Characterization of rutting performance of warm additive modified asphalt mixtures

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  • of

    Brtate

    Warm additive

    Binder rheology

    fuelaininstue ofthathe wixin

    o prodperatully refthese tduce fue of st

    is viewed as not a structure failure, but a serious safety hazard tovehicles because hydroplaning can occur in the presence of ruttingin rainy weather, resulting in serious trafc accidents. Moreover,vehicles tend to be pulled towards the rut path, making it difcultto drive. Many factors can contribute to the rutting distress ofpavement, such as environment (high temperature), truck speedand tire contact pressure; the methods to prevent the rutting are

    and there is possible interaction effect between warm additivesand aging rate. Further, the WMA technology has been evolvedsince its emergence; various warm additive products are availablein the market. The chemical components and physical propertiesvary from product to product. The diversity in the warm additivesmakes the selection of warm additives different; apple-to-applecomparison on their rutting performance should be gained throughfurther research to facilitate the warm additive selection.

    The objective of this research is by incorporating various warmadditives in the study to compare the rutting performance of these

    Corresponding author.

    Construction and Building Materials 31 (2012) 265272

    Contents lists available at

    B

    evE-mail address: yzsjswb.zhao@gmail.com (W. Zhao).regulations (CO2 and noxious substances emission from traditionalasphalt mixture production). Now it has generated waves of inter-est in US among industry practitioners and academic researchers.The general information, industry practices, and environmentalbenets about WMA technology can be found in literature [1,2].

    Rutting is one of the most important distresses for asphalt pave-ments. It is caused by material consolidation and lateral movementdue to repeated heavy wheel loadings on the various pavementlayers/subgrade. The distress is manifested by a depressed rutalong the wheel path on the pavement surface. The rutting distress

    research. Research showed that Sasobit and Evotherm do notincrease the rutting potential, and rutting potential did increasedue to lowered mixing temperature [3,4]. Xiao et al. did researchon the WMA rutting performance with moist aggregate [5], theresults showed the mixture with Sasobit additive exhibited thebest rutting resistance, while the mixture containing Asphamin

    and Evotherm additives generally showed a similar rut resistanceto the controlmixture. However, the research did not quantitativelyseparate the possible effect the warm additives on the asphalt bin-der from the effect of lowered temperature due to reduced aging,1. Introduction

    The technologies that are used tconcrete at a relatively lower temhot mix asphalt (HMA) are generaasphalt (WMA). The occurrence ofnated in Europe in the attempt to reducing asphalt concrete in the fac0950-0618/$ - see front matter 2012 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.12.101uce and place asphaltre than the traditionalerred to as warm mixechnologies was origi-el consumption in pro-ringent environmental

    primarily through engineering an asphalt mixture with improvedshear resistance to withstand problems posed by the environmentand trafc loadings. However, the addition of warm mix additivesinto the asphaltic mixture can complicate the engineering process;more knowledge is needed to assess the inuence of the warmadditives to the pavement rutting performance.

    The rutting performances with some of the commonly usedwarm additives have been investigated individually by previousRuttingPermanent deformation

    performance as the control mixtures. 2012 Elsevier Ltd. All rights reserved.Characterization of rutting performanceasphalt mixtures

    Wenbin Zhao , Feipeng Xiao, Serji N. Amirkhanian,Department of Civil Engineering, Clemson University, Clemson, SC 29634-0911, United S

    a r t i c l e i n f o

    Article history:Received 21 June 2011Received in revised form 27 December 2011Accepted 27 December 2011Available online 28 January 2012

    Keywords:Warm mix asphalt (WMA)

    a b s t r a c t

    Driven by the reduction inthe warm technology has gadditives are available bothWMA. The purpose of thison the rutting performanctions. The results showedto reduced binder aging. Trendered by the lowered m

    Construction and

    journal homepage: www.elsll rights reserved.warm additive modied

    adley J. Putmans

    consumption and CO2 emission in producing and placing asphalt concrete,ed a lot of interests in the recent years in academia and/or industry. Warma liquid and solid state; there are concerns over the rutting performance ofdy is to investigate and characterize the effects of various warm additivesasphalt concrete with different binders and mixing temperature applica-the lowered mixing temperature increases the rutting susceptibility dueax warm additives stiffen the binder, and can offset the rutting problemg temperature, while the chemical warm additives have the same rutting

    SciVerse ScienceDirect

    uilding Materials

    ier .com/locate /conbui ldmat

  • additive modied asphaltic mixtures with the control group andamong themselves, and further to characterize the inuence ofwarm mix modication on permanent deformation performance.

