtoconsideraloadedwheeltester suchasAsphaltPavementAnalyzerandHamburgWheelTesterto“prooftest” thefinalMarshallmixdesignasisdonebyGeorgiaDOT.Thisisespecially necessaryforveryheavytrafficand/orimportanthighwayprojects.The technologyofloadedwheeltestersandrelatedacceptancecriteriaarefully 4,5,11,12,13 developedanddocumentedbyKandhaletal andothers.Itwillbeinthe interestofPPPorBOTcontractorsto“prooftest”theirMarshalldesigned mixes. 14

4.CONSTRUCTIONOPERATIONS 4.1MixingandLaydown TheexistingMORTHtableformixing,layingandrollingtemperaturesforall densemixesneedtoberevised,sinceviscositygradebitumenshavenowreplaced penetrationgradebitumen.Table7shouldbeusednow.Formixturescontaining modifiedbitumenbinders,thesupplier’srecommendationsshouldbefollowed. Normally,themixing,layingandrollingtemperaturesformodifiedbindersare 0 increasedbyasmuchas15 Ccomparedtounmodifiedbinders.Thecontrolof 18 volumetricpropertiesofbituminousmixes duringproductionattheplant needstobemademorespecificinthespecifications. 4.2Compaction Theintialorbreakdownrollingshouldbedonewithavibratoryroller(8to10 tonnesdeadweight),unlessthemixistenderrequiringinitialtwopassesina staticmode(vibrationturnedoff).Theintermediaterollingshouldbedonewith apneumatictyredrollerof12to15tonnesweighthavingninewheelswithatyre pressureofatleast5.6kg/sqcm.Thefinishrollingshouldbedonewith6to8 tonnessmoothwheeledtandemrollers.ItisacommonpracticeintheUStouse thevibratoryrollerinvibratorymodeforinitialorbreakdownrolling.Thisway, thebestpackingofaggregatesandhighdensityisachievedwiththevibrations whilethemixisstillveryhot.Ifastaticmodeisusedfirstforinitialor breakdownrolling,itorientstheaggregateparticlesinacertainmannerbutthat orientationisdisturbedagainduetovibrationsappliedlater.Thevibratory rollershouldbeusedinstaticmode(vibrationsturnedoff)forthefirst2passes onlyifthemixistenderandunstabletosustainvibratorycompaction. Thedensityoffinishedpavinglayershouldnotbelessthanthe92%andnot morethan97%oftheaveragetheoreticalmaximumspecificgravityoftheloose mix(Gmm)obtainedonthedayofpavingfollowingASTMD2041(seeoutlinein 27,28 AnnexureII).ResearchbyKandhalandKoehler andothershasindicated thatprematuredistressofpavementcantakeplaceiftheairvoidcontentinthe constructedmatexceeds8percent(Fig.1). TABLE7.MIXING,LAYINGANDROLLINGTEMPARATURESFORDENSEMIXTURES (DEGREECELCIUS) Bitumen Viscosity Grade

Bitumen Temperature

Aggregate Temperature

Mixed Material Temperature

Laying Temperature

VG-40

160-170

160-175

160-170

150Min

100Min

VG-30

150-165

150-170

150-165

140Min

90Min

15

*Rolling Temp- erature

VG-20

145-165

145-170

145-165

135Min

85Min

VG-10

140-160

140-165

140-160

130Min

80Min

*Finishrollingmustbecompletedbeforethematcoolstotheseminimumtemperatures.

MoststatesintheUSandmanycountrieshavechangedthecompactioncriteria frompercentageofthelabdensityofthecompactedspecimentopercentageof theoreticalmaximumspecificgravity(Gmm)oftheloosebituminousmixture. Theformercriterionhascausedallkindsofproblemsincludingalargeday-todayvariation.Thelatercriteriongivesairvoidsinthepavedmatdirectly.No lessthan92%ofGmmmeansnomorethan8%airvoidsinthecompactedmat. Nomorethan97%meansnolessthan3%airvoidsinthecompactedmat,which mayinducebleedingand/orrutting.Moreandmoreagenciesaremoving towardsGmm,whichistestedanywayduringthemixdesignanddailyMarshall Test.Sononewtestisbeingintroduced.Restrictingpercentairvoidsinthemat alsoallowseasyforensicanalysisofcompactedpavementlaterinitslifewithout lookingforoldrecordsonlabcompacteddensityinfiles.Durabilityof bituminouspavementisdirectlyrelatedtoairvoidsinthematonthedayof construction,andonlyvaguelyandindirectlyrelatedtolabdensityobtainedbya technicianonthedayofconstruction.Thispointhasbeendebatedextensivelyin theUSformanyyears.SomestatesintheUSarerequiring93%minimumofthe theoreticalmaximumspecificgravity(thatisnomorethan7%airvoidsinthe matwhenconstructed),thisisalsorecommendedforIndiatoincreasethe durabilityofbituminousroads. Thereisnotechnicalreasonwhatsoevernottoallowcoringfordensity measurementsduringthefirst24hoursasstipulatedintheMORTH specifications.InfactmanyagenciesintheUSprefertakingcoresonthedayof pavingbeforethematisopenedtotraffic.150-mmdiametercoresshouldbe 0 takenaftertheentirethicknessofthemathascooledbelow60 C,whichmay takeafewhoursdependingontheliftthicknessandprevailingweather.No problemsofcoredistortionwhatsoeverhavebeenencountered.Alargecore diameterof150mmispreferredtoobtainagoodrepresentativesamplefor density.However,coreswithlessthan100mmshouldnotbepermitted.ASTM D2726shouldbeusedtomeasurethedensityoftheextractedcore.

16

Fig.1.Airvoidsversusextentofraveling(afterKandhal,Reference27)

4.3OpeningtoTraffic ThecurrentMORTHspecificationdoesnotallowtrafficfor24hoursafter compaction.Thereisnotechnicalreasonnottoallowtrafficfor24hours.It defeatsthepurposeof  usinghotbituminousmix,whichlendsitselftofast openingtotraffic.Suchunreasonablerequirementof24hoursdoesnotexist anywhereintheworld.Ifthereisafearthatthetrafficwillrutthepavement,it 0 meansthemathasnotbeenrolledenough.Arequirementof60 Cmaximum mattemperatureisinsuranceenough.Inotherwords ,itshouldbeensuredthat trafficisnotallowedonthesurfaceuntilthepavedmathascooledbelowa 0 temperatureof60 Cinitsentiredepth.UnderhotIndianclimaticconditions duringsummer,itisestimatedthata50mmthickbituminouslayershouldcool 0 to60 Cinaboutonehouranda75mmthickbituminouslayershouldcoolto thistemperatureinaboutoneandhalfhour.Thetimewillbeshorterifthe weatherisrelativelycoolerinspringandautumnand/orastrongbreezeis present.

