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CHARACTERIZATIONTESTSFORMINERALFILLERSRELATEDTOPERFORMANCEOFASPHALTPAVINGMIXTURES

By

PrithviS.Kandal

CynthiaY.LynnFrazierParker

PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1638,1998

277TechnologyParkway Auburn,AL36830


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CHARACTERIZATIONTESTSFORMINERALFILLERSRELATEDTO PERFORMANCEOFASPHALTPAVINGMIXTURES

By

PrithviS.Kandhal

AssociateDirectorNationalCenterforAsphaltTechnology

AuburnUniversity,Alabama

CynthiaY.Lynn

GraduateStudentNationalCenterforAsphaltTechnology

AuburnUniversity,Alabama

FrazierParkerDirector

HighwayResearchCenterAuburnUniversity,Alabama

PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1638,1998


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DISCLAIMER

Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

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ABSTRACT

Variousstudieshaveshownthatthepropertiesofmineralfillerespeciallythematerial

passing0.075mm(No.200)sieve(generallycalledP200material)haveasignificanteffectontheperformanceofasphaltpavingmixturesintermsofpermanentdeformation,fatiguecracking,andmoisturesusceptibility.However,researchershaveemployeddifferentcharacterizationtestsforevaluatingtheP200materials.

ThisstudywasundertakentodeterminewhichP200characterizationtestsaremostrelatedtothe

performanceofasphaltpavingmixtures.SixP200materialsrepresentingawiderangeofmineralogicalcompositionandparticlesizeswereused.TheseP200materialswerecharacterizedbysixtestsincludingRigdenvoids,particlesizeanalysis,andmethylenebluetest.Mixeswerepreparedwithtwofines/asphaltratios(0.8and1.5)byweight.MixvalidationtestsincludedtheSuperpavesheartestforevaluatingpermanentdeformationandfatiguecracking,andtheHamburgwheeltrackingtestandAASHTOT283forevaluatingmoisturesusceptibilityofthe12mixturescontainingdifferentP200materialsandfines/asphaltratios.

Theparticlesizesinmicronscorrespondingto60and10percentpassingandthemethylenebluetestweredeterminedtoberelatedtotheperformanceofasphaltpavingmixtures.

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Kandhal,Lynn,&Parker

CHARACTERIZATIONTESTSFORMINERALFILLERSRELATEDTO

PERFORMANCEOFASPHALTPAVINGMIXTURESPrithviS.Kandhal,CynthiaY.Lynn,andFrazierParkerJr.

INTRODUCTION

Accordingtovariousstudiesthepropertiesofmineralfillerespeciallythematerialpassing0.075mm(No.200)sieve(generallycalledP200material)haveasignificanteffectontheperformanceofasphaltpavingmixturesintermsofpermanentdeformation,fatiguecracking,andmoisturesusceptibility.However,researchershaveemployeddifferentcharacterizationtestsforevaluatingtheP200materials.ThisstudywasundertakentodeterminewhichP200characterizationtestsaremostrelatedtotheperformanceofasphaltpavingmixtures.

REVIEWOFLITERATURE

Numerousstudieshaveshownthatthepropertiesofmineralfiller(especiallythematerialpassingNo.200sieve)haveasignificanteffectonthepropertiesoftheHMAmixtures.Theintroductionofenvironmentalregulationsandthesubsequentadoptionofdustcollectionsystem(baghouse)hasencouragedthereturnofmostofthefinestotheHMAmixture.Amaximumfiller/asphaltratioof1@2to1@5,basedonweight,isusedbymanyagenciestolimittheamountoftheminus200material.However,thefinesvaryingradation,particleshape,surfacearea,voidcontent,mineralcomposition,andphysico-chemicalpropertiesand,therefore,theirinfluenceonthepropertiesofHMAmixturesalsovaries(1).Therefore,themaximumallowableamountshouldbedifferentfordifferentfines.

FinescaninfluencetheperformanceofHMAmixturesasfollows.

1.Dependingontheparticlesize,finescanactasafillerorasanextenderofasphaltcementbinder(2,3,4).Inthelattercaseanover-richHMAmixcanresultleadingto

flushingand/orrutting.Inmanycases,theamountofasphaltcementusedmustbereducedtopreventalossofstabilityorableedingpavement(5).2.Somefineshaveaconsiderableeffectontheasphaltcementmakingitactasamuch

stiffergradeofasphaltcementcomparedtotheneatasphaltcementgrade(1,3,6,7),andtherebyaffecttheHMApavementperformanceincludingitsfracturebehavior(8,9).

3.SomefinesmaketheHMAmixturessusceptibletomoisture-induceddamage(1).Water-sensitivityofonesourceofslagbaghousefineshasbeenreportedintheUnitedStates(5),andthewater-sensitivityofotherstonedustshasbeenreportedinGermany(10).StrippingofHMAmixturesasrelatedtothepropertiesoffiller/asphaltcombinations(fillerswereobtainedfromoperatingHMAplants)hasbeenreportedinJapan(11).

ItisveryimportanttocharacterizethefinessothattheperformanceparametersofHMApavements(resistancetopermanentdeformation,stripping,andfatiguecracking)arenotcompromised.

