RESILIENT MODULUS OF MALAYSIAN BASE AND SUBBASE …

Journal - The Institution of Engineers, Malaysia (Vol. 69, No.2, June 2008)54

RESILIENT MODULUS OF MALAYSIAN BASE AND SUBBASE PAVEMENT MATERIALS

(Date received: 24.8.2006)

Ahmad Kamil Arshad and Mohd. Yusof Abd. Rahman * Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 UITM Shah Alam, Selangor

E-mail: [email protected]

ABSTRACT Pavement design approach is shifting towards analytical or mechanistic-based procedures. Resilient modulus is a fundamental parameter used in the procedure and a study was carried out to characterise the parameter for base and subbase pavement materials used in Malaysia according to the Public Works Department of Malaysia’s (PWD) Specification for Road Works (JKR/SPJ/1988). This paper details the study and describes the materials tested, the methodology used and the results obtained from the study. In this study, base (Type II) and subbase (Type E) specimens of 100 mm diameter x 200 mm height were tested using the repeated load triaxial test in accordance with AASHTO T307-99. In addition, the test was carried out at different gradation compositions (but within the required gradation envelope) and moisture contents to study their effects on the resilient modulus value. From the test, the k-θ model was used to characterise the base and subbase materials. Finally, recommendations on a set of resilient modulus values for Malaysian base and subbase materials to be used for mechanistic design of flexible pavements were made, taking into account of the Malaysian environment.

Keywords: Base and Subbase Materials, Flexible Pavement Design, Pavement Materials, Resilient Modulus

(Note: As most of the literature reviewed used U.S. Customary Units, this article used similar units for the purpose of comparing the findings. For conversion: 1 kPa = 6.9 psi)

1 INTRODUCTION AtypicalflexiblepavementinMalaysiaconsistsofasphalticconcretewearingandbindercourse,crushedaggregateorwet-mixbaselayerandgranularsubbase(river/miningsandorquarrydust).Incertaincircumstances,particularlywherethetrafficloadingsarehigh,additionalbituminousmacadamroadbaselayerisincludedabovethecrushedaggregate/wet-mixbaselayer. Current Public Works Department of Malaysia’s (PWDMalaysia) Specifications for Road Works (JKR/SPJ/1988) isa “recipe-based” specification that requires flexible pavementmaterialstocomplywiththephysicalpropertiesdescribedinthespecification [1], such as gradation, compaction density, CBRvalueandplasticity indexformixaggregates,baseandsubbasematerials(Table1).Thesepropertiesensurethatthematerialsareofaspecifiedqualitybutdonotmeasurethestructuralpropertiesrequiredasinputformechanisticpavementdesignmethod.

Requirements Subbase Base

PlasticityIndexLiquidLimitAggregateCrushingValueCBRSoundness(SodiumSulphate)FlakinessIndexFracturedFace(4.75mmsieve)

≤6≤25%≤35≥30---

≤6-

≤30≥30

≤12%≤30

≥80%

Resilientmodulus (MR) isa fundamentalparameterused in themechanisticpavementdesignprocedureandisdefinedastheratioofdeviatorstress,σdovertherecoverablestrain,εr[2]: σdMR=––– (1) εr

A laboratory study was carried out to characterise resilientmodulus for base and subbase pavement materials used inMalaysia according to PWDMalaysia’s Specification for RoadWorks(JKR/SPJ/1988).ThematerialstestedincludebasetypeIIusingcrushed rockaggregates and subbase typeEusingquarrydustandminingsand. The objective of the laboratory tests is to determine thevalues or range of values of resilient modulus for typicalMalaysianflexiblematerialssothatthesecanbeusedinroutinemechanisticbasedflexiblepavementdesign.Testingwascarriedout at different gradation compositions (butwithin the requiredgradationenvelope)andmoisturecontentstostudytheireffectsontheresilientmodulusvalue.

