effect of aggregate gradation on measured asphalt content

8/9/2019 Effect of Aggregate Gradation on Measured Asphalt Content

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EFFECTOFAGGREGATEGRADATIONONMEASUREDASPHALT CONTENT

By

PrithviS.Kandhal

AssistantDirectorNationalCenterforAsphaltTechnology

AuburnUniversity,Alabama

StephenA.Cross

AssistantProfessorUniversityofKansas

PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1417,1993


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DISCLAIMER

Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

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ABSTRACT

Itisnecessarytocontroltheasphaltcontentcloselyinhotmixasphalt(HMA)mixestoobtainoptimumserviceabilityanddurability.However,coarsermixes(binderandbasecourses)madewithlargermaximumparticle-sizedaggregatetendtosegregate,TheresultingvariationintheaggregategradationofthesampledHMAmixcansignificantlyaffectthemeasuredasphaltcontent.Theobjectiveofthisresearchwastoevaluatetheeffectofaggregategradationonthemeasuredasphaltcontent.

Actualmixcomposition(asphaltcontentandgradation)datafromamajorinterstatepaving

projectwasobtainedandanalyzed.Atotalof547bindercourseand147wearingcoursemixsampleswereobtainedbehindthepaverandsubjectedtoextractionanalysis,Asubstantialamountofsegregationwasobservedinthebindercoursemixwhichprovidedtheopportunitytocorrelatetheaggregategradationwiththemeasuredasphaltcontent.

Someofthedeviationinthemeasuredasphaltcontentofthebindercoursemixesfromthejobmixformula(JMF)wasdeterminedtobetheresultofthechangeingradationofthemixfromtheJMF.Thepercentagesofmaterialpassingthe4.75mm(No.4)and2.36mm(No.8)sievesarecorrelatedwithmeasuredasphaltcontents.Forsegregatedbindercoursemixesevaluatedinthisstudy,equationsweredevelopedtoadjustthemeasuredasphaltcontenttoaccountforthechangeingradationfromtheJMFasmeasuredonthe12.5mm(1/2inch)andeither4.75mm(No.4)or2.36mm(No.8)sieves.

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EFFECTOFAGGREGATEGRADATIONONMEASUREDASPHALTCONTENT

PrithviS.KandhalandStephenA.Cross

INTRODUCTIONAsphaltcontentmustbecloselycontrolledinhotmixasphalt(HMA)mixestoobtainoptimumserviceabilityanddurability.AHMApavementcanraveland/orcrackifitisdeficientinasphaltcontentbyaslittleas1/2percent,whereas1/2percentexcessiveasphaltcontentcancauseflushingandrutting.Qualitycontrol(QC)andqualityassurance(QA)ofHMApavementsgenerallyrequirethemeasurementofasphaltcontentinHMAmixesduringproductionusingeitherastandardextractiontestoranuclearasphaltcontentgauge.However,themeasuredvaluecanvaryfromtesttotestbecauseofmaterial,sampling,andtestingvariability.Inrecentyears,thematerialvariabilityhasbeenreducedsubstantiallybytheuseofautomatedHMAfacilities.Testingproficiencycanbeimprovedthroughtraining.ObtainingarepresentativeHMAsamplefortestingstillremainsaproblemeitherbecauseofsegregationorineffectivesampling/splittingtechniques.Whencoarsermixes(binderandbasecourses)madewithlargermaximumparticle-sizedaggregatesareinvolved,thesamplingvariationcanovershadowthematerialvariationandtestingvariation.CoarseHMAmixestendtosegregate.ThecoarseaggregatefractionintheHMAmixholdslessasphaltcementbyweightcomparedtothefineaggregatefraction,Segregationcausestheproportionsofcoarseandfineaggregateparticles(therefore,thegradation)tovaryinHMAsamplesandthusaffectthemeasuredasphaltcontents.ThereisaneedtoevaluatetheeffectofaggregategradationonmeasuredasphaltcontentsothatanadjustedasphaltcontentwhichisclosertotheasphaltcontentactuallyincorporatedintheHMAmix,canbeascertained.

