Effect of Crumb Rubber Particle Size and Content on the Low

Effect of Crumb Rubber Particle Size and Content On The Low Temperature Rheological Properties of Binders

Authors:

Venu T. Gopal1 Peter E. Sebaaly2

Jon Epps3

A Paper Submitted for Publication Transportation Research Board

Annual Meeting January 13-17, 2002

Washington D.C. 1. Graduate Research Assistant, Pavements/Materials Program, Department of Civil Engineering, University of Nevada, Reno, Nevada, 89557. 775-784-1172, gopal@unr.edu 2. Professor and Director, Pavements/Materials Program, Department of Civil Engineering, University of Nevada, Reno, Nevada, 89557. 775-784-6565, Sebaaly@unr.nevada.edu. 3. Materials Engineering Manager, Granite Construction Inc., Sparks, Nevada, 89432. 775-352-1954, Jepps@granite-net.com

TRB 2002 Annual Meeting CD-ROM Original paper submittal – not revised by author .

ABSTRACT: This paper presents a study to evaluate low temperature rheological properties of

crumb rubber modified binders and the impact of the particle size and content on such properties.

Three sizes of the crumb rubber (0.18, 0.425 and 2.0 mm), a control (0%) and two levels of

crumb rubber content (12% and 24%) were used with four asphalt binders. The measured

rheological properties consisted of creep stiffness (St) and logarithmic creep rate (m). Results

showed that: increasing the crumb rubber content decreased the creep stiffness which improves

thermal cracking resistance. The impact of crumb rubber content on the m-value was very

highly inconsistent. The crumb rubber size did not have significant effect on the low temperature

properties. The effect of the size of the crumb rubber on the resistance to thermal cracking was

dependent on the asphalt binder source. The analysis of the data generated in this experiment

showed that some combinations of crumb rubber size and content can either improve or

jeopardize the PG low temperature of the asphalt binder.

KEY WORDS: crumb rubber, Superpave, rheological properties, creep stiffness, logarithmic

creep rate, thermal cracking, low temperature properties.

ACKNOWLEDGMENT: The authors would like to thank the Federal Highways

Administration for providing the funds for this research and the research team at Oregon State

University who were the Principal Investigators for the FHWA Project on Crumb Rubber

Technologies.

INTRODUCTION

Crumb rubber modified (CRM) binders have been used as paving materials since the

1960's. The purpose of using CRM binders is to improve the hot mix asphalt (HMA) mixture’s

resistance to cracking and rutting failures under traffic loading and environmental conditions.

Blending crumb rubber into an asphalt binder is believed to improve its elastic and energy

absorption properties, which are directly related to the binder’s resistance to cracking and rutting

failures.

Cracking failures of HMA pavements are caused by excessive tensile strains within the

HMA layer. The source of excessive tensile strains can be due to bending under traffic loads,

shrinkage at freezing temperatures, or reflection of cracks from the old pavement layer beneath

the new HMA layer. Low temperature cracking starts at the surface and progresses down with

time, because low ambient temperatures chill the road surface first. HMA pavements subjected

to high cooling rates and low temperatures develop tensile stresses due to shrinkage, when these

stresses exceed the fracture strength of the HMA pavement layer, transverse cracking develops.

HMA mixes, which have high stiffness modulus at low temperatures, are very prone to cracking.

Because the low temperature cracking of an HMA pavement is purely a tensile stress

failure, the resistance of the HMA pavement to such failure is mainly provided by the asphalt

binder. Therefore, the low temperature properties of the asphalt binder control the behavior of

the HMA mix under freezing environmental conditions. The Superpave performance based (PG)

binder grading system uses the rheological properties of the asphalt binder to assess its resistance

to low temperature cracking. This paper summarizes the data generated from a research effort to

assess the impact of crumb rubber size and content on the low temperature properties of asphalt

binders as measured by the Superpave (PG) binder grading system.

BACKGROUND

In 1994, Reese evaluated the properties of CRM binders in dense graded and open graded

mixtures used on six Caltrans projects (1, 2). The evaluated binders were blended in the

laboratory and aged according to the projects locations using the thin film oven, tilted thin film

oven and the pressure aging vessel. Reese conducted several evaluations using the rheological

properties of the CRM binders as measured by the dynamic shear rheometer (DSR) and bending

beam rheometer (BBR) including the resistance of CRM binders to fatigue cracking, rutting and

thermal cracking, and the impact of the crumb rubber content. Reese concluded that the use of

the slope of the creep stiffness curve (m) and a maximum stiffness value are sufficient in

determining the resistance of CRM binders to thermal cracking.

