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0360-1323/$ - se
doi:10.1016/j.bu
�Correspond
Building and Environment 43 (2008) 1270–1277
www.elsevier.com/locate/buildenv
Laboratory performance comparison of the elastomer-modifiedasphalt mixtures
Halit Ozena,�, Atakan Aksoyb, Sureyya Tayfurc, Fazıl C- elikb
aDepartment of Civil Engineering, Yıldız Technical University, Istanbul, TurkeybDepartment of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey
cISFALT Asphalt Company, Istanbul, Turkey
Received 2 May 2006; received in revised form 23 February 2007; accepted 10 March 2007
Abstract
In this study, permanent deformation test results on the cylindrical samples produced with the Marshall compaction were compared
with the wheel-tracking test results. Three different elastomeric polymer modifiers (OL, EL, and SB) were used. Repeated creep and
LCPC wheel-tracking tests were realized at different loading conditions and temperatures. Repeated creep tests at 40 1C temperature do
not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Performance level of the elastomeric-modified
asphalt 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 confirmed with other more
reliable tests. Also it is thought that gradation changing is more effectual than compaction effort types in view of evaluating efficiency of
rutting test methods.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: Asphalt mixture; Polymer; Elastomer; Repeated creep; LCPC wheel-tracking test
1. Introduction
On the majority of the world’s roads and airports,conventional penetration grades of bitumen performperfectly 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 traffic 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, andreflective cracking [1].
Properties of the asphalt materials depend on the natureof the crude oil and on the refinery processes employed.These asphalts do not necessarily conform to the endspecifications of pavement and industrial grade asphalts.
e front matter r 2007 Elsevier Ltd. All rights reserved.
ildenv.2007.03.010
ing author.
Also there is a continuing trend towards higher tirepressures. Asphalt pavements have experienced accelerateddeterioration. In recent years, more interests are concern inthe use of polymer modifiers for asphalt cements. For apolymer 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 themodified 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 modificationprocess but thermoplastic elastomers are enjoying wideacceptance as road bitumen modifiers, whereas polyolefinsare used mostly for the preparation of waterproofingmembranes, however, many other polymers are availableand suggested [2].Polymers, which are long-chain molecules of very high-
molecular weight, used by the binder industry are classifiedbased on different criteria. One method classifies polymersinto two general categories—elastomers and plastomers.
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Table 1
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
Stripping resistance (%) ASTM D-1664 55–65
Table 3
The results of tests performed on asphalt cement (AC 60–70)
Test Method Unit Value
Specific gravity (25 1C) ASTM D-70 g/cm3 1.024
Flash point (Cleveland) ASTM D-92 1C 300
Penetration (25 1C) ASTM D-5 0.1mm 64
Ductility (25 1C) ASTM D-113 cm 100+
Heating loss-163 1C % 0.05
Heating loss penetration/
original penetration
ASTM D-5 % 57.8
Ductility after heating loss ASTM D-113 cm 51.5+
Softening point ASTM D-36 1C 55
Table 2
Specific gravities of aggregates (g/cm3)
Properties Coarse Fine Filler
Specific gravity—dry (g/cm3) 2.693 2.671
Specific gravity—sat. (g/cm3) 2.707 2.697
Specific gravity—apparent (g/cm3) 2.732 2.743 2.787
Water absorption (%) 0.531 0.986
H. Ozen et al. / Building and Environment 43 (2008) 1270–1277 1271
The 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 flexible and more prone to fractureunder high strains than elastomers [3].
When a load is applied to the surface of an asphaltpavement 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 trafficked 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 [1].
Although, generally, wheel-tracking tests appear to bewell correlated with rutting in the field, there are at presentno quantified relationships to link wheel-tracking testresults to rutting in the field under variable traffic loadingand environmental conditions. For this reason, wheel-tracking tests cannot as yet be used to provide aquantitative estimate of rutting in the field. 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 modifiedbinders. Experience has shown that these mix types cannotbe properly evaluated by means of conventional tests suchas the unconfined uniaxial static or dynamic creep tests [4].
LCPC wheel-tracking test and repeated creep test gavesimilar 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 [5]. 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-modified asphalt mixtureswere evaluated with different temperatures and loadingconditions.
2. Experimental methods
2.1. Materials used and specimen manufacture
Used materials and experimental procedures in thisstudy were following. Aggregate combination, asphaltcement, and three different additives were used. Aggregate
was sampled from Omerli-Orkisan rock quarry in Turkey.Some properties of the used aggregate are given in Tables 1and 2. 60–70 penetration asphalt cement produced fromIzmit Oil Refinery (TUPRAS) was used. Standard labora-tory test results for asphalt cement are incorporated inTable 3.A typical heavy traffic gradation for hot-mix asphalts
(HMA), designated as wearing coarse (type II) in theTurkish specifications, was selected. The used gradationand specification 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 [5].Three different modifiers were selected. All the modifiers
were elastomeric polymers (OL, EL, and SB). Definingmodification process of the modifiers was applied carefully.OL is a very cohesive product. This additive sticks
aggregate particles very well and the produced thickerasphalt film 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.
