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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 762 Laboratory Validation of an Endurance Limit for Asphalt Pavements Matthew Witczak Michael Mamlouk ArizonA StAte UniverSity Tempe, Arizona Mena Souliman UniverSity of nevAdA Reno, Nevada Waleed Zeiada ArizonA StAte UniverSity Tempe, Arizona Subscriber Categories Highways ⢠Design ⢠Materials TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2013 www.TRB.org Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration
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 Boardâs 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 762 Project 9-44A ISSN 0077-5614 ISBN 978-0-309-28366-3 Library of Congress Control Number 2013953979 © 2013 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION 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. The members of the technical panel selected to monitor this project and to review this report were chosen for their special competencies and with regard for appropriate balance. The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the Governing Board of the National Research Council. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The Transportation Research Board of the National Academies, the National Research Council, and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are considered essential to the object of the report.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars 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 technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy 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 achievements of engineers. Dr. C. D. Mote, Jr., 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 Academyâs purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, 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 Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. C. D. Mote, Jr., are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transporta- tion Research Board is to provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Boardâs varied activities annually engage about 7,000 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 individu- als interested in the development of transportation. www.TRB.org www.national-academies.org
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 AUTHOR ACKNOWLEDGMENTS The authors would like to thank Dr. Kamil Kaloush, Dr. Mohamed El-Basyouny, and Dr. Myung Jeong for their valuable input throughout the study. The extensive laboratory and analysis effort of Dan Rosen- balm, Gustavo Torres, Kenneth Witczak, and other student workers is acknowledged. The authors would like also to thank Dr. Busaba Laungrungrong for helping in the statistical analysis of the test results and in the model development. CRP STAFF FOR NCHRP REPORT 762 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Edward Harrigan, Senior Program Officer Anthony P. Avery, Senior Program Assistant Eileen P. Delaney, Director of Publications Natassja Linzau, Editor NCHRP PROJECT 9-44A PANEL Field of Materials and ConstructionâArea of Bituminous Materials Roger L. Green, Pickerington, OH (Chair) David A. Anderson, State College, PA Danny A. Dawood, The Transtec Group, Mechanicsburg, PA Bruce Dietrich, Tallahassee, FL G. William Maupin, Jr., Crozet, VA Leslie Ann McCarthy, Villanova University, Villanova, PA Carl L. Monismith, University of CaliforniaâBerkeley, Berkeley, CA Amy M. Schutzbach, Illinois DOT, Springfield, IL Linbing Wang, Virginia Tech, Blacksburg, VA Nelson H. Gibson, FHWA Liaison Frederick Hejl, TRB Liaison
F O R E W O R D By Edward Harrigan Staff Officer Transportation Research Board This report presents models for the HMA fatigue endurance limit that are responsive to asphalt binder and mixture properties and healing between load cycles and are suitable for incorporation as algorithms in Pavement ME Design and other design methods. Thus, the report will be of immediate interest to materials and structural design engineers in state highway agencies and engineers in the HMA construction industry. Many well-constructed flexible pavements with a thick HMA structure have been in ser- vice for 40 or more years without any evidence of fatigue cracking. This field experience suggests that an endurance limit, that is, a level of strain below which fatigue damage does not accumulate for any number of load repetitions, is a valid concept for HMA mixtures. NCHRP Project 9-38, âEndurance Limit of Hot Mix Asphalt Mixtures to Prevent Fatigue Cracking in Flexible Pavements,â completed in 2009, confirmed the existence of an HMA fatigue endurance limit through an extensive program of laboratory testing, which further suggested that the endurance limit is influenced by HMA mixture and binder