MATERIALS,TESTS,ANDTESTDATA

P200MaterialsandTests

Sixaggregatesources(Table1)werechosentorepresentawiderangeofmineralogicalcompositionandparticlesizes.Thesematerialswereobtainedbydrysievingfineaggregateparentrockovera75:m(No.200)sieve.

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Table1.P200AggregateTestsResults

P-200TypeTest

P200-1 P200-2 P200-3 P200-4 P200-5 P200-6Natural Lime- Dolomite Granite Blast LimerockSand stone Furnace

Slag

SpecificGravity 2.558 2.760 2.955 2.872 3.043 2.798

RigdenVoid(British 39.3 35.4 32.3 41.4 40.6 34.3Standard),%

RigdenVoid 53.8 38.0 38.9 45.5 49.8 38.5(PennStateModified),%

FinenessModulus 3.67 2.46 4.99 4.50 4.47 2.81

D10(micron) 1.54 1.26 4.18 3.30 2.41 1.38D30(micron) 6.45 3.27 22.58 15.64 12.67 4.23

D60(micron) 26.92 9.98 51.95 40.89 43.41 14.60

SpecificSurfaceArea 12900 17968 6207 7206 8752 15603(cm2/ml)

MethyleneBlue 18.7 1.3 0.3 2.1 2.0 9.5

PlasticityIndex 29 NP NP NP NP NP

GermanFillerTest 35 70 80 60 55 75

ThefollowingtestswereusedtocharacterizetheP200materials.RigdenVoids(BritishStandard)-BS812RigdenVoids(PennStateModified)-Reference13ParticleSizeAnalysisMethyleneBlueTest-OhioDOTProcedurePlasticityIndex-AASHTOT90GermanFillerTest-KochMaterialsCompanyProcedure

Voidcontentinfines(generallycalledRigdenvoids)compactedtomaximumdensityhasbeenusedbyresearchersforcharacterizingthefines.Voidcontentisregulatedbyfourbasicpropertiesoffinesparticleshape,particlesize,particle-sizedistribution,andparticlesurfacestructure(1).Asampleofvacuum-ovendrysampleoffinesiseithervibratedinagraduatecylinder(1)orcompactedinasmallmoldbyacompactionhammer(12,13)tomaximum

packing.Mass(g)ofthecompactedfinesisdividedbythecompactedvolume(cm3)tocalculatebulkspecificgravity(GfB)ofcompactedfines.Apparentspecificgravity(GfS)ofthefinesolidsisdeterminedbyAASHTOT133usingkerosene.Voidcontent(V)inthefinescompactedtomaximumdensityisthencalculatedasfollows:BothBritishStandardBS812(12)andPennStatemodifiedequipment(13)wereusedtodetermineRigdenVoids.Theyarebasedonthesameconceptbutuseadifferentcompactive

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effort.

ParticlesizeanalysiswasconductedwithaCoulterLF200Particlesizeanalyzer.Fromthis

analysis,severalparametersweredetermined.Therelativefinenessofanaggregatecanbe

determinedbythecalculatedfinenessmodulus(FM).FinenessmodulusoftheP200materialwascalculatedbydividingby100thesumofthepercentagesofP200materialcoarserthan75,50,30,20,10,5,3,and1microns.Thefinertheaggregate,thesmallerthefinenessmodulus.ParametersD10,D30,andD60werealsodeterminedfromparticlesizeanalysis.Theseparametersaretheparticlesizesthatcorrespond,respectively,to10,30,and60%ofthematerialpassing.Thespecificsurfacearea(cm2/ml)orSAwasthefinalparameterobtainedfromthisanalysis.

Themethyleneblue(MB)testisusedbytheInternationalSlurrySealAssociation(ISSA)to

quantifytheamountofharmfulclaysofthesmectite(montmorillinite)group,organicmatterandironhydroxidespresentinfineaggregate(14).Theprincipleofthetestistoaddquantitiesofastandardaqueoussolutionofthedye(methyleneblue)toasampleuntiladsorptionofthedye

ceases.TheGermanfillertestisameasureoftheamountofmineralfillerrequiredtoabsorb15grams

ofhydraulicoil.Thehydraulicoilisputinasmallbowl,then45gramsofmineralfillerisaddedandmixed.Anattemptismadetoformaballwiththemixture.Ifaballisformedandholdstogether,moremineralfiller,in5-gincrements,isadded.Thisprocessiscontinueduntilthemixturelosescohesion.Atthispoint,allofthehydraulicoilisfixedinthevoidsoftheP200materialandthereisnoexcesstoholdtheparticlestogether.ThetotalamountofP200addedtothehydraulicoilisreportedasthetestvalue.

Table1containstheresultsoftheP200characterizationtests.Eachvalueistheaverageofthree

replicates.

Table2containsthecorrelationmatrixbetweenaggregateproperties.Thecorrelationcoefficients(Rvalues)arethefirstnumberineachcell.Thesecondnumberineachcellisthestatisticalsignificancelevel(P)correspondingtothecorrelationcoefficient.

