Workability and Performance of Polymer-modified Asphalt Aggregate Mixtures in Cold Regions

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  • This article was downloaded by: [University of Ottawa]On: 01 October 2014, At: 01:18Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

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    Workability and Performance of Polymer-modifiedAsphalt Aggregate Mixtures in Cold RegionsHannele K. Zubeck a , Lutfi Raad b , Stephan Saboundjian c , George Minassian d & P.E.John Ryer ea School of Engineering , University of Alaska Anchorage , Providence Drive, 99508,Anchorage, AK, USAb Transportation Research Center , Institute of Northern Engineering, University of AlaskaFairbanks , Fairbanks, AK, USAc Department of Transportation and Public Facilities Construction Section , Fairbanks, AK,USAd University of Alaska Fairbanks , Fairbanks, AK, USAe Department of Transportation and Public Facilities Construction Section , State of Alaska,Fairbanks, AK, USAPublished online: 11 Oct 2011.

    To cite this article: Hannele K. Zubeck , Lutfi Raad , Stephan Saboundjian , George Minassian & P.E. John Ryer (2003)Workability and Performance of Polymer-modified Asphalt Aggregate Mixtures in Cold Regions , International Journal ofPavement Engineering, 4:1, 25-36, DOI: 10.1080/1029843031000097535

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  • Workability and Performance of Polymer-modified AsphaltAggregate Mixtures in Cold Regions

    HANNELE K. ZUBECKa,*, LUTFI RAADb,, STEPHAN SABOUNDJIANc,, GEORGE MINASSIANd,{ and P.E. JOHN RYERe,

    aSchool of Engineering, University of Alaska Anchorage, 3211 Providence Drive, Anchorage, AK 99508, USA; bTransportation Research Center,Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, AK, USA; cDepartment of Transportation and Public Facilities

    Construction Section, Fairbanks, AK, USA; dUniversity of Alaska Fairbanks, Fairbanks, AK, USA; eState of Alaska, Department of Transportation andPublic Facilities Construction Section, Fairbanks, AK, USA

    (Received 26 March 2001; In revised form 5 November 2002)

    Polymer-modified asphalts have been used in cold regions for about 15 years to address problems withrutting, cracking and premature aging. However, due to the cold climate and remote locationsconstruction problems are sometimes encountered. This paper deals with workability of polymer-modified mixes while assuring that the desired pavement performance is achieved.

    The construction problems arise with possible poor compatibility of the base asphalt and thepolymer, the storage stability of the asphaltpolymer mixture and cold construction temperatures.These properties were tested for several polymer-modified asphalt combinations. A set of products thatwere compatible, storage stable and had improved temperature susceptibility were selected and furthertested in asphalt-aggregate mixtures. A Georgia Wheel rutting test and the Thermal Stress RestrainedSpecimen Test were performed. A questionnaire study was also conducted to collect experiences andspecifications in cold regions.

    Tests indicate that polymer-modified asphalts should always be the end result of an extensive productdevelopment program. The polymer modification improved the performance of all base asphalts incertain polymerasphalt combinations. However, some otherwise acceptable binders smokedexcessively when the temperature was elevated to the recommended mixing temperature. This issuewarrants further investigation.

    Keywords: Low-temperature cracking; Rutting; Cold region; Polymers; Specifications

    INTRODUCTION

    Polymer-modification has been shown to reduce low

    temperature cracking and improve pavement performance

    (Raad et al., 1996; Lu and Isacsson 1997a). However,

    application of modified asphalt concrete is more

    expensive than traditional asphalt pavement. Therefore,

    it is important that the polymer-modified pavement is

    manufactured and constructed properly, assuring that the

    improvement in pavement performance and pavement life

    is achieved. Recently, there have been some problems

    constructing modified asphalt concretes in Alaska,

    particularly in obtaining required compaction levels, and

    roughness of the pavement surface.

    The goals of the research were to analyze modified

    asphalt cements in order to select binders with improved

    performance in the pavement when compared to

    traditional asphalt binders, while being able to be used

    in asphalt-aggregate mixtures without comprehensive

    difficulties in mixing, laying and compaction. In addition,

    the objective was to develop specification recommenda-

    tions for binder properties at the moment of application at

    a hot mixing plant, and to develop guidelines for the

    mixing and compaction temperatures.

    Approximately 40 different combinations of polymer-

    modified binders were mixed from 5 base asphalts and

    4 different polymers. Each of the combinations was tested

    for consistency, compatibility and storage stability. A mix

    design was conducted for testing the binders in asphalt-

    aggregate mixtures. At this phase, the binders were also

    evaluated qualitatively based on the handling properties of

    asphalt-aggregate mixture samples. The asphalt-aggregate

    ISSN 1029-8436 print/ISSN 1477-268X online q 2003 Taylor & Francis Ltd

    DOI: 10.1080/1029843031000097535

    *Corresponding author. E-mail: afhkz@uaa.alaska.eduE-mail: fflr@aurora.alaska.eduE-mail: steve_saboundjian@dot.state.ak.us{E-mail: saboundj@arsc.eduE-mail: john_ryer@dot.state.ak.us

    The International Journal of Pavement Engineering, Vol. 4 (1) March 2003, pp. 2536

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  • mixtures were tested in the Thermal Stress Restrained

    Specimen Test (TSRST) and Georgia Wheel Rutting Test

    (GWRT). A questionnaire study was also conducted to

    collect specifications from other cold regions. This paper

    covers the questionnaire study, gives the most popular

    specifications and summarizes the laboratory test results

    for a narrowed set of binders.