PROJECTDETAILSThetestdataforthisstudywasobtainedfromamajor4-laneinterstatepavingprojectinPennsylvania.Thisrehabilitationprojectinvolved50.8mm(2inches)ofPennsylvaniaID-2bindercourse(adensegradedbindermixwith38,1mmor11/2inchmaximumaggregatesize)and38.1mm(11/2inches)ofPennsylvaniaID-2wearingcourse(adensegradedwearingmixwith12.5mmor1/2inchmaximumaggregatesize).Thejob-mixformulas(JMF)forthebinderandwearingcoursemixturesaregiveninTables1and2,respectively.Northbound(NB)andsouthbound(SB)laneswerepavedwithseparatepavers.SincethemixacceptanceorQAsampleswereobtainedbehindeachpaverseparately,thetestdatahasbeenreportedandanalyzedseparatelyforNBandSBlanes.PennsylvaniaDepartmentofTransportation(PennDOT)hasastatisticallybasedendresultspecificationforHMApavements

whichrequiresobtainingloosemixsamplesbehindthepaveratrandomlocations.Theentireloosemixisscrapedoutofawelldefinedarea(usually229mmx229mmor9inchesx9inches)attheselectedrandomlocationtominimizesegregationduetosamplingoperation.Fiveloosemixsubletsamplesareobtainedforeachlotconsistingofabout500Mg(550tons).ThesesamplesaresenttoPennDOTcentrallaboratoryforextractiontodeterminethemixcomposition.Roadwaycoresarealsoobtainedaftercompactionandsenttothecentrallaboratoryfordeterminingthepavementdensity.Priceadjustmentsforeachlotarecalculatedbythecentrallaboratorythepercentageofmaterialpassing75:mbasedonthreepayitems:asphaltcontent,(No.200)sieve,andtheroadwaydensity.

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Table1.SummaryStatisticsforBinderMixes

TestParameter

JMF NBLanes

n=271

SBLanes

n=276

All

n=547

Mean Std.Dev. Mean Std.Dev. Mean Std.Dev.

Asphalt 4.8 4.70 0.429 4.66 0.416 4.68 0.422Content(%)

Density(pcf) N/A 153.6 1.69 153.5 1.96 153.6 1.83

1-1/2inch 100 99.9 0.77 100.0 0.00 100.0 0.54(%)

1inch(%) 92 92.2 6.74 91.9 5.16 92.0 5.99

1/2inch(%) 56 63.0 8.32 62.2 7.78 62.6 8.05

No.4(%) 39 40.4 5.19 42.7 5.81 41.5 5.63

No.8(%) 30 30.8 3.77 32.3 4.07 31.6 4.00No.16(%) 19 22.1 2.70 22.2 2.81 22.2 2.75

No.30(%) 12 16.3 2.27 15.7 2.16 16.0 2.23

No.50(%) 8 11.2 1.67 10.5 1.69 10.8 1.71

No.100(%) 6 7.59 0.984 7.42 1.094 7.51 1.044

No.200(%) 4.8 5.34 0.693 5.37 0.807 5.36 0.752

Table2.SummaryStatisticsforWearingMixes

Test

Parameter

JMF NBLanes

n=67

SBLanes

n=80

All

n=147Mean Std.Dev. Mean Std.Dev. Mean Std.Dev.

Asphalt 6.6 6.37 0.270 6.45 0.342 6.41 0.313Content(%)

Density(pcf) N/A 143.6 2.38 142.5 2.70 143.0 2.61

1/2Inch(%) 100 100.0 0.00 100.0 0.00 100.0 0.00

3/8Inch(%) 96 96.6 1.43 96.8 1.48 96.7 1.46

No.4(%) 72 70.8 4.35 71.8 3.36 71.3 3.86

No.8(%) 48 49.4 3.82 49.8 2.35 49.6 3.10

No.16(%) 34 35.0 2.49 34.9 1.49 34.9 2.00No.30(%) 24 25.7 1.88 25.5 1.17 25.6 1.53

No.50(%) 16 16.4 1.83 16.6 1.36 16.5 1.59

No.100(%) 10 9.28 1.253 9.54 0.913 9.42 1.085

No.200(%) 4.5 5.54 0.779 5.57 0.654 5.56 0.711

Atotalof547bindermixsamples(271inNBlanesand276147wearingmixsamples(67inNBlanesand80inSBlanes)wereinSBlanes)andobtainedbehindthepaverandtestedbythecentrallaboratory.

