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NATIONAL
NCHRP
REPORT 646
COOPERATIVE
HIGHWAY
RESEARCH
PROGRAM
Validating the Fatigue
Endurance Limit for
Hot Mix Asphalt
OCR for page R2
TRANSPORTATION RESEARCH BOARD 2010 EXECUTIVE COMMITTEE*
OFFICERS
CHAIR: Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington
VICE CHAIR: Neil J. Pedersen, Administrator, Maryland State Highway Administration, Baltimore
EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board
MEMBERS
J. Barry Barker, Executive Director, Transit Authority of River City, Louisville, KY
Allen D. Biehler, Secretary, Pennsylvania DOT, Harrisburg
Larry L. Brown, Sr., Executive Director, Mississippi DOT, Jackson
Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern Corporation, Norfolk, VA
William A.V. Clark, Professor, Department of Geography, University of California, Los Angeles
Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering, and Director, Center for Transportation Studies, University of
Virginia, Charlottesville
Jeffrey W. Hamiel, Executive Director, Metropolitan Airports Commission, Minneapolis, MN
Edward A. (Ned) Helme, President, Center for Clean Air Policy, Washington, DC
Randell H. Iwasaki, Director, California DOT, Sacramento
Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley
Susan Martinovich, Director, Nevada DOT, Carson City
Debra L. Miller, Secretary, Kansas DOT, Topeka
Pete K. Rahn, Director, Missouri DOT, Jefferson City
Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson
Tracy L. Rosser, Vice President, Corporate Traffic, Wal-Mart Stores, Inc., Mandeville, LA
Steven T. Scalzo, Chief Operating Officer, Marine Resources Group, Seattle, WA
Henry G. (Gerry) Schwartz, Jr., Chairman (retired), Jacobs/Sverdrup Civil, Inc., St. Louis, MO
Beverly A. Scott, General Manager and Chief Executive Officer, Metropolitan Atlanta Rapid Transit Authority, Atlanta, GA
David Seltzer, Principal, Mercator Advisors LLC, Philadelphia, PA
Daniel Sperling, Professor of Civil Engineering and Environmental Science and Policy; Director, Institute of Transportation Studies; and Interim
Director, Energy Efficiency Center, University of California, Davis
Douglas W. Stotlar, President and CEO, Con-Way, Inc., Ann Arbor, MI
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, U.S. Department of Homeland Security, Washington, DC
Peter H. Appel, Administrator, Research and Innovative Technology Administration, U.S.DOT
J. Randolph Babbitt, Administrator, Federal Aviation Administration, U.S.DOT
Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA
George Bugliarello, President Emeritus and University Professor, Polytechnic Institute of New York University, Brooklyn; Foreign Secretary,
National Academy of Engineering, Washington, DC
Anne S. Ferro, Administrator, Federal Motor Carrier Safety Administration, U.S.DOT
LeRoy Gishi, Chief, Division of Transportation, Bureau of Indian Affairs, U.S. Department of the Interior, Washington, DC
Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, DC
John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC
David T. Matsuda, Deputy Administrator, Maritime Administration, U.S.DOT
Victor M. Mendez, Administrator, Federal Highway Administration, U.S.DOT
William W. Millar, President, American Public Transportation Association, Washington, DC
Cynthia L. Quarterman, Administrator, Pipeline and Hazardous Materials Safety Administration, U.S.DOT
Peter M. Rogoff, Administrator, Federal Transit Administration, U.S.DOT
David L. Strickland, Administrator, National Highway Traffic Safety Administration, U.S.DOT
Joseph C. Szabo, Administrator, Federal Railroad Administration, U.S.DOT
Polly Trottenberg, Assistant Secretary for Transportation Policy, U.S.DOT
Robert L. Van Antwerp (Lt. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC
*Membership as of February 2010.
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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
NCHRP REPORT 646
Validating the Fatigue Endurance Limit
for Hot Mix Asphalt
Brian D. Prowell
ADVANCED MATERIALS SERVICES, LLC1
Auburn, AL
E. Ray Brown
U.S. ARMY CORPS OF ENGINEERS1
Vicksburg, MS
R. Michael Anderson
ASPHALT INSTITUTE
Lexington, KY
Jo Sias Daniel
Aravind Krishna Swamy
UNIVERSITY OF NEW HAMPSHIRE
Durham, NH
Harold Von Quintus
APPLIED RESEARCH ASSOCIATES, INC.
