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NATIONAL NCHRP REPORT 531 COOPERATIVE HIGHWAY RESEARCH PROGRAM Relationship of Air Voids, Lift Thickness, and Permeability in Hot Mix Asphalt Pavements

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TRANSPORTATION RESEARCH BOARD EXECUTIVE COMMITTEE 2004 (Membership as of July 2004) OFFICERS Chair: Michael S. Townes, President and CEO, Hampton Roads Transit, Hampton, VA Vice Chair: Joseph H. Boardman, Commissioner, New York State DOT Executive Director: Robert E. Skinner, Jr., Transportation Research Board MEMBERS MICHAEL W. BEHRENS, Executive Director, Texas DOT SARAH C. CAMPBELL, President, TransManagement, Inc., Washington, DC E. DEAN CARLSON, Director, Carlson Associates, Topeka, KS JOHN L. CRAIG, Director, Nebraska Department of Roads DOUGLAS G. DUNCAN, President and CEO, FedEx Freight, Memphis, TN GENEVIEVE GIULIANO, Director, Metrans Transportation Center and Professor, School of Policy, Planning, and Development, USC, Los Angeles BERNARD S. GROSECLOSE, JR., President and CEO, South Carolina State Ports Authority SUSAN HANSON, Landry University Professor of Geography, Graduate School of Geography, Clark University JAMES R. HERTWIG, President, CSX Intermodal, Jacksonville, FL GLORIA J. JEFF, Director, Michigan DOT ADIB K. KANAFANI, Cahill Professor of Civil Engineering, University of California, Berkeley RONALD F. KIRBY, Director of Transportation Planning, Metropolitan Washington Council of Governments HERBERT S. LEVINSON, Principal, Herbert S. Levinson Transportation Consultant, New Haven, CT SUE MCNEIL, Director, Urban Transportation Center and Professor, College of Urban Planning and Public Affairs and Department of Civil and Material Engineering, University of Illinois, Chicago MICHAEL D. MEYER, Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology CAROL A. MURRAY, Commissioner, New Hampshire DOT JOHN E. NJORD, Executive Director, Utah DOT DAVID PLAVIN, President, Airports Council International, Washington, DC JOHN H. REBENSDORF, Vice President, Network Planning and Operations, Union Pacific Railroad Co., Omaha, NE PHILIP A. SHUCET, Commissioner, Virginia DOT C. MICHAEL WALTON, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin LINDA S. WATSON, Executive Director, LYNX--Central Florida Regional Transportation Authority, Orlando, FL MARION C. BLAKEY, Federal Aviation Administrator, U.S.DOT (ex officio) SAMUEL G. BONASSO, Acting Administrator, Research and Special Programs Administration, U.S.DOT (ex officio) REBECCA M. BREWSTER, President and COO, American Transportation Research Institute, Smyrna, GA (ex officio) GEORGE BUGLIARELLO, Chancellor, Polytechnic University and Foreign Secretary, National Academy of Engineering (ex officio) THOMAS H. COLLINS (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard (ex officio) JENNIFER L. DORN, Federal Transit Administrator, U.S.DOT (ex officio) EDWARD R. HAMBERGER, President and CEO, Association of American Railroads (ex officio) JOHN C. HORSLEY, Executive Director, American Association of State Highway and Transportation Officials (ex officio) RICK KOWALEWSKI, Deputy Director, Bureau of Transportation Statistics, U.S.DOT (ex officio) WILLIAM W. MILLAR, President, American Public Transportation Association (ex officio) BETTY MONRO, Acting Administrator, Federal Railroad Administration, U.S.DOT (ex officio) MARY E. PETERS, Federal Highway Administrator, U.S.DOT (ex officio) SUZANNE RUDZINSKI, Director, Transportation and Regional Programs, U.S. Environmental Protection Agency (ex officio) JEFFREY W. RUNGE, National Highway Traffic Safety Administrator, U.S.DOT (ex officio) ANNETTE M. SANDBERG, Federal Motor Carrier Safety Administrator, U.S.DOT (ex officio) WILLIAM G. SCHUBERT, Maritime Administrator, U.S.DOT (ex officio) JEFFREY N. SHANE, Under Secretary for Policy, U.S.DOT (ex officio) CARL A. STROCK (Maj. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers (ex officio) ROBERT A. VENEZIA, Program Manager of Public Health Applications, National Aeronautics and Space Administration (ex officio) NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Transportation Research Board Executive Committee Subcommittee for NCHRP MICHAEL S. TOWNES, Hampton Roads Transit, Hampton, VA JOHN C. HORSLEY, American Association of State Highway (Chair) and Transportation Officials JOSEPH H. BOARDMAN, New York State DOT MARY E. PETERS, Federal Highway Administration GENEVIEVE GIULIANO, University of Southern California, ROBERT E. SKINNER, JR., Transportation Research Board Los Angeles C. MICHAEL WALTON, University of Texas, Austin

