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NATIONAL NCHRP REPORT 567 COOPERATIVE HIGHWAY RESEARCH PROGRAM Volumetric Requirements for Superpave Mix Design

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TRANSPORTATION RESEARCH BOARD 2006 EXECUTIVE COMMITTEE* OFFICERS CHAIR: Michael D. Meyer, Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta VICE CHAIR: Linda S. Watson, Executive Director, LYNX--Central Florida Regional Transportation Authority, Orlando EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board MEMBERS Michael W. Behrens, Executive Director, Texas DOT, Austin Allen D. Biehler, Secretary, Pennsylvania DOT, Harrisburg John D. Bowe, Regional President, APL Americas, Oakland, CA Larry L. Brown, Sr., Executive Director, Mississippi DOT, Jackson Deborah H. Butler, Vice President, Customer Service, Norfolk Southern Corporation and Subsidiaries, Atlanta, GA Anne P. Canby, President, Surface Transportation Policy Project, Washington, DC Douglas G. Duncan, President and CEO, FedEx Freight, Memphis, TN Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering, University of Virginia, Charlottesville Angela Gittens, Vice President, Airport Business Services, HNTB Corporation, Miami, FL Genevieve Giuliano, Professor and Senior Associate Dean of Research and Technology, School of Policy, Planning, and Development, and Director, METRANS National Center for Metropolitan Transportation Research, University of Southern California, Los Angeles Susan Hanson, Landry University Professor of Geography, Graduate School of Geography, Clark University, Worcester, MA James R. Hertwig, President, CSX Intermodal, Jacksonville, FL Gloria J. Jeff, General Manager, City of Los Angeles DOT, Los Angeles, CA Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley Harold E. Linnenkohl, Commissioner, Georgia DOT, Atlanta Sue McNeil, Professor, Department of Civil and Environmental Engineering, University of Delaware, Newark Debra L. Miller, Secretary, Kansas DOT, Topeka Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington Carol A. Murray, Commissioner, New Hampshire DOT, Concord John R. Njord, Executive Director, Utah DOT, Salt Lake City Pete K. Rahn, Director, Missouri DOT, Jefferson City Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson Henry Gerard Schwartz, Jr., Senior Professor, Washington University, St. Louis, MO Michael S. Townes, President and CEO, Hampton Roads Transit, Hampton, VA C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin EX OFFICIO MEMBERS Thad Allen (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington, DC Thomas J. Barrett (Vice Adm., U.S. Coast Guard, ret.), Pipeline and Hazardous Materials Safety Administrator, U.S.DOT Marion C. Blakey, Federal Aviation Administrator, U.S.DOT Joseph H. Boardman, Federal Railroad Administrator, U.S.DOT John Bobo, Deputy Administrator, Research and Innovative Technology Administration, U.S.DOT Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA George Bugliarello, Chancellor, Polytechnic University of New York, Brooklyn, and Foreign Secretary, National Academy of Engineering, Washington, DC J. Richard Capka, Federal Highway Administrator, U.S.DOT Sean T. Connaughton, Maritime Administrator, U.S.DOT Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, DC John H. Hill, Federal Motor Carrier Safety Administrator, U.S.DOT John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC J. Edward Johnson, Director, Applied Science Directorate, National Aeronautics and Space Administration, John C. Stennis Space Center, MS William W. Millar, President, American Public Transportation Association, Washington, DC Nicole R. Nason, National Highway Traffic Safety Administrator, U.S.DOT Jeffrey N. Shane, Under Secretary for Policy, U.S.DOT James S. Simpson, Federal Transit Administrator, U.S.DOT Carl A. Strock (Maj. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC *Membership as of September 2006.

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 567 Volumetric Requirements for Superpave Mix Design Donald W. Christensen, Jr. AND Ramon F. Bonaquist ADVANCED ASPHALT TECHNOLOGIES, LLC Sterling, VA Subject Areas Materials and Construction Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2006 www.TRB.org

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NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 567 RESEARCH PROGRAM Systematic, well-designed research provides the most effective Price $31.00 approach to the solution of many problems facing highway Project 9-25/9-31 administrators and engineers. Often, highway problems are of local ISSN 0077-5614 interest and can best be studied by highway departments individually ISBN-13: 978-0-309-09867-0 or in cooperation with their state universities and others. However, the ISBN-10: 0-309-09867-X accelerating growth of highway transportation develops increasingly Library of Congress Control Number 2006935738 complex problems of wide interest to highway authorities. These 2006 Transportation Research Board problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the COPYRIGHT PERMISSION American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program 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 employing modern scientific techniques. This program is supported on published or copyrighted material used herein. a continuing basis by funds from participating member states of the Cooperative Research Programs (CRP) grants permission to reproduce material in this Association and it receives the full cooperation and support of the publication for classroom and not-for-profit purposes. Permission is given with the Federal Highway Administration, United States Department of understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, Transportation. 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 The Transportation Research Board of the National Academies was educational and not-for-profit uses will give appropriate acknowledgment of the source of requested by the Association to administer the research program any reprinted or reproduced material. For other uses of the material, request permission because of the Board's recognized objectivity and understanding of from CRP. 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 NOTICE possesses avenues of communications and cooperation with federal, The project that is the subject of this report was a part of the National Cooperative Highway state and local governmental agencies, universities, and industry; its Research Program conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. Such approval reflects the relationship to the National Research Council is an insurance of Governing Board's judgment that the program concerned is of national importance and objectivity; it maintains a full-time research correlation staff of appropriate with respect to both the purposes and resources of the National Research specialists in highway transportation matters to bring the findings of Council. research directly to those who are in a position to use them. The members of the technical committee selected to monitor this project and to review this The program is developed on the basis of research needs identified 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 by chief administrators of the highway and transportation departments or implied are those of the research agency that performed the research, and, while they have and by committees of AASHTO. Each year, specific areas of research been accepted as appropriate by the technical committee, they are not necessarily those of needs to be included in the program are proposed to the National the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Research Council and the Board by the American Association of State Administration, U.S. Department of Transportation. Highway and Transportation Officials. Research projects to fulfill these Each report is reviewed and accepted for publication by the technical committee according needs are defined by the Board, and qualified research agencies are to procedures established and monitored by the Transportation Research Board Executive selected from those that have submitted proposals. Administration and Committee and the Governing Board of the National Research Council. surveillance of research contracts are the responsibilities of the National The Transportation Research Board of the National Academies, the National Research Research Council and the Transportation Research Board. Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in the National The needs for highway research are many, and the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade Cooperative Highway Research Program can make significant or manufacturers' names appear herein solely because they are considered essential to the contributions to the solution of highway transportation problems of object of this report. 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

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COOPERATIVE RESEARCH PROGRAMS 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

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FOREWORD By Edward Harrigan Staff Officer Transportation Research Board 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;

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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.

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CONTENTS 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

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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.