conventional penetration grades of bitumen perform
Properties of the asphalt materials depend on the natureof the crude oil and on the renery processes employed.These asphalts do not necessarily conform to the end
the use of polymer modiers for asphalt cements. For a
membranes, however, many other polymers are availableand suggested .Polymers, which are long-chain molecules of very high-
ARTICLE IN PRESSspecications of pavement and industrial grade asphalts. molecular weight, used by the binder industry are classiedbased on different criteria. One method classies polymersinto two general categorieselastomers and plastomers.
0360-1323/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
Corresponding author.perfectly satisfactorily as the binder for asphalt mixes.However, the working environment of our roads isbecoming more complex and severe, year on year, andincludes factors such as: increased trafc densities,increased loads, increased axle pressures, shortage of goodquality aggregates, and the effects of high and low ambienttemperatures. The increasing punishment being given toour pavements is taking its toll and the most commonmanifestations of pavement distress include: permanentdeformation, fatigue cracking, stripping, fretting, andreective cracking .
polymer to be effective in road applications, it should blendwith the bitumen and improve its resistance (to rutting,abrasion, cracking, fatigue, stripping, bleeding, aging, etc.)at medium and high temperatures without making themodied bitumen too viscous at mixing temperaturesor too brittle at low temperatures. In other words, itmust improve the overall performance of the pavement.Many polymers have been used in the modicationprocess but thermoplastic elastomers are enjoying wideacceptance as road bitumen modiers, whereas polyolensare used mostly for the preparation of waterproongLCPC wheel-tracking tests were realized at different loading conditions and temperatures. Repeated creep tests at 40 1C temperature donot correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Performance level of the elastomeric-modiedasphalt mixtures can be different for same mixtures at different performance approaches. The evaluation of the dynamic creep test
showed that the test can be used as an indicator of potential rutting, but the results in these cases should be conrmed with other more
reliable tests. Also it is thought that gradation changing is more effectual than compaction effort types in view of evaluating efciency of
rutting test methods.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: Asphalt mixture; Polymer; Elastomer; Repeated creep; LCPC wheel-tracking test
On the majority of the worlds roads and airports,
Also there is a continuing trend towards higher tirepressures. Asphalt pavements have experienced accelerateddeterioration. In recent years, more interests are concern inwith the wheel-tracking test results. Three different elastomeric polymer modiers (OL, EL, and SB) were used. Repeated creep andBuilding and Environment
Laboratory performance compaasphalt
Halit Ozena,, Atakan Aksoyb
aDepartment of Civil Engineering, YldbDepartment of Civil Engineering, Karad
cISFALT Asphalt Co
Received 2 May 2006; received in revised fo
In this study, permanent deformation test results on the cylindr(2008) 12701277
ison of the elastomer-modiedixtures
ureyya Tayfurc, Fazl C- elikb
echnical University, Istanbul, Turkey
Technical University, Trabzon, Turkey
ny, Istanbul, Turkey
23 February 2007; accepted 10 March 2007
samples produced with the Marshall compaction were compared
was sampled from Omerli-Orkisan rock quarry in Turkey.Some properties of the used aggregate are given in Tables 1and 2. 6070 penetration asphalt cement produced fromIzmit Oil Renery (TUPRAS) was used. Standard labora-tory test results for asphalt cement are incorporated inTable 3.A typical heavy trafc gradation for hot-mix asphalts
(HMA), designated as wearing coarse (type II) in theTurkish specications, was selected. The used gradationand specication limits are presented in Table 4 and Fig. 1.Stony skeleton mixtures were used in an earlier researchfor comparing LCPC wheel-tracking test and repeatedcreep test results. The gradation curve is also illustrated inFig. 1 .Three different modiers were selected. All the modiers
were elastomeric polymers (OL, EL, and SB). Deningmodication process of the modiers was applied carefully.OL is a very cohesive product. This additive sticks
aggregate particles very well and the produced thickerasphalt lm is durable. The pre-added asphalt cementcould be stored in conventional units that were already insitu. Additive was blended into asphalt cement at 170 1C ata ratio of the 5% of bitumen content.
