Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction (2017)

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2018 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 RESEARCH REPORT 871 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Y. Richard Kim Cassie Castorena Michael Elwardany Farhad Yousefi Rad North CaroliNa State UNiverSity Raleigh, NC Shane Underwood Akshay Gundla Padmini Gudipudi arizoNa State UNiverSity Tempe, AZ Mike J. Farrar Ronald R. Glaser WeSterN reSearCh iNStitUte Laramie, WY Subscriber Categories Design • Materials • Pavements 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 is the most effective way to solve 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 results in increasingly complex problems of wide inter- est to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the Federal Highway Administration. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving 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 research 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 by going to http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP RESEARCH REPORT 871 Project 09-54 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-44683-9 Library of Congress Control Number 2018935615 © 2018 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, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC 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 research 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 National Academies of Sciences, Engineering, and Medicine. 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 Academies of Sciences, Engineering, and Medicine; or the program sponsors. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of 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 the report.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. C. D. Mote, Jr., is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.national-academies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to increase the benefits that transportation contributes to society by providing leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Board’s varied committees, task forces, and panels 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 individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.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 CRP STAFF FOR NCHRP RESEARCH REPORT 871 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Edward T. Harrigan, Senior Program Officer Anthony P. Avery, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Scott E. Hitchcock, Senior Editor NCHRP PROJECT 09-54 PANEL Field of Materials and Construction—Area of Bituminous Materials Dean A. Maurer, Practical Asphalt Solutions Technology, Lewisberry, PA (Chair) Bouzid Choubane, Florida DOT, Gainesville, FL Shongtao Dai, Minnesota DOT, Maplewood, MN Dale S. Decker, Dale S. Decker, LLC, Eagle, CO Changlin Pan, Nevada DOT, Carson City, NV Murari M. Pradhan, Arizona DOT, Phoenix, AZ Maria C. Rodezno, Auburn University, Auburn, AL Mansour Solaimanian, Pennsylvania State University, University Park, PA Jack Youtcheff, FHWA Liaison Nelson H. Gibson, TRB Liaison

This report presents a proposed standard method for long-term laboratory aging of asphalt mixtures for performance testing; the method is intended for consideration as a replacement for the method in AASHTO R 30, “Mixture Conditioning of Hot Mix Asphalt (HMA).” Thus, the report will be of immediate interest to materials and design engineers in state highway agencies and in the construction industry with responsibility for design and production of hot and warm-mix asphalt. Accurately characterizing the in situ aging of asphalt pavement materials over their long- term service life is of utmost importance to the implementation of mechanistic–empirical pavement design and analysis methods. Current pavement performance prediction models vary in their ability and level of sophistication for numerically simulating the increased stiffness of asphalt materials from oxidative aging and the competing reduction in modulus caused by accumulated pavement damage and deterioration. For the past 25 years, the most commonly used method for aging asphalt materials for performance testing for input to prediction models has been the long-term procedure in AASHTO R 30. R 30 prescribes aging compacted asphalt mixture specimens at 85°C for 5 days, a time and temperature combination that the original Strategic Highway Research Program (SHRP) research estimated—based on limited field calibration—to reflect a criti- cal duration of field exposure from 5 to 10 years. However, an accumulation of laboratory and field data since the end of SHRP has demonstrated that a single time–temperature com- bination cannot reasonably simulate the effects of the range of climates found throughout the United States. Further, these data suggest that this single combination even under- estimates the level of the asphalt pavement aging that occurs in as little as 5 years in many climates. The objective of this research was to develop a long-term aging procedure for asphalt mixtures appropriate to fabricate performance test specimens that provide input data for use with AASHTOWare Pavement ME Design software and other mechanistic design and analysis systems. The research was performed by North Carolina State University, Raleigh, North Carolina; in conjunction with Arizona State University, Tempe, Arizona, and Western Research Institute, Laramie, Wyoming. The long-term aging procedure for asphalt mixtures was developed, calibrated, and vali- dated through a series of laboratory experiments using field cores and original asphalt binders and aggregates from 18 asphalt mixtures, including both HMA and WMA. The mixtures were obtained from nine field projects representing the wide range of climates found in in the United States and Canada. The method improves on R 30 in that the laboratory aging time is specifically determined by the climate at the project location. All aging is conducted F O R E W O R D By Edward T. Harrigan Staff Officer Transportation Research Board

