Evaluation of high temperature performance of SBS + Gilsonite modified binder

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  • nAvailable online 25 June 2011

    Keywords:SBSGilsoniteAsphalt binderRheological properties

    erinrviclly f

    to reduce the SBS content based on a series of rheological testing. While studies on various properties of

    alt binviscoue. Even

    mance of asphalt mixtures. The best known practice in bindermodication is the use of polymer modiers to prevent excessiveplastic deformations at high service temperatures by increasingthe binder stiffness on the contrary, brittle fractures at low temper-atures can be prevented or reduced by decreasing the binder stiff-ness [2]. In recent years, the most commonly used polymermodier is the styrenebutadienestyrene (SBS) in addition to

    rock asphalt, and in different degrees of purity, i.e., the propor-tions of bitumen and other mineral matters. Naturally occurringbitumen deposits, generically termed as asphaltite, is the mostextensively utilized bitumen resources known as Uintaite or Gil-sonite in the market, which contains natural hydrocarbons with apurity of around 99%, and 5770% of asphaltene [5]. Another un-ique feature of Gilsonite is to have higher nitrogen content thanthe oxygen in its structure, which is probably responsible for theGilsonites special surface wetting properties and resistance to freeradical oxidation [6]. Previous studies showed that the use of Trin-idat lake asphalt and Uintaite to modify binders leads to increase in

    Corresponding author. Tel.: +90 424 237 0000/5418; fax: +90 424 234 0114.E-mail addresses: bvural@rat.edu.tr (B.V. Kk), mehmetyilmaz@rat.edu.tr (M.

    Fuel 90 (2011) 30933099

    Contents lists availab

    ue

    .eYilmaz), gmurat@metu.edu.tr (M. Guler).a fraction of mix volume as compared to aggregate, asphalt binderaffects the whole mixture properties and thus the service perfor-mance of asphalt pavements in the eld. Ideally, it is expected thatbinder remains exible enough to withstand thermal stresseswithout cracking at low temperatures, while maintains its stiffnessto withstand under high summer temperatures [1]. Binder modi-cation offers a viable solution to overcome deciencies arisingfrom its temperature susceptibility, thereby improving the perfor-

    tion, continuous polymer phase can be formed throughout thepolymer modied binder (PMB), thereby signicantly modifyingthe base binder properties [4]. The escalating cost of bitumen prod-ucts and energy in addition to the lack of resources available forconstruction have eventually motivated the highway engineers tomodify base binder properties using natural asphalts in lieu of tra-ditional modiers. Natural asphalts are among those alternativeswhich can be found in bitumen deposits, such as lake asphalt or1. Introduction

    The rheological behavior of asphphenomenon, varying from purelyon the loading time and temperatur0016-2361/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.05.021binder that is modied only by Gilsonite are common, we investigate the effect of combining SBS and Gil-sonte in the same base binder. In the rst phase, the binders modied individually with SBS and Gilsoniteare evaluated in terms of based on the outcomes of dynamic shear rheometer and rotational viscosimetertests. Then, the asphalt binders including both SBS and Gilsonite at different contents are subjected to thesame rheological testing. The results show that around 34% times more Gilsonite is needed to replace 1%of SBS when the two modiers are mixed in the same binder depending on the Gilsonite/SBS ratioselected. Besides, the viscosity of modied binders with a percent of SBS replaced with Gilsonite is alwayslower than that of SBS-only modied binder. It is suggested that Gilsonite can be used as an alternativemodier to reduce the cost of asphalt mixture production and compaction in the eld.

    2011 Elsevier Ltd. All rights reserved.

    der is a very complexs to elastic, dependingthough occupies only

    the other type of polymers, such as ethylene-vinyl-acetate (EVA),styrene-butadiene-rubber (SBR) and polyethylene [3]. When SBSis blended with asphalt binder, the elastomeric phase of the SBScopolymer absorbs the oil fractions and swells up to nearly ninetimes as much as its initial volume. Using a suitable SBS concentra-replace some portion of industrial modier products, such as SBS, it would signicantly help reducethe cost of pavement construction. In this study, Gilsonite, a natural asphalt, is used as a binder modierEvaluation of high temperature performa

    Baha Vural Kk a,, Mehmet Yilmaz a, Murat Guler ba Frat University, Department of Civil Engineering, Elazg, TurkeybMiddle East Technical University, Department of Civil Engineering, Ankara, Turkey

    a r t i c l e i n f o

    Article history:Received 15 March 2011Received in revised form 29 April 2011Accepted 19 May 2011

    a b s t r a c t

    SBS is a widely used polymmix asphalt. SBS is nearlyrequirements under hot sethe increased cost especia