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Asubstantialamountofsegregationwasobservedinthecompactedbindercoursemixofthis

projectapparentlyduetomixhandlingandplacingoperations.Obviously,themixgradationofsubletsamplesobtainedbehindthepavervariedconsiderablyanditaffectedtheextractedasphaltcontent.Sincealargenumberofbindermixsampleswereobtainedatrandomlocations

behindthepaveronthisprojectandwereanalyzedformixcomposition(asphaltcontentandgradation),auniqueopportunitywasavailableforevaluatingtheeffectofaggregategradationonthemeasuredasphaltcontents.MaterialproductionvariabilitywasconsideredtobeminimalonthisprojectbecauseanautomatedHMAfacilitywasused,andthemixsamplesobtainedatthefacilitywerereasonablyuniformincomposition.ThetestingvariabilityisalsoconsideredtobeminimalbecauseallextractiontestingwasdoneintheDOTcentrallaboratorybyessentiallythesametestingcrew.ASTMD2172(MethodD)wasusedforextractingtheasphaltcementfromHMAmixsamples.

Itispossibletoconductasimilarstudyinalaboratory.Amixcanbepreparedwithaknown

asphaltcontent,intentionallysegregated,andthenextracted.Thiswouldeliminatetheinherentmaterialvariation.However,itisnotpossibletosimulatethesegregationwhichoccursinthe

field.Also,itisnotpracticaltotestaverylargenumberofsamplesaswasdoneinthisstudy.TESTRESULTS

Duetospacerestrictionsitisnotpossibletoincludethemixcompositiontestdatafor547bindermixsamplesand147wearingmixsamplesinthispaper.However,Tables1and2givethesummarystatisticsforbindermixesandwearingmixes,respectively.Figures1,2,3and4givethecontrolchartsofthetestdataforasphaltcontent,thepercentpassingthe12.5mm(1/2inch),4.75mm(No.4),and2.36mm(No.8)sievesfor271bindermixsamplesobtainedfromtheNBlanesofthepavingproject.ThecontrolchartsofthetestdatafromtheSBlanesaresimilartothoseoftheNBlanesand,therefore,arenotincludedduetospacelimitationsinthepaper.

ANALYSISOFTESTRESULTS

Thepurposeofthisstudywastodeterminetheeffectofachangeingradationonthecorrespondingmeasuredasphaltcontent.Ifastrongcorrelationexistsbetweengradationandasphaltcontent,thenapartofthedeviationfromtheJMFinthemeasuredasphaltcontentcouldbeexplainedbythemeasureddeviationingradation.

Asmentionedearlier,thesummarystatisticsofmeanandstandarddeviationforthequality

assurancedataisshowninTable1forthebindermixesandTable2forthewearingmixes.Forthebindermixes,thestandarddeviationisover5percentforpercentpassingthe25.4mm(1inch),12.5mm(1/2inch)and4.75mm(No.4)sieves,and0.42percentforasphaltcontent.

Table2showslowerstandarddeviationsforthewearingmixesformostsievesizes,andnoneof

thesievesizeshadastandarddeviationover3.9percent.Thestandarddeviationforasphalt

contentwas0.31YOforthewearingmixes.However,areviewofthecontrolchartsshowedthestandarddeviationforasphaltcontentmightbeartificiallyhighduetoanapparentchangeintheJMFasphaltcontentbythecontractorwhichdidnotappearinthetestrecords.

