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Publication Number: FHWA-RD-02-075
Date: October 2000

Understanding The Performance of Modified Asphalt Binders in Mixtures: High-Temperature Characterization

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by

Kevin D. Stuart
Federal Highway Administration
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296
TELEPHONE: (202) 493-3073
FAX: (202) 493-3161

FOREWORD

This report documents the effects of polymer-modified asphalt binders on the rutting resistance of mixtures with diabase and limestone aggregate. It is part of a research study titled "Understanding the Performance of Modified Asphalt Binders in Mixtures." This study is partially funded through National Cooperative Highway Research Program (NCHRP) Project 90-07. The objective of NCHRP Project 90-07 is to determine if asphalt binder performance is captured by the Superpave asphalt binder specification developed under the 1987 through 1993 Strategic Highway Research Program, with an emphasis on evaluating the performances of mixtures containing polymer-modified asphalt binders with identical Superpave performance grades, but varied chemistries. Asphalt binder tests developed under NCHRP Project 09-10, titled "Superpave Protocols for Modified Asphalt Binders," are also being evaluated. NCHRP Project 09-10 was completed in February 2001.

This report will be of interest to highway personnel who use polymer-modified asphalt binders and Superpave. Overall, good correlations between the high-temperature properties of the asphalt binders and mixture rutting resistance were found, but the two laboratory mixture tests did not provide the same conclusions concerning which asphalt binders do not behave as expected. Full-scale pavement tests are needed to determine this.

T. Paul Teng, P.E.
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.

FHWA-RD-02-075

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

UNDERSTANDING THE PERFORMANCE OF MODIFIED ASPHALT BINDERS IN MIXTURES: HIGH-TEMPERATURE CHARACTERIZATION

5. Report Date

 

6. Performing Organization Code
7. Author(s)

Kevin D. Stuart

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

In-House Report

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, Virginia 22101-2296

13. Type of Report and Period Covered

Final Report
October 2000 - March 2002

14. Sponsoring Agency Code

 

15. Supplementary Notes

FHWA Contact: Kevin D. Stuart, HRDI-11. Contractor personnel that worked on this study were Frank Davis, Susan Needham, Scott Parobeck, Naga Shashidhar, and Aroon Shenoy, SaLUT, 6300 Georgetown Pike, McLean, VA 22101-2296.

16. Abstract

The overall objective of this study was to determine if the Superpave high-temperature rheological properties of polymer-modified asphalt binders correlate to asphalt mixture rutting resistance. An emphasis was placed on evaluating polymer-modified asphalt binders with identical (or close) high-temperature performance grades (PG's), but varied polymer chemistries. Eleven asphalt binders were obtained for this study: two unmodified asphalt binders, an air-blown asphalt binder, and eight polymer-modified asphalt binders. High-temperature asphalt binder properties were measured by a dynamic shear rheometer (DSR). Mixture rutting resistance was measured by repeated shear at constant height (RSCH), and the French Pavement Rutting Tester (French PRT).

The first objective was to verify the findings of a previous study using a different aggregate. In the previous study, it was found that the Superpave high-temperature asphalt binder properties correlated to mixture rutting resistance with few outliers, and a change in high-temperature PG from 70 to 76 increased rutting resistance. However, the correlation between RSCH and asphalt binder G*/sind (delta) depended on DSR frequency. The data suggested that a low DSR frequency, such as 0.1 rad/s, might provide a better grading system than the standard DSR frequency of 10.0 rad/s. This would require a change in the current asphalt binder specification. A diabase aggregate was used in a previous study. The data using a second aggregate, a limestone aggregate, in combination with four of the asphalt binders, agreed with the findings from the diabase mixtures.

The second objective was to retest the diabase mixtures at 70 degrees Celsius using RSCH. The test temperatures used in the previous study were 50 degrees Celsius for RSCH and 70 degrees Celsius for the French PRT. The polymer-modified asphalt binders had continuous high-temperature PG's ranging from 71 to 77. Therefore, it was recommended that the test temperature for RSCH be increased to 70 degrees Celsius. Again, the correlation between RSCH and G*/sind was dependent on DSR frequency. The data suggested that a low DSR frequency, such as 0.1 rad/s, might provide a better grading system. However, it is not known whether this finding applies to pavements, or is related to the accelerated nature of the RSCH test. Furthermore, G*/sind (delta) at 0.1 rad/s did not clearly provide a better correlation to RSCH than the high-temperature PG's of the asphalt binders. The degree of correlation between the French PRT and G*/sind at 70 degrees Celsius did not depend on DSR frequency, and there was only one outlier. A correlation between the French PRT and high-temperature PG provided no obvious outliers. No changes to the specification are recommended based on the French PRT results.

