High temperature properties of rubberized binders containing warm asphalt additives

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Construction and Building Materials 23 (2009) 565–573

and Building

MATERIALS

High temperature properties of rubberized binders containingwarm asphalt additives

Chandra K. Akisetty, Soon-Jae Lee *, Serji N. Amirkhanian

Department of Civil Engineering, Clemson University, Clemson, SC 29634-0911, United States

Received 10 September 2007; received in revised form 1 October 2007; accepted 12 October 2007Available online 3 December 2007

Abstract

Several studies have been conducted evaluating the properties of warm mix asphalt (WMA), and it is observed that warm asphaltadditives work in different ways to either reduce the viscosity of the binder or to allow better workability of the mix at lower temper-atures. In terms of rubberized asphalt mixtures, they are compacted at a higher temperature than conventional mixtures, based onthe field experience. If the technologies of warm mix asphalt are incorporated, it is expected to reduce the mixing and compaction tem-peratures of rubberized asphalt mixtures to those of conventional mixtures. This paper presents the high temperature properties of rub-berized binders containing warm asphalt additives. Rubberized binders were produced at 10% by binder weight using five binder sources,and the binders with the additives were produced using two (i.e. Aspha-min� and Sasobit�) of the available processes and artificiallyshort-term aged through the rolling thin film oven (RTFO) method. Tests were conducted on the binders using the rotational viscometerand the Dynamic Shear Rheometer. The results indicated that the viscosity properties of rubberized binders can be changed significantlythrough the use of warm asphalt additives. Also, the addition of the additives was found to improve rutting resistance of the rubberizedbinders.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Warm asphalt additive; Crumb rubber modifier: Viscosity; Rutting resistance

1. Introduction

1.1. Background

Previous studies have indicated that rubberized binderscan produce asphalt pavements that exhibit decreased traf-fic noise, reduced maintenance costs and resistance to rut-ting and cracking [18,14,6,20]. Because of these advantages,there is an increasing interest in utilizing rubberized bindersin hot mix asphalt (HMA) pavements in some states in theUnites States and other countries [2,24,20].

The warm mix asphalt (WMA) refers to technologiesthat allow reducing the mixing and compaction tempera-tures significantly for unmodified binders by reducing the

0950-0618/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.conbuildmat.2007.10.010

* Corresponding author.E-mail addresses: [email protected] (C.K. Akisetty), soonjae93@

gmail.com (S.-J. Lee), [email protected] (S.N. Amirkhanian).

viscosity of the binders [8]. Reduced mix production andpaving temperatures would decrease the energy requiredto make HMA, reduce emissions and odors from plants,and improve the working conditions at the plant and pav-ing site [9]. In terms of rubberized asphalt mixtures, theyshould be compacted at a higher temperature than conven-tional mixtures, based on the field experience [1]. If thetechnologies of warm mix asphalt are incorporated, it ispredicted to observe a reduction in the mixing and compac-tion temperatures of rubberized asphalt mixtures comparedto those of conventional mixtures. The properties of thebinders need to be investigated further prior to utilizingthe rubberized mixtures containing warm asphalt additives.However, the effect of warm asphalt additives on rubber-ized binders is not studied in detail yet.

Among several warm asphalt additives, this study con-centrated on two additives, Aspha-min� and Sasobit�.The Aspha-min� is hydro thermally crystallized as a very

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566 C.K. Akisetty et al. / Construction and Building Materials 23 (2009) 565–573

fine powder. It contains about 21% crystalline water byweight [3]. Sasobit� is long chain aliphatic hydrocarbonobtained from coal gasification. After crystallization, Sas-obit� forms a lattice structure in the binder which is thebasis of the structural stability of the binder containingSasobit� [19].

1.2. Research objectives and scope

The main objective of this research was to investigatethe high temperature properties of rubberized warmasphalt binders through selected Superpave binder tests.The rubberized binders were produced in the laboratoryincorporating one crumb rubber modifier (CRM) source(ambient) and one CRM percentage (10% by weight ofasphalt binder) into five base binders. The rubberizedwarm asphalt binders were manufactured with two differ-

5 PG 64-22

(Sources:

• Control Bin

• Warm Asp

• Warm Asp

Rotational Viscome(unaged)

• 2 Temperatures (135 and 120 C)

• 3 Reaction Times (30, 60, and 90 min

(n = 3)

CRM Bind(10% b

* *

DSR(unaged)

(n* = 3)

*n: sample size

Fig. 1. Flow chart of experim

ent warm asphalt additives, Aspha-min� and Sasobit�,and artificially short-term aged using rolling thin film oven(RTFO) procedure. The viscosity and rutting properties forthe binders in the original state, and the rutting propertiesafter RTFO aging process were evaluated. Fig. 1 shows aflow chart of the experimental design used in this study.

