National Academies Press: OpenBook
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2006. Volumetric Requirements for Superpave Mix Design. Washington, DC: The National Academies Press. doi: 10.17226/13999.
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TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2006 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 567 Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration Subject Areas Materials and Construction Volumetric Requirements for Superpave Mix Design Donald W. Christensen, Jr. A N D Ramon F. Bonaquist ADVANCED ASPHALT TECHNOLOGIES, LLC Sterling, VA

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board’s recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 567 Price $31.00 Project 9-25/9-31 ISSN 0077-5614 ISBN-13: 978-0-309-09867-0 ISBN-10: 0-309-09867-X Library of Congress Control Number 2006935738 © 2006 Transportation Research Board COPYRIGHT PERMISSION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The project that is the subject of this report was a part of the National Cooperative Highway Research Program conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. Such approval reflects the Governing Board’s judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration, U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council. The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of this report.

CRP STAFF FOR NCHRP REPORT 567 Robert J. Reilly, Director, Cooperative Research Programs Crawford F. Jencks, Manager, NCHRP Edward T. Harrigan, Senior Program Officer Eileen P. Delaney, Director of Publications Andrea Briere, Editor NCHRP PROJECT 9-25 PANEL Field of Materials and Construction—Area of Bituminous Materials Gale C. Page, Florida DOT (Chair) Robert F. LaForce, Colorado DOT Rudolf A. Jimenez, University of Arizona Cynthia Y. Lynn, Marbleton, GA Francis J. Manning, Jr., Rhode Island DOT Bruce M. Patterson, Oregon DOT J. Don Powell, Vulcan Materials Company, Birmingham, AL Ronald A. Sines, P.J. Keating Co., Lunenburg, MA John Youtcheff, FHWA Liaison John D’Angelo, Other Liaison Thomas Harman, Other Liaison Leslie Ann McCarthy, Other Liaison Frederick Hejl, TRB Liaison NCHRP PROJECT 9-31 PANEL Field of Materials and Construction—Area of Bituminous Materials Julie E. Nodes, Arizona DOT (Chair) Khaled A. Galal, Virginia DOT Rajinder P. Chawla, New Jersey DOT Dale S. Decker, Bailey, CO Chad Hawkins, South Carolina DOT V.P. Puzinauskas, Silver Spring, MD Darin Tedford, Nevada DOT Greg L. Schiess, FHWA Liaison John D’Angelo, Other Liaison Leslie Ann McCarthy, Other Liaison Frederick Hejl, TRB Liaison C O O P E R A T I V E R E S E A R C H P R O G R A M S

This report presents the findings of two coordinated research projects that investigated whether changes to the recommended Superpave mix design criteria for voids in mineral aggregate, voids filled with asphalt, and air voids content might further enhance the perfor- mance and durability of hot mix asphalt. Its main finding is that, based on an evaluation of the performance properties of hot mix asphalt, major revisions to these volumetric criteria are not needed, although some refinements are possible. The report will be of particular interest to materials engineers in state highway agencies, as well as to materials suppliers and paving contractor personnel responsible for the specification and production of hot mix asphalt. The Superpave mix design method (AASHTO M323 and R35) uses stringent criteria for air voids content (Va), voids in mineral aggregate (VMA), and voids filled with aggregate (VFA) to develop satisfactory hot mix asphalt (HMA) designs. The long delay in develop- ing a suite of reliable material response tests (termed simple performance tests) to verify the performance characteristics of volumetric designs has made the fundamental soundness of these criteria a matter of critical importance. This great reliance on volumetric design cri- teria has been validated by the successful implementation and adoption of the Superpave design method in the United States since its introduction in 1993. Many highway agencies have investigated changes to these volumetric criteria in response to their particular climatic or traffic conditions and local materials properties or to their past experience with HMA designs. The most common changes considered have been (1) establishing maximum VMA values 1.5% to 2.0% above the minimum values; (2) increasing minimum VMA values by 0.5% to 1.0%; and (3) broadening the design air voids content from a fixed value of 4.0% to a range of 3.0% to 5.0%. While there may be sound engineering rationales for such changes in the short term, there is a concern that changes could trigger unacceptable long-term effects on HMA performance and durability, espe- cially since these key volumetric properties are, obviously, interdependent. Under coordinated NCHRP Projects 9-25, “Requirements for Voids in Mineral Aggre- gate for Superpave Mixtures” and 9-31, “Air Void Requirements for Superpave Mix Design,” Advanced Asphalt Technologies, LLC was assigned the tasks of determining the impact of potential changes in the current criteria for Va, VMA, and VFA on the perfor- mance and durability of HMA and recommending any changes deemed desirable. The research team (1) conducted a literature search and critical review of the impact of varia- tion in HMA volumetric properties on mixture performance and durability; (2) carried out a program of laboratory testing to evaluate the effect of changes in Va, VMA, VFA, aggre- gate specific area, and related factors on several performance-related properties of HMA; F O R E W O R D By Edward Harrigan Staff Officer Transportation Research Board