    QUESTIONNAIRE STUDY

    The purpose of the questionnaire study was to collect

    experiences, specifications and recommendations from

    agencies in cold regions. The emphasis of the study was to

    investigate possible constructability problems and factors

    such as compatibility causing these problems. The

    questions included in the questionnaire are given in

    Table I and the responders are given in Table II. The

    responses given are summarized in Tables III and IV.

    Use of Polymer-modified Asphalt Pavements

    Polymer-modified asphalts have been used in pavements

    from 2 to 15 years. In general, no specific constructability

    problems were reported. However, the mixing temperature

    at the hot mix plant was always higher when compared to

    the traditional mixes. Also, the effects of air temperature

    are more critical with polymer-modified mixes than

    traditional mixes. Most of the agencies specify the

    minimum air temperature. As an example, Quebec

    recommends 108C for the minimum pavement tempera-ture during the laydown. All responders were happy with

    the performance of the polymer-modified asphalts. Better

    performance was reported as decreased stripping and

    raveling, low temperature cracking, fatigue cracking and

    plastic deformation.

    Compatibility Studies

    Only the binder-suppliers and contractors reported that

    they study the compatibility of the polymers with asphalts.

    The responders that were agencies or road authorities

    reported that the investigation of the compatibility is the

    responsibility of the supplier and/or the contractor.

    Test Methods

    A variety of test methods is utilized in the characterization

    of the polymer-modified asphalts (Table IV). The most

    commonly used test methods were penetration at 258C,softening point (Ring & Ball), viscosity at various

    temperatures, storage stability, elastic recovery, fluo-

    rescent microscopic analysis and the Gel Permeation

    Chromatography (GPC).

    Materials used in Polymer Modification

    Only few of the responders reported the base asphalt

    sources and grades as well as the polymers used in the

    modified binders. The recipes are normally proprietary

    information of the supplier/contractor. The reported pene-

    tration grades for base asphalts varied from 85 to 300. The

    polymers used are also normally proprietary information,

    but Quebec, Finland and Japan reported that the styrene

    butadienestyrene (SBS) is the most commonly used

    polymer. Also, styrenerubber (SB) and styrenebuta-

    dienerubber (SBR) are used in the polymer modification

    of pavement asphalts by the responders. The modification

    degree is neither specified; however, the reported range

    varies from 2 to 7%. No major changes in the polymer types

    are predicted in the future by any of the responders.

    SUMMARY OF SPECIFICATION FOR POLYMER-

    MODIFIED ASPHALTS IN COLD REGIONS

    A summary of the specifications received for use in cold

    climates is given in Table V. Specifications from Idaho and

    Finland were attached with the questionnaire responses.

    The other specifications were obtained from various

    projects in the states mentioned (unpublished). Note also

    TABLE II Questionnaire responders

    Country or State Agency Responder

    Idaho DOT T. Baker, Materials EngineerQuebec DOT Pierre LangloisSweden VTI Ylva EdwardsSweden Nynas No name given, transmitted

    by Ylva EdwardsNorway Road Adm. Torbjorn JorgensenFinland Neste Oil Timo BlombergFinland VTT Laura ApiloSwitzerland EMPA Martin HugenerSaskatchewan City of Regina Carly LeMurrayJapan Ohbayashi Road Co. No name given, transmitted

    by Ishikawa Nishizawa

    TABLE I Questionnaire

    1 How many years have you been using polymer-modified bindersin asphalt pavements?

    2 Have you had notable difficulties with the constructability ofpolymer-modified asphalt pavements? If yes, how did you fixthe problem?

    3 In general, are you satisfied with the performance of polymer-modified asphalts? If no, why?

    4 Have you investigated the compatibility of the asphalt cementand the modifier?

    5 Which tests do you use in the characterization of the polymer-modified asphalts

    6 What sources of base asphalt are used in the polymer-modifiedbinders?

    7 What grades of base asphalt are used?8 Are these grades designed especially polymer modification in

    mind or for general use?9 Do you conduct chemical analysis on the base asphalts that are

    modified? If yes, which tests?10 Which polymers and specific grades have you used?11 Based on your experience, what is the optimal range for the

    polymer content? Specify for each polymer used, if it varies.12 Which polymers and specific grades will you use in the future?

    H.K. ZUBECK et al.26

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    PERFORMANCE OF PMAS IN COLD REGIONS 27

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  • that parts of the United States are already using or will be

    using the Superpave specifications instead of the

    specifications given here. As an example, the City of

    Regina, SK Canada uses Superpave PG grades 3454 and

    4060.

    All specifications given are end result specifications

    versus recipes including the base asphalt, polymer and

    modification level. However, the AASHTO (1992)

    specifications inform the user with which polymer the

    specifications will be met. The specifications attached

    with the questionnaire by Idaho, are recommended for hot

    climates according to the source, the AASHTO (1992)

    specifications.