on loose mix at 95°C. The use of loose mix provides fast, even aging compared to compacted specimens. Aging at 95°C also substantially reduces the necessary aging time compared to the 85°C specified in R 30; however, the research found that using an aging temperature of 100°C or greater can introduce chemical changes in the asphalt binder not present in field- aged binders. Besides climate, the procedure also accounts for the asphalt mixture’s depth in the pavement. Finally, to simplify the selection of laboratory aging time, the proposed procedure presents a series of laboratory aging duration maps to match 4, 8, and 16 years of field aging at depths of 6 mm, 20 mm, and 50 mm below the pavement surface. The practical outcome of the project is a proposed AASHTO standard method for long- term aging that can replace the procedure in AASHTO R 30. This report fully documents the research and includes the proposed standard method. In addition, the following appendices, not printed herein, are available for download from the TRB website (trb.org) by searching for “NCHRP Research Report 871.” Appendix A: Previous Studies of Laboratory Aging of Compacted Specimens and Loose Mixtures Appendix B: Previous Studies of Modeling Asphalt Binder Aging in Pavements Appendix C: Evaluation of the Sensitivity of the Mechanical Properties of Asphalt Concrete to Asphalt Binder Oxidation Appendix D: Evaluation of Different Chemical and Rheological Aging Index Properties Appendix E: Factors Affecting Oxidation Reaction Mechanisms in Asphalt Concrete Appendix F: Evaluation of Asphalt Mixture Laboratory Long-Term Aging Appendix G: Investigation of Proper Long-Term Aging Temperature Appendix H: Climatic Aging Index Appendix I: Performance Testing of Field Cores

1 Summary 3 Chapter 1 Background 4 Project Objectives and Scope 5 Previous Research into Long-Term Aging of Asphalt Mixtures 5 Compacted Specimen Aging Versus Loose Mixture Aging 6 Oven Aging Versus Pressure Aging 7 Laboratory Aging Temperature 7 Aging Index Properties (AIPs) 8 Modeling of Oxidative Aging 12 Chapter 2 Research Approach 12 Overview of Research Approach 12 AIP Selection 12 Sensitivity Study 14 Selection of the Proposed Aging Method 15 Determination of Project-Specific Aging Durations 15 Climate-Based Determination of Predefined Aging Durations 15 Development of Pavement Aging Model 16 Test Materials and Field Projects 16 Group A Materials 17 Group B Materials/Projects 17 Sample Preparation Methods 17 Asphalt Mastic Preparation 18 FAM Preparation 19 Asphalt Mixture Aging 21 Asphalt Binder Aging 22 Field Core Preparation 22 Micro-Extraction and Recovery 23 Test Methods 23 Asphalt Binders 23 Asphalt Mixtures 24 Chapter 3 Findings and Applications 24 Findings 24 Sensitivity Study 26 Selection of the Chemical and Rheological Aging Index Properties 29 Selection of Long-Term Aging Method 58 Climate-Based Determination of Predefined Aging Durations 78 Aging Model to Predict Field Aging Throughout Pavement Depth 90 Applications 90 Integration of Pavement Aging Model in Mechanistic–Empirical Design C O N T E N T S

94 Conclusions 94 Sensitivity Study 94 Selection of the Chemical and Rheological Aging Index Properties 95 Selection of the Long-Term Aging Method 96 Climate-Based Determination of Predefined Aging Durations 97 Aging Model to Predict Field Aging 97 Integration of the Pavement Aging Model in Mechanistic–Empirical Design 98 Chapter 4 Suggested Future Research 100 Chapter 5 Proposed Standard Method of Test for Long-Term Conditioning of Hot Mix Asphalt (HMA) for Performance Testing 112 References 116 Appendices A–I