    2. Experimental plan

    A three-factor, full level, well balanced experiment was planned and carried outin a well-controlled lab environment to fulll the objectives of this study. Threeexperimental factors are warm additive, mixing and compacting temperaturesand asphalt binder source. Only one aggregate source is utilized. The Asphalt Pave-ment Analyzer (APA) was conducted to evaluate the rutting performance of themixtures. After the APA test, the binders were extracted from some selected mix-ture types, identifying the possible causative relationship between rheologicalproperties and the rutting performance. The experimental design ow chart is pre-sented in Fig. 1. The rationales for the main experimental factors utilized are pre-

    of the G /sind for the original binders Rolling Thin FilmOven (RTFO)residue binders is the same: at their corresponding test tempera-tures, binder C has the highest value, followed by binder N, thenby binder I.

    3.3. Aggregate

    The aggregate used in this research was from a quarry in South

    266 W. Zhao et al. / Construction and Buildsented in the following paragraphs.

    2.1. Warm additive

    To characterize the rutting performance of warm mix asphaltic mixtures, vari-ous warm additives are needed for further inductive reasoning with respect to moregeneral inference. Four warm additive products were identied and employed inthis study, so that their performance can be compared to the traditional HMA con-trol mix and among themselves as well. All the additives are not involved in foam-ing technology/mechanism. Two additives are in solid state at the roomtemperature, while the other two additives are viscous liquid. The warm additiveswere selected in such a way that the characterization of the products from thesetwo categories (wax and chemical) could be possibly investigated.

    2.2. Mixing temperature

    Three levels of mixing and compaction temperatures were adopted in the study.Warm mix asphalt is produced at temperatures in the range of 1655 C (30100 F) lower than the typical hot mix asphalt [2]. The range of mixing temperaturefrom 120 C to 150 C was studied through three temperature levels with an inter-val of 15 C (Table 1). Further, this temperature arrangement allows the effect oftemperatures on rutting performance to be separated from the warm additives.The temperature arrangement can also allow the effect to be evaluated throughchanges in binder aging during the production process. The compaction tempera-tures are lower than the mixing temperatures by 15 C at every treatment level.

    2.3. Binder source

    Three binder sources and one aggregate were utilized in the study. Asphalt iscomprised of various compounds, and is usually melted into a liquid state by apply-ing heat to a predetermined temperature before mixing with aggregates. In thisstudy, the utilized warm additives were either organic waxes or chemicals; at theelevated mixing temperature, the chemicals in the asphalt and warm additivesmay interact with each other in various ways such as physical interaction or chem-ical reaction. The alleged interactions can further inuence the properties of theasphaltic mixtures made with the warm additives. Compared with asphalt, the min-eral components in aggregate material are relatively stable and inert; therefore,warm additives are more likely to interact and undergo chemical reaction with bin-der than aggregate. It is very important to examine whether the effects of the warmadditives on the mixture properties, if any that would be found in this study, will bevalid just in one particular asphalt binder or many binders. Utilizing binder fromdifference sources/grades can provide a wide context in which the warm additiveeffects would be characterized.

    0 (No Additive) Additive A Additive B

    Binder N: PG 58-28 Binder C: PG 64-22 Binder I: PG 64-22

    Additive C Additive D

    High: 150 C

    Medium: 135C

    Low: 120 C

    Mixing Temperature

    Extract binder from selected

    mixtures; Conduct DSR tests

    Fig. 1. The experimental design ow chart.3. Materials

    3.1. Warm additives

    Four warm additive products were investigated in the experi-ment; the binder without any additive was the control and referredas virgin binder throughout this paper. All the additives involveno foaming mechanism in producing WMA. The manufacturer rec-ommended dosages were adopted to add the warm additives intothe asphalt mixtures. Additives A and B are wax products; bothwere added at a rate of 1.5% by the weight of asphalt binder. Addi-tives C and D are identied as chemical products at the room tem-perature, and added at a rate of 0.3% and 0.5% by the weight ofasphalt binder, respectively. The physical properties of the warmadditives are presented in Table 2.

    All the additives were added into the binder before mixing, andthe uniformity of the subsequent binders were achieved by thor-ough hand blending at the target mixing temperatures. During thisblending process, a certain amount of physical effort was requiredto overcome the resistance of the binder to the blending spatula.The degree of resistance was a reection of the viscosities of themodied binders at the corresponding temperatures. Comparedto the virgin binder (no warm additives), the same level of blendingeffort was noticed to stir the additives A and B modied binders.However, an appreciable lower blending effort was required inblending binder with additives C or D, as compared with the effortin blending virgin binder (no warm additives). This may indicatethe manufacturer recommended additive dosage might not be en-ough to obtain and adequate viscosity level such as the one speci-ed for HMA mixing (0.28 0.03 Pa s). When the binders weremixed with aggregate to produce asphaltic mixtures, the mixingtime at lower temperatures for virgin and chemical-modied bind-ers (additives A and B) was extended to a longer period to obtain auniform binder coating. The viscosity reduction and workability ofWMA binder using the same warm additives can be found in an-other study [6]. Nevertheless, this paper mainly focuses on theeffects and characterization of warm additives on the ruttingperformance of WHA mixtures, rather than the workability.