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 531 Relationship of Air Voids, Lift Thickness, and Permeability in Hot Mix Asphalt Pavements E. RAY BROWN M. ROSLI HAININ ALLEN COOLEY GRAHAM HURLEY National Center for Asphalt Technology--Auburn University Auburn, AL S UBJECT A REAS 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. 2004 www.TRB.org

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NATIONAL COOPERATIVE HIGHWAY RESEARCH NCHRP REPORT 531 PROGRAM Systematic, well-designed research provides the most effective Project 9-27 FY'01 approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local ISSN 0077-5614 interest and can best be studied by highway departments ISBN 0-309-088070 individually or in cooperation with their state universities and Library of Congress Control Number 2004111830 others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to 2004 Transportation Research Board highway authorities. These problems are best studied through a coordinated program of cooperative research. Price $19.00 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 NOTICE Department of Transportation. The project that is the subject of this report was a part of the National Cooperative The Transportation Research Board of the National Academies Highway Research Program conducted by the Transportation Research Board with the was requested by the Association to administer the research approval of the Governing Board of the National Research Council. Such approval program because of the Board's recognized objectivity and reflects the Governing Board's judgment that the program concerned is of national understanding of modern research practices. The Board is uniquely importance and appropriate with respect to both the purposes and resources of the suited for this purpose as it maintains an extensive committee National Research Council. structure from which authorities on any highway transportation The members of the technical committee selected to monitor this project and to review subject may be drawn; it possesses avenues of communications and this report were chosen for recognized scholarly competence and with due cooperation with federal, state and local governmental agencies, consideration for the balance of disciplines appropriate to the project. The opinions and universities, and industry; its relationship to the National Research conclusions expressed or implied are those of the research agency that performed the Council is an insurance of objectivity; it maintains a full-time research, and, while they have been accepted as appropriate by the technical committee, research correlation staff of specialists in highway transportation they are not necessarily those of the Transportation Research Board, the National matters to bring the findings of research directly to those who are in Research Council, the American Association of State Highway and Transportation a position to use them. Officials, or the Federal Highway Administration, U.S. Department of Transportation. The program is developed on the basis of research needs Each report is reviewed and accepted for publication by the technical committee identified by chief administrators of the highway and transportation according to procedures established and monitored by the Transportation Research departments and by committees of AASHTO. Each year, specific Board Executive Committee and the Governing Board of the National Research areas of research needs to be included in the program are proposed Council. 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. Published reports of the The needs for highway research are many, and the National NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of are available from: mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or Transportation Research Board duplicate other highway research programs. Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: Note: 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 http://www.national-academies.org/trb/bookstore 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. Printed in the United States of America

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol- ars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and techni- cal matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Acad- emy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achieve- ments of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board's mission is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, the Board facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provides expert advice on transportation policy and programs; and disseminates research results broadly and encourages their implementation. The Board's varied activities annually engage more than 5,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

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COOPERATIVE RESEARCH PROGRAMS STAFF FOR NCHRP REPORT 531 ROBERT J. REILLY, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Manager, NCHRP EDWARD T. HARRIGAN, Senior Program Officer EILEEN P. DELANEY, Director of Publications NCHRP PROJECT 9-27 PANEL Field of Materials and Construction--Area of Bituminous Materials JAMES A. MUSSELMAN, Florida DOT (Chair) MICHAEL E. BIENVENU, Troxler Electronic Laboratories, Inc., Research Triangle Park, NC CHARLES DEAHL, Compaction America, Kewanee, IL DONNA HARMELINK, FHWA--Colorado Region DALE RAND, Texas DOT MICHAEL D. REMILY, Oregon DOT MILTON SIMMS, Maryland DOT JOHN BUKOWSKI, FHWA Liaison Representative LESLIE ANN MYERS, FHWA Liaison Representative RONALD A. SINES, P.J. Keating Co., Lunenburg, MA, Other Liaison FREDERICK HEJL, TRB Liaison Representative