17. Key Words

Superpave, asphalt binder specification, permanent deformation, Superpave Shear Tester, SST, French Pavement Rutting Tester, polymer-modified asphalt binders.

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161..

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

41

22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

TABLE OF CONTENTS

Section

Phase 1--Evaluation of High-Temperature Asphalt Binder Tests Using Mixtures With Limestone and Diabase Aggregate

A. Background

B. Objective

C. Materials

D. Tests

E. Cumulative Permanent Shear Strain

F. French PRT

G. Conclusions

Phase 2--Evaluation of High-Temperature Asphalt Binder Tests Using the RSCH and French PRT Mixture Tests at 70°C

A. Background

B. Objective

C. Materials

D. Tests

E. Cumulative Permanent Shear Strain

F. French PRT

G. Conclusions

H. Recommendations

References

LIST OF FIGURES

Figure No.

1. French PRT rut depth at 70°C vs. high-temperature PG

2. French PRT rut depth at 70°C vs. high-temperature PG for all asphalt binders

3. French PRT rut depth at 70°C vs. G*/sind at 70°C for all asphalt binders

4. RSCH cumulative permanent shear strain vs. high-temperature PG of the asphalt binder

5. RSCH cumulative permanent shear strain at 70°C vs. RSCH cumulative permanent shear strain at 50°C

6. Log RSCH cumulative permanent shear strain at 50°C vs. log (G*/sind ) of the asphalt binder at 50°C and 0.125 rad/s

7. Log RSCH cumulative permanent shear strain at 70°C vs. log (G*/sind ) of the asphalt binder at 70°C and 0.125 rad/s

8. Log RSCH cumulative permanent shear strain at 70°C vs. log (G*/sind ) of the asphalt binder at 70°C and 2.0 rad/s

9. Log RSCH cumulative permanent shear strain at 70°C vs. log (G*/sind ) of the asphalt binder at 70°C and 10.0 rad/s

10. RSCH cumulative permanent shear strain at 70°C vs. high-temperature PG of the asphalt binder

11. RSCH cumulative permanent shear strain at 70°C vs. PG temperature based on 0.125 rad/s

12. Asphalt mixture cumulative permanent shear strain vs. asphalt binder cumulative permanent shear strain

13. Comparison of cumulative permanent shear strain using a log-log transformation

14. French PRT rut depth at 70°C vs. G*/sind of the asphalt binder at 70°C and 0.9 rad/s

15. French PRT rut depth at 70°C vs. G*/sind of the asphalt binder at 70°C and 10.0 rad/s

16. French PRT rut depth at 70°C vs. high-temperature PG

17. G*/sind at 0.9 rad/s vs. G*/sind at 10.0 rad/s

18. French PRT rut depth vs. asphalt binder cumulative permanent shear strain

19. Cumulative permanent shear strain of the asphalt mixture vs. French PRT rut depth of the asphalt mixture

LIST OF TABLES

Table No.

1. DSR and RSCH data

2. Cumulative permanent shear strain from RSCH for the mixtures with limestone aggregate

3. DSR data and French PRT rut depths at 6,000 wheel passes

4. Percent rut depth from the French PRT at 70°C and 6,000 wheel passes

5. DSR data and French PRT rut depths at 20,000 wheel passes

6. DSR data and RSCH data at 70°C and 50°C

7. Replicate cumulative permanent shear strains at 70°C

8. G*/sind 's of the asphalt binders at 10.0, 2.0, and 0.125 rad/s with the asphalt binders listed from highest to lowest G*/sind based on 0.125 rad/s

9. Coefficients of determination between RSCH and DSR properties

10. Cumulative permanent shear strain at 70°C

11. DSR data and French PRT rut depths with the materials listed from lowest to highest rut depth at 6,000 wheel passes

12. Replicate data for the French PRT at 6,000 wheel passes

13. RSCH cumulative permanent strains at 70°C and 5,000 cycles using two asphalt binder contents

SI* (Modern Metric) Conversion Factors

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