Novel Method to Prepare Activated Crumb Rubber Used forSynthesis of Activated Crumb Rubber Modified Asphalt

Maozhen Xu1; Jinjing Liu2; Wenzhi Li3; and Wenfeng Duan4

Abstract: This work introduced a novel method to prepare activated crumb rubber by using ultrasonic focusing apparatus, which could moresignificantly improve the compatibility between the activated crumb rubber and virgin asphalt compared with ordinary crumb rubber. Theobtained activated crumb rubber was used for the synthesis of activated crumb rubber modified asphalt (ACRMA) by blending virgin asphalt,activated crumb rubber, and certain additives (e.g., SBS, antiaging agent, filler). The performance test results indicated that ACRMA hadbetter performance than the ordinary crumb rubber modified asphalt, in terms of high-temperature property, low-temperature stiffness, duc-tility, especially fatigue resistance, and aging resistance. In this case, the application of novel method of activated crumb rubber synthesiscould accelerate the material acceptance rate in pavement engineering. DOI: 10.1061/(ASCE)MT.1943-5533.0001115. © 2014 AmericanSociety of Civil Engineers.

Author keywords: Crumb rubber; Modification; Performance; Interaction effect; Bituminous/flexible pavements.

Introduction

Petroleum asphalt, a complex, heterogeneous mixture of varioushydrocarbons, has been widely used as a binder for aggregatematerial in pavement engineering. However, due to its disadvantageof crack prone in low temperature, poor aging resistance andfatigue resistance, it could not meet high requirement and heavyload of modern traffic on the road (Endres et al. 1951; Navarro et al.2004, 2007; Upadhyay et al. 2008). Therefore, the development ofmodified asphalt has become a hot topic in recent decades.

Crumb rubber modified asphalt (CRMA) has become more andmore popular for its well-known advantages including a noticeablereduction in temperature susceptibility, increased aging propertyand pavement service life, retarded reflection cracking, decreasedtraffic noise, reduced maintenance cost, decreased pollution, andincreased environmental quality (Morrison and Hesp 1995). How-ever, there is still some limitation on the wide application of theCRMA due to the following reasons: the concentration of crumbrubber must be higher than 20% to ensure the desired property,which resulted in the increase of CRMA viscosity. To achievethe processing feasibility, the viscosity of CRMA should bereduced. Increasing process temperature could help the viscositydecrease, but this change may cause CRMA to be aged easily andcreate high-processing risk and environment pollution. Therefore,

a new approach of activation was proposed to improve the compat-ibility between virgin asphalt and crumb rubber and change theirinterface combination.

In this work, we developed a novel method to prepare theactivated crumb rubber using ultrasonic focusing apparatus and se-lected the activated crumb rubber as an asphalt modifier. Comparedwith the current existing method (dynamic desulphurizion), it hadmany advantages as subsequently shown. First of all, this methodhad the better production efficiency compared with the currentexisting method. Then, it would not generate any industrial waste-water and gases in the making process. Lastly, the modificationeffect was quite obvious.

With the application of this method, the mixing amount of ac-tivated crumb rubber in asphalt system was improved significantlyfrom 16 to 25% by weight. Based on the performance of ACRMA,we determined the effect of activated crumb rubber structure ondiffusion and clarified the type of rubber-asphalt interaction byscanning electronic microscope (SEM) and fluorescence micro-scope, respectively. It was expected that the better understandingof asphalt-rubber interaction would be essential to optimizingthe performance of activated crumb rubber modified binder(ACRMB), thus, to accelerating the acceptance rate of these ma-terials in construction field.

Materials and Experimental

Materials

Virgin asphalt (AH-70, pen) was offered by China Petroleum &Chemical Corporation. Table 1 showed its relevant performanceindexes. The ordinary crumb rubber (40 ∼ 80 mesh) was sourcedfrom truck tire and purchased from Huangshi Second RubberPowder Factory; several kinds of modifying agents included stabi-lizer and activator.