    F

    journal homepage: wwwll rights reserved.ce of SBS + Gilsonite modied binder

    modier for asphalt binders to improve the performance properties of hotdispensable when the binder properties do not satisfy the specicatione temperatures. One of the concerns in using such additives, however, isor large-sized construction projects. If a natural modier can be used to

    le at ScienceDirect

    l

    l sevier .com/locate / fuel

  • the complex modulus (G) whereas reduction in the phase angle(d), indicating an overall improvement in the elastic response ofbinder [7]. Gilsonite is generally utilized to improve high temper-ature properties by increasing the binder stiffness; however, itmay also affect the intermediate and low temperature propertiesof binder [8]. Gilsonite modied binders are also proved to success-fully serve as an intermediate layer between aggregate and asphaltbinder preventing crack initiation in asphalt concrete layers [9].The favorable characteristics of Gilsonite becomes a good alterna-

    were mixed at a temperature of 180 C and a rotational speed of

    SBS at different SBS/Gilsonite ratios. The experimental program,therefore, covered a series of rheological testing for asphalt bindersmodied with separate and mixed modiers in the same blend.

    2.2. Dynamic shear rheometer (DSR) test

    At present, the most common method of rheological testing ofasphalt binder is the dynamic oscillatory shear test, generally con-ducted within the region of linear viscoelastic (LVE) response. Theoscillatory shear test is carried out using dynamic shear rheometer(DSR) device at different loading times (frequency) and tempera-tures to measure the complex modulus and phase angle, which to-gether characterize the viscoelastic response of binder.

    Fig. 1. Laboratory scale mixing device.

    Fig. 2. Four-blade impeller.

    3094 B.V. Kk et al. / Fuel 901000 rpm for 1 h.In order to make a comparison, binder blends were prepared

    SBS and then tested to determine the rheological properties rele-vant to high temperature performance. The concentrations of theSBS Kraton D-1101 in the base bitumen were changed from 2% to5% by weight of the base bitumen based on the outcomes of previ-ous studies [12]. In the second phase, blends with varying contentsof Gilsonite between 3% and 12% were tested to determine thesame rheological properties, as in the case of testing binders usingonly SBS modier. Similar sample preparation and testing proce-dure was also used to determine the effect of mixing Gilsonite with

    Table 1Physical and chemical properties of Gilsonite.

    Properties Results

    Penetration (0.1 mm), 100 g, 5 s 0Softening point (C) 126232Moisture content (%) 0.5Specic gravity 1.041.06Carbon (weight %) 84.9Hydrogen (weight %) 10tive to the other commercially available polymer modiers espe-cially in cases where high trafc volume exists under elevatedtemperatures during service conditions [10].

    In the presented study, Gilsonite is used as a modier to im-prove the high temperature performance of base (unmodied) bin-der. A procedure to replace a proper amount of SBS with Gilsoniteis demonstrated based on the rheological evaluation of bindersmodied with separate and combined phases of both modiers.The advantage of using Gilsonite in binder modication is also dis-cussed in view of increasing mix workability and reducing theoverall cost of asphalt pavement constructions.

    2. Materials and method

    2.1. Materials and sample preparation

    Binder specimens were prepared using B 160220 asphalt ce-ment obtained from the Batman Petroleum Renery of Turkey.The selected SBS polymer was Kraton D-1101 supplied by the ShellChemicals Company. The Kraton D-1101 is a linear SBS polymershipped in a powder form consisting of different combinations ofblocks made from polystyrene (31%), and polybutadiene of a veryprecise molecular weight [11]. These blocks are either sequentiallypolymerized from styrene and butadiene and/or coupled to pro-duce a mixture of chained blocks. Gilsonite was obtained fromthe American Gilsonite Company in a natural and resinous hydro-carbon form found in the Uintah Basin in the Northeastern Utah.The physical and chemical properties of the Gilsonite used are gi-ven in Table 1.

    The blends of asphalt binder were produced with the selectedmodiers by using a laboratory scale mixing device (Fig. 1)equipped with a four-blade impeller as shown in Fig. 2. The blendsNitrogen (weight %) 3.3Oxygen (weight %) 1.4(2011) 30933099In this study, the rheological tests were performed by using aBohlin DSRII rheometer under the controlled-stress conditions attemperatures varying between 52 C and 82 C, and 10 rad/s of

  • current practice is to adjust the temperature of binder such that

    content was changed from 2% to 5% and the Gilsonite from 3% to

    from 2% to 5% with the largest rate of change for the 5% SBS con-tent. The effect of using SBS can be easily observed by noticing thatG/Sind of the base binder is signicantly lower than that of themodied binders. Based on the Superpave PG grading system, thebase binder provides 1.0 kPa of G/Sin d at 55 C, and the 2%, 3%,4% and 5% SBS modied binders provide at 65 C, 69 C, 73 Cand 77 C, respectively. Based on these temperature limits, thehigh temperature performance grades were found as PG-52 forthe base binder, PG-64 for 2% and 3%; PG-70 for 4%; and PG-76