2 LITERATURE REVIEWA The Importance of Resilient Modulus The development of mechanistic-based pavement designproceduressuchastheShellPavementDesignManual[3]andtheAsphaltInstitute’sThicknessDesignManual(MS-1)9thedition[4]providetheneedforthemeasurementofresilientmodulusasinputformechanisticdesignofflexiblepavements.Inmechanisticdesign, flexible pavement ismodeled as amulti-layered system

Table 1: PWD Malaysia’s requirements for subbase and base materials [1]


Journal - The Institution of Engineers, Malaysia (Vol. 69, No.2, June 2008) 55

andrequired inputssuchas thematerialproperties, thicknessofeach layerand traffic loadings.Thematerialproperties requiredaretheelasticmodulusandPoisson’sratio(usuallyassumedfromotherstudies).AccordingtoHuang[2],theelasticmodulustobeusedistheresilientmodulus. In addition, although the AASHTO Guide for Design ofPavement Structures [5] is still empirical, the determination oflayercoefficientsforitsdesignprocedurerequiresinputvaluesofresilientmodulusforsubgrade,subbaseandbaselayers.AASHTO[5] recommended direct laboratory measurement using theAASHTOMethodT274-82 for subgrade and unbound granularmaterials(includingbaseandsubbase)andASTMD4123-82forasphaltic concrete andasphalt stabilisedmaterials.Furthermore,the increasing use of performance-based specifications requiresthemeasurement of resilientmodulus of pavementmaterials asoneofthekeypropertiestobeachieved.

B Factors Affecting the Resilient Modulus of Granular Materials Theresilientmodulusofgranularmaterialsareknowntobeafunctionoffactorssuchasstresslevel,density,grading,finescontent, maximum grain size, aggregate type, particle shape,moisturecontent,stresshistoryandnumberof loadapplications[6]. However,most researchers agreed that themost influentialfactorsarethelevelofappliedstressandtheamountofmoisturecontentinthematerial. In a recent study by Khogali and Zeghal [7], fourparameters that affect the resilientmoduluswere investigated,namely:deviatorstress,confiningpressure,moisturecontentandmaterialdrydensity.Itwasfoundthatdeviatorstressisthemostsignificant factor followed by the effect of moisture content.Theremainingfactorsappearedtohavelittleornoeffectontheresilientmodulusvalue.

C Constitutive Models for Material Characterisation Thelaboratorytestingofabaseorsubbasematerialwillprovidedataforconstitutivemodelingofresilientmodulusbehaviouroverarangeofappliedstress.Thepavementresponsesthataretobecalculatedusingmultilayerelasticanalysisaredependentontheconstitutive model selected to represent the materials’ resilientmodulusbehaviour.Variousconstitutivemodelshavebeenusedforpavementdesign. Theconstitutiveequations thathavebeenusedwithvaryingcomplexitiesaregivenbelow:Fine-GrainedSoils–1986/93AASHTODesignGuide[5]: MR=K1(σd)

K3 (2) Coarse-GrainedSoils–1986/93AASHTODesignGuide[5]:

MR=K1(θ)K2 (3)

UniversalEquation(Uzan,1985)[8]:

[θ ]K2 [ θd]

K3 MR=K1Pa

_____ (4) PaPa

ExpandedUniversalConstitutiveEquation(NCHRPProject1-28A)[9]:

θ –3k4 k2 τoct k3

MR=k1pa [______] [ ___ +1] (5)

pa pa

where, θ = σ1 + σ2 + σ3

1 __________________________ τoct = __ √(σ1 – σ2)

2+(σ1 – σ3)2+(σ2 – σ3)

2

3where pa=Atmosphericpressure. θ=Bulkstress: σd =Deviatorstress. σ1=Majorprincipalstress. σ2 =Intermediateprincipalstress. σ3=Minorprincipalstress/confiningpressure. τoct =Octahedralshearstress. k1,k2, k3,k4=Regression constants from repeated load resilient

modulustests.