Sample Preparation

Fig. 1 schematically illustrated the full preparation of activatedcrumb rubber. First of all, the crumb rubber was charged intostorage silo of ultrasonic focusing apparatus and the ultrasonic

1Junior Engineer, Beijing Oriental YuhongWaterproof Technology Co.,Ltd., Concha 2, Shaling, Shunping Rd., Shunyi District, Beijing 101309,China (corresponding author). E-mail: xumz@yuhong.com

2Senior Engineer, Beijing Oriental YuhongWaterproof Technology Co.,Ltd., Concha 2, Shaling, Shunping Rd., Shunyi District, Beijing 101309,China. E-mail: liujj@yuhong.com.cn

3Senior Engineer, Beijing Oriental YuhongWaterproof Technology Co.,Ltd., Concha 2, Shaling, Shunping Rd., Shunyi District, Beijing 101309,China. E-mail: liwz@yuhong.com.cn

4Senior Engineer, Beijing Oriental YuhongWaterproof Technology Co.,Ltd., Concha 2, Shaling, Shunping Rd., Shunyi District, Beijing 101309,China. E-mail: duanwf@yuhong.com.cn

Note. This manuscript was submitted on August 22, 2013; approved onApril 25, 2014; published online on August 8, 2014. Discussion periodopen until January 8, 2015; separate discussions must be submitted for in-dividual papers. This paper is part of the Journal of Materials in CivilEngineering, © ASCE, ISSN 0899-1561/04014173(7)/$25.00.

© ASCE 04014173-1 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

piezoelectric transducer was controlled to treat on the crumb rub-ber. In the treatment process, the out power and frequency of ultra-sonic focusing apparatus was set up as 1,200 W and 20 KHz,respectively. The activated crumb rubber was obtained after treat-ment for 12 ∼ 15 s. The whole process was carried out in a closesystem without releasing polluted gas or water. Fig. 1 described thedetailed information about this machine.

The ACRMB prepared in the laboratory was produced by add-ing 15% crumb rubber by weight of binder to a preheated sample ofasphalt binder. The ACRMB was preheated to 180°C and upon ad-dition of the crumb rubber an impellor rotating at 750 rpm was usedfor 1.5 h to mix the blend.

Characterization of Activated Crumb Rubber Properties

The morphologies of crumb rubber powder pre- and postmodifyingwere observed by scanning electron microscopy (JSM-5510LV,Hitachi Company, Japan). Samples were pretreated by gold sput-tering prior to the observation. The microstructure of ACRMBwas inspected with a fluorescence microscope (DMIRB, LeicaCompany, German).

The analyses of crumb rubber were done accordance to ASTMD 297 and the crumb rubber gradation was determined usingASTM D 5644. The viscosity of ACRMB was tested under the

Brookfield viscometer at seven different temperature conditions(190, 180, 170, 160, 150, 140, and 130°C). A 35% torque wasapplied and the rotation speed was set at 100 rpm. The #29 spindlewas adopted in the tests in favor of the #27 spindle due to the highviscosity of ACRMB. The viscosity test followed the AASHTOT316 standard test specification.

The softening point, fraass breaking point penetration, ductility,elasticity recovery, and separation test of ACRMB were measuredaccording to “Standard Test Methods of Bitumen and BituminousMixtures for Highway Engineering” (JTG E20-2011).

Result and Discussion

ACRMA was fabricated with the blending of virgin asphalt, acti-vated crumb rubber, furfural extract oil, activator, and stabilizer at180°C for 2 h. ACRMA showed good storage stability because ofthe improved compatibility between the activated crumb rubber andvirgin asphalt. According to the asphalt storage stability test, thedifference of softening points between two extreme parts of thealuminum tube could be decreased to 2.5°C. Moreover, ACRMAshowed excellent performance, including high-temperature toler-ance property, low-temperature stiffness, ductility, especiallyfatigue resistance and antiaging, as summarized in Table 1, fromwhich it could be ranked as performance grade (PG) 82-28. Table 1showed the softening point and fraass breaking point of ACRMAwere obviously increased by the modification. Therefore, we dis-cussed the processing of ultrasonic focusing apparatus, crumb rub-ber content, processing temperature, and swelling time on the highand low temperature performance.

