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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 50°F 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