Austin, TX
Shihui Shen2
WASHINGTON STATE UNIVERSITY
Pullman, WA
Samuel H. Carpenter
UNIVERSITY OF ILLINOIS
Urbana-Champaign, IL
Sudip Bhattacharjee3
ALABAMA A&M UNIVERSITY
Huntsville, AL
Saeed Maghsoodloo
NATIONAL CENTER FOR ASPHALT TECHNOLOGY
Auburn, AL
Formerly 1National Center for Asphalt Technology, 2University of Illinois, and 3University of New Hampshire, respectively.
Subscriber Categories
Materials · Pavements
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.
2010
www.TRB.org
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NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 646
RESEARCH PROGRAM
Systematic, well-designed research provides the most effective Project 09-38
approach to the solution of many problems facing highway ISSN 0077-5614
administrators and engineers. Often, highway problems are of local ISBN 978-0-309-11821-7
interest and can best be studied by highway departments individually Library of Congress Control Number 2010921174
or in cooperation with their state universities and others. However, the © 2010 National Academy of Sciences. All rights reserved.
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 COPYRIGHT INFORMATION
cooperative research.
Authors herein are responsible for the authenticity of their materials and for obtaining
In recognition of these needs, the highway administrators of the written permissions from publishers or persons who own the copyright to any previously
American Association of State Highway and Transportation Officials published or copyrighted material used herein.
initiated in 1962 an objective national highway research program Cooperative Research Programs (CRP) grants permission to reproduce material in this
employing modern scientific techniques. This program is supported on 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,
a continuing basis by funds from participating member states of the
FMCSA, FTA, or Transit Development Corporation endorsement of a particular product,
Association and it receives the full cooperation and support of the method, or practice. It is expected that those reproducing the material in this document for
Federal Highway Administration, United States Department of 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
Transportation.
from CRP.
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
NOTICE
modern research practices. The Board is uniquely suited for this
purpose as it maintains an extensive committee structure from which 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
authorities on any highway transportation subject may be drawn; it the Governing Board of the National Research Council. Such approval reflects the
possesses avenues of communications and cooperation with federal, Governing Board's judgment that the program concerned is of national importance and
state and local governmental agencies, universities, and industry; its appropriate with respect to both the purposes and resources of the National Research
Council.
relationship to the National Research Council is an insurance of
The members of the technical committee selected to monitor this project and to review this
objectivity; it maintains a full-time research correlation staff of
report were chosen for recognized scholarly competence and with due consideration for the
specialists in highway transportation matters to bring the findings of balance of disciplines appropriate to the project. The opinions and conclusions expressed
research directly to those who are in a position to use them. 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 program is developed on the basis of research needs identified
the Transportation Research Board, the National Research Council, the American
by chief administrators of the highway and transportation departments Association of State Highway and Transportation Officials, or the Federal Highway
and by committees of AASHTO. Each year, specific areas of research Administration, U.S. Department of Transportation.
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Committee and the Governing Board of the National Research Council.
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Council, the Federal Highway Administration, the American Association of State Highway
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surveillance of research contracts are the responsibilities of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade
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object of this report.
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
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COOPERATIVE RESEARCH PROGRAMS
CRP STAFF FOR NCHRP REPORT 646
Christopher W. Jenks, Director, Cooperative Research Programs
Crawford F. Jencks, Deputy Director, Cooperative Research Programs
Edward T. Harrigan, Senior Program Officer
Melanie Adcock, Senior Program Assistant
Eileen P. Delaney, Director of Publications
Hilary Freer, Senior Editor
NCHRP PROJECT 09-38 PANEL
Field of Materials and Construction--Area of Bituminous Materials
Linda M. Pierce, Applied Pavement Technology, Inc., Santa Fe, NM (Chair)
Steven W. Krebs, Wisconsin DOT, Madison, WI
Allen Cooley, Burns Cooley Dennis, Inc., Ridgeland, MS
G. William Maupin, Jr., Virginia DOT, Charlottesville, VA
Richard W. May, SemMaterials, LP, Tulsa, OK
Leslie Ann McCarthy, Villanova University, Villanova, PA
Carl L. Monismith, University of California - Berkeley, Berkeley, CA
Amy M. Schutzbach, Illinois DOT, Springfield, IL
Gregory A. Sholar, Florida DOT, Gainesville, FL
Linbing Wang, Virginia Polytechnic Institute and State University, Blacksburg, VA
Travis M. Wombwell, Missouri DOT, Macon, MO
Wei-Shih "Wes" Yang, New York State DOT, Albany, NY
Ernest Bastian, FHWA Liaison
John "Jack" Youtcheff, FHWA Liaison
Frederick Hejl, TRB Liaison
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FOREWORD
By Edward T. Harrigan
Staff Officer
Transportation Research Board
This report presents the findings of research performed to investigate the existence of a
fatigue endurance limit for hot mix asphalt (HMA) mixtures, the effect of HMA mixture
characteristics on the endurance limit, and the potential for the limit's incorporation in
structural design methods for flexible pavements. The report describes the research per-
formed and includes proposed standard practices using various experimental and analyti-
cal procedures for determining the endurance limit of HMA mixtures. Thus, the report will
be of immediate interest to materials and structural design engineers in state highway agen-
cies and engineers in the HMA construction industry.