2. Materials and test program

2.1. Materials

2.1.1. Asphalt binders

Five PG 64-22 asphalt binders designated as A, B, C, D,and E from different crude sources were used in this study.Binder A was a mixture of several sources that could not beidentified by the supplier, binder B was from a Venezuelancrude source, binder C was from a Texas, binder D was

Asphalt Binders

A, B, C, D, and E)

der

halt Process 1

halt Process 2

ter

utes)

RTFO aging(163 C for 85 minutes)

er Productiony binder wt.)

177 C30 minutes

DSR(RTFO residual)

(n = 3)

ental design procedures.

Table 1Properties of five base binders (PG 64-22)

Aging states Test properties Binder sources

A B C D E

Unaged binder Viscosity at 135 �C (Pa s) 0.405 0.626 0.457 0.600 0.420G*/sind at 64 �C (kPa) 1.24 1.99 1.12 1.82 1.46Failure temperature (�C) 65.8 69.7 64.9 69.0 67.1

RTFO aged residual G*/sind at 64 �C (kPa) 3.30 6.09 2.53 5.72 4.04Failure temperature (�C) 67.0 72.0 65.1 71.3 68.6

RTFO + PAV aged residual G*sind at 25 �C (kPa) 2970 2420 1704 2110 2565Stiffness at �12 �C (MPa) 183 129 117 120 132m-value at �12 �C 0.311 0.345 0.320 0.356 0.335

C.K. Akisetty et al. / Construction and Building Materials 23 (2009) 565–573 567

from a Middle Eastern source, and binder E was a Cana-dian source. Each binder was graded in accordance withAASHTO M320 to verify the performance grade. Table 1summarizes the properties of the five base binders includedin this study.

2.1.2. Crumb rubber modifier (CRM)The CRM produced by mechanical shredding at ambi-

ent temperature was obtained from one source: �40 mesh(0.425 mm) and used with a gradation as shown in Table2, which is widely used to produce the CRM mixtures inSouth Carolina [22]. To ensure that the consistency ofthe CRM was maintained throughout the study, only onebatch of crumb rubber was used in this study.

2.2. Production of rubberized warm asphalt binders

The binder mixing used in this study was the wet pro-cess, in which the CRM is added to the base asphalt binderbefore introducing it in the asphalt concrete matrix[17,22,25]. The rubberized binder was produced in the lab-oratory at 177 �C for 30 min by an open blade mixer at ablending speed of 700 rpm [11,12,21]. The percentage ofcrumb rubber added for the rubberized binder was 10%by weight of the base binder. This mixing conditionmatches the practices used in South Carolina to producefield mixtures [12,13].

Two of the available commercial warm asphalt additiveswere selected in making the rubberized warm asphalt bin-der. Process 1 included addition of Aspha-min�, a chemicalpowder at specified concentration (0.3% by weight of themixture – a binder content of 6% was assumed, and the

Table 2The gradation of crumb rubber used in this study

Sieve No. (lm) Ambient CRM

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

entire additive was added to the binder) followed by mixingwith a stirrer to disperse the powder throughout the rub-berized binder. Process 2 included addition of Sasobit�,pellets at specified concentration (1.5% by weight of thebinder) followed by mixing with a shear mixer for 5 minto achieve consistent mixing [4].

The rubberized warm asphalt binders were then artifi-cially short-term aged through the rolling thin film oven(RTFO) aging process for 85 min at 163 �C [23].

Fig. 2. Viscosity of rubberized warm asphalt binders: (a) 135 �C and (b)120 �C.


2.3. Superpave binder tests

Each rubberized warm asphalt binder was tested using arotational viscometer and dynamic shear rheometer (DSR)to evaluate its high temperature properties. A Brookfieldrotational viscometer was used to test the viscosity of thebinders at 135 �C, the standard test temperature, and at120 �C, which is the mixing temperature generally usedfor warm asphalt. To evaluate the effect of reaction timeon the viscosity after mixing the warm asphalt additives,viscosity was measured after 30, 60, and 90 min of addingthe warm asphalt additive.