and (3) used these results along with data sets from the literature to develop and validate semi-empirical models for estimating HMA rut resistance, fatigue resistance, mixture per- meability, and age hardening. Based on this experimental work and associated modeling, the research team concluded that the present Superpave volumetric mix design criteria do not need major revision. How- ever, the team found that broadening the air voids content requirement to 3% to 5% is rea- sonable as long as the potential effects on HMA performance are understood. Moreover, while it is not unreasonable to consider changes in the minimum VMA or imposition of a maximum VMA limit, the effects of such changes, especially if coupled with a broader range of air voids content, must be carefully evaluated to avoid lowered rutting and fatigue resis- tance. This final report includes a detailed description of the experimental program, discus- sion of model development and research results, a summary of findings, and recommenda- tions for implementation of key findings. These findings have been referred to the FHWA Asphalt Mixture Expert Task Group for its review and possible recommendation to the AASHTO Highway Subcommittee on Materials for revision of applicable specifications and recommended practices.

C O N T E N T S 1 Summary 5 Chapter 1 Introduction and Research Approach 5 Problem Statement and Research Objective 6 Scope of Study 6 Research Approach 8 Chapter 2 Findings 8 Literature Review and Survey of Practice 10 Laboratory Testing 10 Analysis of Other Data Sets 11 Rut Resistance 17 Fatigue Resistance 22 Permeability and Age Hardening 26 Apparent Film Thickness and HMA Performance 27 Summary 29 Chapter 3 Interpretation, Appraisal, and Applications 29 Summary of Relationships Among HMA Mixture Characteristics and Performance 30 Recent Evolution of HMA Composition and Effects on Performance 32 Possible Revisions in Volumetric Requirements for Superpave Mixtures and Their Effect on Performance 36 General Approaches to Improving the Durability of Mixtures Designed According to the Superpave System and Other HMA Mix Types 39 Implementation 40 Extended Work and Validation Plan 42 Chapter 4 Conclusions and Recommendations 42 Conclusions 42 Recommendations 44 References 46 Glossary

AUTHOR ACKNOWLEDGMENTS The research documented in this report was performed under NCHRP Projects 9-25 and 9-31 by Advanced Asphalt Technologies, LLC. Donald W. Christensen, Jr., Senior Engineer for Advanced Asphalt Technologies, LLC, was Principal Investigator for NCHRP Projects 9-25 and 9-31 and was primarily responsible for technical supervision of this research, including developing the research approach, exper- iment designs, and writing reports documenting the progress and results of the research. Dr. Ramon F. Bonaquist provided significant assistance and technical oversight, including evaluation and revision of various aspects of the research approach, experiment designs, data analysis, and interpretation and edit- ing of reports. The laboratory testing was supervised jointly by Mr. Kevin Knechtel and Mr. Donald Jack.

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TRB's National Cooperative Highway Research Program (NCHRP) Report 567: Volumetric Requirements for Superpave Mix Design examines whether changes to the recommended Superpave mix design criteria for voids in mineral aggregate, voids filled with asphalt, and air voids content might further enhance the performance and durability of hot-mix asphalt.

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