    Most Popular Specifications

    Penetration at 258C is specified by every agency expectCalTrans. The specified penetrations vary from 50 to 160

    1/10 mm. Softening point (Ring & Ball) is also a popular

    specification. A common minimum value for the softening

    point is 608C. Viscosity is required by all agencies atvarying temperatures. A widely used maximum value for

    the viscosity at 1358C is 2000 mm2/s. Storage stability is

    tested by letting the polymer separate from the asphalt at

    1638C for 48 h. A recommended maximum value for thedifference in the softening points for the bottom and top of

    the sample is 48C. Finland requires a maximum differenceof 258C, but the separation conditions are more severe(1808C for 72 h).

    Several agencies specify the binder properties also after

    aging in the Rolling Thin Film Oven Test (RTFOT) or the

    Thin Film Oven Test (TFOT). The minimum penetration

    at 48C (using a load of 200 g and loading time of 60 s) isspecified to be from 15 to 30 1/10 mm. A minimum value

    for the elastic recovery at 258C after the RTFOT variesbetween 45 and 70%.

    LABORATORY BINDER TESTS

    Materials

    Five base asphalts were chosen for this study, three regular

    paving asphalts manufactured in Alaska, USA, and three

    asphalts manufactured specifically for polymer modifi-

    cation in Canada and Washington, USA. Four polymers

    were selected for mixing with the base asphalts, 2 types of

    TABLE IV Responses to question 5; tests used by responders

    Idaho Quebec Sweden Norway Finland Switzerland Saskatchewan Japan

    Fraass Brittle Point x x x xPenetration at 258C x x x x x xPenetration at 408C xSoftening point x x xViscosity at 608C xViscosity at 1358C xViscosity at 1608C x xViscosity at 1808C x x xWeight loss xDuctility xStorage stability: (1638C, 48 h) x x x x (1658C, 72 h) x (1808C, 72 h)Elastic recovery using ductilometer x (108C) x x (58C) x (258C)Elastic recovery using ARRB

    elastometerx

    Span of plasticity (SofteningPoint minus Fraass BrittlePoint)

    x

    Cold bending xNet absorption test xMicroscopic analysis using a

    fluorescent microscopex x x x x

    Superpave test: direct shearrheometer

    x

    Superpave test: bending beamrheometer

    x x

    Superpave test: direct tensiontest

    x

    Chemical analysis:TLC-FID x xHPLC xGPC x x x xIR x x

    Cohesion using the VialitPendulum Ram

    x

    After RTFOT:Decrease in penetration at 258C xIncrease/decrease in softening

    pointx

    Elastic recovery x

    H.K. ZUBECK et al.28

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    PERFORMANCE OF PMAS IN COLD REGIONS 29

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  • styrenebutadienestyrene polymers (SBS) and 2 types

    of styrenebutadienerubber polymers (SBR). The

    selected polymers are only a small sampling of the

    different polymer grades available for paving applications.

    Many polymers are available in the chemical industry that

    are suitable as asphalt modifiers and this study is not

    intended to exclude any of those as effective modifiers.

    Three different pre-manufactured polymer-modified

    binders were also obtained. The type and concentration

    of polymer as well as any special mixing techniques in

    each of these products are proprietary information.

    About 40 mixtures were evaluated for consistency,

    compatibility and storage stability. On the basis of the test

    results reported by Aleshire et al. (1998), seven modified

    asphalts were selected for the further phases of testing.

    In addition, three base asphalts used as pavement asphalts

    in Alaska was tested as control binders.

    Test Procedures for Laboratory Binder Tests

    Traditional standardized tests and a few non-standardized

    test procedures were used. Consistency was determined

    with ASTM test procedures: penetration (D5), viscosity

    (D4402) and softening point (D36). Storage stability was

    examined with a separation test and a slump test.

    Fluorescent microscopic images and elastic recovery

    tests were used to evaluate compatibility. Test methods

    that are not standardized are described below.

    Elastic recovery has been used to evaluate elastic

    properties of polymer-modified asphalts (Muncy et al.,

    1987). The test temperature was selected on the basis of

    test results obtained by Schuller and Forsten (1990); cold

    enough to separate binders but warm enough to allow

    elongation without breaking. The ductilometer and sample

    were conditioned for 90 min at 108C. The sample waselongated 200 mm and held for 5 min, after which it was

    cut in half and left undisturbed for 60 min. The elastic

    recovery is defined as the distance between the two cut

    ends after 60 min and is expressed as a percentage of the

    initial elongation.

    Ultraviolet fluorescent micrographs are used to observe

    the morphology of the polymer-modified binders. Samples

    for the microscopic slides were taken from the mix after it

    had cooled to room temperature. The polymer within the

    binder fluoresces yellow light. Time-exposure photo-

    graphs, usually 57 s, were taken with a camera mounted

    on the microscope.

    For the storage stability tests, two aluminum tubes

    5-1/2 inches long and 1 inch in diameter were filled with

    freshly mixed modified asphalt and sealed. The tubes were

    placed upright in a 1608C oven for 48 h then placed in afreezer to solidify the sample. One sample tube was used

    for the separation test the other for the slump test.