The AASHTO model for coarse-grained soils/granularmaterials isbasedon theworkofHicks [10]whostudiedon thefactors affecting the resilient properties of granular materials.However,VonQuintusandKillingsworth[11]found that theso-called“universalconstitutivemodel”whichisbasedonstudiesmadebyUzan[8]ismoreaccurateinsimulatingtheresponsesmeasuredinthelaboratory.Thisisbecausethemodeltakesintoaccountboththeconfiningstressandthedeviatorstress,comparedtotheHicks’modelwhichonlytakesintoaccountoftheconfiningstress. ThedraftAASHTO2002PavementDesignGuideadopteda modified version of the equation, called the “expandeduniversalconstitutiveequation”whichisapplicabletoalltypesofunboundpavingmaterials,rangingfromplasticclaystocleangranular bases [9]. Von Quintus and Yau[12] found good fitof theequationusingdatafor thepavementmaterialsobtainedfrom the Long Term Pavement Performance (LTPP) programconductedintheUnitedStates. Thispaperfocusedonthek-θmodelbecauseofitssimplicityanditswidespreaduseinmodelinggranularmaterials.Inaddition,the model is also incorporated in multilayer elastic analysissoftwarespresentlyavailablewhichisusedtoanalysepavementstructures. Table 2 shows the k1 and k2 values from previousresearchbyvariousinvestigatorsusingthek-θmodel.

Table 2: Ranges of k1 and k2 for untreated granular materials [2]

Reference Material k1(psi) k2

Hicks(1970)Hicks&Finn(1970)

Allen(1973)Kalcheff&Hicks(1973)

Boyceet.al(1976)Monismith&Wictzak(1980)

Partiallycrushedgavel,crushedrockUntreatedbaseatSanDiegoRoadTest

Gravel,crushedstoneCrushedstone

Well-gradecrushedlimestoneIn-servicebase&subbasematerials

1600-50002100-54001800-80004000-9000

80002900-7750

0.57–0.730.61

0.32-0.700.46-0.640.67

0.46-0.65

AHMAD KAMIL ARSHAD AND MOHD YUSUF ABDUL RAHMAN , et al


3 METHODOLOGYA Equipment UTM-5Pservo-pneumaticallycontrolledtestingmachinewasusedfortheresilientmodulustestingofbaseandsubbasematerials.Realtimecontrolofthemachineandthegenerationoftherequiredwaveformwereprovidedbyadigitalsignalprocessingunit;whileadataacquisitionsystemtookalltransducerreadingsatthesametime.Thesignalprocessingunitandthedataacquisitionsystemwereprovidedinacontrolanddataacquisitionsystem,whichwasintegratedwiththeUTM-5Ptestingmachine.Auniversaltriaxialcellcapableoftesting100mmdiameterx200mmhighspecimenswasusedforrepeatedloadtestofthebaseandsubbasematerials(Figure1).

of the envelope (named Mid+25% thereafter) and (3) betweenmiddleoftheenvelopeandthelowerlimitoftheenvelope(namedMid-25%thereafter).One(1)sampleeachwaspreparedforeachgradationline.

B.2 Subbase Materials Miningsandandquarrydustwereusedforsubbasematerials(typeE).ThegradationofthesubbasematerialswereinaccordancewiththegradationenvelopeasperPWDMalaysia’sSpecificationsforRoadWorks(Table4).Similartobasematerials,three(3)specificgradationlinesweresetforeachgradationenvelope:(1)middleofthe envelope (namedMid thereafter), (2) betweenmiddle of theenvelope and the upper limit of the envelope (namedMid+25%thereafter)and(3)betweenmiddleof theenvelopeandthe lowerlimitoftheenvelope(namedMid-25%thereafter).One(1)sampleeachwaspreparedforeachgradationline.