Controlchartsofthetestdataforasphaltcontentandthepercentpassingthe12.5mm(1/2inch),

4.75mm(No.4),and2.36mm(No.8)sievesforthebindermixes(NBlanes)areshowninFigures1-4.Thepermissibletolerancelimitsforthesefourtestparameterswere0.5,8,and6percent,respectively.Tables3and4showthefrequencythattheabovetestparameterswerewithinandoutsidethespecificationtolerancelimitsforthebinderandwearingmixes,respectively.Forthebindermix,asphaltcontentwasoutsidethespecificationlimits23.4percentofthetimeandthepercentpassingthe12.5mm(1/2inch),4.75mm(No.4),and2.36mm(No.8)sieves28.9,20.3,and17.5percentofthetime,respectively.Fromthecontrolchartsandthedata

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Figure1.ControlChartforAsphaltContentinBinderMixes(NBLanes)

Figure2.ControlChartforPassing1/2InchSieveinBinderMixes (NBLanes)

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Figure3.ControlChartforPassingNo.4SieveinBinderMixes(NB Lanes)

Figure4.ControlChartforPassingNo.8SieveinBinderMixes (NBLanes)

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inTable3,itisobviousthatthebindermixsampledfromtheroadwaywasnotuniform.Review

ofthetestdataandvisualobservationsshowedsegregationofthemixtobeamajorproblemonboththeNBandSBlanes.

Table3.FrequencyDistributionofTestDataforBinderMixes

AsphaltContent

PercentPassing1/2InchSieve

PercentPassingNo.4Sieve


InSpec.

Out-Low

Out-High

InSpec.

Out-Low

Out-High

InSpec.

Out-Low

Out-High

InSpec.

Out-Low

Out-High

NBLanes

74.2

15.9

9.9

67.5

9.2

23.3

84.9

1.5

13.6

87.8

2.2

10.0

SBLanes

79.0

16.7

4.3

74.6

9.8

15.6

74.6

1.5

23.9

77.2

1.8

21.0

All

76.6

16.3

7.1

71.1

9.5

19.4

79.7

1.5

18.8

82.5

2.0

15.5

Table4.FrequencyDistributionofTestDataforWearingMixes

AsphaltContent



InSpec.

Out-Low

Out-High

InSpec.

Out-Low

Out-High

InSpec.

Out-Low

Out-High

NBLanes

76.1

23.9

0.00

95.5

3.0

1.5

89.5

1.5

9.0

SBLanes

80.0

12.5

7.5

100.0

0.0

0.0

98.8

0.0

1.2

All

78.2

17.7

4.1

97.9

1.4

0.7

94.5

0.7

4.8

Table4showsthefrequencythatthewearingmixtestparametersofasphaltcontentandthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sieveswerewithinspecificationtolerancelimits.Thepermissibletolerancelimitsforthesethreetestparameterswere0.4,8,and6percent,respectively.Asphaltcontentwasoutsidethespecificationlimits21.8percentofthetime,andthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sieves2.1and5.5percentofthetime,respectively.Reviewofthecontrolchartsandtestdatashowedthatthegradationofthemixwaswithinprojectlimits95percentofthetime.SomeofthescatterinasphaltcontentoccurredwhenthecontractorloweredtheasphaltcontentontheNBlanesfrom6.6percenttoapproximately6.2percentafter35tests.However,theavailabletestdatadidnotshowacorrespondingchangeintheJMFasphaltcontent.IftheJMFhadbeenchangedto6.2percent,asthedataindicates,andtheapplicabletoleranceof0.4percentapplied,thepercentof

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theasphaltcontenttestswithinspecificationlimitswouldchangefrom76.1percentto97.0

percentfortheNBlanesandfrom78.2percentto87.8percentforallofthedata.

Correlationanalysiswasperformedtodetermineifthematdensityorthepercentagespassing

varioussievesizescorrelatewithasphaltcontent.Table5showstheresultsofthecorrelationanalysisforthebindermixes,bylane,andwithallofthedata.Theresultsshowalloftheparametersexceptunitweight(densityofthecoresamples)andpercentpassingthe38.1mm(11/2inch)sievehaveahighprobabilityofatruecorrelation(alpha=0.0001)withasphaltcontent.Thebestcorrelationswithasphaltcontentforthebindermixeswerewiththepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sieves.

