Influence of compaction temperature onrubberized asphalt mixes and binders

Soon-Jae Lee, Serji N. Amirkhanian, Khaldoun Shatanawi, and Carl Thodesen

Abstract: This research investigates the influence of compaction temperature on rubberized asphalt mixes and binders.For this, four Superpave mix designs for four asphalt binders (control, 3% styrene–butadiene–styrene (SBS)-modified,10% rubber-modified, and 15% rubber-modified) were carried out. A total of 160 specimens were manufactured at fourcompaction temperatures of 116, 135, 154, and 173 8C. The binders were artificially short-term aged for 2 h at the mixturecompaction temperatures prior to the binder tests. The results from this study showed that: (i) the control and SBS-modifiedmixtures could have almost the same air–void contents at a wide range of compaction temperatures; (ii) the compac-tion temperatures significantly affected the volumetric properties of the rubberized mixes; (iii) the aging difference ofasphalt binder in the mixture depending on the compaction temperature is not considered to be a main factor affectingthe volumetric properties of the mixtures.

Key words: compaction temperature, rubberized mixes, volumetric properties.

Resume : La presente recherche a ete entreprise afin d’etudier l’influence de la temperature de compaction sur les melan-ges asphaltiques et les liants caoutchoutes. Quatre melanges Superpave ont donc ete concus pour quatre liants asphaltiques(de reference, modifie avec 3 % de « styrene–butadiene–styrene (SBS) », modifie avec 10 % de caoutchouc et modifieavec 15 % de caoutchouc) ont ete realises. Un total de 160 echantillons a ete fabrique a quatre temperature de compaction,soit 116, 135, 154 et 173 8C. Les liants ont ete vieillis artificiellement pendant deux heures a la temperature de compac-tion de melange avant les essais de liants. Les resultats de cette etude montrent que (i) les melanges de reference et modi-fies par « SBS » pourraient avoir presque le meme contenu de vides interstitiels a une large plage de temperatures decompaction; (ii) les temperatures de compaction affectent grandement les proprietes volumetriques des melanges caout-choutes; (iii) la difference de vieillissement du liant asphaltique dans le melange selon la temperature de compaction n’estpas consideree un facteur important qui affecte les proprietes volumetriques des melanges.

Mots-cles : temperature de compaction, melanges caoutchoutes, proprietes volumetriques.

[Traduit par la Redaction]

Introduction

BackgroundIn hot-mix asphalt (HMA) pavements, compaction is de-

fined as the process by which the volume of air in a HMAmixture is reduced through the application of externalforces. The expulsion of air enables the mix to occupy asmaller space, thereby increasing the unit weight or densityof the mix. Compaction is an essential factor in the designand subsequent production of asphalt mixtures (Roberts etal. 1996).

The compaction temperature influences workability,

which is related to the achieved density of the mixture. Thecompaction temperature recommended in the current Super-pave procedures for asphalt mixtures (The Asphalt Institute2003) is determined as the range of temperatures where anunaged asphalt binder has a viscosity of 0.28 ± 0.03 Pa�s.This requirement was based on experience with conven-tional asphalt binders. In general, the binder in modified as-phalt mixtures is stiffer than in conventional mixtures;therefore, there is a need for a higher compaction tempera-ture. However, previous studies (Bahia 2000; Huner andBrown 2001) on the effect of compaction temperature onthe volumetric properties of asphalt mixtures reported thatspecimens could have the same volumetric properties over avery wide range of compaction temperatures. Azari et al.(2003) also suggested that a temperature range from 119 to159 8C could be used for modified mixtures with thelimestone–Novophalt binder.

In terms of rubberized asphalt mixtures, the compactiontemperature should be determined carefully because the vis-cosity and amount of the asphalt rubber binder, in general, af-fect the compactability of the mixtures. Based on experiencein the field, rubberized asphalt mixtures are compacted at ahigher temperature than conventional mixtures. However, theeffect of compaction temperature on rubberized asphalt mix-tures is considered to be somewhat unclear because the phys-

Received 7 January 2008. Revision accepted 27 March 2008.Published on the NRC Research Press Web site at cjce.nrc.ca on28 August 2008.

