Investigation of rutting performance of asphalt mixtures containing polymer modifiers

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    Tests used to assess the resistance of bituminous mixesto ow rutting are mainly the Marshall Test, the staticcreep test, the dynamic creep test, the wheel tracking test

    repeated loading, which leads to wheel track rutting, isprobably the most important requirement for perfor-mance-based specications. This is because a wide rangeof mixture parameters, not least those associated with theaggregate aects it. By contrast, elastic stiness and fatigueare principally controlled by binder characteristics and vol-

    * Corresponding author.E-mail address: aaksoy@ktu.edu.tr (A. Aksoy).

    Construction and Building Materi

    Construction1. Introduction

    Asphalt concrete mixtures have been exposed to greaterstresses because of the increasing trac volumes, trucktrac and higher tire pressures. Problems related to frac-ture; permanent deformation and surface wear are beingreported by user agencies in the worlds. One of the mostcommon forms of distress of asphalt concrete pavementsis rutting (permanent deformation). Rutting is the denedas the progressive accumulation of permanent deformationof each layer of the pavement structure under repetitiveloading [13].

    and the indirect tensile test. When used to study the resis-tance of bituminous mixtures to ow rutting, these testsprovide qualitative evidence to conclusions from eldobservations. Nevertheless, these tests are useful to com-pare alternative mix compositions from a qualitative pointof view; in addition, determination tests provide access tosome intrinsic mix properties, which can be used in the the-oretical and semi theoretical performance models [4].Detailed description of the models may reveal in the liter-ature [5].

    The implementation of a suitable test for assessing resis-tance to accumulated permanent deformation underAbstract

    The purpose of this study is to evaluate mechanical properties of control and modied asphalt mixtures. Conventional and ve mod-ied asphalt mixtures were studied on hot mix asphalt permanent deformation resistance. Amorphous polyalphaolen, cellulose ber,polyolen, bituminous cellulose ber and styrene butadiene styrene were used as modiers. Indirect tensile strength, indirect tensile, staticand repeated creep and LCPC wheel tracking tests were used for dierent loading conditions and temperatures. Research was focused oncomparing the interaction between LCPC wheel tracking and other mechanical tests. According to the LCPC wheel tracking andrepeated creep test results SBS mixtures were found as the most resistance mixtures in view of the rutting. Additives performed dierentperformance levels but showed more resistance to permanent deformation according to the conventional mixtures. As far as the staticcreep test results are concerned there are controversial results because conventional mixtures are better. It is thought that this result maystem from the static behavior of the load and rheological change of bitumen with modiers. 2005 Elsevier Ltd. All rights reserved.

    Keywords: Asphalt mixture; Rutting; Polymers; LCPC wheel tracking testInvestigation of rutting perfcontaining pol

    Sureyya Tayfur a, Halita ISFALT Asphalt Co

    b Department of Civil Engineering, Ylc Department of Civil Engineering, Karad

    Received 29 July 2004; received in revised foAvailable online0950-0618/$ - see front matter 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.conbuildmat.2005.08.014rmance of asphalt mixturesmer modiers

    zen b, Atakan Aksoy c,*

    any, Istanbul, Turkey

    Technical University, Istanbul, Turkey

    z Technical University, Trabzon, Turkey

    11 August 2005; accepted 12 August 2005November 2005

    www.elsevier.com/locate/conbuildmat

    als 21 (2007) 328337

    and Building

    MATERIALS

  • umetric proportions of the mixture and can be estimatedon the basis of past research for conventional materials.It was for these reasons that the uniaxial static creep testwas introduced in the 1970s. It is now recognized thatrepeated loading is a necessary requirement and, hence,the repeated load axial test has been developed at Notting-ham. This was done originally very much in the context ofmixture design [6].

    Besides laboratory tests, accelerated full-scale tests areworth noting. There are more than twenty full-scale testfacilities in the world (LCPC, CEDEX, IFT, ALF, etc.).

    mineral aggregate weight. It is added directly mixer inplant. BE was added 0.6% of total mixture weight. LikeSE, BE is added directly mixer in plant. PE is used in themixture between percent 0.4% and 1%. PE was used 0.6%of total aggregate weight. SB additive can be mixedbetween 3% and 7% of bitumen weight. In this study, SBwas added to bitumen 5%. Properties of the used modiersreveal in the literature [7]. All additives were dispersedhomogeneously in the mixture. It is not subjected occula-tion and mixing diculty for all the additives. Stone masticasphalt grain-size distribution was selected. Used SMAgradation values are given in Table 3 and gradation curveare represented in Fig. 1.