ARTICLE IN PRESS
Some physical properties of the crushed aggregate
Properties Test method Value
L.A. abrasion (%) ASTM C-131 26
Soundness in NaSO4 (%) ASTM C-88 1.53
Flakiness (%) BS 182 (part 105) 28
nvironment 43 (2008) 12701277 1271The mechanism of resistance to deformation is the basicdifference between these two categories. The load-deforma-tion behavior of elastomers is similar to that of a rubberband such as increasing tensile strength with increasedelongation, which may reach 1300% of the original length,and ability to recover to the initial state after removal ofload. Plastomers, on the other hand, exhibit high earlystrength but are less exible and more prone to fractureunder high strains than elastomers .When a load is applied to the surface of an asphalt
pavement it deforms, but because the asphalt is a visco-elastic material, when the load is removed the vast majorityof the deformation recovers. However, there is a minuteamount of irrecoverable viscous deformation which re-mains in the asphalt and which results in a very smallpermanent residual strain. Accumulation of millions ofthese small strains due to axle loading results in the surfacerutting familiar on heavily trafcked pavements. Labora-tory tests that attempt to measure the stability, i.e. theresistance to permanent deformation of an asphalt mix,are: the Marshall test, static and dynamic creep tests,wheel-tracking tests, and laboratory test track tests .Although, generally, wheel-tracking tests appear to be
well correlated with rutting in the eld, there are at presentno quantied relationships to link wheel-tracking testresults to rutting in the eld under variable trafc loadingand environmental conditions. For this reason, wheel-tracking tests cannot as yet be used to provide aquantitative estimate of rutting in the eld. The test does,however, provide a reliable estimate of the rutting potentialand, hence, can be used to rank mixes according to rutpotential. Wheel-tracking tests are particularly recom-mended for the evaluation of rutting performance ofstone-skeleton mixes, or mixes that include modiedbinders. Experience has shown that these mix types cannotbe properly evaluated by means of conventional tests suchas the unconned uniaxial static or dynamic creep tests .LCPC wheel-tracking test and repeated creep test gave
similar results for selected SMA mixtures. In terms ofrutting tests, it was thought that repeated creep tests maybe a good indicator of SMA mixtures or else stony skeletonmixes . The purpose of this research was to make acomparison between the LCPC wheel-tracking test resultsand traditional tests and to present an approach forpreventing or minimizing rutting problem in context withthe performance tests for the continuous gradation. Con-ventional and three elastomer-modied asphalt mixtureswere evaluated with different temperatures and loadingconditions.
2. Experimental methods
2.1. Materials used and specimen manufacture
Used materials and experimental procedures in this
H. Ozen et al. / Building and Estudy were following. Aggregate combination, asphaltcement, and three different additives were used. AggregateStripping resistance (%) ASTM D-1664 5565
The results of tests performed on asphalt cement (AC 6070)
Test Method Unit Value
Specic gravity (25 1C) ASTM D-70 g/cm3 1.024Flash point (Cleveland) ASTM D-92 1C 300Penetration (25 1C) ASTM D-5 0.1mm 64Ductility (25 1C) ASTM D-113 cm 100+Heating loss-163 1C % 0.05Heating loss penetration/
ASTM D-5 % 57.8
Specic gravities of aggregates (g/cm3)
Properties Coarse Fine Filler
Specic gravitydry (g/cm3) 2.693 2.671
Specic gravitysat. (g/cm3) 2.707 2.697
Specic gravityapparent (g/cm3) 2.732 2.743 2.787
Water absorption (%) 0.531 0.986Ductility after heating loss ASTM D-113 cm 51.5+
Softening point ASTM D-36 1C 55
ARTICLE IN PRESSnviTable 4
Gradation in this study and gradation limits
Sieve size (mm) Percentage passing (%) Lower Upper SMA 
19.00 100 100 100 100
12.50 90.3 83 100 100
9.50 77.7 70 90 72.5
4.75 46.5 40 55 30
2.00 29.2 25 38 21.5
0.43 13.3 10 20 15
0.18 9.4 6 15 11.5
0.08 6.7 4 10 10
SMA gradation 