5.QUALITYCONTROLANDACCEPTANCE

Thepresent2001MORTHspecificationdoesnotadequatelyaddressthequality control/qualityassurance(QC/QA)aspectofthebituminousmixes,whichisa veryimportantelementofaspecification.Qualitycontrolistheresponsibilityof 17

32

thecontractortokeepacontrolontheprocess .Qualityassuranceor acceptanceistheresponsibilityofthespecifyingagency.Forqualitycontrol,the agencyspecifiesthetypesandminimumfrequencyoftheteststobeconducted bythecontractorduringconstruction.WhereastheMORTHspecificationshave addressedthequalitycontrolaspect,itneedstobespecificaboutquality acceptance. Thereisnoquestionthatqualityacceptanceshouldbebasedonstatistical 29 principles .Abituminouspavingprojectshouldbedividedintolotsand paymentfactorsshouldbeappliedonalotbylotbasis.Forexample,alotcanbe definedasoneday’sbituminousmixproductionoramaximumtonnageof bituminousmixsuchas400or500tonnes.Alotisfurtherdividedinto3to5 sublots,whicharesampledandtestedatrandom.Atestvaluesuchasbitumen contentisobtainedforeachsublot.Thetestvaluesofthesublotsareanalyzed statisticallytoassessthequalityofthelotanditspayfactor.Thestandardtest methodfordeterminingthebitumencontenttobeusedshouldbespecifiedsuch asASTMD2171,“StandardTestMethodsforQuantitativeExtractionof BitumenfromBituminousPavingMixtures”.Differenttestmethodsgive differenttestresults. Payfactorsaredeterminedusingthreemainsystems:percentwithinlimits (PWL)ofthespecification;differencebetweenaveragesampletestvalueand targetjob-mixformula(JMF);andprobabilitybased.Samplemeanvaluesare usedinallthreemethods,butonlythePWLandprobabilitybasedspecifications usethesamplestandarddeviationorvariance,whichtakesintoaccountmaterial variability. TheUSFederalHighwayAdministrationisencouragingthestatestoimplement aformofPWLspecification.PWLisdefinedasthepercentageoflotfalling betweenthelowerspecificationlimitandtheupperspecificationlimit.For example,iftheJMFbitumencontentis6.0+/-0.4percent,thepercentageof bituminousmixhavingbitumencontentbetween5.6and6.4percent.The conceptofPWLisbasedonanormaldistributioncurve;thepercentageofthe populationwithincertainlimitscanbecalculatedbyknowingtheareaunderthe curve.Afterthetestvaluesofthesublotsaredetermined,theiraverageand standarddeviationiscalculatedtodefinethenormaldistributionforthelot. Usingtheloweranduppertolerancevalues,thePWLiscalculatedusingasetof formulas.ThepayfactoristhenbasedonthePWLvalue.Normally,apayfactor of1.0(100%pay)isappliedifthePWLisatleast90percent.Thatis,10% materialofslightlylesserqualityisacceptable. AlthoughthePWLsystemofqualityacceptanceispreferred,itmaybetoo complexandhardtocomprehendbythecontractorsandagencyengineersin Indiaatthispointintime.BecauseofthiscomplexitysomestateslikeAlabama intheUSareusingsimplersystems.Alabamausesthearithmeticaverageofthe absolutevalues(negativeorpositive)ofthedeviationsofsublotvaluesfrom target.Forexample,thetargetJMFbitumenis6.0percentandthetestvaluesof 4sublotsare5.7,6.1,5.6,and6.2.Then,theactualdeviationsare-0.3,+0.1,-0.4 and+0.2.Theabsolutedeviationsare0.3,0.1,0.4,and0.2,averagingat0.25.The 18

1

AlabamaDepartmentofTransportationSpecifications givetablesfor determiningpayfactorscorrespondingtothenumberoftests(sublots)andthe arithmeticaverageoftheabsolutevaluesofthedeviations.Table8issuchatable forbitumencontent.Payfactorof1.02means100%plus2%addedbonus,1.00 means100%payment,andsoforth.Similartablesareavailableforvoidsinthe labcompactedMarshallspecimensandin-placematdensity.Whichevertest parametersuchasbitumencontent,voidsinlabcompactedspecimens,andinplacedensitygivesthelowestpayfactor,thatpayfactorisappliedtothebid priceofthewholelot.Thetestparametersgenerallyusedforpriceadjustments inorderofpreferenceare:in-placematdensity,voidsinlabcompacted specimens,bitumencontent,andgradation(usuallyoneortwosievessuchas 2.36mmor0.075mmareadequate,toomanysievesizeswoulddilutethe specificationsunnecessarily).

TABLE8.PAYFACTORSFORBITUMENCONTENT(AFTERALABAMA, TABLE8.PAYFACTORSFORBITUMENCONTENT(AF TERALABAMA, REF.1) ArithmeticAverageoftheAbsoluteValuesoftheDeviationsoftheLOT AcceptanceTestsfromtheJob-MixFormula Lot 1.02 1.00 0. 9 8 0.95 0.90 0.80* Pay Factor →

1 Test

-

0.000.62

0.630.68

0.690.75

0.760.88

Over 0.88

2 Tests

-

0.000.44

0.450.48

0.490.53

0.540.62

Over 0.62

3 Tests

-

0.000.36

0.370.39

0.400.43

0.440.51

Over 0.51

4 Tests

0.000.19

0.000.31

0.320.34

0.350.38

0.390.44

Over 0.44

*TheDepartmentmayrequireremovalandreplacementoftheLot.

ManystatesintheUShavedevelopedtheirownstatisticallybasedquality acceptancecriteriausingtestdatafromsomepilotprojects.Similardataneeds tobedevelopedinIndia.However,specificationssuchasthatofAlabamacanbe introducedasastartingpointsubjecttorevisionlaterbasedontestdata collectedandanalyzedinIndia.

6.CONCLUSIONSANDRECOMMENDATIONS Thefollowinggeneralguidelineshavebeenprovidedinthepapertoobtainlong lastingbituminouspavements: 19

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SpecificationforPavingBitumenIS:73:2006,whichspecifiesviscosity grades(VG)onlyshouldbeusedtoensureoptimumrutresistancein bituminouspavements.Theuseofsubstandardbitumenbasedonthe older,nowdefunctIS:73(whichspecifiedpenetrationgradedbitumen) shouldbediscontinuedimmediately.Forexample,VG-30bitumenshould beusedinlieuof60/70penetrationbitumenandVG-10shouldbeusedin lieuof80/100penetrationbitumen.Thepapergivesguidelinesfor selectionofVGgradesinIndiabasedonclimaticconditions. Thereisaneedtorestricttheamountofnaturalsand(whichtendsto haveroundedparticles)to10percentinwearingandbindercourse (withintop100mmofpavement)andto50percentinbasecourse(more than100mmfromthepavementsurface).Thiswouldreducethe potentialforruttinginbituminouscourses.Rightnow,thereisno restrictionontheamountofnaturalsandinthefineaggregateforall bituminousmixes. AsphaltInstituteMS-2(latestedition)shouldbefollowedcompletelyin designingdensegradedbituminousmixesusingtheMarshallmethod. Thisincludesselectingdesignbitumencontentcorrespondingto4.0 percentairvoids.Maximumspecificgravityofmixshouldnotbe calculatedwithaformulabutmeasuredbyusingASTMD2041.The calculatedmaximumspecificgravityusuallygiveserroneousvaluesofair voidsandVMAbecausetheactualamountofbitumenabsorbedbythe aggregateisnotconsidered.Bulkspecificgravityofcoarseaggregate and fineaggregateshouldbemeasuredinaccordancewithASTMC127and C128,respectively.ThecurrentBISstandardsshouldnotbeusedfor measuringaggregatespecificgravitysincetheyareoutdatedandwillgive erroneousresults. MORTHspecificationsshouldbeabletobeusedonalltypesofroads: NH,SH,MDR,andODR.Therefore,50-blowMarshallDesignshouldbe usedforlowtomediumtrafficroadsand75-blowMarshallDesignshould beusedforhightrafficroads(carryingmorethan1500commercial vehiclesperday).Revisedmixdesignrequirementshavebeenpresented inthepaperforbothlevelsofcompaction. Arevisedtableofmixing,laying,androllingtemperatureshasbeen presentedcorrespondingtonewbitumenviscositygrades. Rightnow,theMORTHspecificationsdonothaveadequatemat compactionrequirements.Ithasbeenrecommendedthatthedensityof thefinishedcompactedlayershouldnotbelessthan92percentnormore than97percentofthetheoreticalmaximumspecificgravityofloosemix determinedbyASTMD2041.150-mmdiametercoresshouldbeobtained tomeasurethepavementdensity.

7.ACKNOWLEDGEMENT Theopinionsexpressedinthispaperarethoseoftheauthorsonly.