In 1995, Bahia and Davis evaluated the impact of crumb rubber types and contents on the

rheological properties of asphalt binders (3). Three types of crumb rubbers were evaluated,

including: ambient shredding (AS), cryogenic grinding (CG) and special extrusion (TP) with

contents ranging between 5 and 20% at 5% intervals blended with two different grades of asphalt

binders. The measured rheological properties included creep stiffness (St) and the logarithmic

creep rate (m) at low temperatures ranging from -20 to 00C. They concluded that the impact of

crumb rubber content (2-20%), on the reduction of stiffness at low temperature (-20 to 00C) is a

linear function of the rubber content and was independent of the rubber source. The research

also concluded that the stiffness decreases by 4% for every 1 percent increase in rubber content

for all three types of crumb rubbers. This trend is highly asphalt specific; the lower the stiffness

of the asphalt the less significant the effect of the rubber. The effect of different rubber sources

were similar. The effect of rubber on the m-value was not significant with respect to the rubber

source or content.

In 1996, Troy et al. Evaluated the applicability of using the Superpave binder grading

system tests to evaluate the rheological properties of CRM binders (4). The research program

covered the use of parallel plate system with 1 and 2mm gaps and the plate and cup system with

BBR. The research recommended the use of the plate and cup system in conjunction with the

BBR to grade CRM binders that contain any rubber particles larger than No. 200. The low

temperature properties of the CRM mixtures as measured by the Thermal Stress Restrained

Specimen Test (TSRST) were highly consistent for the samples tested. The fracture temperature

coincided well with the low temperature grade of the CRM binders evaluated with the BBR.

OBJECTIVE This research project evaluated the effect of crumb rubber size and content on the

resistance of CRM binders to low temperature cracking. The specific objectives of the research

are summarized as follows:

• Evaluate the effect of crumb rubber content on the resistance of CRM binders to low temperature cracking using three levels of crumb rubber contents 0, 12 and 24%.

• Evaluate the effect of crumb rubber size on the resistance of CRM binders to low

temperature cracking using three sizes; 0.18, 0.425 and 2.00 mm.

EXPERIMENTAL PROGRAM

Table 1 summarizes the various combinations of crumb rubber sizes and contents that

were evaluated. The rheological properties: Stiffness (St) and slope of creep curve (m) were

measured for each of the combinations listed in table 1. The St represents the creep stiffness and

m represents the logarithmic creep rate after 60 seconds of loading time.

The four asphalt binders used in this study came from the AASHTO Materials Reference

Laboratory (AMRL). These binders were used in the asphalt research of the Strategic Highway

Research Program (SHRP). The SHRP AAM-1 is a PG64-16, the SHRP AAB-1 is a PG58-22,

the SHRP ABL-3 is a PG58-28, and the SHRP AAA-2 is a PG64-34.

The crumb rubber modifiers were blended into the asphalt binders at the university of

Nevada’s Pavement/Materials laboratory using a low shear blender (1100-1200 rpm). An oil

bath was used to maintain the asphalt binder at the desired temperature throughout the blending

process. A 600 grams sample of the asphalt binder is weighed into a quart can which is then

placed inside an oil bath and maintained at 175±50C. The blender’s blade is inserted into the

asphalt binder sample and operated at 1100-1200 rpm while adding the appropriate amount of

crumb rubber. The blending process is then continued for one hour.

ANALYSIS OF EXPERIMENTAL DATA

The Superpave technology was used to assess the resistance of the crumb rubber

modified binders to low temperature cracking in terms of the creep stiffness (St) and the

logarithmic creep rate (m-value). Each of the crumb rubber modified binders was tested at three

temperatures: the first temperature corresponds to the low temperature grade of the base asphalt

binder and two additional increments of 6 and 12 degrees Celsius below the first temperature. It

should noted here that the BBR testing temperature is 10oC warmer than the low temperature

grade of the binder. The two additional temperature increments were selected to assess the

ability of the crumb rubber to improve the low temperature properties of the binders. Therefore,

the three testing temperatures are different for each binder.