    For the separation test a frozen sample was cut into

    three equal sections. The ring and ball procedure

    described in ASTM D36 was performed on samples

    from the top and bottom of the tube. The difference in

    softening point between top and bottom is an indicator of

    the degree to which the polymer has separated from the

    asphalt (Breuer, 1988). The second frozen tube was sliced

    lengthwise and the aluminum was peeled back and the

    ends of the tubes were cut off or bent back. The samples

    were laid in foil trays and heated in an 808C oven for45 min. Photographs were taken of each sample after it

    was removed from the oven. The purpose of the slump test

    is to subjectively evaluate storage stability.

    Sample Preparation and Binder Selection

    The percent polymer content for each combination was

    calculated based upon total weight. The 30% water con-

    tent of SBR latexes was accounted for in the calculations

    because that water evaporates upon mixing with the hot

    asphalt.

    The samples were mixed at 5000 rpm with a high-shear

    mixer with a slotted disintegrating head. A hot plate was

    used during mixing to raise and maintain the temperature

    of the binder at 1758C. When the mixing process wascomplete the sample containers for the test procedures

    were filled immediately and the remainder of the mixture

    was sealed and stored at room temperature.

    Each polymer and each binder were initially mixed at

    4%. Each 4% mixture was then evaluated for consistency,

    compatibility and storage stability. Based upon these

    results further polymer concentrations were determined.

    The following criteria were used:

    Consistency

    The minimum softening point for the modified binders

    was set at 508C. If the softening point of the 4% mixturedid not exceed 508C then that combination was notmanufactured at lower concentration, because it would

    further decrease the softening point.

    Viscosity

    The maximum ideal hot-plant mixing temperature,

    defined as the temperature at which viscosity equals

    175 mm2/s, was limited to 1858C, near the temperature atwhich the polymer may begin to degrade. If the mixing

    temperature was $1858C the concentration of thepolymer was not increased. For mix designs the ideal

    compaction temperature is defined as the temperature

    at which viscosity equals 280 ^ 30 mm2/s. Aggregate

    gradation may also affect compaction temperature

    (Asphalt Institute SP-2).

    Polymer-modified asphalts may behave as non-

    Newtonian materials; i.e. the viscosity depends upon the

    shear rate. Non-Newtonian behavior increases with

    polymer concentration. Binders with SBS concentrations

    of about 3% are, typically, shear-rate independent while

    concentrations approaching 6% or greater cause shear-

    thinning behavior (Lu and Isacsson, 1997b). Shear sweeps

    were conducted at 1708C, an average hot-plant mixingtemperature, but the shear rate did not affect the mixing

    H.K. ZUBECK et al.30

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  • temperature significantly. However, the effect may be

    larger at lower temperatures.

    Temperature Susceptibility

    The temperature susceptibility was evaluated using the

    penetration index (PI). The PI was calculated using

    McLeods PI equation; the data are shown in Table VI

    (McLeod, 1976). PI was calculated for the interval from

    108C to the softening point. The penetration at 108C wasobtained with 100-g load and 5-s loading time. A

    penetration value of 800 was used for the softening point

    (Shell Pavement Design Manual, 1978).

    Improved temperature susceptibility may indicate less

    low-temperature cracking and reduced pavement defor-

    mation at high temperatures. As PI increases, temperature

    susceptibility improves. Almost all of the manufac-

    tured binders showed increases in PI and only one was

    eliminated because of poor temperature susceptibility.

    Storage Stability

    Storage stability tests evaluate the extent to which the

    polymer phase remains dispersed homogeneously in the

    asphalt after mixing. Results of the ring and ball storage

    stability test and the slump test are given in Table VII. The

    ring and ball separation test results are stated as a percent

    difference in temperature between the top and bottom.

    The slump tests were graded visually on a scale of 110

    where 1 indicates poor storage stability and 10 indicates a

    very stable binder.

    Typically, an unstable binder displays an increased

    softening point in the upper portion of the sample because

    the polymer has floated to the top. AASHTO-AGC-

    ARTBA (1992) specifies a maximum allowable difference

    of 2.28C for SBS-modified asphalts. There is nospecification for asphalts modified with SBR polymers.

    For the purposes of this study a 108C difference wasregarded acceptable for both types of mixes to warranty

    further studies.

    The slump test provides a quick, visual evaluation of

    storage stability. Storage-stable samples remain homo-

    geneous after conditioning in an 808C oven because theentire sample has the same softening point. Unstable

    samples show a definite change from liquid at the

    bottom to solid at the top of the sample.

    Storage stability was the most discriminating factor

    when selecting mixes for the next phases of testing and the

    great majority of the mixes were eliminated from further

    testing because the combination was not storage stable.