Processing of Ultrasonic Focusing Apparatus

Crumb rubber devulcanization by using ultrasonic energy was firstdiscussed in this paper. Ultrasonic devulcanization technologywas actually composed of devulcanization system that utilizedmechanical extrusion and ultrasonic energy to devulcanize crumbrubber. In this type of devulcanization system, crumb rubber par-ticles were loaded into a hopper and subsequently fed into an

Table 1. Test Index of the Virgin Asphalt, CRMA, and ACRMA (theOrdinary Crumb Rubber and Activated Crumb Rubber Account for22% by Weight of CRMA and ACRMA, Respectively)

Properties Virgin asphalt CRMA ACRMA

Softening point (°C) 47.9 59.1 73Fraass breaking point (°C) −6 −14 −2525°C penetration (0.1 mm) 71 103 76Elastic recovery (%) — 67 935°C ductility (cm) 1.3 15.5 46After segregation, difference ofthe softening point/°C

— 5.8 0.7

135°C viscosity (Pa · S) 0.48 4.62 2.35

Fig. 1. Ultrasonic focusing apparatus used in this study (image courtesy of Quanyi Ultrasonic Equipment Co., Ltd)

© ASCE 04014173-2 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

extruder. The extruder mechanically pushed and pulled the crumbrubber to be exposed to ultrasonic energy. The ultrasonic waves, atcertain levels, in the presence of pressure and heat, could quicklybreak up the three-dimensional network in cross-linked vulcanizedrubber. It was an applicable process in which the vulcanizedrubber was devulcanized based on the use of high-power ultra-sound electromagnetic radiation, using 1,200 W and 20 KHz ultra-sonic waves after treatment for 12 ∼ 15 s. Structural studies ofultrasonically-treated rubber showed that the breakup of crumbrubber vulcanization network structures was accompanied by thepartial degradation of the rubber chain. The process apparentlycould break down C-S and S-S bonds by comparing FTIR spectraof crumb rubber before and after modifying. Because the degree ofdegradation of C-C bonds was substantial, the process could notbreak down C-C bonds. As a consequence of the process, ultrasoni-cally devulcanized crumb rubber became soft, enabling thismaterial to be reprocessed in virgin bitumen in the same way asvirgin rubber. Moreover, Table 1 showed the activated ACRMAexhibited good mechanical properties. The process of ultrasonicdevulcanization was very fast, simple, and efficient. This new tech-nology has been used successfully in the laboratory to devulcanizetruck tire rubber.

On the other hand, crumb rubber particles in ultrasonic focusingapparatus near the solid surface experienced two kinds of forces ofparticular interest to this study: adhesion forces—linear and non-linear interactions that arise through interactions of ultrasound with

crumb rubber particles. In general, adhesion forces comprisedcapillary forces, van der Waals forces, electrostatic image forces,and electrical double-layer forces. During the operation, the adhe-sion forces of most importance were van der Waals forces and elec-trical double layer forces. Linear interaction forces included addedmass, drag, lift, and basset forces while nonlinear ones includedradiation pressure forces and drag forces due to acoustic streaming.Linear forces were time dependent and had zero means while non-linear ones had a time-independent component and took nonzerovalues. Linear interaction forces were usually much larger thannonlinear counterparts in conventional applications at moderatefrequencies. Therefore, the crumb rubber vulcanization networkstructures were destroyed and the morphology of crumb rubberchanged under the interaction.

Fig. 2 showed the gradation of crumb rubber and activatedcrumb rubber was determined using ASTM D 5644. This phe-nomenon indicated that the crumb rubber vulcanization networkstructures were destroyed through the physical processing, corre-sponding to the increasing of the covering area of activity units,which revealed the small activity units and chemical reactivityincreased in the activated crumb rubber. Therefore, Fig. 4 showedthe compatibility between the activated crumb rubber and virginasphalt could be largely improved.