Rigdenvoids,BritishmethodandRigdenvoids,PennStatemodifiedhaveagoodcorrelation

(R=0.78,P=0.06)witheachotherbecausebothmeasurethevoidsinthecompactedP200materialalthoughwithdifferentcompactiveefforts.Rigdenvoids,PennStatemodified,hasanexcellentcorrelationwiththeGermanfillertest,whereasRigdenvoids,Britishmethod,hasonlyafaircorrelationwiththeGermanfillertest.

TheGermanfillertestisbasedindirectlyontheRigdenvoidsconcept.IftheRigdenvoidsare

high,theamountofP200materialneededtoreachtheendpointofthetestisrelativelylowbecausemorehydraulicoilisfixedbythehighvoids.TheGermanfillertestdoesnotrequireany

specialequipmentandisverysimpletoperformandcanpotentiallybesubstitutedforRigdenvoids,PennStatemethod.

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Table2.CorrelationMatrixofP200AggregatePropertiesa

Rigden Rigden FM D10 D30 D60 SA MB GermanVoid,BS Void,PS Filler

Rigden 1.0 0.784 0.235 -0.073 -0.051 0.186 -0.250 0.166 -0.749Void,BS 0.065 0.655 0.890 0.923 0.724 0.633 0.753 0.086Rigden 1.0 0.326 -0.092 -0.013 0.277 -0.268 0.557 -0.949Void,PS 0.529 0.863 0.980 0.595 0.607 0.251 0.004FM 1.0 0.899 0.936 0.996 -0.990 -0.302 -0.058

0.015 0.006 0.0001 0.0001 0.561 0.913D10 1.0 0.992 0.907 -0.919 -0.538 0.321

0.0001 0.013 0.010 0.270 0.535D30 1.0 0.947 -0.942 -0.503 0.261

0.004 0.005 0.309 0.617D60 1.0 -0.983 -0.360 -0.001

0.0004 0.483 0.998SA 1.0 0.347 0.000

0.500 0.999MB 1.0 -0.680

0.137German 1.0Filler

aTopvaluesarecorrelationcoefficientsRandbottomvaluesaresignificancelevelsPineachcell.

Thetestparametersfinenessmodulus(FM),specificsurfacearea(SA),D10,D30,andD60arestronglyrelatedwitheachotherasshowninTable2.Allcorrelationsaresignificantatthe5%level.

Rigdenvoids,PennStatemethod,andRigdenvoids,Britishstandard,donothaveany

correlationwiththeparticlesizeparameters.Asmentionedearlier,Rigdenvoidsareregulatedbyparticleshapeandparticlesurfacetexturebesidesparticlesize.

MixtureValidationTests

TwelveHMAmixeswereevaluatedinthisstudy.ThesixP200aggregatesinboth0.8and1.5F/Aratioswerecombinedwithlimestonecoarseandfineaggregatetoproducevalidationmixes.Alllimestonewaswashedovera75:m(No.200)sievepriortobatchingtoremovetheP200material.Limestonewaschosenasthecoarseandfineaggregatesothatmoisturesusceptibilitywouldnotbecausedbythebaseaggregate.Moisturesusceptibilitydifferences,ifany,canthenbeattributedtotheeffectoftheP200material.Figure1showstheHMAmixgradationusedforthe0.8F/Aratio(5%passing75:msieve).TheHMAmixgradationforthe1.5F/Aratiowassameasthatfor0.8F/Aratioexceptithad8%passing75 :msieve.

ASuperpavePG64-22gradeasphaltcementwasusedinallHMAmixtesting.Optimum

asphaltcontentwasdeterminedbySuperpavevolumetricmixdesignforamixcontainingalllimestoneaggregate(includingtheP200fraction)usingthe0.8F/Aratio.Anasphaltcontentof5.3%gave4%airvoidsatNdesign(119gyrations,forintermediatedesigntrafficlevelof10

7ESALs).Thisasphaltcontentandsamecompactiveeffortwasusedforallvalidationmixes.However,relativelylowairvoids(averageof2.8percent)weregenerallyobtainedinvalidationsamples.ItisquitepossiblethatinsomecasesitcanbeattributedtoP200material'spotentialactionasanextender.

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Figure1.HMAMixGradation

PermanentDeformationandFatigueCracking

SpecimensweremadetobetestedbytheSuperpavesheartester(frequencysweepatconstant

heightandsimpleshearatconstantheight)andtheindirecttensiletesterforevaluatingtheHMAresistancetopermanentdeformationandfatiguecracking(15,16).ThetestingofthecompactedspecimenswasperformedbytheAsphaltInstitute.

ThefollowingthreeindividualtestparameterswhichareusedintheSuperpaveintermediatemix

analysiswereusedtodeterminethepropensityoftheHMAmixturestopermanentdeformation(rutting)andfatiguecracking.

1.G*/sin*at0.1hertz.

G*/sin*oftheHMAmixissimilartoG*/sin*(ruttingparameter)ofPGgraded0

asphaltbinder.ItisameasureofHMAstiffnessathighpavementtemperature(40C)ataslowrateofloading(0.1cycle/second).HighervaluesofG*/sin*indicateincreasedstiffnessofHMAmixturesand,therefore,increasedresistancetorutting.

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G*isthecomplexmodulusand*isthephaseanglewhenHMAistestedunderdynamicloading.