    Table 2The results of tests performed on asphalt cement (AC 6070)

    Test Method Unit Value

    Specic gravity (25 C) ASTM D-70 g/cm3 1.024Flash point (Cleveland) ASTM D-92 C 300Penetration (25 C) ASTM D-5 0.1 mm 64Ductility (25 C) ASTM D-113 cm 100+Heating loss-163 C % 0.05Heating loss Pen./original Pen. ASTM D-5 % 57.8Ductility after heating loss ASTM D-113 cm 51.5+Softening point ASTM D-36 C 55

    Table 3Gradation in this study and limits

    Sieve Sieve (mm) Passing (%) Lowerupper limits

    0.01 0.10 1.00 10.00 100.00Log Sieve Size (mm)

    0

    10

    20

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    70

    Perc

    ent P

    assin

    g (%

    )

    Top LimitLower Limit

    S. Tayfur et al. / Construction and Building Materials 21 (2007) 328337 329They make it possible to test full road structures con-structed and loaded like actual roads (materials, equip-ment, and loads). The object is most often to comparethe performance of dierent types of material, or the eectsof dierent construction techniques or loading modes.

    The main objective of this research study is to evaluateow-rutting properties and to compare creep test resultsas regard conventional and modied asphalt mixtures.

    2. Materials

    Used materials and experimental procedures in thisstudy are following. Aggregate combination, asphaltcement and ve dierent additives were used. Coarse aggre-gate was sampled from Corlu; ne-ller aggregate fromGebze in Turkey. Coarse aggregate is basalt in view of min-eralogy and ne-ller aggregate is old calcareous. Someproperties of coarse and ne aggregate were given in Table1.

    Regional factors were observed and 6070 penetrationasphalt cement produced from Yzmit Oil Renery (TUP-RAS) was used. Standard laboratory test results forasphalt cement are incorporated in Table 2.

    Five dierent additives were used. These additives areamorphous polialfaolen (AP), cellulosed ber (SE), cellu-losed ber mixed with bitumen (BE), poliolen (PE) andstiren-butadien-stiren copolymer (SB).

    AP takes parts in plastomer group. It has a granulartype and directly added to the mixture in mixer. It is addedabout percent 57 of bitumen weight. In this study, AP wasadded 6% of bitumen weight. Penetration value (100 g,5 sn, 25 C) is 1622, while softening point is 98110 Cand viscosity is 500012,000 MPa. SE was added 0.4% of

    Table 1Properties of coarse and ne aggregate

    Properties Test method Value

    Coarse aggregate

    L.A. abrasion (%) ASTM C-131 13.0Soundness in NaSO4 (%) ASTM C-88 4.47Flakiness (%) BS 182 (Part 105) 10.8Stripping resistance (%) ASTM D-1664 6070Water absorption (%) ASTM C-127 0.86Polishing value BS-813 0.60Fine aggregate

    Plasticity index Non-plastic1/2 in. 12.7 100 1003/8 in. 9.52 72.5 6580No. 4 4.76 30 2535No. 10 2 21.5 1825No. 40 0.42 15 1218No. 80 0.177 11.5 914No. 200 0.074 10 812

    80

    90

    100Fig. 1. Aggregate distribution on gradation chart.

  • Table 4Summary of Marshall design results

    NR AP

    Asphalt cement (%) 5.96 6.13Stability (kg) 675 650Bulk specic gravity (g/cm3) 2.474 2.472

    330 S. Tayfur et al. / Construction and BuilMarshall method (ASTM D1559) was used for deter-mining optimal bitumen content for conventional andmodied asphalt mixtures. Three identical samples wereproduced for all alternatives. Bitumen range region wasregulated according to the bitumen demand for eachmixture. Six designs were realized and 108 asphalt bri-quettes were fabricated. Compacting energy was appliedas 50 blows. The results of Marshall Test are presentedin Table 4.

    As it shown in Table 4 optimum bitumen content hasbeen increasing for modied mixtures. SE mixture hasthe highest bitumen content. Stability values for modiedmixtures has been increasing for SE, PE, BE and SB mix-tures but decreasing for AP mixtures. Marshall ows wereincreased for SE, PE, SB mixtures but decreased AP andBE mixtures. Voids lled with binder and voids lled withmineral aggregate values for modied mixtures wereincreased. The highest optimal bitumen content obtainedfrom Marshall Test was found in mixture with the cellu-lose ber. This is an expecting result because of wise spe-cic surface area and highly bitumen demand of cellulosebers. Void in mineral aggregate reached 17% for all mix-tures. This value is given a lowest limit for SMA mixtures.Even conventional mixture was reached that limit. It isunderstood that there is enough void for binder in themixture.

    SMA mixtures like porous asphalts are subjected bitu-men drainage problems. Because optimal bitumen contentis high drainage problems are concerned in mixing, trans-

    Void content (%) 4.20 4.10Flow (mm) 3.10 3.00Voids lled asphalt (%) 75.00 76.00Maximum specic gravity (g/cm3) 2.583 2.577Voids lled mineral aggregate (%) 16.95 17.20porting, laying processes. There is no an internationalaccepted drainage test but German Method, Binder drain-age test for gap graded mixtures and 2.36 mm sieve test aregenerally realized [7]. In this study 2.36 mm sieve and Ger-man Methods were used. The top limit in the tests isaccepted as 0.3%. Results are suitable for those criteria(see Table 5).