H. Ozen et al. / Building and E1272EL product is a reactive elastomeric terpolymer. It isadded to the asphalt cement between 1.5% and 3%.Asphalt cement reaches generally lower penetration valueand higher softening point with the modication. Asphaltcement was heated. Additive was mixed to the binder at180 1C temperature with a speed of 5 g/s. Additive ratiowas selected as 1.5% of bitumen content. Modied binderwas mixed at Marshall mixer during 6 h with a speed of80 rpm.SB product is a styrenebutadienestyrene block copo-
lymer. When SBS is added to hot bitumen, it absorbs someof the maltene components from the bitumen whichextends (softens) the polymer and causes it to swell. Theabsorption of the maltenes by the polymer is affected byseveral factors which include: the nature of the bitumen,polymer type, polymer morphology, temperature, anddispersion of the polymer (efciency of mixer/mixingprocess). The uptake of the maltenes generally amountsto some 69 times the weight of the polymer forming thepolymer-rich phase. The blend of bitumen and SBS isnot always homogenous and on cooling a two-phasesystem will become apparent. The second phase, composedof asphaltenes and the balance of the maltenes, is termedthe asphaltene-rich phase. In laboratory simulation testsasphalt mixes made with bitumen/SBS binders lead to
Sieve Size, mm
1.00 10.00 100.00
Fig. 1. Gradation curve of used aggregate and limits.longer pavement service life: the rutting life increased by afactor of at least 10 . SB additive was mixed to the 6070penetration asphalt cement 5% by weight of bitumen inthis research. It is added to bitumen between 3% and 7%by weight of bitumen. Mixing was realized with high-speedstirrer.Marshall mix design procedure was applied with 50
blows on each side of cylindrical samples (ASTM D1559)and the optimum asphalt contents of HMA mixturewere determined (Wa 4.41%). Some properties of theMarshall specimens for conventional and modied mix-tures for repeated creep tests are presented in Table 5.
2.2. Repeated creep tests
Strength of the bituminous mixtures to the plasticdeformation may be determined with the repeated creeptest. Test equipment is the same as the static creep test butrepeated load is applied differently. Efciencies ofsome selected chemical modiers are especially evaluatedwith the repeated creep test, also rutting investigationof asphalt mixtures are done. Experiments were realizedat 5, 25, and 40 1C test temperatures during 1000mspulse period. Samples were exposed to 780N (100 kPa)starting load. Average 1100N (138 kPa) was loadedduration of test. Loads and permanent deformations weresaved at least 20 h. Figs. 24 show the repeated creepcurves.Repeated creep tests on all of the mixtures demonstrated
that the addition of modiers enhanced the permanentdeformation resistance at moderate temperature (25 1C)but different relations are concern at low (5 1C) and high(40 1C) temperatures. Repeated creep tests at 40 1Ctemperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Relativeperformance of modied mixtures at different temperaturescan be different.
2.3. LCPC wheel-tracking tests
Rutting test was veried with the LCPC method. Thistest has been used in France for over 20 years tosuccessfully prevent rutting in HMA pavements. Inrecent years, the test has been used in the United States.This test is capable of simultaneously testing two HMAslabs. Slab dimensions are typically 180mm wide, 500mmlong, and 20100mm thick. Research indicates goodcorrelation between LCPC test results and actual eldperformance [6,7].Samples were prepared at 500mm length, 180mm width,
100mm height. Test temperature was 60 1C. Samples werekept at least 12 h at this temperature. Each tire was applied5000N load. Tire pressure was 0.6MPa (87 psi). Samplesmust be compacted as a determined degree of compacting.Test briquettes were compacted at 98% eld compacting
ronment 43 (2008) 12701277scale. Before the temperature was reached at 60 1C, pre-compacting (1000 cycles) was made. Pre-conditioning
ARTICLE IN PRESSnviTable 5
H. Ozen et al. / Building and Etemperature was regulated and values were saved. After thevalues were saved rutting was calculated. Two identicalsamples were used for each alternative.
Some properties of the Marshall samples and test parameter denition
Sample no. Asphalt
Conventional (NR) mixtures
6 4.41 0.0 63.2 1197.9 702.
7 4.41 0.0 63.1 1185.7 694.
8 4.41 0.0 62.6 1195.0 700.
9 4.41 0.0 63.2 1199.5 703.