8.REFERENCES 20

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21

18.Kandhal,P.S.,K.Y.Foo,andJ.A.D’Angelo.ControlofVolumetricPropertiesofHot-Mix AsphaltbyFieldManagement.TransportationResearchBoard,TransportationResearch Record1543,1996. 19.Kandhal,P.S.andT.Wu.PrecisionofMarshallStabilityandFlowTestUsing6-inch(152.4mm)DiameterSpecimens.ASTM.JournalofTestingandEvaluation,Vol.24,No.1,January, 1996. 20.Kandhal,P.S.,S.A.Cross,andE.R.Brown.HeavyDutyAsphaltPavementsinPennsylvania: AnEvaluationforRutting.TransportationResearchBoard,TransportationResearchRecord 1384,1993. 21.Kandhal,P.S.EvaluationofFineAggregateParticleShapeandTextureandItsEffecton PermanentDeformationofAsphaltPavingMixtures.ASCE,Materials:Performanceand PreventionofDeficienciesandFailures,1992. 22.Kandhal,P.S.,S.A.Cross,andE.R.Brown.EvaluationofHeavyDutyAsphaltPavementsfor Rutting.Proceedings,SeventhInternationalConferenceonAsphaltPavements,Nottingham, U.K.,Vol.4(Construction),1992. 23.Kandhal,P.S.,J.B.Motter,andM.A.Khatri.EvaluationofParticleShapeandTextureof MineralAggregatesandTheirBlends.AsphaltPavingTechnology,Vol.61,1992. 24.Kandhal,P.S.andM.A.Khatri.ImprovedRiceMethodforDeterminingTheoretical MaximumSpecificGravityofAsphaltPavingMixtures.TransportationResearchBoard, TransportationResearchRecord1353,1992. 25.Kandhal,P.S.,J.B.Motter,andM.A.Khatri.EvaluationofParticleShapeandTexture: ManufacturedVersusNaturalSands.TransportationResearchBoard,TransportationResearch Record1301,1991. 26.Kandhal,P.S.LargeStoneAsphaltMixes:DesignandConstruction.Proceedings, AssociationofAsphaltPavingTechnologists,Vol.59,1990. 27.Kandhal,P.S.Pennsylvania'sExperienceinCompactionofAsphaltPavements.American SocietyforTestingandMaterials.SpecialTechnicalPublicationNo.829,1984. 28.Kandhal,P.S.SpecificationsforCompactionofAsphaltPavements.Proceedings,Association ofAsphaltPavingTechnologists,Vol52,1983. 29.Kandhal,P.S.,R.CominskyandJ.A.Motter.DevelopmentandImplementationof StatisticallyBasedSpecificationsforHotMixAsphaltinPennsylvania.TransportationResearch Board,TransportationResearchRecord1389,1993. 30.MinistryofRoadTransport&Highways.SpecificationsforRoadandBridgeWorks,Section 500,FourthRevision,2001,IndianRoadsCongress,NewDelhi. 31.MinistryofRoadTransport&Highways.ManualforConstructionandSupervisionof BituminousWorks.IndianRoadsCongress,NewDelhi,November2001. 32.Rao,S.K.,J.K.DasandP.R.Chowdhury.AsphaltMixDesign–RefusalDensityApproach forHeavilyTraffickedRoads.JournaloftheIndianRoadsCongress,Vol.68-1,April-June2007. 33.Roberts,F.L.,P.S.Kandhal,E.R.Brown,D.Y.Lee,andT.W.Kennedy.HotMixAsphalt Materials,MixtureDesignandConstruction.NCATTextbook,NAPAEducationFoundation, Lanham,Maryland,SecondEdition,1996.

ANNEXURES 22

AnnexureI OutlineofAASHTOT283,“ResistanceofCompactedAsphaltMixturesto Moisture-InducedDamage” ScopeandSummaryofTestMethod Thismethodcoverspreparationofcompactedbituminousmixturesandthe measurementofthechangeofdiametraltensilestrengthresultingfromthe effectsofwatersaturationandlaboratoryacceleratedstrippingphenomenon withafreeze-thawcycle.Theresultmaybeusedtopredictlong-termstripping susceptibilityofbituminousmixturesandevaluateliquidanti-strippingadditives thatareaddedtobitumenorpulverizedmineralmaterialssuchashydrated lime,whichareaddedtothemineralaggregate. Eachsetof6compactedspecimensisdividedintotwoequalsubsets.Onesubset istestedindryconditionforindirecttensilestrength.Theothersubsetis subjectedtovacuumsaturationandafreeze-thawcycle(thawinginahotwater bath)beforetestingforindirecttensilestrength.Numericalindicesofretained indirecttensilestrengthpropertiesarecalculatedfromthetestdataobtainedby testingthetwosubsets:dryandconditioned.

TestingEquipment 1.Vacuumcontainer,vacuumpump,manometer,andotheraccessoriesas specifiedinASTMD2041,“TheoreticalMaximumSpecificGravityand DensityofBituminousPavingMixtures”. 2.Balanceorscaleaccurateto0.1percentofthetestload 3.Twowaterbathscapableofmaintainingtemperaturesof60C+/-1Cand 25C+/-0.5C 4.Freezermaintainedat–18C+/-3C 5.10-mlgraduatecylinder 6.Loadingjackandringdynamometer(Marshallstabilitytestingmachine canbeused)toprovideaverticalrateofdeformationof50mm(2inches) perminuteandcapableofreadingthemaximumfailureload 7.Steelloadingstripswithaconcavesurfacehavingaradiusequaltothe normalradiusofthetestspecimen.Theloadingstripsshallbe12.7mm (0.5inch)wideforspecimens100mm(4inches)indiameter.Theloading stripsfor150mm(6inches)diameterspecimensshallbe19.05mm(0.75 inch)wide.Thelengthoftheloadingstripsshallexceedthethicknessof thespecimens.Steelstripareprovidedatthetopandbottomofspecimens duringindirecttensiletesting. TestProcedure 1.Makeatleast6compactedspecimensforeachmixture,3tobetesteddry and3tobetestedafterpartialsaturationandmoistureconditioningwith afreeze-thawcycle.Someextraspecimenswillneedtobemadeto establishcompactionproceduresinordertoobtainspecifiedairvoid 23

contentsinthetestspecimensbytrialanderror. 2.Compactthe6specimenswithaMarshallcompactorsothatthe compactedspecimenshaveairvoidsof7.0+/-0.5percent.Thislevelof highairvoidscanbeobtainedbyadjustingthenumberofMarshallblows appliedoneachsideofthespecimenbytrialanderror(startatabout10 blowsasastartingpoint).Airvoidcontentmustbecalculatedfromthe bulkspecificgravityofthecompactedspecimen(determinedbysaturated surfacedrymethodasperproceduregivenintheAsphaltInstituteMS-2) andthemaximumtheoreticalspecificgravityoftheloosebituminous mixtureobtainedbyASTMD2041. 3.Separatethe6specimensinto2subsetssothattheaverageairvoidsofthe twosubsetsareapproximatelyequal.Onesetwillbetesteddry.Keepitat roomtemperatureandthenplaceina25C+/-0.5Cwaterbathfor2 hourspriortodeterminingtheirindirecttensilestrength.Theother subsetwillbeconditionedasfollows: (a).Placeandsubmergethe3specimensinthevacuumcontainer filledwithwateratroomtemperature.Applyavacuumof13-67 kPaabsolutepressure(10-26inchesHgpartialpressure)for30 minutes.Removethevacuumandleavethespecimenssubmerged inwaterfor5to10minutes.[Note:Thewatersaturation procedurenotedabovedeviatesfromAASHTOT283,which obtainsaspecifieddegreeofsaturation.Theaboveprocedure keepsthetimeofsaturationconstant.] (b).Wrapaplasticfilmaroundeachsaturatedspecimenandplace thewrappedspecimeninaplasticbagcontaining10mlofwater andsealtheplasticbag.Placetheplasticbaginafreezerat temperatureof–18C+/-3Cforaminimumof16hours.Remove thespecimensfromthefreezer. (c).Placethespecimensinawaterbathmaintainedat60C+/-1C for24hours.Removetheplasticbagandtheplasticfilmfromeach specimenafterplacingthespecimensunderwater. (d).Removethespecimensfromhotwaterbathandplaceina waterbathmaintainedat25C+/-0.5Cfor2hours. (e).Removetheconditionedspecimensandtestforindirecttensile strength. 4.Determinetheindirecttensilestrengthofthe3dryand3 conditionedspecimensat25C+/-0.5Cafterremovingfromwater bath.First,measuretheirmeanthicknesses(t).Thenplacethetwo steelloadingstripsonthebottomandtopofthespecimensacross diameterandplaceintheMarshalltestingmachineora compression-testingmachine.Applyloadtothespecimens diametrallyataverticalrateof50mm(2inches)perminute. 5.Recordthemaximumcompressivestrengthnotedonthetesting machineandcontinueloadinguntilaverticalcrackappearsinthe specimen.Removethecrackedspecimenfromthemachineand visuallyestimatetheapproximatedegreeofmoisturedamage (extentofstrippedorbareaggregate)onthefracturedfacesofthe 24