The Superpave technology specifies that the creep stiffness (St) must not exceed 300

MPa at 60 seconds loading time and the m-value which is the slope of the logarithmic

relationship between the creep stiffness and loading time must be greater than or equal to 0.300

when measured at the 60 seconds loading time. Following the Superpave requirements, the

tested binders were aged through the RFTO and PAV prior to the evaluation of their low

temperature rheological properties in the bending beam rheometer (BBR). The evaluation of the

rheological properties of the modified and unmodified binders followed the Superpave

technology according to AASHTO standard procedures.

The current Superpave binder grading system calls for the use of the BBR and the direct

tension (DT) device to fully assess the resistance of asphalt binders to low temperature cracking

(5). The research presented in this paper was initiated prior to this latest modification of the

grading system and at that time the DT device was not yet perfected, therefore, only the BBR test

was used to assess the low temperature behavior of the modified binders.

The data generated from this research were analyzed to meet the two objectives of the

study: a) evaluate the effect of crumb rubber content and b) evaluate the effect of crumb rubber

size. As indicated in table 1, three crumb rubber sizes: 0.180, 0.425, and 2.000 mm were used at

three different contents: 0, 12 and 24 percent with four asphalt binders. The 0% content was

used as the control. Each of the combinations was tested at three temperatures. Replicate

measurements were made at each test condition. The analysis of variance (ANOVA) statistical

tools were used to evaluate the level of significance of each parameter, i.e. rubber content and

size. Mean comparisons were conducted at a 95% confidence level (" = 0.05).

Figures 1 through 8 graphically present the impact of rubber content and size on the St

and m properties for the four asphalt binders evaluated in this study. Each graph includes a

horizontal thick black solid line indicating the suggested Superpave criteria for St and m. In the

case of St the criteria line represents the maximum stiffness value while in the case of m the

criteria line represents the minimum slope. By visually comparing the values of St and m with

the criteria line, it can be observed whether or not the addition of crumb rubber has improved the

low temperature properties of the asphalt binder.

Tables 2 through 9 summarize the statistically-based comparisons for the various testing

conditions. An entry of “S” indicates that the two treatment being compared generated the same

property, an entry of “L” indicates that the treatment generated a lower property than the

treatment being compared with, and an entry of “H” indicates that the treatment generated a

higher property than the treatment being compared with. For example, in table 2 an entry of “L”

is placed across the St at -6oC, under the columns of 2.00 mm rubber size and 12% vs 0%. This

entry indicates that the addition of 12% of the 2.00 mm crumb rubber generated a St at -6oC that

is lower than the St at -6oC of the binder with 0% rubber (control).

Effect of Crumb Rubber Content on the Stiffness

An examination of the graphical presentations in figures 1, 3, 5, and 7 and the statistical

comparisons in tables 2 through 5 indicates the following:

• For asphalt binders AAM-1 and AAB-1 (tables 2 and 3), the addition of crumb rubber significantly reduced the stiffness at all three temperatures for all three crumb rubber sizes. In all cases, as the crumb rubber content increased, the stiffness decreased (an entry of “L” is shown all across the St values).

• For asphalt binder ABL-3, the addition of crumb rubber at the 12% content significantly

increased the stiffness as compared to the control and the 24% content. This is shown in table 4 by the “H” entries when the 12% is compared with the 0% and by the “L” entries when the 24% is compared with the 12%. The 24% crumb rubber either reduced or maintained the same St as compared to the control. This is shown in table 4 by either “L” or “S” entries when the 24% is compared with the control.

• For asphalt binder AAA-2, the addition of crumb rubber reduced the stiffness except in

the case of the 24% content of the 2.00 mm crumb rubber. This is shown in table 5 by the “L” entries under all cases except when the 24% of the 2.00 mm rubber is compared with the control and the 12% rubber content.

Following the Superpave directive which indicates that decreasing the stiffness means

improving the binder’s resistance to low temperature cracking, it can be concluded that the

addition of crumb rubber improves the resistance of asphalt binders to low temperature cracking.

However, an optimum crumb rubber content must be determined for each crumb rubber size and

asphalt binder.