The DSR was used to determine the high failure temper-ature for each rubberized warm asphalt binder both in theoriginal state (unaged) and after short-term aging in theRTFO in accordance with AASHTO T 315 (with the plate

Table 3Statistical analysis results of the viscosity at 135 �C of rubberized warm aspha

Viscosity (135 �C) Source A Source B

1a 2 3 1 2 3

Source A 1a – S S S S S2 – N S S S3 – S S S

Source B 1 – S N2 – S3 –

Source C 123

Source D 123

Source E 123

N: non-significant (there is no statistical difference between two means); S: siga Rubberized warm asphalt binder 1: Control 2: Aspha-min� 3: Sasobit�.

Table 4Statistical analysis results of the viscosity at 120 �C of rubberized warm aspha

Viscosity (120 �C) Source A Source B

1a 2 3 1 2 3

Source A 1a – S S S S S2 – S S S S3 – S S S

Source B 1 – S S2 – S3 –

Source C 123

Source D 123

Source E 123


gap adjusted to 2 mm). The plate gap adjustment was usedto eliminate the influence of rubber particle size [5,10,26].Three duplicate samples were tested and the results werereported as the average of these tests.

A 10.5 g binder sample of the binders was tested with anumber 27 spindle in the rotational viscometer. For allbinders, each specimen was poured just prior to testing.In the DSR test, the binders were tested using a 25 mm par-allel plate set up at a strain of 12%. The complex shearmodulus (G*) and phase angle (d) of each binder wasmeasured.

2.4. Analysis method

Statistical analysis was performed using the Statisticalanalysis system (SAS) program to conduct analysis of var-

lt binders as a function of additive and binder source (a = 0.05)

Source C Source D Source E

1 2 3 1 2 3 1 2 3

S S S S S S S S SS S S S S S N S SS S S S S S S S NS S S S N S S S SS S S S S S S S SS S S S N S S S S– S S S S S S S S

– S S S S S S S– S S S S S S

– S S S S S– S S S S

– S S S– S S

– S–

nificant (there is statistical difference between two means).

lt binders as a function of additive and binder source (a = 0.05)


1 2 3 1 2 3 1 2 3

S S S S S S S S SS S S S S S S S NS N S S S S S S SS S S S S S S S SS S S S S S S S SS S S N S S S S S– S S S S S S S S

– S S S S S S S– S S S S S S

– S S S S S– N N S S

– S S S– S S

– S–



iance (ANOVA) and Fisher’s least significant difference(LSD) comparison with an a = 0.05. The primary variablesincluded the binder sources (A, B, C, D, and E), the warmasphalt additives (Control, Aspha-min�, and Sasobit�),and the reaction times (30, 60, and 90 min) after mixingthe warm asphalt additives.

Fig. 3. Viscosity of rubberized warm asphalt binders as a function ofreaction time at 135 �C: (a) Control, (b) Aspha-min�, and (c) Sasobit�.

ANOVA was performed first to determine whether sig-nificant differences among sample means existed. In theanalyses of this study, the level of significant was 0.05(a = 0.05). Upon determining that there were differencesamong sample means using the ANOVA, the LSD was cal-culated. The LSD is defined as the observed differences

Fig. 4. Viscosity of rubberized warm asphalt binders as a function ofreaction time at 120 �C: (a) Control, (b) Aspha-min�, and (c) Sasobit�.


between two sample means necessary to declare the corre-sponding population means difference. Once the LSD wascalculated, all pairs of sample means were compared. Ifthe difference between two sample means was greater thanor equal to the LSD, the population means were declaredto be statistically different [16].

3. Results and discussions

3.1. High temperature viscosity

The viscosity of asphalt binders at high temperature isconsidered to be an important property because it repre-sents the binder’s ability to be pumped through an asphaltplant, thoroughly coat aggregate in asphalt concrete mix,and be placed and compacted to form a new pavement sur-face [23]. Fig. 2 illustrates the viscosity values at 135 �C and120 �C for rubberized warm asphalt binders. A generaltrend was found from the results that the addition ofAspha-min� into rubberized binder increased the binder’sviscosity at both testing temperatures, compared to thecontrol rubberized binder. However, the addition of Sas-obit� resulted in reducing the viscosity significantly, andthis finding was true for all binder sources regardless ofthe testing temperature. The increase in the viscosity ofrubberized binder with Aspha-min� is thought to becaused by the addition of fine powder to the binder, whichacts as a filler. In reality, Aspha-min� is added to the mix-ture and a very fine water spray is created as all the crystal-

Table 5Statistical analysis results of the viscosity of rubberized warm asphalt binders a120 �C (binder source A)

Viscosity (135 �C) Control

1a 2 3

(a)Control 1a – N N

2 – N3 –

Aspha-min 123

Sasobit� 123

Viscosity (120 �C) Control1a 2 3

(b)Control 1a – N S

2 – N3 –

Aspha-min� 123

Sasobit� 123

N: non-significant (there is no statistical difference between two means); S: siga Reaction time 1: 30 min 2: 60 min 3: 90 min.

line water is released, which causes volume expansion,thereby increasing the workability and compatibility ofthe mixture [3]. In terms of the rubberized binders contain-ing Sasobit�, Sasobit� is reported to form a homogeneoussolution with the base binder on stirring, and to cause areduction in the binder’s viscosity [19].