    Compatibility

    Fluorescent microscopy and elastic recovery were used to

    determine compatibility. The results of these tests are also

    given in Table VII. The fluorescent micrographs of each

    TABLE VI Results of consistency tests

    Samplecode

    Viscosity mm2/sSoftening

    point (SP, 8C)Ideal mixing

    temperature (8C)Ideal compactiontemperature (8C)

    Pen108C

    Pen258C

    PI(108C to SP)1208C 1808C

    A1 438 43 41.6 142 133 27.7 125.0 20.94A2 363 45 39.0 138 127 29.7 155.0 20.93A5 400 43 37.5 133 124 44.7 231.3 20.51PM1 2950 158 80.5 180+ 162 64.0 182.0 6.87PM3 1438 148 61.7 178 162 50.3 154.0 3.88A1S1-4% 1425 125 48.0 171 154 23.3 98.0 20.07A2S1-5% 2075 160 85.0 180 162 22.3 91.0 4.73A5S1-5% 1438 145 82.8 175 157 44.0 139.0 6.08A2R2-2% 938 115 44.3 168 151 28.3 127.7 20.38A5R2-2% 2125 41.3 180+ 180+ 49.0 207.0 0.20

    Base asphalts: A1, A2, A3, A4, A5Mapco AC2.5, Mapco AC5, Tesoro AC5, Husky, and US Oil in random order.Polymers: SBS1 and SBS2Enichem Europrenew SOL TE6317 and Shell Kratonw 1101 in random order; SBR1 and SBR2Ultrapavew UP70 and BASF Butanolw NS 175in random order.Pre-mixed Binders: PM1, PM2 and PM3one modified binder manufactured by Husky Oil and two by US Oil in random order.

    TABLE VII Results of storage stability and compatibility tests

    Sample code

    Separation test,% difference

    in softening pointSlump test

    (Good = 10, Fair = 5, Poor = 1)Elastic

    recovery %

    Fluorescent micrographs(Good = 10, Fair = 5,

    Poor = 1)

    PM1 6.1 10 96.0 510PM3 0.9 10 92.5 510A1S14% 5.7 10 64.0 510A2S15% 4.9 10 91.5 510A5S15% 22.1 5 96.8 510A2R22% 2.1 10 55.5 510A5R22% 3.6 10 51.8 510

    PERFORMANCE OF PMAS IN COLD REGIONS 31

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  • modified binder were visually graded on a scale of 110

    where 1 indicates an incompatible mixture and 10

    indicates a very compatible mixture.

    For the study of polymer-modified binders, compati-

    bility describes industrial blends that are thermodynami-

    cally immiscible. Within compatible mixtures the 2

    phases, polymer and asphalt, form a stable microscopic

    dispersion that resists complete separation. Incompatible

    blends are not stable and as a result the immiscible phases

    separate, which is apparent in the fluorescent microscopic

    images (Kraus, 1982; Moran, 1986). Figure 1 shows an

    incompatible SBS mixture. Note that incompatible blend

    may still be storage stable, if the phases do not separate on

    macroscopic level.

    For compatible SBS-modified binders, at the micro-

    scopic level, there are two types of binder morphology

    directly related to concentration, polymer-rich as discrete

    particles and polymer-rich as continua. As concentration

    increases, the morphology progresses from discrete

    particle to continua. Figure 2 shows fluorescent micro-

    graphs of two A1S1 combinations.

    The majority of the mixes viewed were classified as

    discrete particle morphology. The butadiene domains are

    visible in the microscopic images as very small, uniformly

    distributed white spots. Binders in this category

    typically behave more as a plastic than as a true elastic

    material (Kraus, 1982).

    The polymer-rich as continua morphology is character-

    istic of high SBS-polymer concentrations, 6% or greater,

    when the butadiene phases begin to interact with each

    other. The butadiene domains form a continuous rubber

    structure and the binder begins to behave as a rubber; i.e.

    elastic recoveries approach 100%. The continuous rubber

    morphology is not necessary for a binder to display very

    high elastic recoveries. SBR combinations consistently

    display discrete particle morphology. The chain structures

    characteristic of SBR polymers are often evident in 4%

    concentrations. There were no binders that were eliminated

    solely upon the basis of poor fluorescent microscopic

    images. Poor compatibility indicated in the micrographs

    confirmed unsatisfactory results in the consistency and

    storage stability tests.

    Elastic recovery is useful for evaluating compatibility.

    Reduced tensile strength can be an indicator that the two

    phases are separated (Grimm, 1989). According to test

    results, elastic recovery was dependent most upon

    polymer concentration and not polymer type. All of the

    mixes showed improved elastic properties compared to

    base asphalts and none of the mixes were eliminated

    because of inadequate elastic recovery.

    Binders Selected for Further Studies

    Of the 36 polymer-modified asphalts tested only nine met

    the criteria set for the compatibility, storage stability,

    improved temperature susceptibility and mixing tempera-

    ture. This shows that polymer modified asphalts should

    always be an end result of an extensive product

    development program. The probability of creating an

    acceptable product out of proper materials using proper

    blending technique, was ,20%. The three premixedbinders, that are end results of extensive product

    development programs, satisfied all criteria. It was

    shown that the binder properties depend upon polymer

    type, polymer concentration, base asphalt and method

    used in mixing the polymer with the asphalt.

    Total of 26 binders did not meet the storage stability

    criterion, and 18 binders did not meet the maximum hot-

    plant mixing temperature criterion. Both the storage

    stability and too high mixing temperature cause

    constructability problems. Unstable binders will form

    clusters of very high polymer concentration whereas

    FIGURE 1 Fluorescent micrograph of A4S24%; example of apolymer that is incompatible with the base asphalt.