It has been reported that the crumb rubber type and size havesignificant impact on the high temperature viscosity of ACRMA(Upadhyay et al. 2008; Sabbagh and Lesser 1998; Xiang et al.2009). Herein, we selected 40 ∼ 80 mesh truck tire crumb rubberin diameter, which was beneficial for asphalt swelling. Moreover,the ordinary truck tire crumb rubber must be modified to obtain theactivated crumb rubber by ultrasonic focusing apparatus (observedin Fig. 1). During making process, the activated crumb rubber withpopcorn appearance (observed in Fig. 3) was obtained due to ultra-sonic cavitation, resulting in a much higher complex modulus andphase angle of ACRMA by DSR frequency sweep test. The com-plex modulus, defined as the ratio of maximum stress to maximumstrain, provided a measure of the total resistance to deformation dueto repeated shearing force. The phase angle, defined as the phasedifference between the peak stress and strain, represented the timedelay between the applied stress and measured strain withlimiting values of 0° for purely elastic behavior and π=2 for purelyviscous behavior. In other words, it was a direct measure of theratio of the viscous to elastic contribution to the overall responsein the CRMA and ACRMA. Thus the ACRMA could keepbetter elasticity to resistant rutting than the CRMA according toDSR results.

Fig. 2. Passing percent gradation of crumb rubber and activated crumbrubber

Fig. 3. SEM images of (a) preactivated crumb rubber; (b) postactivated crumb rubber

© ASCE 04014173-3 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

Table 1 showed the comparison of the properties of ordinaryCRMA and ACRMA a significant performance improvement ofACRMA was achieved through the modification. Based on themain effects of compatibility between the activated crumb rubberand virgin asphalt on the performance of ACRMA, the morphologi-cal characteristics of crumb rubber and ACRMAwere examined bySEM and fluorescence microscope, respectively. We found that theapparent morphology of activated crumb rubber showed a stronginfluence on the performance of ACRMA. Fig. 3(a) showed theinterface of traditional crumb rubber was clear, which indicatedpoor compatibility between virgin asphalt and ordinary crumb rub-ber as shown in Fig. 4(a). It showed that the swelling of crumbrubber was very poor, and the light components of asphalt couldnot ultimately permeate into crumb rubber. In the perspective ofthermodynamics, the CRMA system was very unstable, andtwo-phase separation occurred easily (Khaldoun et al. 2012). ThusTable 1 summarized CRMA obtained with ordinary crumb rubberhad poorer performance.

However, the interface of activated crumb rubber turned out tobe indistinct, which provided higher surface area than ordinarycrumb rubber. Herein, the activated crumb rubber provided a largearea to create chemical bonds and homogeneously dispersed in bi-tumen phase due to the good compatibility between virgin asphaltand the activated crumb rubber as seen in Fig. 4(b). Meanwhile, thepresence of swollen activated crumb rubber particles would behelpful to reinforce the friction and embedding of aggregates toform a high-strength mixture structure, which increased the cohe-sion and flexibility, and limited the temperature sensitivity of as-phalt. Obviously, the dispersion degree and swelling capacity ofcrumb rubber had been improved by the activation, and the crumbrubber swelling could promote the formation of elastic network ofACRMA, as well as the improving properties of ACRMA dis-played in Table 1 (Upadhyay et al. 2008; Xiang et al. 2009).

In the making process of ACRMA, the activated crumb rubbercould easily absorb the light oil component in bituminous phase,which reduced the content of free radicals and indicated asignificant increasing in storage stability. Moreover, because ofdevulcanization and depolymerization, the activated crumb rubberhomogeneously dispersed in virgin asphalt and formed perfectpolymer reticular structure with the function of additives and sta-bilizers, which contributed to increasing softening point, fraassbreaking point, elastic recovery of ACRMA, and decreasing pen-etration of ACRMA. In addition, there were many antioxidant andantiozone agents in crumb rubber, which contributed directly to

improving the antioxidative capacity of ACRMA (Sabbagh andLesser 1998; Navarro et al. 2005).

Table 2 showed the basic chemical properties of crumb rubberdisplayed significant effects on the performance of CRMA. Theextract content (acetone and chloroform) played an important rolein improving CRMA properties. The higher content of the extractwas corresponding to the higher content of resinlike (high fattyacid, steroid, etc.) in crumb rubber. Adding this type of crumb rub-ber to matrix asphalt, the resinlike could permeate through matrixasphalt under thermal energy and mechanical force, while saturatesand aromatics in matrix asphalt could also wrap and swell macro-molecules in crumb rubber. Remarkable swelling and compatibilitywere achieved through mutual infiltration of the components ofcrumb rubber and matrix asphalt, which improved the performanceof CRMA obviously. The lower ash content of crumb rubber couldindicate the minor superiority; the ductility at low temperature,cohesive force, and elastic recovery of CRMA would be better.