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Table 4
Gradation in this study and gradation limits
Sieve size (mm) Percentage passing (%) Lower Upper SMA [5]
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
0
10
20
30
40
50
60
70
80
90
100
used gradation
lower values
upper values
SMA gradation [5]
Perc
enta
ge P
assin
g, %
0.01 0.10
Sieve Size, mm
1.00 10.00 100.00
Fig. 1. Gradation curve of used aggregate and limits.
H. Ozen et al. / Building and Environment 43 (2008) 1270–12771272
EL 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 modification. 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. Modified binderwas mixed at Marshall mixer during 6 h with a speed of80 rpm.
SB product is a styrene–butadiene–styrene 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 (efficiency of mixer/mixingprocess). The uptake of the maltenes generally amountsto some 6–9 times the weight of the polymer forming the‘‘polymer-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
longer pavement service life: the rutting life increased by afactor of at least 10 [1]. SB additive was mixed to the 60–70penetration 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 ¼ 4.41%). Some properties of theMarshall specimens for conventional and modified 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. Efficiencies ofsome selected chemical modifiers 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. 2–4 show the repeated creepcurves.Repeated creep tests on all of the mixtures demonstrated
that the addition of modifiers 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 modified mixtures at different temperaturescan be different.
2.3. LCPC wheel-tracking tests
Rutting test was verified 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 20–100mm thick. Research indicates goodcorrelation between LCPC test results and actual fieldperformance [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% field compactingscale. Before the temperature was reached at 60 1C, pre-compacting (1000 cycles) was made. Pre-conditioning
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Table 5
Some properties of the Marshall samples and test parameter definition
Sample no. Asphalt
cement
(Wa) (%)
Percent
add. (%)
Height
(mm)
Weight in
weather (g)
Weight in
water (g)
Volume
(cm3)
Mix density
(g/cm3)
Test Temperature
(1C)
Conventional (NR) mixtures
6 4.41 0.0 63.2 1197.9 702.9 495.0 2.420 Repeated
creep test
25
7 4.41 0.0 63.1 1185.7 694.5 491.2 2.414 25
8 4.41 0.0 62.6 1195.0 700.7 494.3 2.418 5
9 4.41 0.0 63.2 1199.5 703.7 495.8 2.419 5
11 4.41 0.0 61.8 1192.1 706.7 485.4 2.456 40
13 4.41 0.0 61.9 1193.3 707.5 485.8 2.456 40
OL mixtures
7 4.41 5.0 62.3 1194.2 705.5 488.7 2.444 Repeated
creep test
5
8 4.41 5.0 62.8 1199.3 707.5 491.8 2.439 5
11 4.41 5.0 62.4 1192.1 704.9 487.2 2.447 25
13 4.41 5.0 62.5 1194.0 706.4 487.6 2.449 25
17 4.41 5.0 62.0 1193.6 707.4 486.2 2.455 40
18 4.41 5.0 62.8 1197.9 709.8 488.1 2.454 40
EL mixtures
4 4.41 1.5 62.9 1199.0 705.5 493.5 2.430 Repeated
creep test
5
5 4.41 1.5 62.1 1198.8 705.1 493.7 2.428 5
10 4.41 1.5 62.7 1193.9 701.0 492.9 2.422 25
17 4.41 1.5 62.4 1198.6 707.4 491.2 2.440 40
21 4.41 1.5 63.1 1197.8 705.5 492.3 2.433 25
22 4.41 1.5 61.7 1195.7 705.2 490.5 2.438 40
SB mixtures
6 4.41 3.0 62.3 1201.5 709.5 492.0 2.442 Repeated
creep test
25
7 4.41 3.0 61.6 1195.9 708.1 487.8 2.452 25
12 4.41 3.0 61.8 1201.3 711.7 489.6 2.454 40
13 4.41 3.0 61.8 1200.0 713.3 486.7 2.466 40
14 4.41 3.0 62.3 1200.5 707.8 492.7 2.437 5
15 4.41 3.0 62.1 1199.0 711.2 487.8 2.458 5
0
500
1000
1500
2000
2500
3000
3500
4000
1 10 100 1000
Perm
anen
t def
orm
atio
n
NR
OL
EL
SB
Log loading time (seconds)
10000 100000
Fig. 2. Number of cycles versus permanent deformation (5 1C).
0
1000
2000
3000
4000
5000
6000
7000
1 10 100 1000
Perm
anen
t def
orm
atio
n
NR
OL
EL
SB
Log loading time (seconds)
10000 100000
Fig. 3. Number of cycles versus permanent deformation (25 1C).
H. Ozen et al. / Building and Environment 43 (2008) 1270–1277 1273
temperature was regulated and values were saved. After thevalues were saved rutting was calculated. Two identicalsamples were used for each alternative.