Many well-constructed flexible pavements with a thick HMA structure have been in
service for 40 or more years without any evidence of bottom-up fatigue cracking. This field
experience suggests that an endurance limit, that is, a level of strain below which fatigue damage
does not occur for any number of load repetitions, is a valid concept for HMA mixtures.
The concept of an endurance limit is widely recognized in many areas of materials science,
especially that of ferrous metals. The endurance limit is usually calculated from the relationship
of strain to load repetitions to failure. Defining an endurance limit for HMA mixtures will
result in more efficient structural design of flexible pavements built with mixtures of
varying properties. For instance, small increases in the binder content of HMA mixtures
provide longer fatigue lives (presumably because of a higher strain level for the endurance
limit of these mixtures). Other factors likely to determine the value of the fatigue endurance
limit for a given HMA mixture are the incorporation of a modifier in the asphalt binder, the
aggregate type and gradation, the asphalt binder grade, and the mixture's volumetric
properties.
Previous research suggested that the fatigue behavior of flexible pavements is consistent
with the existence of an endurance limit with an approximate value of 70 microstrains.
However, few laboratory studies corroborate this value. Moreover, pavement design
approaches, including the Mechanistic-Empirical Pavement Design Guide (MEPDG)
developed in NCHRP Projects 1-37A and 1-40, do not fully incorporate the endurance limit
concept. This is because, to date, research into the fatigue of HMA mixtures has been
limited to strain levels well above the hypothesized value of 70 microstrains.
The objectives of this research were to (1) test the hypothesis that there is an endurance
limit in the fatigue behavior of HMA mixtures, (2) measure the value of the endurance limit
for a representative range of HMA mixtures, and (3) recommend a procedure to incorporate
the effects of the endurance limit into mechanistic pavement design methods. The research
was performed by the National Center for Asphalt Technology, Auburn University,
Auburn, AL, with the assistance of the following organizations: Applied Research Associates,
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Inc., Round Rock, TX; the Asphalt Institute, Lexington, KY; the University of Illinois,
Urbana-Champaign, IL; and the University of New Hampshire, Durham, NH.
The report fully documents the design and conduct of an extensive laboratory program
of beam fatigue and uniaxial tension testing that experimentally confirmed the existence of
an HMA fatigue endurance limit and quantified how the value of the 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 methodology to estimate the endurance limit
in the laboratory. Analysis of in-service pavements by the research team also demonstrated
the existence of the endurance limit and indicated that polymer modification of asphalt
binders improves the fatigue performance of HMA mixtures and flexible pavements.
Finally, sensitivity analyses were conducted that indicated that the value of the endurance
limit can affect the recommended thickness of perpetual pavements designed with the
MEPDG and PerRoad methodologies significantly.
This report includes six appendices as follows:
· Appendix A: A Proposed Standard Practice for Predicting the Endurance Limit of Hot Mix
Asphalt (HMA) for Long-Life Pavement Design;
· Appendix B: A Proposed Standard Practice for Predicting the Endurance Limit of Hot Mix
Asphalt (HMA) by Pseudo Strain Approach;
· Appendix C: A Proposed Standard Practice for Extrapolating Long-Life Beam Fatigue Tests
Using the Ratio of Dissipated Energy Change (RDEC);
· Appendix D: A summary of results of the beam fatigue testing accomplished during the project;
· Appendix E: An analytical method for construction of a damage characteristic curve through
calculation of pseudo strains; and
· Appendix F: A proposed design for an interlaboratory study to develop a precision statement
for AASHTO T321, Standard Method of Test for Determining the Fatigue Life of Compacted
Hot-Mix Asphalt (HMA) Subjected to Repeated Flexural Bending.
The proposed standard practices are under consideration for possible adoption by the
AASHTO Highway Subcommittee on Materials and the AASHTO Joint Technical Commit-
tee on Pavements.