    4 5413.7 2845.75 7010.3 3987.6

    Gilsonite content (%)4 2206.5 944.25 2398.0 1080.56 2623.5 1232.17 3016.2 1416.28 3443.0 1631.09 3992.4 1895.610 4531.8 2146.911 5193.9 2447.912 5919.5 2793.714 7650.6 3545.0

    Combined additive content SBS-Gilsonite (%)28 5647.7 2862.9210 8014.9 4038.5212 9529.8 5216.6214 12764.1 6395.435 6810.0 3341.837 7338.6 4016.039 9067.2 4809.8311 12369.2 6325.544 7725.7 3892.246 9680.8 4986.248 11067.0 5944.8410 13702.3 7536.8

    Fig. 3. G/Sin d of base and SBS modied binders versus temperature.

    l 9012% when the modication to the base binder was applied sepa-rately. Binder modication using the combined modiers was alsoincluded in the experimental program by changing the SBS andGilsonite content together. A summary of the test congurationis given Table 2. The evaluation of the high temperature propertieswas done based on the Superpave asphalt binder test specicationsas dened in AASHTO TP5. One of the main distresses in asphaltpavement roads is the rutting failure which depends on the hightemperature properties of binder. The specication checks for theG/Sin d parameter to be less than 1.0 kPa for unaged binders and2.2 kPa for aged binders processed from the Rolling Thin FilmOven (RTFO) test simulating the aging of binder during mix pro-duction. In terms of the eld performance, a binder with higherG and lower Sin d is desired because it maximizes the G/Sin dindicating an improved binder resistance to rutting under elevatedtemperatures.

    mixing and compaction are achieved at specied viscosity levels,whether using base or modied bitumen, according to the Super-pave mix design methodology. The design specication requires aviscosity level for base binders that need to be lower than 3.0Pa.s at 135C to maintain a reasonable level of workability, in otherwords, easy handling of hot mix asphalt during manufacturing andconstruction. In this study, Brookeld DV-III rotational viscometerwas used to measure the viscosity of base and modied binders.The mixing and compaction temperatures for each combination,e.g., base binder, SBS modied, Gilsonite modied and SBS + Gil-sonite modied binders, were determined based on the viscositylevels at 165 C and 135 C, respectively.

    3. Results and discussion

    3.1. Dynamic shear rheometer test results

    The rheological tests using DSR were conducted to determinethe high temperature properties of the base and modied bindersusing SBS and Gilsonite modiers at varying percentages. The SBSfrequency using 25 mm diameter plate and 1 mm gap opening. Thestress amplitude selected for all the test binders was adjusted toremain within the linear viscoelastic region during the rheologicaltesting.

    The principal viscoelastic parameters obtained from a DSR testare the magnitude of the complex shear modulus (G) and thephase angle (d). G is dened as the ratio of the maximum (shear)stress to the maximum shear strain and provides a measure of thetotal resistance to deformation when the asphalt binder is sub-jected to shear loading [13]. It contains both elastic and viscouscomponents, which are designated as (shear) storage modulus(G0) and (shear) loss modulus (G00), respectively. These two compo-nents are related to the complex (shear) modulus through thephase angle (d), which denes the time lag between the appliedshear stress and shear strain responses during the oscillatory sheartest.

    2.3. Rotational viscosimeter (RV) test

    Asphalt binders must remain sufciently uid or workable athigh temperatures, so that the energy required during the plantmixing, laydown, and compaction phases is minimized. The rota-tional viscometer measures the viscosity of asphalt binder to eval-uate its workability during mixing and compaction processes. The

    B.V. Kk et al. / FueThe measured G /Sin d for the SBS modied binders are given inFig. 3 for the temperature range between 58 C and 82 C. It can beseen that the G/Sin d is improved as the SBS content is increasedTable 2G/Sin d values of test binders.

    Base binder Temperature

    58 C 64 CG/Sin d (Pa)

    801.7 372.4

    SBS content (%)2 2243.7 1139.23 3549.5 1806.3

    (2011) 30933099 3095for 5% SBS modied binder.Using the similar testing procedure, the G/Sin d values for the

    Gilsonite modied binders were also determined and plotted in

  • 903096 B.V. Kk et al. / FuelFig. 4 together with the base binder results. It can be seen thatincreasing the Gilsonite content also improves the rutting param-eter, however, the amount of Gilsonite needed to achieve the sameG/Sind of SBS modied binders nearly doubles. Using the mea-sured temperature limits, the PG grades were found as PG-58 for3%; PG-64 for 6% and 9%; and PG-70 for 12% Gilsonite modiedbinders.

    The change in the rutting parameter for both modiers,however, seems to be more pronounced at relatively lower tem-peratures. As the test temperature is increased the effect of SBSor Gilsonite...

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