Table 4: Gradation envelope for subbase type E [1]

B.S.Sieve Size

% Passing by weight

Subbase ‘E’

50.0mm25.0mm9.5mm4.75mm2.00mm425um75um

--

10055–10040–10020–506–20

C Testing Procedure Foreachtypeofsample,theoptimummoisturecontentwasfirstdeterminedusingmodifiedproctortest(4.5kgrammer).Theoven-driedsamplewasthenpreparedatthree(3)differentlevelsofmoisturecontentbyaddingwatertotherequiredamountpriortocompaction:optimummoisturecontent(OMC),OMC-2%andOMC+2%. Eachofthe100mmdiameterx200mmhighspecimenwaspreparedusing a split sand former, using a 0.3mm thick rubbermembrane over it. The split sand former was placed above atriaxial base-plate,with a porous stonebeingplacedon the baseplatepedestal.For each specimen, avibratoryhammerwasused

Figure 2: Gradation lines and envelope for base (Type II)

Figure 1: Repeated load triaxial cell and UTM 5-P machine

B MaterialsB.1 Base Materials CrushedrockaggregateswereusedforbasetypeIImaterial.ThegradationinaccordancetoPWDMalaysia’sspecificationsisasfollows:

Table 3 : Gradation envelope for base type II [1]

BS SieveSize (mm)

% Passing by weight

50 100

37.5 85–100

28 70–100

20 60–90

10 40–65

5 30–55

2 20–40

0.425 10–25

0.075 2–10

Three(3)specificgradationlinesweresetforeachgradationenvelope (Figure 2): (1) middle of the envelope (named Midthereafter),(2)betweenmiddleoftheenvelopeandtheupperlimit



tocompactfiveequallayersofapproximately40mminthickness(Figure3).The split sand formerwas then removedandanotherlayerofrubbermembranewasplacedaroundthespecimentomakeit air-tight.The triaxial top capand theporous stonewasplacedon the specimen; rubberO-ringswere thenplaced around it andthebottompedestal,priortotheplacementofthespecimeninthetriaxialchamber. Figure4shows theset-upof therepeated loadtriaxialtestforbaseandsubbasematerials[13].

Figure 3: Compaction of samples using vibratory hammer

ThespecimensweretestedforresilientmodulususingtheUTM-5PmachineatthedeviatorstressandconfiningpressuresasperAASHTOT307-99 test [13].The repeated loadwas setat adurationof0.1 secondswith a restperiodof0.9 seconds.Pre-conditioningofthespecimenwascarriedoutataconfining

pressureof103.4kPaandamaximumaxialstressof103.4kPafor 1000 repetitions for basematerials and 500 repetitions forsubbbase materials. Resilient modulus tests were then carriedout at the required confining pressures and deviator stress (15cycles)for100repetitions(Table5).Theaverageofthelastfivereadingsforeachcycleistakenastheresilientmodulusfortheparticularcycle.

Table 5 : Testing sequences for base/subbase materials [13]

SequenceNo.ConfiningPressure,

S3

Max.AxialStress,Smax

CyclicStressScyclic

ConstantStress0.1Smax No.ofLoad

ApplicationskPa psi kPa psi KPa psi kPa Psi

0123456789101112131415

103.420.720.720.734.534.534.568.968.968.9103.4103.4103.4137.9137.9137.9

15333555101010151515202020

103.420.741.462.134.568.9103.468.9137.9206.868.9103.4206.8103.4137.9275.8

1536951015102030101530152040

93.118.637.355.931.062.093.162.0124.1186.162.093.1186.193.1124.1248.2

13.52.75.48.14.59.013.59.018.027.09.013.527.013.518.036.0

10.32.14.16.23.56.910.36.913.820.76.910.320.710.313.827.6

1.50.30.60.90.51.01.51.02.03.01.01.53.01.52.04.0

500–1000100100100100100100100100100100100100100100100

Figure 4: Set-up of the repeated load triaxial test [13]



Thedataobtainedforthe15cycleswerethenplotted(Figure5) based on the following relationship for the base/subbasematerials[5]:

MR(psi)=k1(θ)k2 (6)

where θ= StressinvariantorBulkstress(psi)=(σ1 + σ2+ σ3) =(σd+3σ3). σ1= Majorprincipalstress(psi). σ2 = Intermediateprincipalstress(psi). σ3= Minorprincipalstress/confiningpressure(psi). σd= Deviatorstress(psi).k1,k2 = Regression constants from repeated load resilient

modulustests.