11 4.41 0.0 61.8 1192.1 706.
13 4.41 0.0 61.9 1193.3 707.
7 4.41 5.0 62.3 1194.2 705.
8 4.41 5.0 62.8 1199.3 707.
11 4.41 5.0 62.4 1192.1 704.
13 4.41 5.0 62.5 1194.0 706.
17 4.41 5.0 62.0 1193.6 707.
18 4.41 5.0 62.8 1197.9 709.
4 4.41 1.5 62.9 1199.0 705.
5 4.41 1.5 62.1 1198.8 705.
10 4.41 1.5 62.7 1193.9 701.
17 4.41 1.5 62.4 1198.6 707.
21 4.41 1.5 63.1 1197.8 705.
22 4.41 1.5 61.7 1195.7 705.
6 4.41 3.0 62.3 1201.5 709.
7 4.41 3.0 61.6 1195.9 708.
12 4.41 3.0 61.8 1201.3 711.
13 4.41 3.0 61.8 1200.0 713.
14 4.41 3.0 62.3 1200.5 707.
15 4.41 3.0 62.1 1199.0 711.
1 10 100 1000
Log loading time (seconds)10000 100000
Fig. 2. Number of cycles versus permanent deformation (5 1C).ronment 43 (2008) 12701277 1273LCPC rutting test results for conventional and modiedmixtures are shown in Fig. 5. Conventional mixtures showthe highest permanent deformation in this test.
9 495.0 2.420 Repeated
5 491.2 2.414 25
7 494.3 2.418 5
7 495.8 2.419 5
7 485.4 2.456 40
5 485.8 2.456 40
5 488.7 2.444 Repeated
5 491.8 2.439 5
9 487.2 2.447 25
4 487.6 2.449 25
4 486.2 2.455 40
8 488.1 2.454 40
5 493.5 2.430 Repeated
1 493.7 2.428 5
0 492.9 2.422 25
4 491.2 2.440 40
5 492.3 2.433 25
2 490.5 2.438 40
5 492.0 2.442 Repeated
1 487.8 2.452 25
7 489.6 2.454 40
3 486.7 2.466 40
8 492.7 2.437 5
2 487.8 2.458 5
1 10 100 1000
Log loading time (seconds)10000 100000
Fig. 3. Number of cycles versus permanent deformation (25 1C).
ARTICLE IN PRESS
H. Ozen et al. / Building and E12743. Evaluation
In this research performance known mixtures wereused. Permanent deformation problem was evaluatedwith repeated creep tests and LCPC wheel-trackingtests. Many identical samples were prepared with greatcare and specic gravities were observed. It is knownfrom the literature that repeated creep test for cylindri-cally compacted and laboratory-prepared samples andwheel-tracking tests for slabs may be used for evalu-ating rutting developing. The misleading or controversialresults are also concern in literature and researches aregoing on.
1 10 100 1000
Log loading time (seconds)10000010000
Fig. 4. Number of cycles versus permanent deformation (40 1C).
0 10000 20000 40000
Number of load cycles30000 50000
Fig. 5. LCPC wheel-tracking test results.12.00
ronment 43 (2008) 12701277From an earlier study rutting problem was evaluatedwith the same tests for stony skeleton (SMA) mixtures.Harmonious results were obtained from this investigation.
0 10000 300000.00
Number of Load Cycles20000 40000 50000
Fig. 6. LCPC wheel-tracking test results .
1 10 100 1000
Number of Load Cycles10000 100000
Fig. 7. Number of cycles versus permanent deformation (25 1C) .
1 10 100 1000
Number of Load Cycles10000 100000
Fig. 8. Number of cycles versus permanent deformation (40 1C) .