2.Slope(m)ofthefrequencyvsG*plot.Themvaluewasobtainedfromthefrequencysweepatconstantheightconductedby

theSuperpavesheartester(SST)athigheffectivetemperature(40C)forpermanentdeformationorTeff(PD)withfrequenciesrangingfrom0.01hertzto10hertz.Inotherwords,G*(stiffness)ofthecompactedHMAspecimenismeasuredatdifferentfrequencies.Theslope(m)ofthebestfitlineonthefrequencyvsG*plotiscalculated.ThissloperepresentstherateofdevelopmentofruttingforthetestedmixandisusedintheSuperpavemodelassuch.Thelowerthemslope,thebetteristhemix'sresistancetorutting.

3.G*sin*at1.0hertzG*sin*oftheHMAmixissimilartoG*sin*(fatiguefactor)oftheasphaltbinder.ItisameasureofthestiffnessatintermediateeffectivepavementtemperaturesforfatiguecrackingorTeff(FC).G*sin*wasmeasuredat1.0hertztorepresentfastmovingtraffic.AT

eff(FC)of20Cwasused.HighvaluesofG*sin*at1.0hertz

indicatehighstiffnessatintermediatetemperaturesand,therefore,lowresistancetofatiguecrackingaccordingtoSuperpave.

MoistureSusceptibility(Stripping)

KochMaterialsCompanyperformedtheHamburgwheeltrackingtestintheirlaboratoryinTerre

Haute,Indiana.TheHamburgwheeltrackingdevice(HWTD)measuresthecombinedeffectsofruttingandmoisturedamagebyrollingasteelwheelbackandforthacrossthesurfaceofaHMAslabthatissubmergedinhotwatermaintainedat50C(122F).Thetestingdurationis20,000cyclesanddeformationisrecordedandplottedaftereachcycle.Onthecyclesversusdeformationplottwodistinctlinesaregenerallyobserved.Thefirstline(ruttingline)indicatesruttingintheHMAunaffectedbystripping.Thefollowingsecondline(strippingline)withasteeperslopeindicatesruttingduetostripping.Thepoint(numberofcycles)wheretheslopeof

theruttinglineandtheslopeofthestrippinglineintersectiscalledtheinflectionpoint.Thisisthepointwherestrippingisassumedtohavebeeninitiated.Inflectionpoint(expressedintermsofnumberofcycles)isthetestparameterofinterestforthisstudy.TheHMAslabsgenerallyhadanairvoidcontentof71percent.

AASHTOT-283wasalsousedtomeasurethemoisture-susceptibilityoftheHMAmixesin

termsoftensilestrengthratio(TSR).

MixtureValidationDataandStatisticalAnalysis

Table3containsallmixturevalidationtestresults.ThemainobjectiveofthestatisticalanalysisistocorrelatetheP200aggregatepropertieswithHMApropertiesdeterminedbythemixvalidationtests.Table4showsthecorrelationmatrixbetweentheP200aggregatepropertiesand

theHMApropertiesatthe0.8F/Agradation.Table5showsthecorrelationmatrixbetweentheP200aggregatepropertiesandHMApropertiesatthe1.5F/Agradation.

G*/sin*@0.1hzandm(theslopeofthebestfitlineonthefrequencyvsG*plot)werethetwoHMAparameterschosentoindicatetheruttingpotential,asmentionedpreviously.NeitheroftheseparameterscorrelatestoanyoftheP200aggregatetestsatasignificantlevel(P


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Table3.P200MixtureValidationTestResults

RuttingParameters

HighTemperature(40C)

FatigueCrackingParameter

IntermediateTemperature(20C)

MoistureSusceptibilityParameters

MixDesignation

G*/sin*@m0.1hz,psi

G*sin*@1.0hzpsi

TSRPercent

InflectionPoint(Hamburg)

1A 8722 0.43373 98051 66.2 7000

2A 9830 0.40572 89829 64.6 8400

3A 11034 0.40931 97967 51.7

200004A 9682 0.43596 88811 55.0

86005A 11271 0.40282 85644 57.5

100006A 12934 0.39183 93707 64.1

100001B 21700 0.31559 109560 64.7 6000

2B 21752 0.30167 98782 59.9 14400

3B 10269 0.40396 93318 52.4 98004B

11872 0.37874 84319 54.7 64005B

9510 0.41171 86723 64.5 80006B

25900 0.29158 95502 68.1 5000

Table4.CorrelationMatrixBetweenP200AggregatePropertiesandHMAProperties(0.8

F/AGradation)a

Rutting Fatigue Stripping

G*/sin*@0.1 m G*sin*@1.0hzTSR Inflectionhz Point

RigdenVoids -0.468 0.599 -0.556 0.033 -0.665(British 0.35 0.21 0.25 0.95 0.15Standard)

RigdenVoids -0.526 0.599 -0.051 0.157 -0.463(PennState 0.28 0.21 0.92 0.77 0.36Method)

Fineness -0.094 0.365 0.039 -0.865 0.561Modulus 0.86 0.48 0.94 0.03 0.25

D10 0.007 0.248 0.110 -0.968 0.758

0.99 0.63 0.84 0.001 0.08D30 0.01 0.228 0.113 -0.961 0.766

0.99 0.66 0.83 0.002 0.08

D60 -0.048 0.294 0.016 -0.886 0.6060.93 0.57 0.98 0.02 0.20

SpecificSurface0.049 -0.367 0.009 0.896 -0.543Area 0.92 0.47 0.99 0.02 0.27

MethyleneBlue-0.255 0.306 0.534 0.693 -0.4760.63 0.56 0.28 0.13 0.34

GermanFiller 0.657 -0.644 -0.003 -0.409 0.6470.16 0.17 0.99 0.42 0.17

a

TopvaluesarecorrelationcoefficientsRandbottomvaluesaresignificancelevelsPineachcell.