AASHTOT307-99 require the samples to be tested at thein-situmoisturecontentorOMCifthein-situmoisturecontentisnotknown/unavailable.Table5liststhevaluesofk1andk2forthebasematerialsobtainedatOMC:

Table 5: Values of k1 and k2 for different gradations of base type II at OMC

Base Type

Moisture Content

(%)

Max. Dry Density (Mg/m3)

k1 k2

Mid-25% 5.40 2.342 2,831.7 0.6968

Mid 5.70 2.350 2,8114.0 0.6917

Mid+25% 6.30 2.363 2,729.7 0.6576

Fromtheabovetable,itcouldbeseenthatbasematerialwithMid-25% grading line has the highest k1 value,which is likelyduetothelowerfinescontent(particlespassingthe75umsieve)andlowermoisturecontentwhichproducesamuchstiffermaterialthan the base materials with higher fines content and highermoisturecontent.Thevaluesobtainedabovecanbecomparedtothefollowingk1andk2valuesthatweresuggestedbyAASHTOforbasematerials:

Table 6: Typical values of k1 and k2 for Base Materials [5]

Moisture Condition K1 K2

DryDampWet

6,000 – 10,0004,000 – 6,0002,000 – 4,000

0.5 – 0.70.5 – 0.70.5 – 0.7

Table6abovesuggeststhatk1valuesareaffectedbymoisturecontentwhereask2valuesarewithinarangebetween0.5to0.7.ReferringtoTable5, itcouldbeseenthatmostofthek1valuesobtained in the laboratoryareat the lowerendof thesuggestedrange(wetmoisturecondition),whilefork2,mostofthevaluesarewithintherangeofthesuggestedvalues. It is likely that the base moisture condition is below theoptimummoisturecontentas thecurrentpractice inMalaysia istocompactthebaseindryconditionsandachieveminimum95%ofthemaximumdrydensityobtainedinthelaboratorymodifiedproctor test. In addition, Bulman and Smith [14] measuredsubgrademoisturecontentunderthepavement’sbaseandsubbaselayersat73differentlocationsinMalaysiaandfoundthatmorethanhalfofthesemoisturecontentswereequalordrierthantheoptimummoisturecontent(OMC)ofthesubgradesoilgivenbytheBritishStandard2.5kgrammercompactiontest.Furthermore,CroneyandBulman[15]foundthatthereisnoevidenceoflong-term moisture exchange with the subgrade sufficient to affectthestrengthofthesub-base/baselayers.Therefore,itispossiblethat theresilientmodulusatOMC-2%ismorerepresentativeoftheconditionsachieveatsite.Figure7belowshowstheresilientmodulusplotforallgradationstestedatOMC–2%.ReferringtoTables6and7,itcouldbeseenthatthek1valuesareinthedryconditionwhilefork2,mostofthevaluesarewithintherangeofthesuggestedvalues.This,however,havetobeconfirmedatsitebymeasuringthein-situmoisturecontentofthebasematerialintheactualpavementconstructed.

Figure 5: Plot of resilient modulus-bulk stress for base and subbase materials

Figure 6: Resilient modulus plot for base type II (Mid-Gradation)

4 RESULTS AND DISCUSSION Thissectionpresents theresults,analysisanddiscussionofthelaboratoryresilientmodulustestingcarriedoutonbaseTypeIIandsubbaseTypeE(quarrydustandminingsand).