properties. Based on these results, a practical definition of the endurance limit was developed, along with a method to estimate its value in the laboratory. NCHRP Project 9-44A was designed to extend the results and findings of Project 9-38, with particular attention to the influence of asphalt binder and mixture properties on the endurance limit and to the relationship of the endurance limit to the phenomenon of heal- ing hypothesized to occur in asphalt mixtures during the rest period between load appli- cations in the laboratory and in pavements. The specific objectives of the project were to (1) carry out a laboratory experiment to identify the mixture and pavement layer design features related to an endurance limit for bottom-initiated fatigue cracking of HMA and (2) develop an algorithm to incorporate this endurance limit into the Pavement ME Design software and other selected pavement design methods. The research was performed by Ari- zona State University, Tempe, Arizona, in association with AMEC (formerly MACTEC), Phoenix, Arizona. The research investigated the relationship of the fatigue endurance limit to factors such as asphalt binder rheology, air voids, asphalt content, temperature, strain level, number of load cycles, and rest period between load cycles. Both beam fatigue (AASHTO T321) and uniaxial compression-tension testing were conducted according to a factorial design that permitted statistical analysis of the main factor and up to three-factor interactions. Robust regression models were developed that described the effect of the main factors and factor interactions on the stiffness ratio, SR, which is defined as the ratio of the stiffness measured at any load cycle during beam fatigue or uniaxial fatigue testing to the initial stiffness of the specimen. Testing was conducted with rest periods of 0, 1, 5, and 10s between load cycles.
The endurance limit can then be determined for any mixture initial stiffness as the strain at SR = 1, i.e., for the condition in which complete healing of the fatigue damage takes place after each load cycle. Thus, this research reaffirmed the existence of the HMA fatigue endurance limit and demonstrated that the endurance limit is the result of a balance between loading damage and the healing, i.e., damage recovery, that happens during rest periods and that the value of the limit varies with the mixture initial stiffness (acting as a surrogate for binder rheology, air voids, asphalt content, and temperature) and the duration of the rest period. It was also found that for a load cycle of 0.1s, a rest period greater than 5 to 10s (from beam fatigue testing) or greater than 3s (from uniaxial testing) will not produce additional healing of the fatigue damage in the laboratory. Finally, the report recommends that the beam fatigue model be used for future study of the endurance limit and its implementation. The beam fatigue test is better established than the uniaxial test and has a larger database of results in the literature. This report fully documents the research and discusses incorporation of the endurance limit derived from the SR regression model formalism as an algorithm in Pavement ME Design software and other design methods. The report includes three appendixes available online at http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=2518: ⢠Appendix 1, Integrated Predictive Model for Healing and Fatigue Endurance Limit for Asphalt Concrete ⢠Appendix 2, Endurance Limit for HMA Based on Healing Phenomena Using Viscoelastic Continuum Damage Analysis ⢠Appendix 3, Project Lab Test Results Inserted into the Mechanistic Empirical Distress Prediction Models (M-E_DPM) Database
C O N T E N T S Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions. 1 Chapter 1 Introduction 2 Objectives 2 HMA Endurance Limit and Healing 3 Materials, Mix Design, and Fatigue Testing 5 Chapter 2 Developing of Endurance Limit Model Based on Beam Fatigue Tests 5 Beam Fatigue Testing 5 Sinusoidal versus Haversine Waveforms 6 Experimental Design 8 Model Development 10 Estimation of Endurance Limit Based on Beam Fatigue Testing Model 13 Chapter 3 Developing of Endurance Limit Model Based on Uniaxial Fatigue Tests 13 Continuum Damage Approach 14 Complex Modulus Testing 14 Uniaxial Fatigue Testing 15 Waveform Selection 15 Experimental Design 15 Model Development 17 Estimation of Endurance Limit Based on Uniaxial Fatigue Testing Model 20 Chapter 4 Recommended Fatigue Test and Endurance Limit Implementation 20 Comparison of Endurance Limits of Beam and Uniaxial Fatigue Tests 20 Incorporating the Endurance Limit in Fatigue Relationships 21 Incorporating the Endurance Limit in the Pavement ME Design 22 Chapter 5 Summary and Findings 23 Suggested Future Research 24 References 26 Appendixes 1, 2, and 3