specimenonascaleof0to5(5beingthemoststripping). 6.CalculatethetensilestrengthofeachspecimenasfollowsinSI units:

St=2000P/πtd Where,St=tensilestrength,kPa   P P= =m max axim imum uml loa oads ds, ,N N t=specimenthickness,mm d=specimendiameter,mm 7.Expressthenumericalindexofresistanceofbituminousmixtureto thedetrimentaleffectsofwaterastheratiooftheoriginalstrength thatisretainedafteracceleratedmoistureandfreeze-thaw conditioning. 8.Calculatethetensilestrengthratio(TSR)asfollows: Tensilestrengthratio(TSR)=S 2/S1 Where, S1=averagetensilestrengthofthedrysubset,kPa S2=averagetensilestrengthoftheconditionedsubset,kPa

**************** AnnexureII OutlineofASTMD2041,“TheoreticalMaximumSpecificGravityandDensity ofBituminousPavingMixtures” ScopeandSummaryoftheTestMethod Thistestmethodcoversthedeterminationofthetheoreticalmaximumspecific gravityanddensityofuncompactedbituminouspavingmixturesat25C.The theoreticalmaximumspecificgravity(Gmm)isused:(a)tocalculateairvoidsin compactedbituminousmixtures,(b)tocalculatetheamountofbitumen absorbedbytheaggregate,and(c)toprovidetargetvalueforthecompactionof pavingmixturesinthefield. Asampleofloosepavingmixtureisplacedinataredvacuumvessel.Waterat25 Cisaddedtocompletelysubmergethesample.Aspecifiedamountofvacuumis graduallyappliedtoremovetheairbubblesentrappedbetweenbituminousmix particles.Afterthevacuumisreleased,thevolumeofthesampleofthevoidless pavingmixtureisobtainedbyeitherimmersingthevacuumcontainerwiththe sampleinawaterbathandweighingorbyfillingthecalibratedvacuum containerlevelfullofwaterandweighinginair. 25

TestingEquipment 1.Container(eitheraorbbelow) (a)Vacuumbowls–Eitherametalorplasticbowlwitha diameterrangingfrom180to260mmandabowlheight ofatleast160mm.Thebowlshallbeequippedwitha stiff,transparentcoverfittedwitharubbergasketanda connectionforthevacuumline.Thehoseconnectionshall becoveredwithasmallpieceoffinewiremeshto minimizelossofanyfinematerialfromthemix. (b)Vacuumflaskforweighinginaironly–Athick-walled volumetricglassflaskwithacapacityofapprox.4000ml, fittedwitharubberstopperwithaconnectionforthe vacuumline.Thehoseconnectionshallbecoveredwitha smallpieceoffinewiremeshtominimizelossofanyfine materialfromthemix. 2.Balancecapableofbeingreadtothenearest0.1gram.If weighingistobedoneunderwater,asuitablesuspension arrangementshallbeprovidedforweighingthesamplewhile suspendedfromthecenterofthebalance 3.Vacuumpump,capableofevacuatingairfromthevacuum containertoaresidualpressureof4.0kPa(30mmofHg)or less.Provideasuitabletrapbetweenthepumpandcontainerto minimizewatervapourenteringthevacuumpump. 4.Residualpressuremanometerorcalibratedabsolutepressure gaugewithableedvalvetoadjustthevacuumlevel. 5.Waterbathcapableofmaintainingaconstanttemperatureof25 +/-1Candsuitableforimmersionofthesuspendedcontainer. CalibrationofContainers (a)Bowls–Determinethemass(B)ofthecontainerimmersedin waterat25+/-1C.Ifthebowlisusedforweighinginair,place thevolumetriclidonthebowlwhileunderwater.Removethe water-filledbowlwiththelidinplaceanddrypriortodetermining thecombinedmassofthebowl,lidandwater.Repeat3timesand averagethe3masses.DesignatetheaveragemassasD. (b)Flasks–Calibratethevolumetricflaskbyaccuratelydetermining themassoftheflaskfilledwithwaterat25+/-1C.Useaglass coverplatetoensuretheflaskiscompletelyfull. TestProcedure 1.Separatetheparticlesoftheloosepavingmixture(whileitiswarm) byhandsothattheparticlesarenotlargerthanabout6mm. Don’tfracturetheaggregate.Placethemixsampledirectlyinto thetaredbowlorflask.Weighthecontainerwiththesampleand designatethenetmassofthesampleonlyasA.[Note:The 26

minimumsamplesizeshallbe1500gformixeswithnominal maximumaggregatesizesof12.5mmorsmaller;andshallbe 2500gformixeswithnominalmaximumaggregatesizesfrom19to 25mm.] 2.Addsufficientwaterat25Ctocoverthesamplecompletely.Place thecover(bowels)orstopper(flasks)onthecontainers. 3.Placethecontainerwiththesampleandwateronamechanical agitationdeviceoragitatemanuallyatfrequentintervals(2to3 minutes).Beginremovingentrappedairbygraduallyapplying vacuumandincreasingthevacuumpressureuntiltheresidual manometerreads3.7+/-0.3kPa(27.5+/-2.5mmofHg).After achievingthislevelwithin2minutes,continuethevacuumand agitationfor15+/-2minutes.Graduallyreleasethevacuumwith thebleedvalve. 4.Weighinginwater–Suspendthebowl(withoutlid)andcontentsin waterfor10+/-1minutesandthendeterminemass.Designatethe massunderwaterofthebowlandsampleasC. 5.Weighinginair Bowl–Submergethebowlandsampleslowlyinthe25+/-1 Cwaterbath.Keepittherefor10+/-1minutes.Immerse thelidinwaterandslideitontothebowlwithout removingwaterfromthebowlsothatnoairistrapped insidethebowl.Removethebowlwiththelidinplace fromthewaterbath.Drythebowlandlidwithadry cloth.Determinethemassofthebowl,sample,andlid anddesignateitasE. Flask–Filltheflaskslowlywithwaterensuringnotto introduceanyairintothesample.Placetheflaskinwater bathfor10+/-1minutestostabilizethetemperatureat 25Cwithoutsubmergingthetopoftheflask.Completely filltheflaskwithwaterusingacoverplatewithout entrappingairbeneaththecoverplate.Wipetheexterior oftheflaskandcoverplate.Determinethemassofthe flask,plateanditscontentscompletelyfilledwithwater. DesignatethismassasE. 6.Calculations Calculatethemaximumspecificgravityofthesampleofloose pavingmixtureasfollows:

BowlsUsedUnderWaterDetermination: Gmm=A/[A-(C-B)] Where: Gmm=maximumspecificgravityofthemixture A=massofthedrysampleinair,g B=massofbowlunderwater,g C=massofbowlandsampleunderwater,g 27