    FIGURE 2 Fluorescent micrographs of A1S1 combinations; left: discrete particle morphology, A1S14%; right: polymer-rich as continuamorphology, A1S16%.

    H.K. ZUBECK et al.32

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  • the rest of the binder has a very low polymer

    concentration. The clusters will be hard if not impossible

    to mix and compact. Too high mixing temperature

    requires special equipment, is not cost effective, may

    cause smoking and may destroy the polymer. If the

    required mixing and compaction temperatures are not

    achieved, it is very hard if not impossible to get adequate

    aggregate coverage and the specified level of compaction.

    If the aggregate is not covered thoroughly, stripping will

    occur later. The high failure rate of the manufactured

    binders explains the construction difficulties in the field.

    To avoid these potential problems, a maximum viscosity

    should be specified. Also, a storage stability test should be

    added to specifications. Or, the binder samples tested for

    quality control from the hot-plant should be taken just

    before the binder hits the hot aggregate in the mixer. This

    allows the contractor to address the storage stability

    question with techniques, such as tank circulation.

    On the basis of the test results, seven modified asphalts

    were selected for the next phases of testing. Two binders

    that met all criteria, PM2 and A5S14%, were dropped to

    limit the number of binders without limiting the number of

    variables in further testing. In addition, three base asphalts

    used as pavement asphalts in Alaska was tested as

    control binders.

    LABORATORY MIXTURE TESTS

    A mix design was conducted for each binder, and the

    asphalt-aggregate mixtures were evaluated qualitatively

    based on the handling and workability properties. The

    aggregate was a crushed gravelly sand that was comprised

    predominately of well-rounded quartzite. A single

    gradation given in Table VIII was used for all of the

    mixtures, and only the type of binder was varied.

    The mix designs were conducted in accordance with

    AASHTO (1997), using the mechanically operated

    hammer option using optimal mixing and compacting

    temperatures and an optimum asphalt content for each

    binder. Each mix was evaluated using 75 hammer blows,

    and the optimum binder content varied from 4.8 to 5.2%.

    To determine the need for anti-strip additive, the binders

    were tested in accordance with Alaska Test Method T-14

    (State of Alaska Department of Transportation and Public

    Facilities, 1993). All binders were treated with 0.25% of

    anti-strip additive (Pavebond by Morton Thiokol).

    Workability, Smoking and Odor

    Workability appears to be a function of polymer type and

    concentration, and of mixing/compacting the mixture at

    an adequately high temperature. The pre-manufactured

    proprietary polymer-modified asphalt products (PM1 and

    PM3) showed good workability at the design construction

    temperatures. The SBR mixes were extremely stringy and

    difficult to handle.

    Three of the 10 mixes tested smoked profusely when

    the temperature was elevated to the recommended

    mixing temperature. The limited tests conducted by this

    study were not sufficient to determine whether polymer,

    base asphalt type or concentration was the most

    significant cause for the smoking. One modified blend

    of the 10 binders tested had a very strong noxious odor.

    This caused extreme discomfort to the operator, even

    with the hood running and the operator wearing a

    respirator.

    Testing of Binder-aggregate Mixtures

    The asphalt-aggregate mixture samples were prepared

    using the ideal mixing and compaction temperatures and

    optimum binder contents. The samples were compacted

    into beam specimens (65 125 300 mm3) using arolling wheel compactor. Some smoking occurred during

    the mixing but was not objectionable for SBS blends. For

    the SBR blends, however, the smoking increased and had a

    distinct odor.

    The GWRT test is an index test related to the rutting of

    pavement due to plastic deformation. The samples are

    stressed under repetitive loading cycles and the depth of

    the resulting rut is measured. Each test was conducted on

    three beam specimens that were tested at 408C under aload of 445N applied to a rubber hose with pressure equal

    to 690 kPa. A maximum rut depth of 3 mm after the 8000

    load cycles is considered acceptable. The test results

    are given in Table IX and Fig. 3. The following were

    concluded from the test results:

    . SBS-modification improved the rutting resistancedramatically, especially for the A5 asphalt.

    TABLE VIII Aggregate gradation

    SieveOpening

    size (mm) % Passing SieveOpening

    size (mm) % Passing

    3/400 19.0 100 #16 1.18 22.21/200 12.5 85 #30 0.600 14.83/800 9.5 73 #50 0.300 10.2#4 4.75 50 #100 0.150 7.4#8 2.36 34.2 #200 0.075 5

    TABLE IX GWRT and TSRST test results

    Mix

    Averagerut depth (mm)at 8000 cycles

    Averagefracture

    temperature (8C)

    Averagefracture

    strength (MPa)

    A1 6.860 225.1 2.842A2 4.116 225.7 3.702A5 13.323 229.2 2.480PM1 2.067 234.2 4.090PM3 2.882 235.9 4.744A1S124% 2.733 226.5 3.232A2S15% 1.400 225.4 3.602A5S15% 2.257 231.0 3.508A2R22% 4.643 227.7 4.185A5R22% 5.558 232.2 3.687

    PERFORMANCE OF PMAS IN COLD REGIONS 33

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  • . The SBR-modification also improved the ruttingresistance when compared to the straight asphalts,

    except for sample with A2R-2%.

