Laboratory performance comparison of the elastomer-modified asphalt mixtures

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  • 43

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    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 [2].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.

    doi:10.1016/j.buildenv.2007.03.010

    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 [1].

    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

    1. Introduction

    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

    Abstract

    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

    www.elsevier.com/locate/buildenv

  • 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 [5].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

    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

    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 [3].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 [1].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 [4].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 [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-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

    Table 3

    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/

    original penetration

    ASTM D-5 % 57.8

    Table 2

    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 [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

    30

    40

    50

    60

    70

    80

    90

    100

    used gradation

    lower values

    upper values

    SMA gradation [5]

    erc

    enta

    ge P

    assin

    g, %

    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

    0

    10

    20

    P

    0.01 0.10

    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 [1]. 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

    cement

    (Wa) (%)

    Percent

    add. (%)

    Height

    (mm)

    Weight in

    weather (g)

    Wei

    wate

    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.

    OL mixtures

    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.

    EL mixtures

    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.

    SB mixtures

    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.

    0

    500

    1000

    1500

    2000

    2500

    3000

    3500

    4000

    1 10 100 1000

    Perm

    anen

    t def

    orm

    atio

    n

    NROLELSB

    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.

    ght in

    r (g)

    Volume

    (cm3)

    Mix density

    (g/cm3)

    Test Temperature

    (1C)

    9 495.0 2.420 Repeated

    creep test

    25

    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

    creep test

    5

    5 491.8 2....

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