A Base Materials The resilient modulus values obtained at various confiningpressuresanddeviatorstresseswereplottedonalog-loggraphandthevaluesofk1andk2wereobtainedfromthegraph.Atotalof3specimens(Mid,Mid-25%andMid+25%)weretestedat three(3)differentmoisturecontents(OMC,OMC-2%andOMC+2%).Figure6showsatypicalplotofresilientmodulus-stressinvariant(bulk stress) relationship for base type II (mid-gradation) at thethreedifferentmoisturecontents. Itcouldbeseen that the lowerthemoisturecontentthehigheristhek1value,howeverk2valueincreaseslightlywiththeincreaseinmoisturecontent.



Table 7: Values of k1 and k2 for different gradations of base type II at OMC-2%

Base Type k1 k2

Mid-25% 8,841.1 0.4819

Mid 7,357.0 0.5324

Mid+25% 6,518.5 0.5028

4.1 SUBBASE MATERIALS Figures8and9showtheresilientmodulusplotofsubbasematerials(TypeE)usingquarrydustandminingsandforthree(3)differentgradationstestedatOMC.Thek1andk2valuesobtainedaresummarizedinTable9andcanbecomparedtothefollowingk1 and k2values thatwere suggestedbyAASHTOfor subbasematerials:

Table 8: Typical values of k1 and k2 for subbase materials [5]

Moisture Condition k1 k2

DryDampWet

6,000 – 8,0004,000 – 6,0001,500 – 4,000

0.4 – 0.60.4 – 0.60.4 – 0.6

Figure 8: Resilient modulus plot for subbase type E (quarry dust) at OMC

ItcouldbeseenthatbycomparingTables7and9thatsubbasematerialshavemuchlowerk1valuesthanbasematerialsandonlyslightdifferencesink2values.Thisispossiblyduetothefactthatsubbasematerialshaveasmallermaximumaggregatesize thanbasematerialsandalsobecauseofthehigheroptimummoisturecontent(OMC)thanbasematerials.Gray[16]reportedthattheresilient modulus increased with increasing maximum particlesizeforaggregateswithsameamountoffinesandsimilarshapeof size distribution. Also, Hicks andMonismith [10], Dawsonet al. [17] andHeydinger et al. [18] reported that the resilientmodulus of granular materials decreases with the increase inmoisturecontent.

MID-25% : y = 8.8411x0.4819

R2 = 0.8242

MID : y = 7.357x0.5324

R2 = 0.6721

MID+25%: y = 6.5185x0.5029

R2= 0.8597

1

10

100

1 10 100Stress Invariant (psi)

Res

ilien

t Mod

ulus

(x10

3 psi

)

MID - 25% : y = 2.948x0.4826

R2 = 0.9031

MID + 25% : y = 1.6246x0.5251

R2 = 0.7435

MID : y = 1.9291x0.5172

R2 = 0.7621

1.0

10.0

100.0

1.0 10.0 100.0Stress Invariant (psi)

Res

ilien

t Mod

ulus

(x 1

000

psi)

MID + 25% : y = 4.0748x0.5451

R2 = 0.939

MID - 25% : y = 6.5863x0.5682

R2 = 0.6756MID : y = 4.7077x0.5305

R2 = 0.6715

1.0

10.0

100.0

1.0 10.0 100.0Stress Invariant (psi)

Res

ilien

t Mod

ulus

(x 1

000

psi)

Figure 7: Resilient modulus plot for all gradations at OMC

Figure 9 : Resilient Modulus plot for subbase type E (Mining Sand) at OMC

ReferringtotheTables8and9,itcouldalsobeseenthatforquarrydustatOMC,mostofthek1valuesobtainedareatthelowerendofthesuggestedrange(wetmoisturecondition),whilefork2,thevaluesarewithintherangeofthesuggestedvalues.MID-25%gradationhasthehighestk1valuesforbothquarrydustandminingsand,whileMID+25%gradationhas the lowest k1 values.Thissuggestthatthegradationwiththelowerfinescontent(%passing75µm)hasahigherk1value.