S. Lee,1,2 S.N. Amirkhanian, K. Shatanawi, and C. Thodesen.Department of Civil Engineering, Clemson University. Clemson,SC 29634-0911, USA.

Written discussion of this article is welcomed and will bereceived by the Editor until 31 January 2009.

1Corresponding author (e-mail: soonjae93@gmail.com).2Present address: Department of Technology, Texas StateUniversity - San Marcos, San Marcos, TX 78666, USA.

908

Can. J. Civ. Eng. 35: 908–917 (2008) doi:10.1139/L08-045 # 2008 NRC Canada

Fig. 1. Flowchart of experimental design procedures for evaluating the effect of compaction temperature on (a) four asphalt mixtures and(b) four asphalt binders. SBS, styrene–butadiene–styrene; STOA, short-term oven aging; SGC, Superpave gyratory compactor; RTFO, roll-ing thin film oven test; DSR, dynamic shear rheometer; GPC, gel permeation chromatography.

Lee et al. 909

# 2008 NRC Canada

ical and chemical properties of the mixtures as a function ofthe compaction temperature are not well understood.

Research objective and scopeThe main objective of this research was to investigate the

effect of compaction temperature on the properties ofrubberized asphalt mixtures and binders. Four mixtures[control: performance grade (PG) 64–22, 3% styrene–butadiene–styrene (SBS)-modified PG 76–22, 10% rubber-modified, and 15% rubber-modified binders] were designedusing Superpave mix design specifications. The mixtureswere compacted at temperatures of 116, 135, 154, and173 8C. Volumetric properties of these mixtures, includingair voids of as-compacted, horizontally-cut, and vertically-cutspecimens, were evaluated. Also, binder stiffness at com-paction temperatures, rutting resistance factor G*/sind, andmolecular size distribution of binders after short-term agingat compaction temperatures were measured. Figure 1 showsa flowchart of the experimental design used in this study.

Materials and test program

MaterialsThe crumb rubber modifier (CRM), produced by mechan-

ical shredding at ambient temperature, was obtained fromone source, No. 40 mesh (0.425 mm), and was used with agradation as shown in Table 1, which is widely used to pro-duce CRM mixtures in South Carolina. To ensure that theconsistency of the CRM was maintained throughout thestudy, only one batch of crumb rubber was used in thisstudy.

Four binders (control PG 64–22, 3% SBS-modified PG76–22, 10% rubber-modified, and 15% rubber-modifiedbinders) were used in this study. The control and 3% SBS-modified binders were collected from one source. Rubber-modified binders were manufactured in the laboratory bymixing the CRM with the binder at 177 8C using an open-blade mixer at a blending speed of 700 rpm for 30 min(Shen et al. 2006). This mixing condition matches the fieldpractices used in South Carolina to produce field mixtures.The properties of all the binders are shown in Table 2.

One granite aggregate source was used for preparingsamples. Hydrated lime, which was used as an anti-stripadditive, was added at a rate of 1% by dry mass of aggregate.

Superpave mix designsA nominal maximum size 9.5 mm Superpave mixture was

used for the mix design in this study. The procedures de-scribed in the American Association of State Highway andTransportation Officials (AASHTO) standard AASHTOT312 (AASHTO 2008) regarding the preparation of HMAspecimens were followed. All mixtures used an identicalstructure of aggregate to distinguish the influence of thebinders. Optimum asphalt contents were determined fromthese designs and used to produce specimens at four differ-ent compaction temperatures.

Compaction as a function of temperatureThe mixing of the aggregate with the asphalt binders was

conducted at temperatures determined using a plot of viscos-ity versus temperature. The loose asphalt–aggregate mix-

tures were oven aged at the compaction temperatures for2 h prior to the compaction. The four compaction tempera-tures used were 116, 135, 154, and 173 8C. This range wasselected based on the temperatures (135 8C and 154 8C)which are commonly used as short-term oven aging temper-atures in the laboratory to simulate binder aging and absorp-tion during the construction of HMA pavements (TheAsphalt Institute 2003).