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Table5.CorrelationMatrixBetweenP200AggregatePropertiesandHMAProperties(1.5

F/AGradation)a

Rutting Fatigue Stripping

G*/sin*@0.1hz m G*sin*@1.0hz TSR InflectionPoint

RigdenVoids -0.293 0.251 -0.257 0.143 -0.355(British 0.57 0.63 0.62 0.79 0.49Standard)

RigdenVoids -0.201 0.221 0.206 0.286 -0.465(PennState 0.70 0.67 0.70 0.58 0.35Method)

Fineness -0.901 0.926 -0.488 -0.584 -0.249Modulus 0.01 0.008 0.33 0.22 0.63

D10 -0.838 0.836 -0.560 -0.824 -0.0320.04 0.04 0.25 0.04 0.95

D30 -0.871 0.881 -0.532 -0.771 -0.0490.02 0.02 0.28 0.07 0.92

D60 -0.920 0.948 -0.511 -0.590 -0.1920.009 0.004 0.30 0.22 0.72

SpecificSurface 0.895 -0.915 0.572 0.609 0.288Area 0.016 0.01 0.24 0.20 0.58

MethyleneBlue 0.615 -0.559 0.776 0.613 -0.5590.19 0.25 0.07 0.20 0.25

GermanFiller -0.05 0.060 -0.413 -0.361 0.359

0.92 0.91 0.42 0.48 0.49aTopvaluesarecorrelationcoefficientsRandbottomvaluesaresignificancelevelsPineachcell.

TherewerenosignificantcorrelationsbetweenP200propertiesandG*sin*(fatiguefactor)ineither0.8F/Aratioor1.5F/Aratiogradations.TSRcorrelatedwellwiththegradationparametersatthe0.8F/Aratio.However,withthisexception,nosignificantcorrelationswereseenbetweenstrippingparametersandP200aggregatetestsateitherthe0.8F/Aratioorthe1.5F/Aratio.

ThecorrelationsaregenerallybetterfortheF/Aratioof1.5(becausehigheramountsofP200

wereused)thanF/Aratioof0.8.Therefore,P200testscanbebetterrelatedtoHMAperformanceatF/Aratioof1.5whichwillbeprimarilyusedinthisstudytoselecttheP200testswhicharerelatedtoHMAperformance.ItappearsfromTable5thatthefinenessofP200materialexpressedbythetestparametersD60,D30,D10,finenessmodulus,andspecificsurfaceareaissignificantlyrelatedtopermanentdeformationofHMAathighconcentrationlevelsofP200inthemix.

Asmentionedearlier,nosignificantrelationshipsareobservedbetweenP200aggregate

propertiesandHMAruttingparameters(G*/sin*@0.1hzandm)orHMAfatigueparameter(G*sin*)ataF/Aratioof0.8.ThisindicatesthatatlowconcentrationlevelsofP200,theeffectonruttingandfatigueisnotstatisticallysignificant.

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ItappearsfromTable5thatthefinenessoftheP200material(especiallyD10)hasasignificant

effectontheretainedtensilestrength(TSR).Sinceparentrocks(limestone)ofthecoarseaggregateandfineaggregatearethesameinallmixes(onlytheP200isdifferent),theeffectofbinderstiffening(causedbytheP200material)appearstobedominantinthesemixes.The

smallerthesizeofP200(especiallyD10),themorethebinderisbeingmodifiedand/orextendedandthusgivesincreasedresistancetostrippinginAASHTOT283test.

Surprisingly,noP200aggregatetestshasanysignificantrelationshipwithstrippingwhen

measuredbytheHamburgwheeltrackingdevice.Methylenebluehasthehighest(althoughinsignificantatthe0.05level)relationshipwiththeinflectionpoint.Obviously,theHamburgwheeltrackingtest,whichisconductedwithHMAslabssubmergedinhotwater(50C)andsubjectedtomechanicalaction,issignificantlydifferentthanthestrippingprocessinAASHTOT283,whichdoesnotinvolveanymechanicalaction.

Again,similartotheresultsobtainedinmixeswithF/Aratioof1.5,thefinenessoftheP200

materialhasasignificanteffectontheretainedtensilestrength(TSR)ataF/Aratioof0.8(Table

4).AsalsoobservedinmixeswithF/Aratioof1.5,noP200testhasanysignificantrelationship

withstrippingwhenmeasuredbytheHamburgwheeltrackingdevice.Methyleneblueistheonlyindependentvariablewhichhasthehighest(butnotsignificantatthe0.05level)correlationwithinflectionpoint(R=-0.48,P=0.34).