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This report presents recommended guidelines for hot mix asphalt pavement con- FOREWORD struction to achieve satisfactory levels of in-place air voids and permeability. These By Edward T. Harrigan guidelines were developed from the findings of a research project that examined the Senior Program Officer relationship of air voids content to permeability and hot mix asphalt lift thickness. The Transportation Research report will be of particular interest to materials and construction engineers in state high- Board way agencies, as well as to materials supplier and paving contractor personnel respon- sible for the production and placement of hot mix asphalt. For satisfactory performance, hot mix asphalt (HMA) pavements must be con- structed with adequate field density and impermeability to moisture. During the transi- tion to the use of the Superpave mix design method since 1994, several states reported problems with greater than expected permeability associated with the use of coarse- graded mixes. In addition, there has been ongoing debate over the in-place air voids content and layer thickness needed to ensure an impermeable pavement. Some state highway agencies have addressed these issues by increasing their field density require- ments, lift thickness requirements, or both, when coarse-graded mixes are used. Such changes, however, entail increased expense. So other states have elected (1) to reduce the nominal maximum aggregate size of given lifts (e.g., use of a 19.0-mm in place of a 25.0-mm mix) or (2) to eliminate pavement layers (such as a binder layer) and increase the thickness of the remaining layers to keep the total pavement thickness at typically used levels. However, many agencies are reluctant to adopt any such change without the support of specific research results that justify the increased cost or provide evidence of satisfactory long-term performance. Under NCHRP Project 9-27, "Relationships of HMA In-Place Air Voids, Lift Thickness, and Permeability," the National Center for Asphalt Technology (NCAT) at Auburn University was assigned the tasks of (1) determining the minimum ratio of layer thickness, t, to nominal maximum aggregate size, NMAS, needed to achieve desirable pavement density levels, and thus impermeable pavements; (2) evaluating the permeability characteristics of different thicknesses of compacted HMA; and (3) assessing factors affecting the relationship between in-place air voids, permeability, and lift thickness. To accomplish these tasks, the research team (1) conducted a criti- cal review of the literature on the relationship of HMA lift thicknesses to in-place air voids, the relationship of in-place air voids to permeability, and their effects on pave- ment performance; (2) evaluated current state DOT guidelines and requirements for minimum lift thickness and minimum in-place density; and (3) designed and carried out coordinated laboratory and field experiments to establish relationships among air voids, lift thickness, and permeability from which to develop practical field compaction guidelines. The NCAT project team found that the HMA pavement density that can be obtained under normal rolling conditions is clearly related to the ratio t/NMAS of the

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HMA. For improved compactibility, the agency recommended that t/NMAS be at least 3 for fine-graded mixes and at least 4 for coarse-graded mixes. The data for SMA mixes indicate that the ratio should also be at least 4. Ratios less than these suggested values can be used but a greater than normal compactive effort will generally be required in these situations to obtain the desired in-place density. The results of an experiment to evaluate the effect of mix temperature on the rela- tionship between pavement density and t/NMAS found that the more rapid cooling of the HMA is a key reason for low density in thinner sections (lower t/NMAS). Hence, for thin HMA layers NCAT emphasized the importance of paving rollers staying very close to the paving machine so that rolling can be accomplished prior to excessive cool- ing. The project team further identified the in-place air voids content as the most sig- nificant factor impacting permeability of HMA mixtures, followed by coarse aggregate ratio and VMA. As the coarse aggregate ratio increases, permeability increases, but it decreases as VMA increases at constant air voids content. The variability of perme- ability between various mixtures is very high; some mixtures are permeable in the range of 8 to 10 percent air voids while others are not. However, to ensure that perme- ability is not a problem NCAT recommends an in-place air voids content between 6 and 7 percent or lower. This appears to be true for a wide range of mixtures regardless of NMAS and aggregate gradation. The project final report presents detailed descriptions of the coordinated laboratory (Task 3) and field (Task 5) experiments; a discussion of the research results from both experiments; and the project findings, conclusions, and recommendations in five volumes: Volume I: Task 3--Parts 1 and 2; Volume II: Task 3--Part 3; Volume III: Task 5; Volume IV: Appendices for Volumes I, II, and III; and Volume V: Executive Summary. This report includes Volume V only; Volumes I through IV will be available online at http://www4.trb.org/trb/onlinepubs.nsf/web/nchrp_web_documents as NCHRP Web Document 68. The recommended guidelines from Project 9-27 have been referred to the TRB Mixtures and Aggregate Expert Task Group for its review and possible recommenda- tion to the AASHTO Highway Subcommittees on Materials and Construction for revi- sion of appropriate specifications and recommended practices.

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CONTENTS 1 CHAPTER 1 Introduction and Problem Statement 2 CHAPTER 2 Objective 3 CHAPTER 3 Research Approach 5 CHAPTER 4 Test Results and Analysis 4.1 Part 1--Mix Designs for Specimens to Study the Effect of t/NMAS on Density, 5 4.2 Evaluation of Effect of t/NMAS on Density Using Gyratory Compactor, 5 4.3 Evaluation of Effect of t/NMAS on Density Using Vibratory Compactor, 6 4.4 Evaluation of Effect of t/NMAS on Density from Field Study, 10 4.5 Evaluation of Effect of Temperature on the Relationship Between Density and t/NMAS, 20 4.6 Evaluation of Effect of t/NMAS on Permeability Using Gyratory Compactor, 22 4.7 Evaluation of Effect of t/NMAS on Permeability Using Vibratory Compactor, 22 4.8 Evaluation of Effect of t/NMAS on Permeability From Field Study, 27 4.9 Part 2--Evaluation of Relationship of Laboratory Permeability, Density, and Lift Thickness of Field Compacted Cores, 27 4.10 Controlled Laboratory Experiment to Evaluate Methods of Measuring the Bulk Specific Gravity of Compacted HMA, 28 4.11 Field Validation of Relationships Between Permeability, Lift Thickness and In-Place Density, 32 35 CHAPTER 5 Conclusions and Recommendations 37 CHAPTER 6 References A-1 APPENDICES A Through E