The specimens were fabricated to the two target air–voidcontents of 7 ± 1% and 4 ± 1% using 30 and 70 gyrations ofa Superpave gyratory compactor (SGC), respectively. Eachspecimen was 150 mm in diameter and 100 ± 5 mm inheight. A total of 160 specimens [4 binders � 4 compactiontemperatures � 2 gyration levels � 6 (for 30 gyrations) or 4repetitions (for 70 gyrations)] were prepared and tested.

Volumetric propertiesAfter the air–void contents were measured, four speci-

mens from each set (10 specimens) were three-slice cut hor-izontally and two of the four specimens were cut verticallyas shown in Fig. 2. The specimens were cut using diamond-tipped saw blades. The volumetric properties of cut speci-mens were measured.

Rotational viscometerSuperpave binder specifications (The Asphalt Institute

2003) include a maximum 135 8C viscosity requirement (3Pa�s) for an unaged binder. In this study, a rotational viscos-ity test [AASHTO T316 (AASHTO 2006)] was conducted atfour different test temperatures of 116, 135, 154, and 173 8Cto verify the viscosity change as a function of temperature.

Dynamic shear rheometerTo evaluate the effect of short-term oven aging (STOA) at

compaction temperatures on the binders, G*/sind of thebinders was measured using the dynamic shear rheometer(DSR) test [AASHTO T 315 (AASHTO 2008)]. The testwas conducted at 64 8C with the binders being short-termaged for 2 h at temperatures of 116, 135, 154, and 173 8Cusing a rolling thin film oven (RTFO) procedure prior tothe testing.

Gel permeation chromatographyTypically, the gel permeation chromatography (GPC) test

is used to measure the molecular size distribution of a sub-stance with silica gel porous columns through which thesample solution is pumped. The response obtained by thedetector of the GPC is recorded as the elution time in-creases. A sample of asphalt binder was first weighed andallowed to dissolve in a tetrahydrofuran solvent with the

Table 1. Gradation of crumb rubber.

Ambient crumb rubber

Sieve No. (mm) Retained (%) Cumulative retained (%)30 (600) 0 040 (425) 9.0 9.050 (300) 31.9 40.980 (180) 32.9 73.8100 (150) 7.6 81.4200 (75) 18.6 100.0

910 Can. J. Civ. Eng. Vol. 35, 2008

# 2008 NRC Canada

asphalt concentration in the solvent adjusted to 1/400. Next,the solution was drawn with an injector and then filteredthrough a 0.45 mm filter to ensure the purity of the solution.Third, 0.5 mL of the solution was then immediately drawnand injected into the GPC system. The solution waspumped through the gel permeation columns and allowed

to flow at a rate of 1 mL/min. This test was conducted at35 8C for 30 min for each injection, and three duplicateinjections were used for each binder sample. A more de-tailed explanation regarding the GPC test method can befound in previous studies (Kim et al. 1995, 2006; Shen etal. 2007).

Table 2. Properties of four binders.

Aging states Test properties Control PG 64–22 3% SBS-modified 10% rubber-modified 15% rubber-modifiedUnaged binder Viscosity @ 135 8C (Pa�s) 0.430 1.475 1.226 2.308

G*/sind @ 64 8C (kPa) 1.279 — 2.974 —G*/sind @ 76 8C (kPa) — 1.338 0.742 1.294

RTFO agedresidue

G*/sind @ 64 8C (kPa) 2.810 — — —

G*/sind @ 76 8C (kPa) — 2.508 2.060 2.990RTFO + PAV

aged residueG*sind @ 25 8C (kPa) 4074 — — —

G*sind @ 31 8C (kPa) — 2129 4480 4112Stiffness @ –12 8C (MPa) 217 212 243 225m-value @ –12 8C 0.307 0.310 0.330 0.331

Note: G*/sind, rutting resistance factor; Control PG 64-22, virgin binder; SBS, styrene–butadiene–styrene; RTFO, rolling thin film oven; PAV, pressureaging vessel; m-value, low-temperature cracking property.