The statistical significance of the change in the viscosityas a function of warm asphalt additive and binder sourcewas examined and the results are summarized in Tables 3and 4. In general, the data indicated that the binder sourcehas a significant effect on the viscosity of the rubberizedwarm asphalt binders. When compared within each bindersource, the binders were found to have a significant differ-ence in the viscosity depending on the warm asphalt addi-tive for all binder sources, with only 3 exceptions among all30 comparisons at two test temperatures of 135 �C and120 �C.

Figs. 3 and 4 show the effect of reaction time after mix-ing the warm asphalt additives for five different bindersources. Generally, the longer period after mixing the addi-tives seemed to lead to increase the viscosity values of bind-ers. However, it was quite difficult to find consistentfindings for all asphalt binder sources. Also, it wasobserved that the addition of the additives increased thevariance of viscosity tests, especially at lower test tempera-ture of 120 �C.

Table 5 shows the statistical results of the change in theviscosity as a function of the warm asphalt additive and thereaction time after mixing the additive (for binder source

s a function of additive and reaction time (a = 0.05) at (a) 135 �C and (b)

Aspha-min� Sasobit�

1 2 3 1 2 3

S N N S S SN N N S S SN N N S S S– S N N S S

– N S S S– S S S

– N N– N

–

Aspha-min� Sasobit1 2 3 1 2 3

S S S N N NS S S S N NS N S S S N– N N S S S

– N S S S– S S S

– N S– N

–


Fig. 5. High failure temperature of rubberized warm asphalt binders (noaging).

Fig. 6. High failure temperature of rubberized warm asphalt binders(RTFO aging).


A). It is evident from the results that the viscosity changebetween 60 and 90 min is statistically insignificant withineach warm asphalt additive. Overall, there was significantdifference as a function of reaction time between rubberizedbinders with Aspha-min� and Sasobit�. Also, the viscositydifferences beween the control binders and the binders con-taining Aspha-min� at a test temperature of 120 �C werestatistically significant for all reaction times used in thisstudy.

3.2. High failure temperature

3.2.1. Original state binder (no aging)

The higher failure temperature values are generally con-sidered desirable attributes from the standpoint of resis-tance to permanent deformation at high pavmenttemperature [23]. The high failure temperature of rubber-

Table 6Statistical analysis results of the high failure temperature of rubberized warm(a = 0.05)

Failure temperature (�C) Source A Source B

1a 2 3 1 2 3

Source A 1a – S S S S S2 – S S S S3 – S S S

Source B 1 – N S2 – N3 –

Source C 123

Source D 123

Source E 123


ized warm asphalt binders in original state was measuredand the results are shown in Fig. 5. In general, the rubber-ized binder with Sasobit� resulted in the highest failuretemperature, followed by the rubberized binder containingAspha-min�. For all five binder sources, the control rub-berized binder (i.e. without warm asphalt additive) showedthe lowest failure temperature. Based on the results, it ispredicted that the rubberized binders containing the inor-ganic additive Aspha-min� or the aliphatic hydrocarbonSasobit� have better rutting resistance compared to thecontrol rubberized binder. Similar to the viscosity results,the rubberized warm asphalt binders produced with bindersource B showed significantly higher failure temperaturevalues than those made from the other binder sources(i.e. A, C, D, and E). This is thought to be attributed tothe initial higher failure temperature of the base binder B(Table 1).

asphalt binders (no aging) as a function of additive and binder source


1 2 3 1 2 3 1 2 3

S N N S S S S S SS S N N S S N S SS S S N S N S N NS S S S S S S S SS S S S S S S S SS S S S S S S S S– S S S S S S S S

– N S S S S S S– S S S N S S

– S N S N N– N S N N

– S N N– S S

– N–


Table 7Statistical analysis results of the high failure temperature of rubberized warm asphalt binders (RTFO residual) as a function of additive and binder source(a = 0.05)

Failure Temperature (�C) Source A Source B Source C Source D Source E

1a 2 3 1 2 3 1 2 3 1 2 3 1 2 3

Source A 1a – S S S S S S S S S S S N S S2 – N S N N S S S N S S S S S3 – N N S S S N S S S S S

Source B 1 – S S S S S S S S S N S2 – N S S S N N N S S S3 – S S S N N S S S S

Source C 1 – N N S S S S S S2 – N S S S S S S3 – S S S S S S

Source D 1 – N N S S S2 – N S S S3 – S S S

Source E 1 – S S2 – N3 –

N: non-significant (there is no statistical difference between two means); S: significant (there is statistical difference between two means).a Rubberized warm asphalt binder 1: Control 2: Aspha-min� 3: Sasobit�.