    Table 5Summarized binder drainage test results

    Type of mixing NR AP SE BE PE SB

    2.36 Sieve analysis 0.0 0.0 0.0 0.0 0.0 0.0German method 0.2 0.015 0.010 0.011 0.013 0.0163. Performance tests

    Conventional and modied mixtures were evaluatedwith the indirect tension strength test, indirect tension test,static creep test, repeated creep test and LCPC rutting test.Tests were realized at optimum asphalt content for allmixtures.

    3.1. Indirect tensile strength test

    The indirect tensile strength test is used to determine thetensile properties of the asphalt concrete which can be fur-ther related to the cracking properties of the pavement.This test is summarized in applying compressive loadsalong a diametrical plane through two opposite loadingstrips. This type of loading produces a relatively uniformtensile stress which acts perpendicular to the applied loadplane, and the specimen usually fails by splitting alongthe loaded plane [8].

    Test is the simple and Marshall Specimens may be used.Surface irregularities do not seriously aect the results andthe coecient of the variation of the test results is low [9].This test was applied at 25 C on briquettes both on con-ventional mixture and modied ones. Duration of the testload and deformation values was saved until breakingpoint. Poisson ratio was used as 0.35 like other researchersand calculated horizontal deformations [1013]. Variationof indirect tension strengths of the mixtures were illustratedin Fig. 2.

    SE PE BE SB

    6.98 6.50 6.60 6.69695 730 690 6902.440 2.450 2.468 2.4583.90 4.40 3.60 3.804.35 3.65 3.00 3.9079.00 76.00 79.00 79.002.546 2.564 2.560 2.55718.60 18.14 17.64 18.00

    ding Materials 21 (2007) 328337The typical values of the indirect tensile strength of spec-imens (18 Marshall Specimens) obtained from this studyranged from 683 to 917 kPa. Modied mixtures showedan increase in the tensile strength at 25 C. PE and SBmodied mixtures gave the highest strengths. Summarizedvalues are presented in Appendix A.

    The use of low density polyethylene (plastiphalt) asbitumen modier has been investigated and the resultsshow that an improvement in the quality of the binderand mix properties. The indirect tensile strength valueswere found to be much higher [14]. Low temperaturecracking, fatigue and rutting are three major distressesmechanism. Numerous researches have been conductedrelating the tensile strength of asphalt mixtures to the per-formance of asphalt pavements [15,16]. A higher tensile

  • good indicator of measuring permanent deformation forstone mastic asphalt mixtures.

    3.2. Indirect tensile test

    In recent years, there has been a change in philosophyin asphalt pavement design from the more empirical

    Building Materials 21 (2007) 328337 331strength corresponds to a stronger low temperature crack-ing resistance [17].

    In this study, the indirect tensile strengths of the modi-ed mixtures were also higher than the control mix. Thisindicates that the mixtures containing additives have highervalues of tensile strength at failure indirect tensile strengthunder static loading. This would further imply that modi-ed mixtures appear to be capable of withstanding largertensile strains prior to cracking. Conventional densegraded mixes normally combine high stability with lowow values and hence high MQ values indicating a highstiness mix with a greater ability to spread the appliedload and resist creep deformation. Care must be exercisedwith very high stiness mixes due to their lower tensilestrain capacity to failure, i.e., such mixes are more likelyto fail by cracking particularly when laid over foundationswhich fail to provide adequate support. Although the Mar-

    0

    200

    400

    600

    800

    1000

    NR AP SE PE BE SBMixture

    Indi

    rect

    Te

    nsio

    n S

    tren

    gth

    (Kpa

    )

    Fig. 2. Indirect tension strength of the mixtures.

    S. Tayfur et al. / Construction andshall stability of the plastiphalt mix is much higher than thecontrol mix, the ow values of plastiphalt mixes are alsogreater indicating higher strain capacities to achieve failure.The value of MQ of the plastiphalt is higher than of thecontrol mix. It is well recognized that the MQ is a measureof the materials resistance to shear stresses, permanentdeformation and hence rutting [18].

    Internal resistances in hot mix asphalts were evaluated.This research indicated that the aggregate interlockinggreatly occurred in the coarse aggregate. The image evalu-ation of aggregate morphological characteristic demon-strated that a stable aggregate skeleton resulted in moreinternal resistance. Traditional tests such as Marshall Sta-bility and the indirect tensile strength were considered tobe inadequate to measure the internal resistance in HMA[19].

    Marshall Stability values were found generally higherthan the control mixtures. Only AP mixture gives lowerstability. AP and BE mixtures have lower ow value. Asfar as the Marshall test results are concerned for both con-trol and modied mixtures Marshall Quotient may not be aapproach to the mechanistic approach based on elastictheory. AASHTO in 1986, this mechanistic approach inthe form of elastic theo...

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