Fig. 2. Specimens: (a) as-compacted, (b) horizontally-cut, and (c) vertically-cut.

Lee et al. 911

# 2008 NRC Canada

Analysis methodStatistical analysis was conducted using analysis of var-

iance (ANOVA) of the statistical analysis system (SAS),version 8.0, software program (SAS Institute Inc., Cary,N.C.). The significance level used in this study was 0.95(a = 0.05), which means that each finding has a 95% chanceof being true. The primary variables included the effects ofthe binder types (control, SBS-modified, 10% rubber-modified, and 15% rubber-modified binders), the compac-tion temperatures (116, 135, 154, and 173 8C), and thespecimen sections (top, middle, and base of specimen).

Results and discussion

Superpave mix designsTable 3 shows the optimum asphalt content (OAC), max-

imum specific gravity (MSG), and bulk specific gravity(BSG) data of the mix designs with four different binders.The optimum asphalt contents (OACs) were observed to be4.6%, 4.7%, 6.0%, and 6.2% for the mixtures with control,SBS-modified, 10% rubber-modified, and 15% rubber-modified binders, respectively. This finding is consistentwith the previous research indicating that the OACs forthe CRM mixtures are approximately 1% higher than thoseobtained for conventional mixtures (Shen et al. 2006; Xiaoet al. 2007). Researchers have indicated that the higherOAC for mixtures using the CRM binder is attributed tothe thicker film of the CRM binder coating the aggregatedue to the presence of the rubber particles.

Air–void properties as a function of compactiontemperature

As-compacted specimensFigure 3 illustrates the air–void contents of the as-com-

pacted specimens as a function of the compaction tempera-ture. In general, it was found that specimens made withcontrol or SBS-modified binders had almost the same air–void content over a very wide range of compaction temper-atures (116 to 173 8C). This means that it is possible to sat-isfy the two target air–void contents of 7 ± 1% and 4 ± 1%using 30 and 70 gyration levels, respectively, of SGC at allcompaction temperatures used in this study. However, interms of rubber-modified mixtures, the air–void contentssignificantly decreased with an increase in the compactiontemperature. For 30 gyrations (Fig. 3a), with 10% rubber-modified asphalt, the suitable compaction temperature wasfound to be slightly higher than 154 8C, but not more than173 8C. For the 15% rubber-modified asphalt, the compac-tion temperature to satisfy the target air–void contents wasbetween 160 8C and 173 8C. For 70 gyrations (Fig. 3b), thesuitable compaction temperature for both the 10% and 15%

rubber-modified asphalt was approximately 154 8C, meaningthat the compaction temperature range for rubber-modifiedasphalts is narrower than that of the control or SBS-modified binders. Based on the findings, it is recom-mended that a compaction temperature of at least 154 8C,in the mix design stage, is needed for the two rubber-modified asphalts used in this study.

Table 4 shows the statistical results regarding the changein the air voids with the increase in compaction temperature.The air–void contents of the rubber-modified mixture wereobserved to be affected significantly by compaction temper-ature. Still, there was no significant difference at the a =0.05 level among the air–void contents of four compactiontemperatures in both control and SBS-modified mixtures.This finding has been reported through previous research(Azari et al. 2003; Bahia 2000; Lee et al. 2007). The othervolumetric properties, such as % voids filled with asphalt(VFA), % voids in mineral aggregates (VMA), and ruttingproperties depending on compaction conditions (four tem-peratures and five levels) are discussed in a previous paper(Lee et al. 2007).