BowlsinAirDetermination: Gmm=A/(A+D-E) Where: Gmm=maximumspecificgravityofthemixture A=massofdrysampleinair,g D=massoflidandbowlwithwaterat25C,g E=massoflid,bowl,sampleandwaterat25C,g FlaskDetermination Gmm=A/(A+D-E) Where; Gmm=maximumspecificgravityofthemixture A=massofdrysampleinair,g D=massofcoverplateandflaskfilledwithwaterat25C,g E=massofflask,coverplate,sample,andwaterat25C,g

CommentsonPaperNo.564,“GuidelinesforLongLastingBituminous PavementsinIndia” by Prof.P.S.Kandhal,Prof.A.Veeraragavan&R.K.Jain

B.M.Bhagabat DoesDBMhaveadvantageoverBMandSDBCinurbanroadconstruction? A.K.Sinha Ourexperiencehasshownthatpremixcarpet(PC)withsealcoatisflexiblein characterandmoresuitableforlessimportanthighwayespeciallywhereoneis notverysureaboutthebasebelow.DoyousuggestuseofPCinaforesaid situationoryousuggestdiscardingitandusingBCorsimilarwearingcourse? S.DasGupta Isitadvisabletousesealcoatoverpremixcarpet(PC)fromthelonglasting pointofviewofbituminouspavementsinhighprecipitationareas? Col.A.K.Tiwari 1. Howwilllife/performanceofbituminouspavementbeaffecteddueto reductioninelasticrecoveryintherecentlyrevisedIRC:SP:53? 2. Unlessbiddocumentsinsistonequipmentforviscosityandtorsion recoverytest,therevisedIRC:SP:53willbeuseless. 28

3. Stonematrixasphalt(SMA)mustbedonewithPMBandnotplain bitumen. ShriGhanshamDas Itisawellestablishedfactthatpolymermodifiedbitumen(SBSbased)enhances thelifeofpavementsanditsperformanceinbetterthananyothertypesof bitumen.MORTHandIRCshouldinsistonstategovernmentstousePMBin particularsectionsofroads. Dr.P.K.Jain 1. WhereSMAshouldbeused?Ifitisusedinbindercoursedoesitserve purposeoflonglastingasphaltpavements? 2. WhatisyouropinionorexperiencewiththinSMAformaintenanceof cityroads? 3. WhatisyourrecommendationforuseofPMBinbinderandbasecourse forlonglastingpavements?

Dr.(Ms)VandanaTare I have have qu ques esti tion on rega regard rdin ing g nu numb mber er of blow blows s to be give given n for for prep prepar arat atio ion n of samp ample. le. The bitu itumino inous mix undergoes oes densif sifica ication ion due to second ondary compac compaction tion, , what should should be the recommen recommended ded compac compaction tion level level for highway highways s carryingdifferenttrafficlevelsandurbanroads? ShriNarayan.C.Bagalkot For For allo allowi wing ng traf traffi fic c over over bitu bitum men/a en/asp spha halt lt surf surfac ace e it is said said that that ther there e is no technicalreasonnottoallowtrafficfor24hrs.Ifthisisthecase,underPaperno. 562, 562, co-au co-auth thor or Dr. Dr. A. Veer Veerara aragav gavan an has come come out with with inves investig tigati ative ve repor report t sayingthat‘DBM’ sayingthat‘DBM’ hasfailed due toallowingtraffi toallowingtraffic cimm immedi ediatel ately yover over it. DBM lifecomesdowndrasticallybydoingso.Canyouexplainplease? A.C.Bordoloi InnortheastIndia,wealwayshavecontinuousrainfallduringrainyseasonasa resu result lt of whic which h we face face many many prob proble lems ms in maint aintai aini ning ng our our high highwa ways ys – like like occurrenceofbigpotholes,strippingofbituminoussurface,etc. BM, SDBC,PCandSC SDBC,PCandSC layersare layersare highlyporou highlyporous,water s,water usually usually enters enters through through porescausingpotholesin2to3yearsoldsurface.Onlystonedustisusedas fillerinbituminouscourse. Now, ow, during the las last 2 - 3 year yearss, DBM and and BC laye ayers have been used in bitu bitumi minou nous s surfac surface e with with limes limeston tone e fille filler r whic which h has very very good good anti anti-s -stri tripp ppin ing g qualities.Insomecases,add qualities.Insomecases,additionalant itionalanti-strip i-strippingagen pingagenthasalsobeenuse thasalsobeenused.Itis d.Itis observedthatwiththeadoptionofthisspecification,thequalityofpavementand durabilityofsurfaceandridingqualityhasincreasedsignificantly. Iagreewiththeviewsofproposingfourdensegradedmixes.Also,useoflime stone stone filler filler in regular regular courses courses will definit definitely ely give durabil durability ity and better better riding riding qualityandalsomaintenancecostwillreducesignificantly. 29

ShriRajibChattaraj Inthispaper,theauthorshaveaddressedalmostalltheissuesrelatingtothe design,constructionandqualitycontrolofdensegradedbituminousmixeswhere th thepresent4 RevisionofMinistry’sSpecificationneedsrevision.However,let mehaveclarificationsonsomepointsasfollows: 1.Longlastingpavements–whatistheperspectiveofthedurabilityof bituminouspavementthathasbeenconsidered–20years,30years,40yearsor 50years? 2.Inpara“3:DesignofMix”aftertable6,ithasbeenmentioned:The maximumspecificgravityofthebituminousmixshouldbedeterminedbyusing ASTMD2041andnotbytheformula. Maximumspecificgravityofbituminousmixshouldbedeterminedcorrectlyfor ascertainingairvoidsofthemixwhichisveryimportantrathermostimportant feature.Heretheconceptofeffectivespecificgravityoftheaggregatescomes intoplay. TheprecisionofthetestasperASTMD2041isthebestwhentheBituminous Mixisclosetothedesignasphaltcontent.Thus,themaximumspecificgravity (Gmm)asdeterminedbythetestasperASTMD2041(withasphaltcontentclose todesignasphaltcontentfromexperience)maybeusedtodeterminethe effectivespecificgravityofaggregateGsefromtheequation– Gse=

Pmm

−

Pmn

Pb Pb

asperclause4.06ofMS-2(SixthEdition).

−

Gmm

Gb

[Gmm=Maximumspecificgravityofthepavingmix(noairvoid)determinedas perASTMD2041. Gse= Effectivespec Effectivespecificgra ificgravityofagg vityofaggregate. regate. Pmm= Percentbyw Percentbyweightof eightoftotall totalloosem oosemix(100) ix(100) Pb= Asphaltconte Asphaltcontentat ntatwhich whichASTM ASTMD204 D2041waspe 1wasperformed rformed,per ,percentby centbytotal total weightofmix.(shouldbeclosetodesignasphaltcontentfortheparticulartype ofmix,say5.3%forBC) Gb= Specifi Specificg cgravi ravity tyofa ofasph sphalt] alt]. . ThisGsevalueshouldbeusedtodetermineGmmofbituminousmixeswith differentasphaltcontent(fromdesignasphaltcontent)bytheformula– Gmm=

Pmm Ps

Pb

asperclause4.07ofMS-2(SixtyEdition)

+

Gse

[Gmm= Pmm = Ps = Pb = Gse = Gb =

Gb

Maxim aximum um spec specif ific ic grav gravit ity yof ofp pav avin ing gm mix (no (noai air rvo void ids) s) (also known as Rice density after the name of inventor) Perce ercen nt by weigh ight oft ftota otallo lloos osee mixtu xture (100) 100) Aggr ggregate gate content, percen cent byt ytota otalwe lweiight ght of mixt ixture. Asph sphalt alt cont ontent, percent by total weigh ight ofm fmixtu xture. Effective specific gravity of aggregate. Specific gravity of asphalt]. 30