TheforwardselectionmultiplevariablesproceduregivenintheSASprogramwasusedtoselect

theP200testswhicharerelatedtoHMAperformanceparameters.Theforwardselectionprocedurebeginsbyfindingthevariablethatproducestheoptimumone-variablesubset,thatis,thevariablewiththelargestcoefficientofdeterminationorR2.Inthesecondstep,theprocedurefindsthatvariablewhich,whenaddedtothealreadychosenvariable,resultsinthelargestincreaseinR2andsoon.Theprocesscontinuesuntilnovariableconsideredforadditiontothe

modelprovidesanincreasesinR2

consideredstatisticallysignificantatthespecifiedlevel(P=0.05forthisstudy).

Table6containstheP200testsselectedintheforwardselectionprocedureandthe

correspondingregressionequationsrelatingtheP200aggregateteststotheHMAperformanceparameters.

TheselectionoftheP200aggregateteststhatbestrelatetotheHMAperformancepropertieswill

bebasedsolelyontheinformationtakenfromthe1.5F/Agradationtesting.Thisisbecause1.5F/AratioseemstocorrelatemuchbetterwiththeHMAperformancepropertiescomparedto0.8F/AratioduetoanincreasedamountofP200materialinthemix.Themodelsof0.8F/AratiogenerallyhavelowcoefficientofdeterminationorR2valuesandinsignificantPvalues.

PermanentDeformation

G*/sin*@0.1hertzatHighTemperatureHighG*/sin*valuesindicateincreasedresistancetopermanentdeformationorrutting.Thetwo-variablemodel(seeTable6andFigure2)givesD60astheprimaryindependentvariableandmethyleneblueasthesecondindependentvariable.ThecoefficientofdeterminationorR2valueofthismodelis0.94(P=0.015)whichisexcellent.Astheparticlesize(at60%passing)decreases,theG*/sin*(stiffnessorresistancetorutting)increases.ItappearsthatthefinertheP200material,themoreitmodifiestheasphaltbinderandstiffenstheHMAmix.Themodelalsoindicatesthatthehigherthemethylenebluevalue(anotherindicationofthepresenceofveryfineP200),thehigherisG*/sin*.

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Table6.RegressionEquationsBetweenP200AggregateTestsandHMAValidationTests

0.8F/AGradation

Performance Step Dependent Independent Equation R2 P

Parameter

Permanent 1 G*/sin* German G*/sin 0.43 0.16Deformation @0.1hz Filler *=6845.29+59.737(German

Filler)

Permanent 2 G*/sin* Rigden G*/sin*=- 0.52 0.32Deformation @0.1hz Voids(Penn 8062.28+217.88(Rigden

State) Voids,PennState)+144.60(GermanFiler)

Permanent 1 m German m=0.457-0.000699(German 0.42 0.17Deformation Filler Filler)

Permanent 2 m D10 m=0.450+0.0076(D10)- 0.65 0.21Deformation 0.000876(GermanFiller)

Fatigue 1 G*sin* Rigden G*sin*=120620.9- 0.31 [email protected] Voids 760.41(RigdenVoids,British

(British Standard)Standard)

Fatigue 2 G*sin* Methylene G*sin*=123483.4-- 0.71 [email protected] Blue 906.9(RigdenVoids,British

Standard)+457.7(Methylene Blue)

1.5F/AGradation

Performance Step Dependent Independent Equation R2

PParameter

Permanent 1 G*/sin* D60 G*/sin*=28961.36- 0.85 0.09Deformation @0.1hz 387.56(D60)

Permanent 2 G*/sin* Methylene G*/sin*=25596.17- 0.94 0.01Deformation @0.1hz Blue 338.18(D60)+321.94(Methyl 5

eneBlue)

Permanent 1 m D60 m=0.256+0.003(D60) 0.90 0.00Deformation 4

Permanent 2 m Methylene m=0.275+0.0027(D60)- 0.95 0.01Deformation Blue 0.0019(MethyleneBlue)

Fatigue 1 G*sin* Methylene G*sin*=89153.7+981.26(Me 0.60 [email protected] Blue thyleneBlue)

Fatigue 2 G*sin* Rigden G*sin*=124586.23- 0.75 [email protected] Voids 965.21(RigdenVoids,British

(British Standard)+1064.7(MethyleneStandard) Blue)

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Figure2.PredictedG*/sin*Valuesvs.ActualG*/sin*UsingaTwo-Variable(D60and

MethyleneBlue)Model

mValue(SlopeoftheFrequencyvs.G*Plot)atHighTemperature HighmvaluesindicateincreasingrateofrutdevelopmentinHMAmixes.Thetwo-variablemodel(R2=0.95,P=0.01)givesD60astheprimaryindependentvariableandmethyleneblueasthesecondaryindependentvariableaffectingm(seeTable6andFigure3).ThisissimilartoG*/sin*@0.1hertz.

ItisrecommendedtouseD60andmethyleneblueastheP200testswhicharerelatedtoHMA

performanceintermsofpermanentdeformation.