Table 9: Values of k1 and k2 for subbase materials at OMC

Subase Type k1 k2

QuarryDustMid-25%Mid

Mid+25%

2,948.01,929.11,624.6

0.48260.51720.5251

MiningSandMid-25%Mid

Mid+25%

6,586.34,707.74,074.8

0.56820.53050.5451

Also,mining sandwas found to have higher k1 value thanquarrydust,whilek2valuedoesnotshowanyspecifictrendwithchangesinmoisturecontent.Asthek1valueforquarrydustislowatOMC(andthushasalowerresilientmodulusvalue),itislikelythatquarrydustisunsuitableasasubbasematerialasitisadverselyaffectedbyanincreaseinmoisturecontent.Forminingsand,theOMCvaluegivesthehighestk1valueandthusisappropriatetobe



testedatOMC.Thereasonsforthisdifferencesarepossiblyduetofirstly,thelowermoisturecontentanddegreeofsaturationatOMCforminingsandandsecondly,itislikelythatthefinescontentofminingsand(below0.075mm)iscoarserthanthefinescontentofquarrydust,thusislessplasticandislessinfluencedbytheincreaseinmoisturecontentatOMC.

5 RESlLIENT MODULUS OF BASE AND SUBBASE MATERIALS TO BE USED IN PAVEMENT DESIGN Base and subbase materials are granular in nature andthereforetheresilientmodulusforgranularmaterialsisnon-linearand depends on particularly the confining pressure that exist intheparticularlayer.Todeterminetheresilientmodulus,iterativecalculationsmustbecarriedoutandthisisnormallydoneusingcomputer software that calculate the stresses using elastic layerassumptionsorfiniteelementprocedures.However,AASHTO[5]providessomesuggestionsregardingthevaluestobeused.

A Base Materials Thebasemodulusisnotonlyafunctionofmoisturebutalsothestressstatewhichinturn,varywiththesubgrademodulusandthicknessoftheasphalticconcretesurfacinglayer.Thefollowingis recommended values by AASHTO [5] for use in design ofpavements:

Table 10: Values of stress state of base recommended by AASHTO [5]

Asphalt Concrete Thickness (inches)

Subgrade Soil Resilient Modulus (psi)

3,000 7,500 15,000Less than 2

2 - 44 - 6

Greater than 6

201055

2515105

3020155

In Malaysia, most pavements are designed based on anassumed CBR value of 5 and asphaltic concrete thickness ofbetween4-6inches(100-150mm).Subgraderesilientmodulusareusuallycalculatedbasedonthefollowingrelationship:

MR(psi)=1500×CBR(7)

AsCBR=5,MR=7,500psi(51.8MPa)Thestressstatetobeusedis10psi.(0.069MPa)AssumingthebasematerialtobeusedisfromtheMIDgradationline (moisture content of OMC-2%), the following equationderivedfromthelaboratorytestisused:

Mr(psi)=7357θ 0.5324

Usingθ=10psi, Mr(psi)=7357(10)0.5324

Mr(psi)=25,067psi.

Ifafactorof1.2isusedtocompensateforthereductionofresilientmodulusvalueduetothescalpingofmaterialslargerthan25mminthelaboratorytesting(Barksdaleetal.1997),then:

MR(psi)=25,067psi×1.2=30,080psi(207.6Mpa)

ForMalaysianBaseTypeII,MIDgradationline(moisturecontent of OMC-2%), the recommended values of resilientmodulusisshowninTable11.Itshouldbenotedthattheresilientmodulus is dependant onboth asphaltic concrete thickness andtheresilientmodulusofthesubgradesoil.Forthesameasphalticconcretethickness,thehigherthesubgraderesilientmodulus,thehigher is the resilientmodulus value of the base.On the otherhand, for the same subgrade modulus value, the increase inthe thicknessof theasphalticconcretewill result in lowerbaseresilientmodulusvalue.