ARTICLE IN PRESSnviRutting curves are given in Figs. 68. More performancedeveloping was obtained from various polymer-modiedmixtures (NR-conventional mixtures, APSEPEBESBpolymer-modied mixtures). Identical samples were pre-pared with great care because of angularity effects of usedrock combination .Although different polymer modiers were used such as
elastomeric or plastomeric polymers, drainage inhibitors,mostly higher-performance levels were observed in all tests. Repeated creep tests on Marshall samples may be usedfor explaining permanent deformation .Repeated creep curves and wheel-tracking test results are
given in Figs. 24. Repeated creep tests on all of themixtures demonstrated that the addition of modiersenhanced the permanent deformation resistance at moder-ate temperature (25 1C) but different relations are concernat low (5 1C) and high (40 1C) temperatures. Repeatedcreep tests at 40 1C temperature do not correlate well withthe LCPC wheel-tracking test results at high temperature(60 1C). Relative performance of modied mixtures atdifferent temperatures can be different. It was understoodthat this difference may stem from the gradation changing.For the laboratory mixes, it was the intention to assess
most HMA mix types currently used in South Africa.These included both stone-skeleton mixes (stone-masticasphalt and semi-open asphalt with bitumen-rubberbinder) and sand-skeleton mixes (gap- and continuouslygraded asphalt). Porous asphalt was not included. TheTransportek wheel-tracking test gave reasonable results,and is recommended for all high reliability projects. Thetest is appropriate for all mix types, including mixescontaining modied binders and stone-skeleton mixes. Forstone-skeleton mixes, the test must be performed at therefusal air void content otherwise the mix could deformexcessively, which is not expected if the mix is wellcompacted in the eld provided that it is designedcorrectly. Because the dynamic creep does not correctlydetermine the rutting resistance of all mixes, and theperformance ratings do not agree with the the Transportekwheel-tracking test, the dynamic creep test is not recom-mended for assessing the rutting potential of HMA otherthan sand-skeleton mixes manufactured with unmodiedbinders, unless evaluated in conjunction with other ruttingtests. The evaluation of the dynamic creep test showed thatthe test can be used as an indicator of potential rutting, butthe results in these cases should be conrmed with othermore reliable tests .Although, generally, wheel-tracking tests appear to be
well correlated with rutting in the eld, there are at presentno quantied relationships to link wheel-tracking testresults to rutting in the eld under variable trafc loadingand environmental conditions. For this reason, wheel-tracking tests cannot as yet be used to provide aquantitative estimate of rutting in the eld. The test does,however, provide a reliable estimate of the rutting potential
H. Ozen et al. / Building and Eand, hence, can be used to rank mixes according to rutpotential. Wheel-tracking tests are particularly recom-mended for the evaluation of rutting performanceof stone-skeleton mixes, or mixes that include modiedbinders. Experience has shown that these mix typescannot be properly evaluated by means of conventionaltests such as the unconned uniaxial static or dynamiccreep tests .The usual testing methods (Marshall test, wheel-tracking
test, repeated load uniaxial test) are inadequate for thecharacterization of the resistance to the permanentdeformation of asphalt. This is not to say that these testswould be unsuitable for other applications, for example, ina mixture design procedure within given compositionlimits. However, reliable comparisons of the deformationbehavior of various sorts of mixtures are not possible onthe basis of these tests .By evaluating asphalt mixes and pavements from a
functional point of view, the possibility to develop betterproducts that better stand up to demands of today andtomorrow will increase. To be able to use demands onfunctional properties there is however a necessity forfunctional methods of measurement that fulll demands ongood relevance, high exibility, and low cost. The rst stepin the development of functional methods of measurementis to have for certainty samples with a good afnity to realconditions on the road. A study made in Sweden hasproven that the traditional Marshall method is not suitablein this regard. The unsuitability of the Marshall method ofcompaction has also been proven by several otherinvestigators in other countries. A study for alternativeshas emphasized the importance of a kneading ingredient inthe compaction effort, which is in accordance withmethods like rolling wheel and gyratory compactor. Thesame study showed that a sample compacted in thelaboratory, at the same degree of compaction, usually getsbetter mechanical properties (indirect tensile stiffnessmodulus, dynamic creep test, and indirect tensile test) thana sample compacted in the eld and that the differencebetween laboratory and eld is not the same for differenttypes of mixes .The dynamic creep test is an interesting alternative to the