    The TSRST simulates low temperature cracking of pave-

    ment in the field. The TSRST fracture temperature represents

    the temperature in the field at which the pavement is antici-

    pated to crack and the TSRST fracture strength represents the

    corresponding thermal stress (Kanerva et al., 1996).

    The TSRST tests were performed at a cooling rate of

    9.5 to108C/h. A minimum of three specimens was testedfor each mix and the average value of the fracture tem-

    perature and fracture strength was recorded. All the speci-

    mens broke on the first cooling cycle. The test results are

    given in Table IX and in Fig. 4.

    The following was concluded from the test results:

    . Mixtures with the pre-manufactured binders, PM1and PM3, exhibited the best low temperature cracking

    performance.

    . The polymer-modification improved the low tempera-ture cracking resistance of the base asphalts slightly.

    When the superior performance of the pre-manufac-

    tured binders are considered, there is evidence that the

    polymer-modification improves the cracking resistance

    of the mixtures.

    Comparison between Binder and Mixture Test Results

    In the first phase of study, binder properties were used to

    eliminate binders that did not satisfy criteria set on

    improved temperature susceptibility, storage stability and

    tolerable mixing temperature. It is important to check, if the

    chosen properties correlate with the mixture test results.

    If they do, the use of the chosen binder properties is

    justified. Also, if binder specifications are established on

    the basis of these test results, it is important to see that

    the tested binder properties correlate with the mixture test

    results.

    FIGURE 3 Rut depth at 8000 load cycles.

    FIGURE 4 TSRST fracture temperatures.

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  • Binder Tests versus GWRT Results

    The binder test is most closely related to the rutting of

    pavements is softening point. The softening points with

    the GWRT rut depths are given in Fig. 5. According to a

    regression analysis, the softening point did not correlate

    well with the GWRT rut depth (P-value 0.03). However, all

    the binders that had a softening point $488C, met thecriterion for the GWRT maximum rut depth of 3 mm, which

    justifies the use of softening point to select binders in the

    first phase of this research and also to consider the use

    softening point in binder specifications. Binders that had

    softening point lower than 488C had higher rut depth than3 mm.

    Binder Tests versus TSRST Results

    The binder test that relates most closely to the cold

    temperature behavior of pavements in this study is

    the penetration test at 108C. According to Kanerva (1992)penetration at low temperatures, e.g. 4 and 108C (load,100 g, loading time 5 s) is related to the fracture

    temperature in the TSRST. The penetration at 108C withthe TSRST fracture temperature is given in Fig. 6.

    According to a regression analysis, the penetration at 108Ccorrelates well with the TSRST fracture temperature

    P-value 0:007; which means that it was justified touse the low temperature range temperature susceptibility

    as an indicator for improvement in pavement performance

    related to low temperature cracking. Based on these test

    results, the binder test results predicted the low

    temperature-cracking tendency of the asphalt-aggregate

    mixtures. Therefore, specification recommendations could

    be made based on the binder test results.

    CONCLUSIONS AND RECOMMENDATIONS

    According to the user survey, polymer-modified asphalts

    are commonly used in cold regions. The users report that

    polymer-modification increases the pavement life by

    decreasing the amount of cracking and rutting. In general,

    the users are happy with the current techniques and

    materials.

    On the basis of the test results, the following

    conclusions and recommendations were obtained:

    . Polymer-modified products should be an end result ofcomprehensive product development program, in

    which a compatible base asphalt and polymer will be

    combined using optimized procedure and optimized

    polymer content to achieve (1) lowest possible

    construction temperatures with (2) improved pavement

    performance. This will reduce construction problems,

    including the smoking and air quality issues, and

    reduce pavement life-cycle costs.

    . Excess smoking and noxious odors were observed forsome binders. Workability appears to be a function of

    polymer type and concentration, and of mixing and

    compacting the mixture at an adequately high

    temperature. Both of the pre-manufactured proprietary

    polymer-modified asphalt products showed good

    workability at the design construction temperatures.

    The use of these types of products is recommended,

    where economically feasible, if they meet all other

    criteria.

    . SBS-modification improved the rutting resistancedramatically, especially for the A5 asphalt. The SBR-

    modification also improved the rutting resistance

    when compared to the straight asphalts, except for

    one case.

    . Mixtures with the pre-manufactured binders, exhibitedthe best low temperature cracking performance.

    In general, the polymer-modification improved the

    low temperature cracking resistance slightly.

    . All the binders that had a softening point $488C, metthe criterion for the GWRT maximum rut depth of

    3 mm, which justifies the use of softening point to

    select binders in the first phase of this research and also

    to use softening point in binder specifications (e.g.

    minimum of 50608C).. The penetration at 108C correlates well with the

    TSRST fracture temperature, which means that it was

    justified to use the low temperature range temperature

    susceptibility as an indicator for improvement in

    pavement performance related to low temperature

    cracking. Based on these test results, the binder test

    results predicted the low temperature-cracking ten-

    dency of the asphalt-aggregate mixtures. Therefore,

    FIGURE 5 GWRT rut depth versus softening point.

    FIGURE 6 TSRST fracture temperature versus penetration at 108C.