Effect of Crumb Rubber Content on the m-Value

comparisons in tables 2 through 5 indicates the following: • For the AAM-1 binder (table 2), the addition of the 12% rubber significantly increased

the m-value at the -12 and -18oC while the addition of the 24% rubber significantly increased the m-value at all three temperatures.

• For the AAB-1 and AAA-2 (tables 3 and 5) binders, the addition of 12% and 24% crumb

rubber significantly reduced the m-value in the majority of the cases. This is shown in tables 3 and 5 as more “L” entries are present than both “S” and “H” entries combined (28 “L”, 12 “S”, and 14 “H”).

• For the ABL-3 binder, the addition of 12% crumb rubber significantly reduced the m-

value for all crumb rubber sizes and all three temperatures. The addition of 24% rubber showed an improvement over the 12% but still significnaly below the control (0%).

The above observations indicate that the impact of crumb rubber content on the m-value

is not as predictable as its impact on the stiffness. The addition of crumb rubber significantly

increases the m-value only for very limited and very specific combinations of asphalt binder and

crumb rubber. Materials engineers should be very cautions in using crumb rubber to improve the

m-value of asphalt binders.

Effect of Crumb Rubber Size on Stiffness

comparisons in tables 6 through 9 indicates the following:

• For the AAM-1 binder (table 6), increasing the size of the crumb rubber significantly

increased the stiffness at -6oC while it had no significant impact at the colder temperatures of -12 and -18oC.

• For the AAB-1 binder (table 7), increasing the size of the crumb rubber had no significant

impact on the stiffness. • For the ABL-3 binder (table 8), the impact of increasing the size of the crumb rubber on

the stiffness was inconsistent. In some cases it significantly increased the stiffness while in other cases, it significantly reduced the stiffness.

• For the AAA-2 binder (table 9), increasing the crumb rubber size did not significantly

impact the stiffness at the 12% rubber content while it significantly increased the stiffness at the 24% rubber content.

In general, increasing the crumb rubber size can either increase or maintain the low

temperature stiffness property of an asphalt binder. According to the Superpave criteria this does

not constitute an improvement in the resistance of binders to low temperature cracking.

Effect of Crumb Rubber Size on m-Value

comparisons in tables 6 through 9 indicates the following: • For all four binders evaluated in this study, increasing the size of the crumb rubber either

maintains the m-value or significantly reduces it except in the case of the ABL-3 binder where increasing the rubber size increased the m-value when used at 24% and at -30oC temperature.

Similar to the case of the impact of rubber size on the stiffness, this type of impact does

not constitute an improvement in the resistance of of binder to low temperature cracking.

Impact of Crumb rubber on the PG Grade

This analysis examines the cases where the addition of certain combination of crumb

rubber size and content would impact the PG low temperature grade of a binder. In other words,

this analysis will identify the cases where by using crumb rubber the PG low temperature grade

of a binder has been improved or jeopardized. This analysis identified the St and m-value for

each CRM binder and checks them against the Superpave criteria of St being less or equal than

300 MPa and m being greater or equal to 0.300 at the low temperature grade.

AAM-1 Binder

The unmodified AAM-1 binder has a PG low temperature grade of -16. The data

generated in this research showed that the following combinations of crumb rubber sizes and

contents would improve the PG low temperature grade of the AAM-1 binder to -22:

0.425 mm at 12% 0.180 mm at 12% 0.425 mm at 24% 0.180 mm at 24%

And the following combinations of crumb rubber sizes and contents would improve the PG low

temperature grade of the AAM-1 binder to -28: 0.425 mm at 24% 0.180 mm at 24%

The data generated in this research also showed that none of the evaluated combinations

of crumb rubber sizes and contents would jeopardize the current PG low temperature grade of

the AAM-1 binder of -16.

AAB-1 Binder

The unmodified AAB-1 binder has a PG low temperature grade of -22. The data

generated in this research showed that none of the evaluated combinations of crumb rubber sizes

and contents would improve the PG low temperature grade of the AAM-1 binder to -28.

The data generated in this research also showed that the following combination of crumb

rubber sizes and contents would jeopardize the current PG low temperature grade of the AAB-1

binder of -22 by failing the m-value criterion (figure 4):

2.00 mm at 24%

ABL-3 Binder

The unmodified AAB-1 binder has a PG low temperature grade of -28. The data

and contents would improve the PG low temperature grade of the ABL-3 binder to -34.