Table5.SummaryofCorrelationCoefficients(R)withAsphaltContentforBinderMixes

Parameter

R

NBLanes

n=271

Alpha*

R

SBLanes

n=276

Alpha*

R

All

n=547

Alpha*

Density 0.121 0.0474 -0.033 0.589 0.040 0.354611/2Inch 0.056 0.3577 N/A N/A N/A N/A1

Inch 0.413 0.0001 0.517 0.0001 0.455 0.0001

1/2Inch 0.649 0.0001 0.790 0.0001 0.716 0.0001

No.4 0.822 0.0001 0.842 0.0001 0.800 0.0001

No.8 0.819 0.0001 0.825 0.0001 0.795 0.0001

No.16 0.738 0.0001 0.682 0.0001 0.707 0.0001

No.30 0.635 0.0001 0.556 0.0001 0.597 0.0001

No.50 0.586 0.0001 0.457 0.0001 0.521 0.0001

No.100 0.640 0.0001 0.474 0.0001 0.554 0.0001

No.200 0.611 0.0001 0.476 0.0001 0.535 0.0001*1-Alpha=Probabilitycorrelationcoefficient(R)notequalto0. TheresultsofthecorrelationanalysisforthewearingmixesareshowninTable6.Theanalysisshowsthehighestprobabilityofatruecorrelation(alpha=0.0001)withasphaltcontentforthe

percentpassingthe300 :m2(No.50),150:m(No.100)and75:m(No.200)sieves.However,the

correlationcoefficients(R)arenotonlytoolowtobeuseful,theyindicateanunexpectedtrend,thatis,theasphaltcontentdecreaseswithincreaseinthematerialpassingthesesieves.

Tofurtherinvestigatetherelationshipbetweenasphaltcontentandgradation,regressionanalysiswasperformed.Thepurposeofthisstudyistodetermineifasphaltcontentcouldbepredictedfrommeasuredgradation;therefore,asphaltcontentwasselectedasthedependentvariableandgradationtheindependentvariable,Table7isasummaryofthebestcoefficientsofdetermination(R2),bylaneandbymixtype,forthebinderandwearingmixes.

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Table6.SummaryofCorrelationCoefficients(R)withAsphaltContentforWearingMixes

Parameter

R

NBLanes

n=67

Alpha*

R

SBLanes

n=80

Alpha*

R

ALL

n=147

Alpha*

Density -0.022 0.8577 -0.003 0.9807 -0.038 0.6489

1/2Inch N/A N/A N/A N/A N/A N/A

3/8Inch 0.443 0.0002 0.114 0.3135 0.247 0.0025

No.4 -0.106 0.3942 0.073 0.5174 0.009 0.9144

No.8 -0.165 0.1824 0.124 0.2716 -0.014 0.8653

No.16 -0.113 0.3637 0.242 0.0307 0.050 0.5495

No.30 -0.264 0.0308 0.078 0.4940 -0.101 0.2229

No.50 -0.418 0.0004 -0.330 0.0028 -0.345 0.0001

No.100 -0.326 0.0071 -0.490 0.0001 -0.375 0.0001

No.200 -0.257 0.0356 -0.522 0.0001 391 0.0001*1-Alpha=Probabilitycorrelationcoefficient(R)notequalto0. ThedatainTable7indicatesthatnocorrelationexistsbetweenasphaltcontentandthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sievesforthewearingmix.Thereisverylittlespreadinthegradationdata,andnosegregationwasobservedinthefield.Therefore,allofthescatterappearstobeduetothenormalvariationinthematerial,samplingandtestingoperations.