    PERFORMANCE OF PMAS IN COLD REGIONS 35

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  • specification recommendations could be made based

    on the binder test results.

    . A storage stability test should be added to speci-fications (e.g. 5108C difference between the top andbottom softening points after conditioning at 1638Cfor 48 h). Or, the binder samples tested for quality

    control from the hot-plant should be taken just before

    the binder hits the hot aggregate in the mixer, to

    allow the contractor to address the storage stability

    question with techniques, such as tank circulation.

    FUTURE RESEARCH

    The research conducted was a laboratory research. The

    recommended specifications should be verified in a field

    study. Test sections should be constructed using

    recommended binder criteria and the same aggregate

    and aggregate gradation as used in this research. Rutting

    due permanent deformation and low temperature cracking

    should be observed with time.

    Questions still remain in the selected mixing and

    compaction temperatures. The current state-of-the-art in

    determining these temperatures is done according to

    ASTM 1559. Recommended temperatures are determined

    from limiting viscosities that are applicable to conven-

    tional asphalts but not necessary to polymer-modified

    binders. It is important to study the influence of the binder-

    aggregate temperature on mixing, placement, compact-

    ability and performance (i.e. rutting, thermal cracking)

    and find a range of mixing and compaction temperatures

    that are practically acceptable.

    Acknowledgements

    The authors are grateful to the U.S. Department of

    Transportation Federal Highway Administration for

    providing funding and technical support for the project.

    The authors would also like to thank the following persons

    who contributed their valuable time for this project: Scott

    Gartin, David Sterley, Aaron Weston, Billy Connor,

    Denny Wohlgemuth, Maureen Lee, Lynn Aleshire, Matt

    Mann and Sean Bakinsky.

    References

    AASHTO-AGC-ARTBA (1992). Joint Committee, Subcommittee onNew Highway Materials, Task Force 31 Report, Guide Specifications,Polymer-modified Asphalt.

    AASHTO (1997) Standard Specifications for Transportation Materialsand Methods of Sampling and Testing, AASHTO T 245, Edition 18,Part II Tests.

    Aleshire, L., Mann, M., Zubeck, H., Raad, L. and Ryer, J. (1998).Constructability of Polymer-Modified Asphalts in Alaska. NinthInternational Conference on Cold Regions Engineering, Duluth,Minnesota, September 2730, ISBN 0-7844-0379-1.

    Breuer, J.U. (1988) Storage stability testhomogeneity test for hotstored polymer modified binder. Proceedings, RILEM ResidentialSeminar, Dubrovnik, Yugoslavia, p. 83.

    Grimm, G. (1989) Application of microscopic methods in the field ofpolymerbitumen binders. Proceedings of 4th Eurobitume Sym-posium, Madrid, October, 1989, Vol. I, pp. 5459.

    Kanerva, H.K. (1992) Effects of Asphalt Properties on LowTemperature Cracking of Asphalt Mixtures. Proceedings, 7thInternational Conference on Asphalt Pavements, ISAP, Nottingham,England, ISBN 1-874633-05-3.

    Kanerva, H.K., Vinson, T.S. (1996) Prediction of Low TemperatureCracking of Asphalt Concrete Mixtures with Thermal StressRestrained Specimen Test Results. TRB, National Research Council,Washington DC, ISBN 0-309-05916-X.

    Kraus, G. (1982) Modification of asphalt by block polymers ofbutadiene and styrene, Rubber Chemistry and Technology 55,13891402.

    Lu, X. and Isacsson, U. (1997a) Rheological characterization ofstyrenebutadienestyrene copolymer modified bitumens, Con-struction and Building Materials 11(1), 2332.

    Lu, X. and Isacsson, U. (1997b) Influence of styrene butadienestyrenepolymer modification on bitumen viscosity, Fuel 76(15),13531359.

    McLeod, N.W. (1976) Asphalt cements: pen-vis number and itsapplication to moduli of stiffness, ASTM Journal of Testing andEvaluation 4(4).

    Moran, L.E., (1986) Compatibilitythe key to modified asphaltperformance. Proceedings of the 31st Annual Conference ofCanadian Technical Asphalt Association, pp. 8295.

    Muncy, H.W., King, G.N. and Prudhomme, J.B. (1987) Improvedrheological properties of polymer-modified asphalts, In: Briscoe,O.E., ed, Asphalt Rheology: Relationship to Mixture, ASTM STP941 (American Society for Testing and Materials, Philadelphia),pp. 146165.

    Raad, L., Sebaaly, J., Epps, J., Coetzee, N. and Camilli, R. (1996) Lowtemperature cracking of polymer-modified AC mixes. AlaskaCooperative Transportation and Public Facilities Research Program,Project No. SPR-95-14 Task Report.

    Schuller, S. and Forsten, L. (1990) Polymeerimodifioitujen bitumienominaisuudet ja tutkimusmenetelmat. ASTO TR3/1, VTT No. 814,Finland, in Finnish.

    Shell Pavement Design Manual (1978) Shell International Petroleum Co.Ltd.

    State of Alaska Department of Transportation and Public Facilities,(1993) Laboratory Manual of Alaska Test Methods and StandardPractices.

    H.K. ZUBECK et al.36

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