LCPC rutting test results for conventional and modifiedmixtures are shown in Fig. 5. Conventional mixtures showthe highest permanent deformation in this test.
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0
2000
4000
6000
8000
1 10 100 1000
Perm
anen
t def
orm
atio
n
NR
OL
EL
SB
12000
10000
Log loading time (seconds)
10000010000
Fig. 4. Number of cycles versus permanent deformation (40 1C).
0
1
2
3
4
5
6
0 10000 20000 40000
Perm
anen
t def
orm
atio
n
NR
OL
EL
SB
Number of load cycles
30000 50000
Fig. 5. LCPC wheel-tracking test results.
0 10000 30000
Perm
anen
t Def
orm
atio
n 10
-6 in
/in
NR
AP
SE
PE
BE
SB
12.00
10.00
8.00
6.00
4.00
2.00
0.00
Number of Load Cycles
20000 40000 50000
Fig. 6. LCPC wheel-tracking test results [5].
0
2000
4000
6000
8000
10000
1 10 100 1000
Perm
anen
t Def
orm
atio
n 10
-6 in
/in
NR
AP
SE
PE
BE
SB
Number of Load Cycles
10000 100000
12000
Fig. 7. Number of cycles versus permanent deformation (25 1C) [5].
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
1 10 100 1000
Perm
anen
t Def
orm
atio
n 10
-6 in
/in
NR
AP
SE
PE
BE
SB
Number of Load Cycles
10000 100000
Fig. 8. Number of cycles versus permanent deformation (40 1C) [5].
H. Ozen et al. / Building and Environment 43 (2008) 1270–12771274
3. 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 specific 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.
From an earlier study rutting problem was evaluatedwith the same tests for stony skeleton (SMA) mixtures.Harmonious results were obtained from this investigation.
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Rutting curves are given in Figs. 6–8. More performancedeveloping was obtained from various polymer-modifiedmixtures (NR-conventional mixtures, AP–SE–PE–BE–SBpolymer-modified mixtures). Identical samples were pre-pared with great care because of angularity effects of usedrock combination [5].
Although different polymer modifiers were used such aselastomeric or plastomeric polymers, drainage inhibitors,mostly higher-performance levels were observed in all tests[5]. Repeated creep tests on Marshall samples may be usedfor explaining permanent deformation [8].
Repeated creep curves and wheel-tracking test results aregiven in Figs. 2–4. Repeated creep tests on all of themixtures demonstrated that the addition of modifiersenhanced 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 modified 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 assessmost 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 modified 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 field 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 unmodifiedbinders, 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 confirmed with othermore reliable tests [4].
Although, generally, wheel-tracking tests appear to bewell correlated with rutting in the field, there are at presentno quantified relationships to link wheel-tracking testresults to rutting in the field under variable traffic loadingand environmental conditions. For this reason, wheel-tracking tests cannot as yet be used to provide aquantitative estimate of rutting in the field. 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 performanceof stone-skeleton mixes, or mixes that include modifiedbinders. Experience has shown that these mix typescannot be properly evaluated by means of conventionaltests such as the unconfined uniaxial static or dynamiccreep tests [4].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 [9].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 fulfill demands ongood relevance, high flexibility, and low cost. The first stepin the development of functional methods of measurementis to have for certainty samples with a good affinity 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 field and that the differencebetween laboratory and field is not the same for differenttypes of mixes [10].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 bettercoefficient of correlation (0.91) with the wheel-tracking testfor the modified model (diameter of sample 150mm anddiameter of platen 100mm) than for the traditional model(0.36) with the same diameter for sample and platen [10]. Inthis research 100mm diameter Marshall samples weretested in dynamic creep test and controversial results wereobtained from these two tests. Unlike this the same
ARTICLE IN PRESSH. Ozen et al. / Building and Environment 43 (2008) 1270–12771276
diameter was used in earlier study but logical trends wereobtained for SMA mixtures [5].
The failure of the Marshall test to describe ruttingresistance 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-modifiedbinders 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-modified binders. Fortunately, this fact has nowa-days been recognized by authorities who aim to implementrational performance-based specifications in the SHRP inthe USA and in Europe in CEN specifications [11].
It is well recognized from the literature that theaggregate 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 [12].
If asphalt mixes are regarded and judged from theirfunctional 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 fulfill demands ongood relevance, high flexibility, 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 affinity 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 firststep 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].
4. Conclusions
A study has been conducted to understand permanentdeformation properties of the asphalt mixtures containingelastomeric polymer modifiers (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 demonstratedthat the addition of modifiers enhanced the permanentdeformation 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 ofmodified mixtures at different temperatures can be different.In this research performance known mixtures were
tested. Obtained data were compared with the earlierresearch [5]. 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 confirmed with other morereliable tests. Also it is thought that gradation changing ismore important than compacting efforting types in view ofevaluating efficiency of rutting test methods.
Acknowledgments
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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