Thiswillbeusefultodetermineairvoidsofbituminousmixeswithdifferent asphaltcontent(fromdesignasphaltcontent)andwillhelpinplottingthecurve airvoid-vs-bitumencontent.Withthisapproach,G mmdeterminedbyASTM D2041andthatdeterminedbytheoreticalformulashouldbeequalatdesign asphaltcontent. ItistrueifwecheckthenumericalexampleasgiveninMS-2(Table4.2) MaximumspecificgravityofpavingmixGmm,determinedasperASTMD2041= 2.535,correspondingtotheAsphaltContent=5.3%bywt.oftotalmix. WiththisGseiscalculatedas:-

100 − 5.3 100

5 .3 −

2.535

94.7 =

=

2.761

39.45 − 5.15

1.030

ThisvalueofGsemaybeusedformixwithanyasphaltcontent,todetermine Gmmtheoretically. Forexample,with4%asphaltcontent:- Gmm=

100 96

100 4.0

+

2.761

=

=

2.535

34.299 + 5.146

1.030

WhichisthesamevalueasdeterminedbyASTMD2041. Thus,boththemethodsfordeterminationofMaximumSpecificGravityofmix areuseful[fordifferentpurpose]. 3.ItisalsostatedthatasperthelatesteditionofAsphaltInstituteManualMS-2, thedesignbitumencontentshouldbeselectedtocorrespondwith4.0%airvoids foralltypesofmixtures.Butasper“5.15:Selectionoffinalmixdesign”ofMS-2 (SixthEdition)itisratherstated,“themixshouldnotbedesignedtooptimize oneparticularproperty.Thedesignasphaltcontentshouldbeacompromiseand selectedtobalanceallofthemixproperties…Differentpropertiesaremore criticalfordifferentcircumstancesdependingontraffic,structure,climate, constructionequipmentandotherfactors”. However,thecurrentpracticeofdeterminingtheoptimumbitumencontentby averagingwithequalweightageofthebitumencontentcorrespondingto(i) maximumstability(ii)maximumdensity(iii)4%airvoidhasshortcominginthe way–itisgenerallyseenthatthebitumencontentscorrespondingtomaximum stabilityandmaximumdensityarenearertoeachotherandaresomewhatmore thanthatcorrespondingto4%airvoid.Thus,thedesignbitumencontentby averagingthreebitumencontents,doesnotcorrespondsto4%airvoid. Onthatotherhand,if4%airvoidbeconsideredastheonlyguidingparameter forselectionofdesignbitumencontent,thenitwillcomedownby0.2to0.3% thatwhatitgenerallymatcheswiththecurrentpractice. Inthatcasetoo,willitbejustifiedtodecrease0.2to0.3%furtherindesign 31

bitumencontent(donewith75no.ofblowsofcompactionlevel)forheavily traffickedroad,assuggestedinpriorityno.4inthelistofalternativewaysof superiormixdesignmethods? 4.Inpara4.2:Compaction:-Itismentionedthatintermediaterollingshouldbe donewithPTRof12or15tonesweighthavingninewheels–whyninewheels,if thenumberwheelsareseventhenloadperwheelwillbemorewhichwould ratherbeadvantageforimpartingmorekneadingaction,whichinturnwillbe helpfultoachievebettershearstrength? 5.In4.2Compaction–lastpara:-fordensitymeasurement-cuttingcoresfrom thepavingmathasbeenmentioned.Well,itisagreedthattakingcoresisthe bestwaytojudge,howevernothinghasbeenmentionedhereaboutnondestructivewaysofcheckingdensity. Ifthecoresarecutfromthepavingmat,thenwhythosecoresaretestedfor checkingdensityalong,thevolumetricproperties,stability,flow,bitumen contentetc.shouldalsobechecked. 6.Inthispapercaptionedas“Guidelinesforlonglastingbituminouspavements inIndia”,allthegoodpracticeofdesignandconstructionofbituminous pavementshavebeenthoroughlycovered.Probablyitdoesnotrelatedtothe conceptofLong-lifepavement(Europeanterm)whichissameasPerpetual pavement(AmericanTerm).

 RepliesbytheAuthors(Paperno  RepliesbytheAuthor s(Paperno.564) .564) Theauthorsareencouragedbythenumerouscommentsreceivedonthispaper at the the tim time of pres presen enta tati tion on as well well as afte afterw rwar ards ds. . Th This is show shows s that that exis existi ting ng MORTHbituminousspecificationswhicharemorethantenyearsoldneedtobe revis revised ed to keep keep abrea abreast st of latest latest techn technolo ologie gies s as well well as to obtain obtain long long lasti lasting ng pavements. B.M.Bhagab B.M.Bhagabathasaskedwhet athasaskedwhether her DBM has advanta advantageoverBMand geoverBMand SDBCin SDBCin urba urban n road road cons constr truc ucti tion on. . Be Besi side des s othe other r disa disadv dvan anta tage ges s of BM and and SDBC SDBC as expl explai aine ned d in deta detail il in the the pape paper, r, thes these e mixe mixes s brin bring g open open or sem semi dens dense e trap trap moistu sture/ re/wat water wit within the pave avement syst ystem inc increa reasin sing the potential for for stripping.ThisisallthemorecriticalforurbanroadsinIndia,wheredrainageis usually usually lacking lacking and roads roads get flooded flooded during during monsoon monsoons. s. Both BM and SDBC SDBC shouldbedeletedfromthespecifications.Onlythefourdensegradedbituminous mixesrecommendedinthepapershouldbeused. Concer Concernin ning gA.K A.K.Sinha’ .Sinha’scommen scommentson tson the useof premixcarpet premixcarpet (PC) withseal withseal coat, coat, it can can be used used for for low volum volume e rural rural roads roads such such as PMGS PMGSY Y over over WBM, WBM, wher where e ther there e is adeq adequat uate e drain drainage age for surfa surface ce water water. . By nature nature, , PC is highl highly y porousandthereforeitswaterpermeabilityisveryhigh.Thatiswhy;wetryto sealitatsurfacewithaseal sealitatsurfacewithasealcoat.Howev coat.However,inarea er,inareaswheresealc swheresealcoathasnotbee oathasnotbeen n appliedproperlyorhasbeeneroded,watercangetintothePCeasilyandspread 32