Fig. 5 shows the viscosity graphical plots for the CRMB andACRMB, respectively. It was clear that the viscosity of CRMBand ACRMB decreased with increasing test temperature, withthe same trend holding true for the virgin asphalt. The additionof crumb rubber could greatly increase the binder viscosity, whichwas vital in increasing the binder film thickness for coating aggre-gates in the hot mixture. As expected, the viscosity of the ACRMBwas significantly lower than the CRMB. In this respect, it was alsoevident that the activation of crumb rubber could significantly im-prove the compatibility between the activated crumb rubber andvirgin asphalt compared with ordinary crumb rubber. Moreover,the viscosity of CRMB and ACRMB decreased with the increasedtest temperature.

Effect of Crumb Rubber Content

Crumb rubber was a special flexible powder, which was preparedby mechanical grinding from waste truck tire; consisting of rubber,

Fig. 4. Fluorescence micrographs at 400 magnification of modified asphalt by (a) ordinary crumb rubber; (b) activated crumb rubber

Table 2. Chemical Composition of Crumb Rubber Used in This Study

Major rubber components (%) Crumb rubber (%)

Natural and synthetic rubber 55.7Extract content (acetone and chloroform) (wt%) 14.6Ash content (wt%) 7.2Carbon black content (wt%) 32.1

© ASCE 04014173-4 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

carbon black, softener, vulcanization promoting agent, and someother ingredients as shown in Table 2, whose surface was inert withcross-linked structure (Navarro et al. 2005; Miknis and Michon1998). Hence, we treated ordinary crumb rubber to obtain theactivated crumb rubber, which could significantly enhance theperformance of ACRMA, including high-temperature property,low-temperature stiffness, ductility, especially fatigue resistanceand aging resistance.

Compared with ordinary crumb rubber (max 20% of the weightof virgin asphalt), the activated crumb rubber content was found tobe the main factor that affected the performance of ACRMA in thepreparation of ACRMA. The concentration analysis of activatedcrumb rubber demonstrated that it had a significant effect on theproperties of ACRMA. Fig. 6 illustrated that when the concentra-tion of activated crumb rubber was very low, the activated crumbrubber could not form network structure in ACRMA, the modifiedeffects were relatively poor, and the high- and low-temperatureperformances of ACRMA got minor improvement. While withthe activated crumb rubber content increasing to a proper value,the ACRMA system would be stable homogeneously. The soften-ing point, fraass breaking point, the ductility, and elastic recoveryof ACRMA was obviously improved (Liu et al. 2009; Thodesenet al. 2009).

However, the higher activated crumb rubber content resulted ina significant decrease in compatibility degree between the activatedcrumb rubber and bituminous phase. It was assumed that insolubleactivated crumb rubber particles remained in ACRMA and led to aheterogeneous substance and an uneven system. That meant theactivated crumb rubber modification was a physical modificationrather than a polymeric modification (Navarro et al. 2005; Liu et al.2009). Therefore, compared with the softening point, fraass break-ing point, viscosity, and penetration, the addition of activatedcrumb rubber must be controlled in a proper range (15 ∼ 25%

of the weight of virgin asphalt).

Effect of Processing Temperature

It was well known that an increase in processing temperature led toan increase in both the amount of crumb rubber digestion and theasphalt aging phenomenon (Miknis and Michon 1998; Ruan et al.2003; Chipps et al. 2001; Akisetty et al. 2009). Fig. 7 showed theevolution of high- and low-temperature properties as a function ofprocessing temperature. As expected, the increase up to180°C ledto a significant increase in softening point and fraass breaking pointdue to a higher amount of activated crumb rubber digestion andlower interaction among solid particles in ACRMA. Under theprocessing condition, the effect of aging on ACRMAwas less sig-nificant than the effect of digesting crumb rubber. Nevertheless,increasing the processing temperature to 200°C changed the evo-lution of this balance. At 200°C, the effect of aging on ACRMAdominated the effect of digestion, leading to the decrease of fraassbreaking point observed in Fig. 7. But then, the softening point andpenetration grade remained effectively independent of processingtemperature, showing little aging effect on ACRMA illustratedin Fig. 7.

