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February 2012 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Responsible Senior Program Officer: E. T. Harrigan Research Results Digest 370 GUIDELINES FOR PROJECT SELECTION AND MATERIALS SAMPLING, CONDITIONING, AND TESTING IN WMA RESEARCH STUDIES This digest summarizes the results of a "Workshop to Coordinate Key WMA Research Projects" sponsored by NCHRP Project Panels 9-43, 9-47, and 9-49 in conjunction with the AASHTO Highway Subcommittee on Materials, the Federal Highway Administration, and the National Asphalt Pavement Association. The workshop was held on May 13, 2011 at the National Academies' Arnold and Mabel Beckman Center, Irvine, CA. The notes on which this digest is based were prepared by Mr. Tom Baker, Washington State Department of Transportation; Messrs. Matthew Corrigan and John Bukowski, Federal Highway Administration; Dr. Jon Epps, Texas Transportation Institute; Dr. David Newcomb, formerly of the National Asphalt Pavement Association; and Dr. Edward Harrigan, National Cooperative Highway Research Program. INTRODUCTION production has substantially grown in the United States. For example, the FHWA Warm mix asphalt (WMA) refers to estimates that 10% of the 358 million tons asphalt mixtures produced at temperatures at of asphalt mix placed nationwide in 2010 least 50F cooler than those typically used in was WMA. the production of hot mix asphalt (HMA). As the use of WMA has widened, so The goal of WMA is to produce mixtures have the number of WMA technologies with similar strength, durability, and perfor- available to the industry. In 2011, 30 or mance characteristics as HMA using sub- more WMA technologies were available, stantially reduced production temperatures. classified into three broad categories: Important environmental and health benefits (1) those using organic additives, including are associated with reduced production tem- waxes; (2) those using chemical additives; peratures, including lower greenhouse gas and (3) those using water-based foaming emissions, lower mix plant fuel consump- processes. Moreover, as these numbers tion, and reduced exposure of workers to suggest, WMA has rapidly moved from use asphalt fumes. Lower production tempera- in pilot and experimental projects to more tures also can potentially improve pavement routine, large-scale use. At present, at C O N T E N T S performance by reducing binder aging, pro- least 30 state departments of transportation viding added time for mixture compaction, (DOTs) have established specifications per- Introduction, 1 and allowing improved compaction during mitting the use of WMA. Workshop Results, 2 cold weather paving. This rapid growth in use of WMA use References, 14 The first WMA pavements were con- naturally raises questions about WMA Appendix A, A-1 structed in Europe in 1995 and in North pavement construction processes and Appendix B, B-1 America in 2004. Since that time, WMA the pavements' long-term durability and