tran transve sverse rsely ly thro through ughou out t the the PC causi causing ng strip strippi ping ng and and dete deterio riorat ration ion. . Th This is is evide evident nt in case case of secti section ons s of PMGS PMGSY Y roads roads cons constru truct cted ed with with PC, PC, whic which h fall fall with withiin vill villag ages es wher where e ther there e is no surf surfac ace e wate water r drai draina nage ge. . Th Thes ese e sect sectio ions ns deterioraterapidlyandneedtobeconstructedwithcementconcrete.A.K.Sinha is refe referr rred ed to the the foll follow owin ing g link link wher wherei ein n this this ph phen enom omen enon on of PC has has been been describedindetailwithillustrationsandphotographs. http://www.scribd.com/doc/37020149/Premix-Carpet-is-Killing-Our-Roads-inTowns-and-Cities In case case of medi medium um traf traffi fic c road roads, s, 50-m 50-mm m BC wear wearin ing g cour course se can can be plac placed ed directlyoverWBMorWMMasdescribedinthepaperbecauseBCisreasonably flexibleduetoitslowernominalmaximumaggregatesize(NMAS)andrelatively higherbitumencontent. DasGuptaisreferredtotheprecedingresponsetoShriSinha.Itisnotadvisable tousePCwithorwithoutsealinhighprecipitationareas. Col.Tiwarihasmaderefere Col.Tiwarihasmadereferencetotherecentlyrevis ncetotherecentlyrevisedIRC:SP edIRC:SP:53-2010. :53-2010.Priorto Priorto this this revised revised edition edition, , IRC:SP: IRC:SP:53-2 53-2002 002 had four separat separate e specifi specificat cation ion tables tables for diff differ eren ent t type types s of modif odifie ied d bitu bitum men: en: PMB PMB (ela (elast stom omer er); ); PMB PMB (pla (plast stom omer er); ); CRMB CRMB; ; and and NRMB NRMB. . Th These ese table tables s had diffe differe rent nt requir requirem emen ents ts for minim minimum um elast astic recov ecoveery depend ending ing on the modifi ifier type, whi which is expe xpected and and reaso reasonab nable le. . PMB PMB (elas (elastom tomer) er) had highe higher r mini minimi mium um elasti elastic c recov recovery ery of 75% 75% comparedto50%forCRMB.However,IRC:SP:53-2010hascombinedalltypes ofmodifiersanddevelopedacommonspecificationfor“modifiedbitumen”.To accommodate accommodateCRMB, CRMB, thecommon the common specification specificationwas was diluted diluted and theminim the minimum um elasticrecoverywasreducedto50-60%.Obvious elasticrecoverywasreducedto50-60%.Obviously,thiswouldlowe ly,thiswouldlowerthequality rthequality ofPMB(elastomer)andsubsequentlyadverselyaffecttheperformanceandlife ofthebituminouspavement. TheauthorsconcurwithCol TheauthorsconcurwithCol.Tiwarithatthe .Tiwarithatthemodifiedbitu modifiedbitumenshoul menshouldbetested dbetested withspecifiedtestingequipmentwhenitisdeliveredtothecontractors. Concer Concernin ning g Col. Col. Tiwari’ Tiwari’s s commen comments ts on the use of PMB in SMA the followin following g observationsaremade.WhenSMAwasimportedfromEuropeintotheUSin the late 1980s 1980s numerou numerous s SMA projects projects were constru constructed cted there there using using cellulos cellulose e fiberandunmodifiedbitumensuchasVG-30andVG-20.ThoseSMAprojects performedinanexcellentmannerwithoutanyproblemwithrutting.However, inlateryearsPMBwithelastomer(primarilyPG76-22Super inlateryearsPMBwithelastome r(primarilyPG76-22Superpaveperform paveperformance ance grade)wasincorporatedintoSMAalongwithcellulosefiber.Itisbelievedthat PMBfurtherenhancedtheperformanceandservicelifeofSMApavement. The authors authors concur concur with with Shri Shri Ghansh Ghansham am Das that that polymer polymer modifie modified d bitume bitumen n (wit (with h elas elasto tome mers rs) ) give gives s bett better er pave paveme ment nt perf perfor orm mance ance com compare pared d to othe other r modifie modified d bitume bitumen n binder binders. s. However However, , elastom elastomers ers need need not be restric restricted ted to SBS onlyaslongasotherelastomersmeetthesamespecificationrequirements. Dr.P.K.JainhasaskedabouttheuseofSMA. Dr.P.K.JainhasaskedabouttheuseofSMA.Asmentione Asmentionedinthepaper,SMA dinthepaper,SMA 33

shou should ld be used used on very ery heav heavil ily y traf traffi fick cked ed road roads s espe especi cial ally ly thos those e carr carryi ying ng overl overload oaded ed truc trucks ks. . Since Since rutt ruttin ing g is expe experi rien enced ced in bitu bitumi mino nous us layer layers s usuall usually y within100mmfromtheroadsurface,itisrecommendedtouseSMAinthe bind binder er cours course e as well well un unles less s the the BC bind binder er course course is highly highly rut rut resist resistan ant t and comparablewithSuperpavedesigneddensegradedmixasusedintheUS.IRC: SP:79SP:79-2008 2008 Specifi Specificati cation on for SMA gives gives gradatio gradation n for both both binder binder course course and wearingcourse. Thin SMA Thin SMA is not reco recom mmend mended ed for for maint ainten enan ance ce of city city road roads s at this this tim time because because city roads roads arenot subject subjectedto edto very heavyloads.Moreo heavyloads.Moreover ver, , thin thin SMA wouldrequiredesignin wouldrequiredesigningtheSMAwithlowerNMAS,whichmak gtheSMAwithlowerNMAS,whichmakesthemixvery esthemixvery sensitivetochangesingradation.IRC:SP:79-2008doesnothaveanySMAmix withlowerNMAS. Concer Concernin ning gthe the useof PMB,it PMB,it isrecommend isrecommendedto edto use itin bitumin bituminouscour ouscourses ses within100 within100 mm of the road surface, surface, which which are likelyto likelyto rut under under traffic. traffic. This This meansPMBshouldbeusedprimarilyinthewearingandbindercoursesandnot inbasecourses. In respons response e to Shri Shri S.K. S.K. Singh Singh it should should benot be noted ed that that we have switch switched ed from penetr penetratio ation n gradedbitum gradedbitumento ento viscosit viscosity y gradedbitum gradedbitumensince2006, ensince2006, whichis whichis a signific significant ant step step forward forward in getting getting better better quality quality paving paving bitume bitumen. n. If we really really need need to analyze analyze the stress/s stress/strai train n charact characteris eristics tics of bitume bitumen, n, then then India India should should move move forward forward to perform performanc ance e grading grading (PG) (PG) system system adopte adopted d in the US, which which requirescomplextestingsystemforcharacterizingbitumenbasedonengineering prin princip ciple les. s. It is not not nece necessa ssary ry for user users s to test test the the crud crude e which which is used used by the the refineriesforproducingpavingbitumensolongasthebitumenspecificationis based based on perfo perform rman ance ce obser observe ved d in the the field field throu through gh comp compreh rehen ensiv sive e rese researc arch h projects. Inresponseto InresponsetoDr.Van Dr.VandanaTare’s danaTare’squery,itistobeinforme query,itistobeinformedthatindesigning dthatindesigning a mix bythe Marshal Marshall l method method, ,itis itis “assume “assumed”thatthe d”thatthe laborato laboratory rycom compact pactive ive effortusedintermsofnumberofblowswouldobtainalaboratorydensitywhich will “approx “approxima imate” te” themat density density inthe in the field field after after 2-3yearsof densifi densificati cation on undertraffic.Obviously,thislaboratorydensitycannotbeachievedphysicallyin the field field at the time time of constru constructi ction on and further further densifi densificati cation on does take place place undertraffi undertraffic.Since c.Since more moreden densific sificatio ation n takesplacein takesplacein case ofheavily traffick trafficked ed roads roads we apply apply 75 blows blows to “approx “approxima imate” te” themat density density after after 2-3 years. years. In case of light light to medium medium traffic traffic roads roads we apply apply 50 blows blows to “appro “approxim ximate” ate” the mat density density after after 2-3years undertraffic undertraffic. . Insum In summar mary, y, the simulat simulationbetwee ionbetween n the the labor laborato atory ry compac compactiv tive e eff effort orts s and the the ultim ultimate ate mat mat dens density ity in the field field is approximateatbest. Inres In respons ponse e toShri Bagalko Bagalkot,thereis t,thereis nocontradic nocontradiction tion between between the stateme statements nts about about allowin allowing g traffic traffic on bitumi bituminou nous s pavement pavements s just after after constru construction ction in this this paper paperand and the Paper Paper No. 562presentedby 562presentedby Prof.Veerara Prof.Veeraragava gavan.If n.If a pavemen pavement t has has adeq adequa uate te thic thickn knes ess/ s/st stru ruct ctur ural al stre streng ngth th to sust sustai ain n traf traffi fic c load loads s and and it is surfaced/resurfacedwithabituminouscourse,trafficcanbeopenedassoonas theconstructedbituminouscoursehascooleddowntoambienttemperaturein 34