Horizontally-cut specimensTo examine the homogeneity of air–void contents

throughout each specimen, four specimens from each setwere randomly selected and three-slice cut horizontally(Fig. 2), and the air–void content of each slice was meas-ured (Fig. 4). The results indicated that the middle sectionof all specimens had the lowest air-void content comparedwith the top or base sections of specimens. The result isthought to be associated with the two smooth surfaces ofthe middle section, whereas the top and base sections havea smooth surface and a rough surface. Similarly, Hunter etal. (2004) reported that gyratory compaction created a speci-men with a high air–void content peripherally and low air–void content centrally. Before measuring air– void contentsof horizontally-cut specimens, it was predicted that the airvoid of the top section may be less than that of the base sec-tion. In Fig. 4, it is difficult to find this trend (the air void ofthe top section is less than the air void of the base section)in the control or SBS-modified mixture. With respect to therubber-modified mixtures, a general trend can be observed:the air–void difference between the top and base sections isdependent on the air–void content. In most cases of rubber-ized mixtures, the air void of the top section was lower thanthat of the base section when the air void was relativelyhigh. On the other hand, a relatively low air void resultedin the higher air void for the top section.

Vertically-cut specimensThe side-by-side halves were also compared in terms of

differences in air–void contents. One-way and two-way

Table 3. Results of superpave mix designs.

Mixtures

Properties Control 3% SBS-modified 10% rubber-modified 15% rubber-modifiedOAC (%) 4.6 4.7 6.0 6.2MSG 2.438 2.433 2.387 2.375BSG 2.331 2.336 2.291 2.269

Note: OAC, optimum asphalt content; MSG, maximum specific gravity; BSG, bulk specific gravity; SBS,styrene–butadiene–styrene.

912 Can. J. Civ. Eng. Vol. 35, 2008

# 2008 NRC Canada

analyses of variance of the air–void data measured from theside-by-side specimens indicated that the difference in theair–void content is not statistically significant at the 5%level for all mixtures.

Binder viscosity as a function of compaction temperatureFigure 5 depicts the change in viscosity of four asphalt

binders as the test temperature increases from 116 to173 8C. As expected, the higher test temperature led to a de-

Table 4. Statistical analysis results for air–void gradient of as-compacted specimen (a = 0.05).

Mixtures

Air void Control 3% SBS-modified 10% rubber-modified 15% rubber-modified30 gyrations 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

A A A A A A A A A B B C A A A* CB B B{

70 gyrations 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4A A A A A A A A A A A B A A A* C

B B B{

Note: SBS, styrene–butadiene–styrene; 1, 116 8C (compaction temperature); 2, 135 8C; 3, 154 8C; 4, 173 8C. Air voids of compactiontemperatures with the same letter are not significantly different at the 95% level within each mixture.*Pertains to 1 and 2 in row above.{Pertains to 2 and 3, two rows above.

Fig. 3. Change in air–void contents as a function of compaction temperature with (a) 30 gyration level and (b) 70 gyration level of Super-pave gyratory compactor. SBS, styrene–butadiene–styrene.

Lee et al. 913

# 2008 NRC Canada

crease in the high temperature viscosity of the binderstested. At 116 8C, the viscosity of 3% SBS-modified binderwas approximately five times higher than that of controlbinder, but the mixtures with SBS-modified or control bind-ers showed almost the same volumetric properties at thecompaction temperature of 116 8C (Fig. 3). A possible rea-

son may be that the SGC will compact specimens to nearlythe same density unless the workability is changed drasti-cally. However, this trend was not consistent for mixtureswith rubber-modified binders. Because of the presence ofrubber particles, the viscosity and amount of the asphalt rub-ber binder are considered to affect the compactability of the

Fig. 4. Air–void contents of horizontally-cut specimens. SBS, styrene–butadiene–styrene; T, top of specimen; M, middle of specimen; B,base of specimen; V, air void of top is greater than air void of base; =, air void of top is same as air void of base; ^, air void of top is lessthan air void of base.

914 Can. J. Civ. Eng. Vol. 35, 2008

# 2008 NRC Canada

mixtures. From the results, it was observed that the viscosityproperties of rubber-modified binders cannot be used to de-termine the compaction temperature of the mixtures.