Table 11: Recommended values of resilient modulus (psi) for Malaysian Base Type II material (MID gradation, OMC-2%)

using stress state values suggested by AASHTO [5]

Asphalt Concrete Thickness (inches)

Subgrade Soil Resilient Modulus (psi)

3,000(CBR = 2)

7,500(CBR = 5)

15,000(CBR = 10)

Less than 22 - 44 - 6

Greater than 6

43,50030,10020,80020,800

49,00037,30030,10020,800

54,00043,50037,30020,800

B Subbase Materials Themodulus of the subbase is dependant on the asphalticconcrete thickness and for subbase thickness between 6 and 12inches (150 mm to 300 mm), AASHTO [5] recommended thefollowingstressstates(inpsi):

Asphalt ConcreteThickness (inches)

Stress State (psi)

less than 22 – 4

greater than 4

107.55

Using subbase Type E (mining sand-mid gradation) as anexample,andassumingthatthethicknessofasphalticconcreteisgreaterthan4inches(100mm)theresilientmodulusisdeterminedasfollows:

MR=4,707.7(θ)0.5305

=4,707.7(5)0.5305 =11,056psi(76.3MPa)

TherecommendedvaluesofresilientmodulusforMalaysiansubbase Type E, using mid-gradation line (moisture content atOMC),isshowninTable13.Itshouldbenotedthattheresilientmodulus of the subbase is dependant on the asphaltic concretethickness.Theincreaseinthethicknessoftheasphalticconcretewillresultinlowersubbaseresilientmodulusvalue.

Table 13: Recommended values of resilient modulus (psi) for Malaysian Subbase Type E material (mid-gradation, OMC)

using stress state values suggested by AASHTO [5]

Asphalt ConcreteThickness (inches)

Mining Sand (psi)

Quarry Dust (psi)

less than 22 – 4

greater than 4

16,00013,70011,100

6,3005,5004,400

Table 12: Values of stress state of subbase recommended by AASHTO[5]



ENGR. DR. MOHD. YUSOF BIN ABD. RAHMAN CurrentlyanAssociateProfessorintheFacultyofCivilEngineering,UniversityTeknologiMARA,ShahAlam.HespecialisesintheareaofHighwayandTransportationEngineering.

PROFILES

CONCLUSION Themeasurement of resilientmodulus of base type II andsubbase type E using quarry dust andmining sandwas carriedout by laboratory testing according to the procedures set out inAASHTOT307-99.For thebasematerials,MID-25%gradationhas the highest resilient modulus value at OMC. However,comparingwithvaluesobtainedbyresearchelsewhere,itislikelythatthevalueshouldbebasedonlowermoisturecontent,possiblyatOMC-2%.Forsubbasematerials,miningsandgavethehigherresilientmodulus values than quarry dust atOMC.As subbaselayer is located adjacent to the subgrade, itsmoisture conditionislikelytobehigherandpossiblyattheOMC.Resilientmodulusvaluesofbase(TypeII)andsubbase(TypeE)forthemid-gradationlinewasrecommendedbasedonthestressstatevaluessuggestedAASHTO. Field verification using non-destructive techniquessuchasfallingweightdeflectometer(FWD)andthemeasurementofin-situmoisturecontentofbaseandsubbaseshouldbecarriedout to compare the values obtained in the laboratory and thosemeasuredin-situ.n

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ENGR. AHMAD KAMIL BIN ARSHAD CurrentlyaPhDstudentintheFacultyofCivilEngineering,UniversitiTeknologiMARA,ShahAlam.HereceivedhisB.E.(Civil)fromCurtinUniversityofTechnology,WesternAustraliain1987andhisM.S.(HighwayandTransportationEngineering)fromUniversitiPutraMalaysiain2003.

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RESILIENT MODULUS OF MALAYSIAN BASE AND SUBBASE …