its its entir entire e dept depth. h. Howev However er, , if a new new pavem pavemen ent t is being being const constru ruct cted ed and all the the structuralcoursessuchasbasecoursearenotinplace,thepavementcannotbe open opened ed to full full fled fledged ged traff traffic ic becau because se it will will fail fail in fatig fatigue ue du due e to inad inadeq equat uate e pavemen pavement t thickn thickness/ ess/stru structu ctural ral strengt strength. h. This This latter latter situatio situation n was mention mentioned ed in Paper PaperNo.562. No.562. It should shouldalso also be mention mentioned edthat that if DBM is constru constructe cted d intwo in two courses,donotuseDBMGr courses,donotuseDBMGrading1inanycourse ading1inanycoursebecauseitishighly becauseitishighlypermeab permeable le towaterandwillsoakinwaterasmentionedinthispaper.UseDBMGrading2 asbasecourseandBCGrading1asbindercourseasmentionedinthispaper. The auth The author ors s are are enco encour urage aged d with with the the comme comment nts s made made by Sh Shri ri Bord Bordolo oloi. i. His His adversefieldexperiencewithhighlyporousBM,SDBCandPCinhighrainfall areasconfirmsauthors’observationsinthepaper.Healsoagreesthatthefour densegradedbituminousmixesrecommendedinthepapershouldbeused. ShriRajibChattarajhassoughtclarificationsonsomeitemsasfollows: 1. Definitionoflonglastingpavement.Thispaperdoesnotdealwiththeso called called “perpet “perpetual ual pavemen pavement”. t”. A long lasting lasting pavemen pavement t should should not have have anyproblemwithbaseandbindercourseduringthedesignperiod(for example20yearsorso).Itswearingcourseshouldlastforusuallifeof810yearsafterwhichitwouldneedtobereplacedorresurfaced. 2. Theauthorsconcurwithwhateve TheauthorsconcurwithwhateverShriChattarajhasquote rShriChattarajhasquotedfromMS-2 dfromMS-2 (Sixth (Sixth Edition Edition) ) in regard regard to determ determinin ining g the maximum maximum specific specific gravity, gravity, Gmm, of bitu itumino inous mixes xes at diffe ifferrent bitu itumen contents. He has correctlystatedthattheGmmshouldbedetermineddirectlyusingASTM D2041testincaseofatleastonemixwithknownbitumencontent..Then the Gmm for other mixes at different bitumen contents can be theoreticallycalculatedbyaformulausingtheeffectivespecificgravity, Gse,ofcombinedaggregatesinthemix. Obviously,intheprecedingprocedureGmmwasdetermineddirectlyon atleastonemixsampleofknownbitumencontent. Unfo Unfort rtun unat atel ely, y, many any cont contra ract ctor ors s in Indi India a do not not even even have have the the test test equipmentforASTMD2041and,therefore,theycannot/donotmeasure the Gmm ofany bitumi bituminous nous mix directl directly.Rathe y.Rather rthe they yjus just tcalc calculat ulate ethe the Gmm Gmm for for all all bitu bitum minou inous s mixes ixes from from a “for “form mula” ula” usin using g the the spec specif ific ic gravityof“individual”aggregatesandspecificgravityofbitumen.That “formu “formula”isnolonger la”isnolonger intheMS-2now.Asstated intheMS-2now.Asstatedby by theauthorsinthe theauthorsinthe pape paper r that that (old (old) ) form formul ula a shoul hould d not not be used sed by the the cont contra ract ctor ors s for for calculatingGmm.TheyshoulddetermineGmmdirectlywithASTMtest D2041.Obviously,the‘theoreticalformula”mentionedbyShriChattaraj inhiscommentsisdifferentthanthe“formula”mentionedinthepaper. So,thisisaclearcaseofmisunderstanding. 3. Optimumbitumen Optimumbitumencontent.MS-2recomme content.MS-2recommendsselectingtheinitialdesign ndsselectingtheinitialdesign bitumenconten bitumencontentcorrespond tcorrespondingto4.0%airvoi ingto4.0%airvoids.Thenitgoe ds.Thenitgoesontostate sontostate thatdifferentpropertiesshouldbebalanced“fordifferentcircumstances 35

depe depend ndin ing g on traff traffic ic, , stru struct ctur ure, e, clima climate te, , cons constr truc uctio tion n equi equipm pmen ent t and othe other r fact factor ors” s”. . Th That at is easi easier er said said than than done done. . Th The e late latest st US nati nation onal al researchonairvoidshasrecommendedtodesignmixeswithanarrower rangeof3.5to4.5%ratherthan3to5%forairvoidstooptimizefatigue and and rut rut resi resist stan ance ce prop proper erti ties es. . Th This is leav leaves es no choi choice ce bu but t to sele select ct the the optimumbitumencontentcorrespondingto4.0%airvoids.Thatiswhy; Superppavemixdesignalsouses4.0%airvoidsasthecriteriatoselect theoptimumbitumencontent.Thisiswhathasbeenrecommendedinthe pape paper r and and this this is what what also also has has been been inco incorp rpor orat ated ed in the the late latest st IRC IRC Spec Sp ecifi ifica catio tion n IRC: IRC:111 111-2 -2009 009 for Dens Dense e Gr Grade aded d Bitu Bitumi minou nous s Mixes Mixes. . We agree agree with Shri Shri Chattar Chattaraj aj that that there there is some confusi confusion onin inMSMS-2 2 on this this point. point. If it is desired desired to have have optimum optimum bitume bitumen n conten content t approxim approximatin ating g Supe Su perp rpave ave mix mix desig design, n, then then the the optim optimum um bitu bitume men n conte content nt selec selected ted at 4.0% 4.0% air air voids voids usin using g 75 blows blows of Marsh Marshall all hamme hammer r shoul should d be furt furthe her r reducedby0.2to0.3percent. 4. Compact Compaction. ion. Apneumatictires Apneumatictires rollermay rollermay have 7or9 7 or9 wheeldepen wheeldependin ding g on its its widt width. h. It is the the infl inflat atio ion n pres pressu sure re in the the tyre tyres s whic which h is most ost importantforeffectivecompactionofthebituminousmat.Theinflation pressurecanbeincreasedordecreaseddependingonthestrengthofthe bituminousmix. 5. Densitymeasurement.Nondestructivewayofcheckingdensityisgoodfor qualit lity control by the contract actor during ing the comp ompact action proce ocess. ss. However,theacceptanceofmatdensityinthefieldbytheusershouldbe based basedoncores.Corescannot oncores.Corescannot beused effecti effectively vely formeasuringstabil formeasuringstability ity and and flow flow of the the mix. mix. Marsh Marshall all speci specime mens ns compac compacte ted d daily daily in the the plant plant labo labora rato tory ry shou should ld be used used for for this this pu purp rpos ose. e. Howe Howeve ver, r, core cores s can can be analyzedforvolumetricpropertiessuchasairvoids. 6. Guidelinesforlonglastin Guidelinesforlonglastingpavement gpavements.Theseguidel s.Theseguidelinesshould inesshouldbeusedto beusedto revis revise e the the exist existing ing MORT MORTH H spec specifi ificat cation ions s for for bitum bitumino inous us pavem pavement ents, s, whichareover10yearsold.Thes whichareover10yearsold.Theseguideli eguidelinesarenotme nesarenotmeantforobtain antforobtaining ing “perpetualpavements”asmentionedearlier. Inclosing,theauthor Inclosing,theauthorswould swould liketo liketo state statetha that tmost most ofthese guidelin guidelineson eson long lastingpavem lastingpavement ents s relatedto relatedto specifi specificat cations ions of bitumin bituminouspavem ouspavement ents s have been been inco incorp rpor orat ated ed in the the rece recent nt IRC: IRC:11 1111-20 2009 09 Sp Spec ecif ific icat atio ions ns for for Dens Dense e Gr Grad aded ed BituminousMixes.However,itistheMORTHspecificationwhichiscommonly usedbymosthighwayagenciesinIndia.UntilMORTHspecificationisrevised alongsimilarlines,wewouldnotachieveourobjectiveoflonglastingbituminous pavements.

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