Binder properties after short-term aging at compactiontemperature

Figure 6 shows the relationship between the G*/sindvalue at 64 8C and the RTFO aging temperature for four as-phalt binders. The G*/sind value significantly increased asthe short-term aging temperature increased from one temper-ature to the next. The change in large molecular size (LMS)value of the asphalt binder with aging temperature is illus-trated in Fig. 7. All four asphalt binders exhibited higherLMS values for the higher aging temperature, a trend similarto the G*/sind value from the DSR test. It is generallyconsidered that there is significant correlation between LMSvalues and physical properties of binders, and rubber-modified binders seem to have similar correlation betweenthe LMS value and the G*/sind value. As binder propertiesmeasured in this study were too sensitive to the aging tem-perature, it was difficult to find any relationship betweenthe volumetric properties of the mixture and the propertiesof the asphalt binder in the mixture at the compaction tem-perature. In other words, the aging difference of asphaltbinder in the mixture depending on the compaction temper-ature is not considered to be a main factor affecting themixture properties tested in this study.

Summary and conclusionsTo investigate the effect of compaction temperature on as-

phalt mixtures with rubber-modified binders, two rubberizedmixtures were designed with one aggregate source and tworubber contents. Two other mixtures (control binder of PG64–22 and 3% SBS-modified binder of PG 76–22) werealso made using the same aggregate source and gradationfor comparison purposes. The rubber-modified binders wereproduced using a base binder of PG 64–22 with 10% or 15%ambient rubber by weight of the binder. A total of 160specimens were fabricated using a Superpave gyratory com-pactor at four compaction temperatures of 116, 135, 154,

and 173 8C. Volumetric properties of the mixtures weremeasured of the as-compacted, horizontally-cut, and verti-cally-cut specimens. In addition, the binder stiffness at thecompaction temperatures, and G*/sind and molecular sizedistribution of binders after short-term aging at the mixturecompaction temperatures, were obtained and evaluated.From these test results, the following conclusions weredrawn:

� Similar to the previous studies, the difference in the air–void contents as a function of the compaction tempera-tures was observed to be statistically insignificant for thecontrol and SBS-modified mixtures. The specimens couldhave the same volumetric properties at a wide range ofcompaction temperatures from 116 to 173 8C.

� In the mixtures containing rubber-modifeid binders, theair–void contents significantly decreased with an increasein compaction temperature. The compaction temperaturewas found to have statistically significant influence onthe air–void contents of the mixtures. Also, the mixtureswith rubber-modified binders were found to satisfy thetarget air–void content of 4% at a compaction tempera-ture of approximately 154 8C.

� Generally, the specimens of rubberized mixtures thatwere three-slice cut horizontally showed that the air–void content of the top section was less than that of thebase section when the total air–void content was rela-tively high.

� The differences in the air–void contents of the specimensthat were cut vertically were not statistically significantat the 5% level, irrespective of mix type.

� Binder properties after being subjected to short-termaging at the compaction temperature were too sensitiveto the aging temperature and it is concluded that the bin-der properties used in this study are not considered to beassociated with the volumetric properties of the mixturesat the compaction temperatures.

� It is recommended that another study be conducted with ahigher rubber percentage than 15% and various crumbrubber sizes, and that the engineering properties of rub-berized mixtures, to correlate with the volumetric proper-

Fig. 5. Change in viscosity of asphalt binder with temperature. SBS, styrene–butadiene–styrene.

Lee et al. 915

# 2008 NRC Canada

ties of the mixtures at different compaction temperatures,be evaluated.

AcknowledgementsThis study was supported by the Asphalt Rubber Technol-

ogy Service of the Civil Engineering Department, ClemsonUniversity, Clemson, South Carolina, USA. The authorswish to acknowledge and thank South Carolina’s Depart-ment of Health and Environmental Control for their finan-cial support of this project.

ReferencesAASHTO. 2006. Standard method of test for viscosity determina-

tion of asphalt binder using rotational viscometer. Single userdigital publication. American Association of State Highway andTransportation Officials (AASHTO), Washington, D.C.