In this respect, the evolution of certain technological propertieswith processing temperature was also discovered (results notshown). Along with the increase of processing temperature, the ac-tivated crumb rubber was digested in asphalt accompanied by thepartial depolymerization and devocalization of crumb rubber net-work, which led to an increase in the number of components thatwere incorporated to the bituminous phase. Thus, activated crumbrubber delivered cohesive property and plasticity to ACRMA,which contributed to increasing of elastic recovery and decreasingof penetration. However, when the processing temperature ex-ceeded the optimum temperature (190°C), the digestion of activated

Fig. 5. Viscosities of CRMB and ACRMB

Fig. 6. Effects of activated crumb rubber content on the performancesof ACRMA

Fig. 7. Effects of processing temperature on the performances ofACRMA

© ASCE 04014173-5 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

crumb rubber and aging process was improved. Thus, the globaleffect of these conflicting phenomena was a decrease in mechanicalproperties, followed by an increase in viscosity due to aging(Upadhyay et al. 2008; Chipps et al. 2001; Akisetty et al. 2009;Jeong et al. 2010; Wang et al. 2012).

Effect of Swelling Time

At 180°C, crumb rubber could not be fully swollen in shortblending time, but the excessive blending time led to excessivedecomposition and aging. Consequently, it was possible to seta high-optimum processing temperature to ensure a higher quan-tity of ACRMA (Dong et al. 2012). Fig. 8 showed the single factorexperimental results of swelling time for the blending of activatedcrumb rubber, virgin asphalt, and certain additives. As can beseen, the swelling time effect did not manifest significant differ-ence. In processing prophase, progressively prolonging swellingtime could digest crumb rubber into ACRMA system, thusimproving the softening point and fraass breaking point ofACRMA.

When the length of swelling time exceeded a certain threshold(2 h) at 180°C, the result was just the opposite and mix propertieswere impoverished. It led to an exponential increase in viscositydue to primary aging of the bituminous base, with a consequentloss of improvement in the mechanical properties of ACRMA.The low-temperature stiffness would slowly degrade due to theaging of ACRMA observed in Fig. 8. At the same time, a decreasein viscosity took place as a result of the increase in the amount ofactivated crumb rubber digestion. Nevertheless, the ductility andelastic recovery of ACRMA was independent of swelling timein processing (Jeong et al. 2010; Gawel et al. 2006). Therefore,the swelling time of ACRMAmust be controlled in a suitable range(1 ∼ 2 h).

Conclusions

The activated method could destroy the crossing-linked networkstructure of crumb rubber in a close system without pollutiongas or water. The activated crumb rubber was used as a modifierfor asphalt to modify asphalt, which achieved the favorable proper-ties of ACRMA and the substitution of SBS. The combined modi-fication with activated crumb rubber and certain additives wasan effective method to improve the performance of ACRMA.The influential factors on performance include: crumb rubber

structure, activated crumb rubber content, processing temperature,and swelling time. Based on laboratory investigations, singlefactor analyses on the processing of ACRMA were carried outin this study. Herein, the topgallant activated crumb rubber contentwas 25% of the weight of virgin asphalt, the optimum processingtemperature was 180°C, and the adequate swelling time was 2 h.Thus, ACRMA possessed excellent performance including high-temperature stability, low-temperature stiffness, deformation re-sistance, elastic recovery, viscosity, and ductility. The ACRMAseparation could completely meet the standard of modifiedasphalt and applied in pavement engineering.

References

Akisetty, C. K., Lee, S. J., and Amirkhanian, S. N. (2009). “High temper-ature properties of rubberized binders containing warm asphaltadditives.” Constr. Build. Mater., 23(1), 565–573.

Chipps, J. F., Davison, R. R., and Glover, C. J. (2001). “A model foroxidative aging of rubber-modified asphalts and implications to perfor-mance analysis.” Energy Fuels, 15(3), 637–647.