The data generated in this research also showed that the following combinations of crumb

rubber sizes and contents would jeopardize the current PG low temperature grade of the ABL-3

binder of -28 by failing the St and m-value criteria (figures 5 and 6): 2.00 mm at 12% 0.425mm at 12% 0.18 mm at 12%

AAA-2 Binder

The unmodified AAA-2 binder has a PG low temperature grade of -34. The data

and contents would improve the PG low temperature grade of the AAA-2 binder to -40.

The data generated in this research also showed that the following combinations of crumb

rubber sizes and contents would jeopardize the current PG low temperature grade of the AAA-2

binder of -34 by failing the m-value criterion (figure 8): 2.00 mm at 24%

CONCLUSIONS AND RECOMMENDATIONS

This experimental program evaluated the impact of crumb rubber contents and sizes on

the low temperature properties of four asphalt binders. A total of 108 combinations were tested

in the bending beam rheometer to evaluate their St and m-value. All of the evaluated binders

were aged in the RTFO and PAV according to applicable AASHTO procedures. Based on the

analysis of the data generated from this experiment, the following conclusions and

recommendations can be made:

• In general crumb, rubbers can be used within a wide range of contents and sizes to reduce

the low temperature stiffness of asphalt binders. However, an optimum crumb rubber content must be determined for each crumb rubber size and asphalt binder.

• The impact of crumb rubber on the m-value is highly dependent on the properties of the

asphalt binder. This experiment showed that crumb rubbers are not effective in increasing the m-value of asphalt binders.

• In general, crumb rubbers can be used over a wide rage of contents and sizes without

affecting the PG low temperature grade of the asphalt binder. However, in some limited cases, the use of certain combinations of crumb rubber size and content can either improve or jeopardize the PG low temperature grade of the asphalt binder.

It is highly recommended that when crumb rubbers are used to improve the resistance of

asphalt binders to permanent deformation and fatigue failures, the impact of these modifications

on the low temperature properties of the binder should be carefully assessed. The results

presented in this paper show that crumb rubbers can be used to improve the low temperature

properties of asphalt binders but only if carefully designed and evaluated.

REFERENCES 1. Reese, R., “Development of a Physical Property Specification for Asphalt-Rubber

Binder,” Journal of the Association of Asphalt Paving Technologists, vol. 63, 1994, p. 373-413.

1. Reese, R., “Properties of Aged Asphalt Binder Related to Asphalt Concrete Fatigue

Life,” Journal of the Association of Asphalt Paving Technologists, vol. 66, 1997, p. 604-632.

1. Bahia, H. and Davies, R., “Role of Crumb Rubber Content and Type in Changing Critical

Properties of Asphalt Binders,” Journal of the Association of Asphalt Paving Technologists, vol. 64, 1995, p. 130-162.

1. Troy, K., Sebaaly, P.E., Epps, J., “Evaluation Systems for Crumb Rubber Modified

Binders and Mixtures,” Transportation Research Record, no.1530, 1996, p.3-10. 1. AASHTO Provisional Standards, 2001, “MP1a, Specifications for Performance Garded

Asphalt Binder,” Washington, D.C., 2001.

Table 1.Laboratory Experimental Program.

Asphalt Binder Crumb Rubber Size (mm)

Crumb Rubber Content (%)

Test Temperature (C)

AAM-1 (PG64-16) 0.18, 0.425, 2.00 0, 12, 24 -6, -12, -18

AAB-1 (PG58-22) 0.18, 0.425, 2.00 0, 12, 24 -12, -18, -24

ABL-3 (PG58-28) 0.18, 0.425, 2.00 0, 12, 24 -18, -24, -30

AAA-2 (PG64-34) 0.18, 0.425, 2.00 0, 12, 24 -24, -30, -33

Table 2. Statistical comparison of St and m at various rubber contents for asphalt binder AAM-1. Property

2.00 mm 0.425 mm 0.18 mm

12% vs 0%

24% vs 0% 24% vs 12%

12% vs 0% 24% vs 0% 24% vs 12%

St @ -6oC L L L L L L L L L

m @ -6oC S S S S H H S S S

m @ -12oC S H S H H H H H H

m @ -18oC S H H H H S H H H

Table 3. Statistical comparison of St and m at various rubber contents for asphalt binder AAB-1. Property

2.00 mm 0.425 mm 0.18 mm

12% vs 0%

24% vs 0% 24% vs 12%

12% vs 0% 24% vs 0% 24% vs 12%

m @ -120C L L L L L L L L L

m @ -18oC L L S S S S S S S

m @ -24oC S H H H H H H H H

L: Lower S: Same H: Higher

B 2002 A

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Original paper subm

ittal – not revised by author.