Table7.SummaryofCoefficientsofDetermination(R2)withAsphaltContentfor

Id2Mixes

NumberofObservations

IndependentVariable

1/2InchSieve

No.4Sieve

No.8Sieve

1/2Inch&No.4Sieves

1/2Inch&No.8Sieves

No.4Sieve

No.8Sieve

N13Lanes

n=271

R2

0.422

0.676

0.671

0.686

0.685

0.011

0.027

SBLanes

n=276

R2

ID2BinderMixes

0.625

0.708

0.680

0.722

0.729

ID2WearingMixes

0.005

0.016

All

n=547

R2

0.515

0.640

0.632

0.669

0.676

0.000

0.000

Figures5and6showtherelationshipbetweenasphaltcontentandthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sievesforthebindermixinbothlanes,respectively.Theresultsshowthatthereisarelationshipbetweenchangeingradationandmeasuredasphaltcontent.Therelationshipsshowthatasthemixbecomesfinerforthegivensievesize,theasphaltcontentincreases.Therelationshipshavethefollowingform:

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Figure5.PercentagePassingNo.4Sievevs.AsphaltContent(BinderMixesfromBothLanes)

Figure6.PercentagePassingNo.8Sievevs.AsphaltContent(BinderMixesfromBothLanes)

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AC=2.186+0.060(P4) (1)

R-square=0.64

AC=2.025+0.084(P8) (2)

R-square=0.63

where,AC=AsphaltcontentP4=Percentpassingthe4.75mm(No.4)sieveP8=Percentpassingthe2.36mm(No.8)sieve

Equations1and2indicatethatthemeasuredasphaltcontentsofthebindercoursemixinthis

studyincreaseby0.06and0.08percent(basedonslopesoftheregressionlines)witheachonepercentincreaseinthematerialpassing4.75mm(No.4)and2.36mm(No.8)sieves,respectively,fromtheJMF.Conversely,therewillbeasimilardecreaseinthemeasuredasphaltcontentsifthesampledmixiscoarserthantheJMF.Theseso-called"correctionfactors"canbe

usedtocorrectthemeasuredasphaltcontentforeachonepercentdeviationfromtheJMF.Someresearchers(1,2,and3)havedevelopedthefollowing"correctionfactors"forbindercoursemixes(maximumaggregatesizegreaterthan25.4mmor1inch)basedonthematerialpassing2.36mm(No.8)sieveafteranalyzinglimitedfielddata.

CorrectionFactor,%

CustomaryinUKforrolled-asphaltmixpriorto1970(1)

GoodsallandMathews(l)

Warden(2)

Brownetal(3)

KandhalandCross(Thispaper)

0.08

0.14

0.16

0.10

0.08The"correctionfactor"isexpectedtobegenerallydependentonthefineaggregategradation,theparticleshapeandsurfacetextureoftheaggregates,andtheactualasphaltcontentofthebindercoursemix.Furtheranalysiswasperformedtodetermineifamulti-variablemodelwouldgiveastatisticallystrongermodel.Thebestmulti-variablemodelwasfoundbyincludingthe12.5mm(1/2inch)sievewitheitherthe4.75mm(No.4)or2.36mm(No.8)sieve.Therelationshipbetweenasphaltcontentandthepercentpassingthe12.5mm(1/2inch)sieveisshowninFigure7.TherelationshiphasanR2of0.52.Bycombiningthe12.5mm(1/2inch)sievewiththe4.75mm(No.

4)sievethemodelhasanR2

of0.67.Therelationshiphasthefollowingform:AC=1.947+0.014(P1/2)+0.045(P4) (3)

R-square=0.67

Where,

AC=AsphaltcontentP1/2=Percentpassing12.5mm(1/2inch)sieveP4=Percentpassing4.75mm(No.4)sieve

Aslightlystrongermodelwasfoundutilizingthe12.5mm(1/2inch)and2.36mm(No.8)sieves.

TherelationshipisshowninFigure8andhasthefollowingform:

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Figure7.PercentagePassing1/2InchSievevs.AsphaltContent(BinderMixesfromBothLanes)

Figure8.Actualvs.PredictedAsphaltContent(BinderMixesfromBothLanes)

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AC=1.757+0.016(P1/2)+0.061(P8) (4)

R-square=0.68where,

AC=Asphaltcontent

P1/2=Percentpassing12.5mm(1/2inch)sieveP8=Percentpassing2.36mm(No.8)sieve

ThedatashowninFigures6-8showthatthemeasuredasphaltcontentisaffectedbyachangein

gradation.Achangeingradationwillcauseacorrespondingchangeinthemeasuredasphaltcontent.Byutilizingeitheroftheabovefourmodels,themeasuredasphaltcontentcanbeadjustedfortheamountcausedbythechangeingradation.TheadjustedasphaltcontentcanthenbecheckedagainstthetolerancelimitsfortheJMFasphaltcontenttodetermineifthevariationinasphaltcontentisduetothechangeingradation,segregation,oratruechangeintheasphaltcontent.