    3.2. Asphalt binders

    Two PG 62-22 binders were used in this study. They were desig-nated as binder C and I, respectively. One PG 58-28 softer binderwas utilized and designated as binder N; it came from the same as-phalt binder terminal as binder I. The Superpave binder physicalproperties are listed in Table 3. It should be noted that the ranking

    Table 1Mixing and compacting temperatures.

    Treatment levels Mixing temperatures Compacting temperatures

    C F C F

    High level 150 302 135 275Medium level 135 275 120 248Low level 120 248 105 221

    ing Materials 31 (2012) 265272Carolina. It is composed predominantly of quartz and potassiumfeldspar. The related physical properties of the aggregate are re-ported in Table 4.

  • Table 2Warm additive physical and chemical properties.

    Properties A B

    Ingredients Solid saturated hydrocarbons Fatty polyamines, polymcomponents, fatty amine

    Physical state Pastilles, akes Solid pelletsColor Off-white to pale brown BrownOder Practically odorless Amine likeMolecular weight Approx. 1000 g/mole Specic gravity 0.9 (25 C) Vapor density Bulk density Ph values Neutral Boiling point Flash point 285C (ASTM D92) Closed cup:>93.3 CSolubility in water Insoluble Insoluble in cold water

    Table 3Superpave binder properties for the virgin binders.

    Parameters Bin

    C (

    OriginalViscosity, Ps-s (135 C) 0.6G/sind, (Pa) (64/58 C) 180

    RTFO residueMass change, (%) (165 C) 0G/sind, (Pa) (64/58 C) 460

    PAV residueGsind, (kPa) (25/19 C) 242Stiffness (60 s), (MPa) (12/18 C) 129m-value (60 s) (12/18 C) 0.3

    Table 4Aggregate physical properties.

    Coarse aggregate

    L.A. abrasion loss (%) Absorption (%) Specic gravity

    Dry (BLK) SSD (BLK) Appa

    30 0.5 2.63 2.64 2.66

    Fine aggregateFineness modulus Absorption (%) Specic gravity, SSD (BLK)

    3.2 0.6 2.64

    Fig. 2. Aggregate gradation chart.

    W. Zhao et al. / Construction and BuildC D

    er, non-ionic, glycol

    Polymer, fatty acid amine Modied tall oil fatty acidpolyamine condensate water

    Liquid Viscous liquidAmber (dark)Fishy, amine-like

    1.0 1.031.08 100 C>100 C Insoluble Soluble

    ing Materials 31 (2012) 265272 2674. Gradation, mix design and specimen fabrication

    The South Carolina Department of Transportation (SCDOT)technical specication for Hot-Mix Asphalt material properties[7] was followed to conduct the aggregate gradation and mix de-sign. Aggregate gradation chart is shown in Fig. 2; along with itare the curves of other restrictive requirements, such as the SC highand low spec limits, AASHTO control points, and Superpave maxi-mum density line. The designed aggregate gradation meets thetype B surface course (high volume primary roads) requirementsstipulated by the SC DOT technical specications. The nominalmaximum aggregate size (NMAS) is 12.5 mm. The optimum bindercontent was determined to correspond to the air voids content of4% in the total mix under 75 gyrations. The optimum binder con-tent is 5.35% in this study.

    Identical specimens were prepared by compacting the samplesusing Superpave Gyratory compactor for both the HMA and WMA

    der source

    PG64-22) I (PG64-22) N (PG58-28)

    26 0.405 0.311 1207 1378

    .24 0.02 8 2815 3875

    0 2970 4064183 249

    54 0.311 0.281

    Soundness % loss at 5 cycles Sand equivalent Hardness

    rent 3/43/8 3/8#4

    1.7 4.1 53 6

    Soundness % loss

    0.1

  • mixtures involved in this study. The target air voids content wasset at 4% for the APA rut test. Two replicates were fabricated foreach treatment combination.

    5. Test method

    5.1. The APA test

    Asphalt Pavement Analyzer was utilized to investigate therutting susceptibility of the mixtures. The standard test procedure

    268 W. Zhao et al. / Construction and Buildthat was followed in this study can be found in AASHTO TP 63...

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