United States Department of Transportation
i
Regional implementation of warm mix asphalt.
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2014-09-01
[PDF-1.38 MB]
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Abstract:Asphalt is used in over 94 percent of all paved roadways in the United States. The ability to reduce its cost and emissions
while improving its performance has benefits that could potentially change the direction the asphalt industry moves toward in
the future. Warm-mix asphalt (WMA) technology is becoming more prevalent in routine roadway construction across the
country. It provides many benefits over conventional hot-mix asphalt (HMA).
There are three groups of technologies currently being used to achieve these lower temperatures. They are chemical additive,
organic additive (wax), and water additive (foamed). Each of these technologies is different, yet they all function on the same
basic concept. They each decrease the viscosity of the liquid binder, thus allowing the binder to more easily coat the aggregate
at a cooler temperature.
In the last decade, WMA has increasingly been used across the country. Many states have developed special provisions or
have modified their standard specifications to accommodate the use of WMA. In an attempt to quantify the use of WMA
technology in the southeastern region of the United States, this study was initiated with the following objectives.
1. To inform research agencies of the work that is ongoing, as well as the work that has already been done.
2. To provide a document that can be used to educate and inform contractors from an unbiased perspective of the costs and
benefits associated with the different types of warm mix asphalt.
3. To assist government agencies in establishing acceptance criteria for warm mix asphalt, thus allowing it as a suitable
replacement for hot mix asphalt.
A survey was sent to 12 southeastern states to attempt to answer the questions listed above. Also, internet searches were
conducted to determine specification and policy changes that were made in the subject states to accommodate WMA
technology.
Results of the research indicated that WMA technology is being used in all of the southeastern states and that all of the states
have made changes in standard specification and special provisions to permit the use of WMA. The most significant change
made in specifications is the permission to allow the mixing and placing of WMA at cooler temperatures.
Although more long-term performance data is needed, it appears that at this time the performance of WMA technology is
comparable to that of conventional HMA. The cost between HMA and WMA does not currently appear to be significant.
WMA appears to be a viable technology, and its use is expected to increase in the immediate future.
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