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CONTENTS
1 Summary
5 Chapter 1 Introduction and Research Approach
5 Introduction
6 Research Problem Statement
6 Objectives
6 Scope
7 Chapter 2 State of Practice
7 Arguments for the Existence of the Endurance Limit
9 Factors Affecting Fatigue Life
9 Strategies to Produce Long-Life Pavements
12 Laboratory Fatigue Tests and Analysis Methods
13 Laboratory Studies to Quantify the Endurance Limit
13 Modeling Fatigue and Relationship to Field Performance
15 Chapter 3 Research Plan
15 Introduction
16 Materials
17 Test Methods
20 Chapter 4 Beam Fatigue Test Results and Analyses
20 Extrapolation Methods to Predict Fatigue Life
32 Existence of the Endurance Limit
41 Estimate of Precision of Beam Fatigue Tests
42 Indirect Tensile Strength as a Surrogate for Endurance
Limit Determination
44 Chapter 5 Uniaxial Tension Results and Analyses
44 Test Specimens
44 Dynamic Modulus and Phase Angle Master Curves
49 Damage Characteristic Curve
53 Evaluation of Endurance Limit
59 Chapter 6 Examination of LTPP Database for Indications
of an Endurance Limit
59 Introduction
59 Including the Endurance Limit Design Premise into
Mechanistic-Empirical-Based Pavement Design Procedures
62 Defining the Endurance Limit--A Survivability Analysis
66 Updated Survivability Analysis Using LTPP Data
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73 Chapter 7 Sensitivity of Pavement Thickness
to the Endurance Limit
73 Summary of Predicted Endurance Limits
73 Estimate of Shift Factors between Laboratory Tests and
Field Performance
83 Sensitivity of Mechanistic-Empirical Pavement Design Methods
to the Endurance Limit
88 Considerations for Incorporating the Endurance Limit
into M-E Design Procedures
91 Chapter 8 Conclusions and Recommendations
91 Conclusions
91 Recommendations
93 References
97 APPENDIX A Proposed Standard Practice for Predicting the
Endurance Limit of Hot Mix Asphalt (HMA) for
Long-Life Pavement Design
106 APPENDIX B Proposed Standard Practice for Predicting the
Endurance Limit of Hot Mix Asphalt (HMA) by
Pseudo Strain Approach
112 APPENDIX C Proposed Standard Practice for Extrapolating
Long-Life Beam Fatigue Tests Using the Ratio
of Dissipated Energy Change (RDEC)
117 APPENDIX D NCHRP 9-38 Beam Fatigue Data
122 APPENDIX E Construction of Characteristic Curve
127 APPENDIX F NCHRP 9-38 Beam Fatigue Round Robin
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AUTHOR ACKNOWLEDGMENTS
The research described herein was performed under NCHRP Project 9-38 by the National Center for
Asphalt Technology (NCAT) at Auburn University. Ray Brown served as the Principal Investigator and
Brian Prowell and Michael Anderson served as Co-Principal Investigators. Brown and Prowell were
employed by NCAT when this research began.
The research team included the Asphalt Institute; the University of New Hampshire; Applied Research
Associates, Inc.; the University of Illinois, and, later, Advanced Materials Services, LLC. The Asphalt Insti-
tute assisted in beam fatigue testing in Phases I and II of the project. Jo Daniel oversaw uniaxial tension
testing and analyses at the University of New Hampshire. Harold Von Quintus with Applied Research
Associates, Inc., performed survival analyses of in-service pavements and provided guidance on the
MEPDG. Samuel Carpenter oversaw beam fatigue testing in Phase II of the study with Shihui Shen at the
University of Illinois and provided expertise on analyses using the ratio of dissipated energy. Brian Prowell
was primarily responsible for the technical content of the remaining sections and for assembling the final
report. Pamela Turner supervised laboratory testing at NCAT.
The project team appreciates the support and technical assistance of Bor-Wen Tsai of the University of
California, Berkeley; Rich May of SEM Materials; and Bill Maupin, Jr., of the Virginia Transportation
Research Council. These three agencies volunteered to participate in the beam fatigue mini round-robin
to help develop a better understanding of the variability of beam fatigue tests. They also assisted in the
evaluation of the draft protocols for determining the endurance limit.
Other individuals provided invaluable assistance to the project. Bor-Wen Tsai provided significant
technical assistance with the single- and three-stage Weibull method. Chris Wagner (FHWA) assisted
with the MEPDG. Buzz Powell provided technical data from the NCAT Test Track. David Timm and
Richard Willis provided advice and guidance for calculating shift factors based on field strain measure-
ments and incorporating the endurance limit into M-E pavement design.
