Hot Mix Asphalt Technology - May/June 2011 - (Page 16)

Warm-Mix Asphalt: Best Practices by Brian D. Prowell, Graham C. Hurley, and Bob Frank ndustry’s interest in warm-mix asphalt (WMA) initially focused on improving working conditions at the paving site and reducing greenhouse gas emissions. While WMA has provided these benefits, contractors have also discovered a wide range NAPA’s Definitive New Technical Manual Tells All About Warm Mix Editor’s note: Warm-mix asphalt applications have expanded rapidly since the first introduction to the market just eight years ago. This excerpt from the newly released second edition of NAPA’s Warm-Mix Asphalt: Best Practices publication outlines 10 documented benefits of the technology. I of new construction benefits. The many potential benefits have helped to fuel its rapid implementation. Warm-mix asphalt offers several benefits to asphalt construction. These include use as a compaction aid, extension of the paving season, longer haul distances, and incorporation of higher percentages of RAP. Other warm-mix benefits accrue in specific pavement rehabilitation situations. For example, reduced emissions may allow contractors to pave on more days in air quality non-attainment areas. Each of these is discussed in the following sections. 1 Compaction Aid Asphalt mixtures that contain highly modified asphalt binders, those incorporating high percentages of RAP (reclaimed asphalt pavement) or RAS (reclaimed asphalt shingles), or specialty mixtures such as stone-matrix asphalt (SMA), have been known to be stiff and fairly difficult to compact. This difficulty in compaction can lead to lower in-place densities and the possibility of penalties being assessed to the contractor. As a result, contractors may be tempted to increase placement temperatures to ensure adequate compaction. Even if adequate in-place density is achieved, the required effort may cause excessive aggregate breakdown or otherwise damage the asphalt mat. Using warm-mix technologies at “typical” compaction temperatures will aid in the compaction of these stiffer mixes. Some technologies were, in fact, initially used for their stiffening effect at high in-service temperatures, when it was observed that the materials aided compaction at standard paving temperatures. Many instances of using WMA technologies as a compaction aid have been reported. Massachusetts Department of Transportation now specifies warm mix for all of their gap-graded asphalt rubber mixtures. Sasobit has been used in several high-performance commercial paving projects throughout the United States. These projects used highly modified PG 82-22 and PG 82-28 asphalt binders with approximately 1 percent Sasobit added. Compaction temperatures were above 300 °F (149 °C) and compaction was successfully achieved in all cases. Aspha-min has been used to improve the workability of open-graded friction courses in areas requiring hand work (NAPA 2008). The mixture was placed at 320 °F (160 °C). 16 • View past issues of HMAT online at

Table of Contents for the Digital Edition of Hot Mix Asphalt Technology - May/June 2011

Hot Mix Asphalt Technology - May/June 2011
Chairman’s Commentary: Who Knew Asphalt Could Be So Green?
Industry News
Warm-Mix Asphalt: Best Practices
States Stride Ahead With Warm Mix
Roads to Rubble: De-Paving a Half-Century of Progress
NCAT Explains the AMP Tester
Tools for the Trade
Calendar of Events
Index of Advertisers/

Hot Mix Asphalt Technology - May/June 2011