mixing and compaction temperatures for hot mix asphalt concrete

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  • Technical Report Documentation Page

    1. Report No.

    1250-5

    2. Government Accession No. 3. Recipients Catalog No.

    5. Report Date

    January 2000

    4. Title and Subtitle

    MIXING AND COMPACTION TEMPERATURES FOR HOT MIX ASPHALT CONCRETE

    6. Performing Organization Code

    7. Author(s)

    Yetkin Yildirim, Mansour Solaimanian, and Thomas W. Kennedy

    8. Performing Organization Report No.

    1250-5

    10. Work Unit No. (TRAIS)

    9. Performing Organization Name and Address

    Center for Transportation Research The University of Texas at Austin 3208 Red River, Suite 200 Austin, TX 78705-2650

    11. Contract or Grant No.

    0-1250

    13. Type of Report and Period Covered

    Research Report (9/98 8/99)

    12. Sponsoring Agency Name and Address

    Texas Department of Transportation Research and Technology Transfer Section/Construction Division P.O. Box 5080 Austin, TX 78763-5080

    14. Sponsoring Agency Code

    15. Supplementary Notes

    Project conducted in cooperation with the Federal Highway Administration.

    16. Abstract

    According to Superpave mixture design, gyratory specimens are mixed and compacted at equiviscous binder temperatures corresponding to viscosities of 0.17 and 0.28 Pas, respectively. These were the values previously used in the Marshal mix design method to determine the mixing and compaction temperatures. In order to estimate the appropriate mixing and compaction temperatures for Superpave mixture design, a temperature-viscosity relationship for the binder should be developed (ASTM D 2493, Calculation of Mixing and Compaction Temperatures). This approach is simple and provides reasonable temperatures for unmodified binders. However, some modified binders have exhibited unreasonably high temperatures for mixing and compaction using this technique. These high temperatures could result in construction problems, asphalt damage, and fume production. ASTM D 2493 was established for unmodified asphalt binders, which are Newtonian fluids at high temperatures. For these materials, viscosity does not depend on shear rate. However, most of the modified asphalt binders exhibit a phenomenon known as pseudoplasticity, in which viscosity depends on shear rate. Thus, at the high shear rates that occur during mixing and compaction, it is not necessary to use very high temperatures. A research study was undertaken to determine the shear rate during compaction so that the effect of this parameter could be included during viscosity measurements. The use of practical shear rate results in reasonable mixing and compaction temperatures for hot mix asphalt design and construction with modified asphalt binders. It was found that application of the shear rate concept rather than the traditional approach used for unmodified binders can reduce the mixing and compaction temperatures between roughly 14 to 38 C for the former and 10 to 27 C for the latter, depending on the type and the amount of modifier.

    17. Key Words

    Superpave, asphalt pavements, shear rate, mixing and compaction temperature

    18. Distribution Statement

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

    19. Security Classif. (of report)

    Unclassified

    20. Security Classif. (of this page)

    Unclassified

    21. No. of pages

    100

    22. Price

    Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

  • MIXING AND COMPACTION TEMPERATURES FOR HOT MIX ASPHALT CONCRETE

    by

    Yetkin Yildirim, Mansour Solaimanian, and Thomas W. Kennedy

    Research Report Number 1250-5

    Research Project 0-1250

    South Central Superpave Center

    Conducted for the

    TEXAS DEPARTMENT OF TRANSPORTATION

    in cooperation with the

    U.S. DEPARTMENT OF TRANSPORTATION

    FEDERAL HIGHWAY ADMINISTRATION

    by the

    CENTER FOR TRANSPORTATION RESEARCH

    Bureau of Engineering Research

    THE UNIVERSITY OF TEXAS AT AUSTIN

    January 2000

  • iv

  • v

    PREFACE

    This is the fifth report from the South Central Superpave Center. It presents the results, findings, conclusions, and recommendations based on a comprehensive laboratory study conducted at the Center. The extensive laboratory testing was performed during a 2-year period to provide sufficient information for the project.

    IMPLEMENTATION RECOMMENDATIONS

    Superpave mixture design requires that gyratory specimens be mixed and compacted at equiviscous binder temperatures corresponding to viscosities of 0.17 and 0.28 Pas (Pascal second), respectively. For many years those values have been used in the Marshal mix design method to determine mixing and compaction temperatures. Estimation of the proper mixing and compaction temperatures involves developing a temperature viscosity relationship for the binder. This approach is simple and provides reasonable temperatures for unmodified binders. However, some modified binders have exhibited unreasonably high mixing and compaction temperatures using this technique. This is due to the fact that modified binders are very sensitive to shear rate.

    A research study was conducted at South Central Superpave Center (SCSC) to address this issue. After a 2-year study, researchers developed a new method for calculation of mixing and compaction temperatures. This study was completed in two parts. In the first part, the shear rate on the asphalt binders during compaction was determined. During this study the shear rate was found to be approximately 500 1/s. In the second part, a new method for calculation of mixing and compaction temperatures was developed by considering the effect of this shear rate. The new approach indicates that the mixing temperature will be between 14 to 38 C lower and the compaction temperature will be about 10 to 27 C lower when the shear rate is taken into account.

    ACKNOWLEDGMENTS

    The authors would like to thank the Texas Department of Transportation and Federal Highway Administration for their support. Special thanks are extended to Mr. Robert McGennis for his support and assistance. The authors would like to acknowledge Mr. Gary L. Fitts, Mr. Aroon V. Shenoy, and Dr. Kara Kockelman for their help. Great appreciation is extended to Mr. Maghsoud Tahmoressi, the project director, for his guidance and also to the personnel from Materials Section, Construction Division of TxDOT for their assistance. Special thanks are extended to the binder supplier companies for this project.

    The support of the Center for Transportation Research, especially the assistance provided by Mr. Ray Donley and Ms. Clair LaVaye, is also greatly appreciated.

  • vi

    DISCLAIMERS

    The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of either the Federal Highway Administration or the Texas Department of Transportation. This report does not constitute a standard, specification, or regulation.

    NOT INTENDED FOR CONSTRUCTION, BIDDING, OR PERMIT PURPOSES

    Thomas W. Kennedy, P.E. (Texas No. 29596)

    Research Supervisor

    Research performed in cooperation with the Texas Department of Transportation and the U.S. Department of Transportation, Federal Highway Administration.

  • vii

    TABLE OF CONTENTS CHAPTER 1. INTRODUCTION ............................................................................................ 1 CHAPTER 2. BACKGROUND .............................................................................................. 5

    Mixing and Compaction................................................................................................ 5 Basic Terminology for Viscosity Calculations ............................................................. 5

    Viscosity.................................................................................................................. 6 Newtonian Fluids .................................................................................................... 7 Non-Newtonian Fluids ............................................................................................ 8

    Evaluation of Viscosity of Asphalt Binders at High Temperatures .............................. 9 Current Procedure for Calculation of Mixing and Compaction Temperatures........... 11 Shear Rate Inside the Superpave Gyratory Compactor............................................... 12

    CHAPTER 3. EXPERIMENTAL PROGRAM ..................................................................... 13

    Materials...................................................................................................................... 13 Asphalt Binders ........................................................................................................... 13 Performance Graded Binder Specification.................................................................. 14 Aggregates................................................................................................................... 14

    Aggregate Testing Requirements .......................................................................... 14 Gradation............................................................................................................... 15 Specific Gravity of Aggregate............................................................................... 15 Mineral Aggregate Properties ............................................................................... 16 Consensus Aggr

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