AASHTO. 2008. Standard method of test for preparing and deter-mining the density of hot mix asphalt (HMA) specimens bymeans of the Superpave gyratory compactor. Single user digitalpublication. American Association of State Highway and Trans-portation Officials (AASHTO), Washington, D.C.

Azari, H., McCuen, R.H., and Stuart, K.D. 2003. Optimum com-paction temperature for modified binders. Journal of Transporta-tion Engineering, 129(5): 531–537. doi:10.1061/(ASCE)0733-947X(2003)129:5(531).

Bahia, H.U. 2000. Recommendations for mixing and compactiontemperatures of modified binders. National Cooperative High-way Research Program Report 9–10, Transportation ResearchCouncil, Washington, D.C.

Huner, M.H., and Brown, E.R. 2001. Effects of re-heating andcompaction temperature on hot mix asphalt volumetric. NationalCenter for Asphalt Technology Report 01–04, Auburn, Ala.

Hunter, A.E., Airey, G.D., and Collop, A.C. 2004. Aggregate orien-tation and segregation in laboratory-compacted asphalt samples.

Fig. 7. Change in large molecular size (LMS) of asphalt binder with change in aging temperature. RTFO, rolling thin film oven; SBS,styrene–butadiene–styrene.

Fig. 6. Change in G*/sind of asphalt binder with change in aging temperature (test temperature = 64 8C). RTFO, rolling thin film oven;SBS, styrene–butadiene–styrene.

916 Can. J. Civ. Eng. Vol. 35, 2008

# 2008 NRC Canada

Transportation Research Record, 1891: 8–15. doi:10.3141/1891-02.

Kim, K.W., Burati, J.L., and Park, J.S. 1995. Methodology for de-fining LMS portion in asphalt chromatogram. Journal of Materi-als in Civil Engineering, 7(1): 31–40. doi:10.1061/(ASCE)0899-1561(1995)7:1(31).

Kim, K.W., Kim, K.A., Doh, Y.S., and Amirkhanian, S.N. 2006.Estimation of RAP’s binder viscosity using GPC without binderrecovery. Journal of Materials in Civil Engineering, 18(4): 561–567. doi:10.1061/(ASCE)0899-1561(2006)18:4(561).

Lee, S.-J., Amirkhanian, S.N., Putman, B.J., and Kim, K.W. 2007.Laboratory study of the effects of compaction on the volumetricand rutting properties of CRM asphalt mixtures. Journal of Ma-terials in Civil Engineering, 19(12): 1079–1088. doi:10.1061/(ASCE)0899-1561(2007)19:12(1079).

Roberts, F.L., Kandhal, P.S., Brown, E.R., Lee, D.-Y., and Ken-nedy, T.W. 1996. Hot mix asphalt materials, mixture designand construction. National Asphalt Pavement Association Re-search and Education Foundation, Lanham, Md.

Shen, J., Amirkhanian, S.N., Lee, S.-J., and Putman, B.J. 2006. Re-cycling of laboratory prepared RAP mixtures containing crumbrubber modified binders in HMA. Transportation Research Re-cord, 1962: 71–78. doi:10.3141/1962-09.

Shen, J., Amirkhanian, S.N,, and Lee, S.-J. 2007. HP-GPC charac-terization of rejuvenated aged CRM binders. Journal of Materi-als in Civil Engineering, 19(6): 515–522. doi:10.1061/(ASCE)0899-1561(2007)19:6(515).

The Asphalt Institute. 2003. Performance graded asphalt binderspecification and testing, SP-1. The Asphalt Institute, Lexington,Ky.

Xiao, F.P., Amirkhanian, S.N., and Juang, H.S. 2007. Rutting resis-tance of rubberized asphalt concrete pavements containing re-claimed asphalt pavement mixtures. Journal of Materials inCivil Engineering, 19(6): 475–483. doi:10.1061/(ASCE)0899-1561(2007)19:6(475).

Lee et al. 917

# 2008 NRC Canada