The statistical results of the change in the failure temper-ature are shown in Table 6. When compared to the controlrubberized binders, the addition of warm asphalt additivegenerally caused statistically significant difference in termsof rutting properties. In addition, the difference of failuretemperature values between rubberized binders withAspha-min� and Sasobit� was not significant at the 5%level within each binder source. The only exception wasthe binders made with binder source A. In general, the bin-der source was found to have a significant effect on the fail-ure temperature of the rubberized warm asphalt bindersregardless of the warm asphalt additive.

3.2.2. Short-term aging (RTFO aging)After the RTFO aging procedure at 163 �C for 85 min,

the high failure temperature properties of the rubberizedwarm asphalt binders (RTFO residual) was measuredand the results are depicted in Fig. 6. Similar to the findings

Fig. 7. Relationship of high failure temperature between unaged andRTFO-aged rubberized warm asphalt binders.

for the properties of original state binder, two warmasphalt additives, Aspha-min� and Sasobit�, were foundto have an effect to increase in the high failure temperatureof rubberized binders, except for binder source D. Also, therutting properties were affected insignificantly between thebinders with Aspha-min� or Sasobit�, when comparedwithin each binder source (Table 7).

Fig. 7 shows the relationship of high failure temperaturebetween unaged and RTFO aged rubberized warm asphaltbinders. Generally, a linear relationship was observed, andthe finding is consistent to the previous studies. However,the binders resulted in relatively lower coefficient of deter-mination (R2) value of 0.446. This is probably due to thevariability of rubberized binders and the interaction effectof warm asphalt additive during the RTFO aging process.Also, previous studies reported similar findings regardingunusual aging characteristics of rubberized binders afterRTFO aging [7,15,12].

4. Summary and conclusions

To evaluate the high temperature properties of rubber-ized binders with warm asphalt additives, rubberized bind-ers were manufactured using one CRM source (ambient),one CRM percentage (10% by binder weight), and five bin-der sources. The rubberized warm asphalt binders wereproduced with two additives, and artificially short-termaged in the laboratory. The high temperature viscosityand rutting properties for the binders were measured usingthe rotational viscometer and the dynamic shear rheometer(DSR). From these test results, the following conclusionswere drawn for the materials used in this study.

(1) The addition of warm asphalt additives significantlyincreased or decreased the viscosity of the rubberizedbinders at the temperatures of 135 �C and 120 �C.


The viscosity of rubberized binder with Aspha-min�increased due to the filling effect of the additive, andSasobit� was found to decrease the high temperatureviscosity of the binders.

(2) In general, the longer reaction time after mixing theadditive into the rubberized binder led to result inan increase in the viscosity regardless of the additivetype, but it was difficult to find consistent trenddepending on the binder source.

(3) The rubberized binders with the inorganic additiveAspha-min� or the aliphatic hydrocarbon Sasobit�

were observed to have higher failure temperaturethan the control rubberized binders, indicating betterresistance on permanent deformation at hightemperature.

(4) Similar to the original state, the two warm asphaltadditives, Aspha-min� and Sasobit�, were found tohave an effect to increase in the high failure tempera-ture of rubberized binders (RTFO residual) aftershort-term aging, and the difference depending onthe additive was statistically insignificant.

(5) Generally, the binder sources, as expected, wereobserved to have a significant effect on the high tem-perature properties of the rubberized warm asphaltbinders.

(6) It is suggested to conduct a study to evaluate theintermediate and low temperature properties of rub-berized warm asphalt binders after long-term aging.Also, further study with many other binder andCRM sources is needed to generalize these findings.

Acknowledgements

This study was supported by the Asphalt Rubber Tech-nology Service (ARTS) at Civil Engineering Department,Clemson University, Clemson, South Carolina, USA. Theauthors wish to acknowledge and thank South Carolina’sDepartment of Health and Environmental Control(DHEC) for their financial support of this project.

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High temperature properties of rubberized binders containing warm asphalt additives