FatigueCracking

G*sin*@1.0HertzatIntermediateTemperatureHighvaluesofG*sin*indicatehighmixturestiffnessatintermediatetemperatureandthereforeincreasedfatiguecracking.Thetwo-variablemodelforG*sin*@1.0hertzindicatesmethyleneblueastheprimaryindependentvariableandRigdenvoids,Britishstandardasthesecondaryvariable.Thisissimilartothe

ruttingmodels2inthathighervaluesofmethyleneblueindicatestifferHMAmixes.However,the

modelhasaRvalueof0.75andalevelofsignificanceof0.12(greaterthanthedesired0.05).Therefore,itappearsthattheeffectofP200materialatthe1.5F/Aratioisstatisticallynotsignificantand,therefore,noP200testisrecommendedforfatiguecracking.

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Figure3.PredictedRUTMValuesvs.ActualRUTMValuesUsingaTwo-Variable(D60andMethyleneBlue)Model

Stripping

Twomixvalidationtests:AASHTOT283(ModifiedLottman)andHamburgwheeltracking

device,wereusedtodetermineHMAperformanceintermsofresistancetostrippingormoisturesusceptibility.

AASHTOT283Higherretainedtensilestrength(TSR)obtainedbythistestindicatesincreased

resistancetostripping.Thetwo-variablemodelforTSRataF/Aratioof1.5(R2=0.82,P=0.08)consistsofD10(P200sizeat10%passing)astheprimaryindependentvariable(R2=0.68,

P=0.04)andspecificsurfacearea(SA)ofP200asthesecondaryindependentvariable(Table7).TSRincreasesastheP200becomesfinerat10%passing(D10decreases).ItappearsthatveryfinesizeP200at10%passinglevelisstiffeningtheF/Abinderandthusprovidingincreasedresistancetostripping.Theliteraturereviewhasindicatedthathighviscosityasphaltbindersofferincreasedresistancetostrippingcomparedtolowviscosityasphaltbinders,allotherthingsbeingequal.

Thetwovariablemodel(seeTable7)2forTSRobtainedat0.8F/Aratioismuchbetterthanthat

obtainedata1.5F/Aratio.IthasaRvalueof0.98(P=0.003)andithasD10andmethyleneblueastheprimaryandsecondaryindependentvariablesaffectingHMAstripping.This

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Table7.RegressionEquationsBetweenP200AggregateTestsandStripping

0.8F/AGradation

Performance Step Dependent Independent Equation R2 P

Parameter

Stripping 1 TSR D10 TSR=71.21-4.844(D10) 0.94 0.002

Stripping 2 TSR Methylene TSR=68.54- 0.98 0.003Blue 4.19(D10)+0.201(Methylene

Blue)

1.5F/AGradation

Performance Step Dependent Independent Equation R2 PParameter

Stripping 1 TSR D10 TSR=70.78-4.29(D10) 0.68 0.04

Stripping 2 TSR Specific TSR=95.47-8.84(D10)- 0.82 0.08Surface 0.001(SpecificSurfaceArea)Area

0.8F/AGradation

Step Dependent Independent Equation R2 PPerformanceParameter

Rutting 1 Inflection D30 InflectionPoint= 0.59 0.076Point 5496.7+478.4(D30)

Rutting 2 Inflection Rigden InflectionPoint= 0.98 0.003

Point Voids 35183.4+458.4(D30)-792.2British (RigdenVoidsBritishStandard)Standard

1.5F/AGradation

Performanc Step Dependent Independent Equation R2 PeParameter

Rutting 1 Inflection Methylene InflectionPoint=9784.9-268.6 0.31 0.25Point Blue (MethyleneBlue)

Rutting 2 Inflection Surface InflectionPoint=5792.6-359.9 0.58 0.28Point Area (MethyleneBlue)+0.39

(SurfaceArea)

indicatesthatthefineness(D10)ofthematerialaswellasthenature(methyleneblue)oftheP200materialaffectsHMAresistancetostripping(Figure4).Itappearsthatthetwo-variablemodelforTSRobtainedata1.5F/AratiohadalowerR2valueandhigherPvaluebecauselargeamountsoffinesstiffenedtheasphaltbindertoomuchandmaskedtheeffectofthenatureofthefines.

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Figure4.PredictedTSRValuesvs.ActualTSRValuesfortheTwo-Variable(D10and

MethyleneBlue)Model

BasedontheTSRobtainedbyAASHTOT283,D10andmethylenebluearetherecommendedP200aggregatetestswhicharerelatedtostrippingofHMAmixes.Asstatedearlier,D10indicatesthefinenessoftheP200materialandmethyleneblueindicatesbothfinenessandnatureoftheP200material.

HamburgWheelTrackingTheinflectionpointobtainedinthistestrepresentsthenumberof

passesatwhichstrippingstartstooccurintheHMAmix.Thelargertheinflectionpoint(numberofpasses),thehigheristhemix'sresistancetostripping.Thetwo-variablemodelforinflection

pointata1.5F/AratiohasalowR2(0.58)andhighPvalue(0.28)andtherefore,isnotconsideredstatisticallysignificant(Table7).Thismodelhasmethyleneblueandspecificsurfaceareaastheprimaryandsecondaryindependentvariablesaffectingstripping.Thehigherthemethylenebluevalue,thelowertheinflectionpointandhenceresistancetostripping.ThisisinagreementwiththeobservationmadeincaseofTSRobtainedbyAASHTOT283.