Table 4. Statistical comparison of St and m at various rubber contents for asphalt binder ABL-3. Property

2.00 mm 0.425 mm 0.18 mm

12% vs 0%

24% vs 0% 24% vs 12%

12% vs 0% 24% vs 0% 24% vs 12%

St @ -18oC H L L H L L H S L

St @ -24oC H S L H S L H S L

St @ -30oC H S L H S L H S L

m @ -18oC L L H L S H L S H

m @ -24oC L L H L S H L L H

m @ -30oC L L H L L H L L H

Table 5. Statistical comparison of St and m at various rubber contents for asphalt binder AAA-2. Property

2.00 mm 0.425 mm 0.18 mm

12% vs 0%

24% vs 0% 24% vs 12%

12% vs 0% 24% vs 0% 24% vs 12%

St @ -24oC L H H L L L L L L

St @ -30oC L S H L L L L L L

St @ -33oC L H H L L L L L L

m @ -24oC L L L L L L S L L

m @ -30oC L L L S L L S L L

m @ -33oC S L L H H H H H H

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Original paper subm

Table 6. Statistical comparison of St and m a various rubber sizes for asphalt binder AAM-1. Property

12 % 24%

2.00 vs .425 2.00 vs .18 .425 vs .18 2.00 vs .425 2.00 vs .18 .425 vs .18

St @ -6oC H H H H H S

St @ -12oC H S S H S L

St @ -18oC S S S S S S

m @ -6oC S S S L L S

m @ -12oC L L S L L S

Table 7. Statistical comparison of St and m a various rubber sizes for asphalt binder AAB-1. Property

12 % 24%

2.00 vs .425 2.00 vs .18 .425 vs .18 2.00 vs .425 2.00 vs .18 .425 vs .18

St @ -24oC S S S L L S

m @ -120C L L L L L S

B 2002 A

nnual Meeting C

Original paper subm

Table 8. Statistical comparison of St and m a various rubber sizes for asphalt binder ABL-3. Property

12 % 24%

2.00 vs .425 2.00 vs .18 .425 vs .18 2.00 vs .425 2.00 vs .18 .425 vs .18

St @ -18oC L L L S L L

St @ -24oC L S H S S S

St @ -30oC L L S L L S

m @ -18oC S S S L S H

m @ -24oC S S S L S H

m @ -30oC L L L S H H

Table 9. Statistical comparison of St and m a various rubber sizes for asphalt binder AAA-2. Property

12 % 24%

2.00 vs .425 2.00 vs .18 .425 vs .18 2.00 vs .425 2.00 vs .18 .425 vs .18

St @ -24oC S S S H H S

B 2002 A

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Original paper subm

Figure 1: Effect of crumb rubber size and content on stiffness for the AAM-1 binder

-6 -12 -18

Temperature (C)

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 2: Effect of crumb rubber size and content on m-Value for the AAM-1 binder

-6 -12 -18Temperature (C)

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 3: Effect of crumb rubber size and content on stiffness for the AAB-1 binder

-12 -18 -24

Temperature (C)

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 4: Effect of crumb rubber size and content on m-Value for the AAB-1 binder

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 6: Effect of crumb rubber size and content on m-Value for the ABL-3 binder

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 5: Effect of crumb rubber size and content on stiffness for the ABL-3 binder

1000.0

1100.0

1200.0

-18 -24 -30

Temperature (C)

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 7: Effect of crumb rubber size and content on stiffness for the AAA-2 binder

-24 -30 -33

Temperature (C)

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

Figure 8: Effect of crumb rubber size and content on m-Value for the AAA-2 binder

Control C-2.00-12% C-0.425-12% C-0.18-12%

C-2.00-24% C-0.425-24% C-0.18-24%

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