wheel-tracking test for measuring the sensibility forpermanent deformations, but there is some doubt aboutthe ability of the traditional method to be able to work as afunctional method of measurement and to distinguishbetween different types of mixes. Enlarging the sample to adiameter of 150mm while the platen is kept at normal size,i.e. 100mm, accomplishes a limited lateral pressure, whichgives more justice to mixes, which get their stability not somuch by forces of cohesion but much more so by the innerfriction of the aggregate. Trials have shown a much bettercoefcient of correlation (0.91) with the wheel-tracking testfor the modied model (diameter of sample 150mm anddiameter of platen 100mm) than for the traditional model(0.36) with the same diameter for sample and platen . Inthis research 100mm diameter Marshall samples were
ronment 43 (2008) 12701277 1275tested in dynamic creep test and controversial results wereobtained from these two tests. Unlike this the same
ARTICLE IN PRESSnvidiameter was used in earlier study but logical trends wereobtained for SMA mixtures .The failure of the Marshall test to describe rutting
resistance of asphalt mixes is demonstrated where theMarshall stability is plotted versus the rut depth at 50,000wheels passes as determined in a laboratory test trackexperiment. Several conventional and polymer-modiedbinders were used in the experiments. From these results itis clear that no relation exists between the Marshallstability and rutting under actual wheel loading in theLTT. The Marshall test should therefore not be consideredrelevant to characterize the resistance of mixes withpolymer-modied binders. Fortunately, this fact has nowa-days been recognized by authorities who aim to implementrational performance-based specications in the SHRP inthe USA and in Europe in CEN specications .It is well recognized from the literature that the
aggregate interlocking greatly occurred in the coarseaggregate. The image evaluation of aggregate morpholo-gical characteristic demonstrated that a stable aggregateskeleton resulted in more internal resistance. Traditionaltests such as Marshall stability and the indirect tensilestrength are considered to be inadequate to measure theinternal resistance in HMA .If asphalt mixes are regarded and judged from their
functional abilities there is a demand for functional methodsof measurement, methods that are not in existence todayconcerning all the parameters that are essential for the goodbehavior of the asphalt pavement. To be able to use demandson functional properties, there is however a necessity forfunctional methods of measurement that fulll demands ongood relevance, high exibility, and low cost. The discussionsabout this subject started in Sweden in the late eighties. Aftera period of time it was clear, which should have been self-evident, that functional methods of measurement demandsamples that have a good afnity with real conditions on theroad. There were at this time a lot of people that had come tothe conclusion that the Marshall method of compaction wasnot a suitable method in this regard. Because of this the rststep in the development of functional methods of measure-ment was to study alternatives to use instead of the Marshallmethod. The unsuitability of the Marshall method ofcompaction has since then been proven by several otherinvestigators in other countries [13,14].
A study has been conducted to understand permanentdeformation properties of the asphalt mixtures containingelastomeric polymer modiers (OL, EL, SB). An evalua-tion between the rutting potential of the cylindrical samplesproduced with the Marshall compaction and wheel-tracking test results was done.Repeated creep tests on all of the mixtures demonstrated
that the addition of modiers enhanced the permanent
H. Ozen et al. / Building and E1276deformation resistance at moderate temperature (25 1C) butdifferent relations are concern at low (5 1C) and high (40 1C)temperatures. Repeated creep tests at 40 1C temperature donot correlate well with the LCPC wheel-tracking test resultsat high temperature (60 1C). Relative performance ofmodied mixtures at different temperatures can be different.In this research performance known mixtures were
tested. Obtained data were compared with the earlierresearch . Unlike this research continuous gradation wasoffered and the result was that repeated creep test andwheel-tracking test did not give parallel result. Theevaluation of the dynamic creep test showed that the testcan be used as an indicator of potential rutting, but theresults in these cases should be conrmed with other morereliable tests. Also it is thought that gradation changing ismore important than compacting efforting types in view ofevaluating efciency of rutting test methods.
ISFALT Asphalt and Dogus- Construction Companiesare gratefully acknowledged for their laboratory capabil-ities. The authors are also indebted to Mr. T. Erol and Mr.N. Bugan for assistance in laboratories.
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ARTICLE IN PRESSH. Ozen et al. / Building and Environment 43 (2008) 12701277 1277
Laboratory performance comparison of the elastomer-modified asphalt mixturesIntroductionExperimental methodsMaterials used and specimen manufactureRepeated creep testsLCPC wheel-tracking tests