Thetwo-variablemodelforinflectionpointata0.8F/Aratioissignificantlybetterthanthatata

1.5F/Aratio(Table7).ThisisinagreementwiththetrendseeninthecaseofTSR.Thetwo-variablemodel(R2=0.98,P=0.003)hasD30astheprimaryindependentvariableandRigdenvoids,Britishstandardasthesecondaryindependentvariableaffectingresistancetostripping.It

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shouldbenotedthatD30hasahighcorrelation(R=0.99,P=0.0001)withD10whichwas

selectedastheprimaryindependentvariableincaseofTSR.ItisnotunderstoodwhytheRigdenvoids,Britishstandardwasselectedasthesecondaryindependentvariablebythestatisticalanalysis.Normally,higherRigdenvoidscausestifferF/Asystemsand,therefore,shouldresult

inincreasedresistancetostripping(orhighervaluesofinflectionpoint).However,themodelshowsanoppositeeffect,becausetheslopeofregressionisnegative.

ItshouldberealizedthatAASHTOT283andtheHamburgwheeltrackingdeviceare

significantlydifferentstrippingtests,althoughtheVTMvaluesofthetestspecimensarecomparable(71percent).AASHTOT283involvescuringofthemixina60Covenfor16hoursfollowedbyvacuumsaturationofHMA,thenimmersioninahot(60C)waterbathfor24hours,transferto25Cwaterbathfortwohours,andthentestingfortensilestrength.Hamburgwheeltrackingdoesnotinvolveanyvacuumsaturation.ItdoesinvolveimmersionoftheHMAina50Cwaterbath.However,whileimmersed,thesampleissubjectedtotheloadedwheeltrackingdeviceandrutdepthmeasurementsaretaken.Arepeated,dynamicmechanicalloadisappliedtotheHMAinHamburgwheeltrackingdevicewhereasnosuchloadingisappliedin

AASHTOT283.TheconditioningandtestingofHMAissignificantlydifferentinthesetwotests.Therefore,itisnotsurprisingthatdifferentindependentvariableswereselectedinthesetwomixvalidationtests.

ItisrecommendedthatD10andmethylenebluebeusedforHMAperformanceintermsof

stripping,takingintoconsiderationbothAASHTOT283andHamburgwheeltrackingtests.

D10istheprimaryindependentvariableincaseofTSR.IthashighcorrelationwithD30

(R=0.992,P=0.0001)whichwasselectedastheprimaryindependentvariableinHamburgwheeltrackingtest.

MethyleneblueisthesecondaryindependentvariableincaseofTSR.Thistestindicatesthe

natureandfinenessoftheP200material.

CONCLUSIONSANDRECOMMENDATIONS

Thefollowingconclusionscanbedrawnfromthisstudy.

1.Permanentdeformation.ThepermanentdeformationdataobtainedbytheSuperpavesheartesterintermsofG*/sin*@0.1hertzandmvalue(slopeoffrequencyvs.G*plot)indicatesthatD60(theparticlesizeofP200materialat60%passing)istheprimaryindependentvariableandthemethylenebluevalueisthesecondaryindependentvariableaffectingpermanentdeformationofHMAmixtures.ItappearsthatthefinertheP200material,themoreitmodifiestheasphaltbinderandstiffenstheHMAmix.BothlowervaluesofD60andhighervaluesofmethyleneblueindicatefinerP200material.

2.Fatiguecracking.ThefatiguecrackingdataobtainedbytheSuperpavesheartesterin

termsofG*/sin*@1hertzdidnotindicateanystatisticallysignificantcorrelationwithanyoftheP200propertiesevaluatedinthisstudy.

3.Stripping.ThestrippingdataobtainedbyAASHTOT283indicatesthatD10(theparticlesizeofP200at10%passing)istheprimaryindependentvariableandmethyleneblueisthesecondaryindependentvariableaffectingthestrippingpotentialofHMAmixes.D10indicatesthefinenessoftheP200materialandmethyleneblueindicatesbothfinenessandnatureoftheP200material.

ThefollowingteststhatarerelatedtoHMAperformancearerecommendedforevaluating

aggregatesforhotmixasphaltmixtures.

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PerformanceParameterPermanentDeformationFatigueCracking

Stripping

RecommendedP200TestD60andMethyleneBlueNone

D10andMethyleneBlue

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September1975.BS812:MethodsforSamplingandTestingofMineralAggregates,SandsandProperties.BritishStandardInstitution,London,1975.Anderson,D.A.GuidelinesonUseofBaghouseFines.NAPA,InformationServices101,1987.InternationalSlurrySealAssociation.TestMethodforDeterminationofMethyleneBlueAbsorptionValue(MBV)ofMineralAggregateFillersandFines.ISSA,Bulletin145,1989.TestMethodforDeterminingthePermanentDeformationandFatigueCrackingCharacteristicsofHotMixAsphalt(HMA)UsingtheSimpleShearTest(SST)Device.TP7-94,AASHTOProvisionalStandards,June1996.TestMethodforDeterminingCreepComplianceandStrengthofHotMixAsphaltUsingtheIndirectTensileTestDevice.TP9-94,AASHTOProvisionalStandards,June1996.

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