Dong, D. W., Huang, X. X., Li, X. L., and Zhang, L. Q. (2012). “Swellingprocess of rubber in asphalt and its effect on the structure andproperties of rubber and asphalt.” Constr. Build. Mater., 29(4),316–322.

Endres, H. A., Coleman, R. J., Pierson, R. M., and Sinclair, E. A. (1951).“Effect of synthetic elastomers on properties of petroleum asphalts.”Ind. Eng. Chem. Res., 43(2), 334–340.

Gawel, I., Stepkowski, R., and Czechowski, F. (2006). “Molecular inter-actions between rubber and asphalt.” Ind. Eng. Chem. Res., 45(9),3044–3049.

Jeong, K. D., Lee, S. J., Amirkhanian, S. N., and Kim, K. W. (2010).“Interaction effects of crumb rubber modified asphalt binders.” Constr.Build. Mater., 24(5), 824–831.

Khaldoun, M. S., Szabolcs, B., Andras, G., and Serji, N. A. (2012). “Effectsof furfural activated crumb rubber on the properties of rubberizedasphalt.” Constr. Build. Mater., 28(1), 96–103.

Liu, S. T., Cao, W. D., Fang, J. G., and Shang, S. J. (2009). “Varianceanalysis and performance evaluation of different crumb rubbermodified (CRM) asphalt.” Constr. Build. Mater., 23(7),2701–2708.

Morrison, G. R., and Hesp, S. A. M. (1995). “A new look at rubber-modified asphalt binders.” J. Mat. Sci., 30(10), 2584–2590.

Miknis, F. P., and Michon, L. C. (1998). “Some applications of nuclearmagnetic resonance imaging to crumb rubber modified asphalts.” Fuel,77(5), 393–397.

Navarro, F. J., Partal, P., Martínez-Boza, F., and Gallegos, C. (2004).“Thermo-rheological behaviour and storage stability of ground tirerubber-modified bitumens.” Fuel, 83(14–15), 2041–2049.

Navarro, F. J., Partal, P., Martínez-Boza, F., and Gallegos, C. (2005).“Influence of crumb rubber concentration on the rheologicalbehavior of a crumb rubber modified bitumen.” Energy Fuels, 19(5),1984–1990.

Navarro, F. J., Partal, P., Martínez-Boza, F., Gallegos, C., Bordado, J. C. M.,and Diogo, A. C. (2007). “Rheology and microstructure of MDI–PEGreactive prepolymer-modified bitumen.” Mech. Time-Depend. Mater.,10(4), 347–359.

Ruan, Y. H., Davison, R. R., and Glover, C. J. (2003). “Oxidation andviscosity hardening of polymer-modified asphalts.” Energy Fuels,17(4), 991–998.

Sabbagh, A. B., and Lesser, A. J. (1998). “Effect of particle morphologyon the emulsion stability and mechanical performance ofpolyolefin modified asphalts.” Polym. Eng. Sci., 38(5), 707–715.

Thodesen, C., Shatanawi, K., and Amirkhanian, S. (2009). “Effect ofcrumb rubber characteristics on crumb rubber modified (CRM)binder viscosity.” Constr. Build. Mater., 23(1), 295–303.

Fig. 8. Effects of swelling time on the performances of ACRMA

© ASCE 04014173-6 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

Upadhyay, S., Mallikarjunan, V., Subbaraj, V. K., and Varughese, S. (2008).“Swelling and diffusion characteristics of polar and nonpolar polymersin asphalt.” J. Appl. Polym. Sci., 109(1), 135–143.

Wang, H. N., You, Z. P., Julian, M. B., and Hao, P. W. (2012). “Laboratoryevaluation on high temperature viscosity and low temperature stiffness

of asphalt binder with high percent scrap tire rubber.” Constr. Build.Mater., 26(1), 583–590.

Xiang, L., Cheng, J., and Que, G. H. (2009). “Microstructure and perfor-mance of crumb rubber modified asphalt.” Constr. Build. Mater.,23(12), 3586–3590.

© ASCE 04014173-7 J. Mater. Civ. Eng.

J. Mater. Civ. Eng.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

vers

ity o

f T

exas

At A

ustin

on

12/0

4/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.