Tocheckthemodelsdeveloped,themeasuredasphaltcontentswereadjustedforthemeasured

changeingradationusingequations1,2and4.Theadjustedasphaltcontent(AAC)isdeterminedbyaddingthedifferencebetweenthemeasuredasphaltcontent(MAC)andthepredictedasphaltcontent(PAC),totheJMF.TheadjustedasphaltcontentisthencheckedagainsttheupperandlowertolerancelimitsoftheJMFasphaltcontent.

where,

AAC=JMFAC+(MAC-PAC)

AAC=AsphaltcontentadjustedforgradationJMFAC=JobmixformulaasphaltcontentMAC=MeasuredasphaltcontentPAC=PredictedasphaltcontentfromEq.1,2,3or4

(5)

Figure9showsthecontrolchartsfortheasphaltcontentadjustedutilizingequation5forbindermixsamplesfromNBlanes.Table8showsthefrequencythattheadjustedasphaltcontent,adjustedutilizingequations1,2and4,arewithinspecificationlimits.Theresultsshow95percentoftheadjustedasphaltcontentswithinspecificationlimitsregardlessoftheequationsutilized.Theadjustedasphaltcontentsforthebindermixshowacompliancepercentageverysimilartothatobtainedforthewearingmixeswheresegregationwasnotaproblem.

Table8.FrequencyDistributionofAdjustedAsphaltContentforBinderMixes

AsphaltContent NBLanes SBLanes All

InSpec. 93.7 96.7 95.2

AdjustedonNo.Out-Low 0.4 0.8 0.5

4Sieve(Eq.1)Out-High 5.9 2.5 4.2

InSpec. 94.1 96.0 95.1

AdjustedonNo.Out-Low

8Sieve(Eq.2)Out-High

0.4

5.5

2.9

1.1

1.6

3.3

Adjustedon

1/2"&No.8Sieve(Eq.4)

InSpec.

Out-Low

Out-High

94.8

1.5

3.7

96.4

0.7

2.9

95.6

1.1

3.3

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Figure9.ControlChartforAsphaltContentAdjustedfor1/2InchandNo.8Sieves(BinderMixesfromNBLanes)

CONCLUSIONSANDRECOMMENDATIONS

Basedonthedataobtainedinthisstudythefollowingconclusionsarewarranted.1.InsegregatedHMApavements,someofthedeviationinasphaltcontentfromthejobmixformula(JMF)iscontrolledbythechangeingradationofthemixfromtheJMF.

2.Whensegregatedbindercoursemixesweresampledbehindthepaver,thepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sievescorrelatedwithmeasuredasphaltcontent.

3.Forsegregatedbindercoursemixes,theasphaltcontentcanbeadjustedtoaccountforthechangeingradationfromtheJMFasmeasuredonthe12.5mm(1/2inch)andeitherthe4.75mm(No.4)or2.36mm(No.8)sievesasshowninequations3and4.However,theseequationsarevalidfortheaggregatesandtheJMFusedinthisstudy.Careshouldbetakeninapplyingtheseformulastoothermixes.

4.Sincenosignificantsegregationoccurredduringthelaydownofthewearingcoursemix,gradationcouldnotberelatedtothemeasuredasphaltcontent.

DISCLAIMER

Theopinions,findings,andconclusionsexpressedherearethoseoftheauthorsandnotnecessarilythoseoftheNationalCenterforAsphaltTechnologyorAuburnUniversityortheUniversityofKansas.

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REFERENCES

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effect of aggregate gradation on measured asphalt content

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