Performance of Warm Mix Asphalt and Low Energy Mixes, Phase 3

Warm Mix Asphalt (WMA) is a suite of technologies that allows a reduction in traditional hot-mix asphalt (HMA) production and paving temperatures. There are currently four different WMA categories (organic additives, inorganic additives, chemical foaming processes, and mechanical foaming processes), with 14 known technologies currently available in the USA. The California Department of Transportation (Caltrans), county and local government road authorities, and the construction industry are interested in the evaluation of WMA products for: (1) Worker health and safety benefits (lower temperatures, less fumes); (2) Environmental benefits (reduced stack and construction emissions); (3) Opportunities to extend the paving season, undertake more night time paving, and to allow longer hauls of HMA; (4) Potential increased pavement service life (from improved compaction); and (5) Higher productivity at asphalt plants (higher throughput, less wear-and-tear, longer operating hours in areas with controlled stack emissions, etc). Caltrans has been evaluating WMA technologies under a variety of applications, including field test sections throughout the state (predominantly thin open-graded friction overlays) and Heavy Vehicle Simulator (HVS) and associated laboratory testing at the University of California Pavement Research Center (UCPRC). Three of the four WMA categories (organic, inorganic, and chemical foaming) have been evaluated in these studies. To date, all research has been undertaken on conventional HMA mixes. Now that the mechanisms and potential benefits of WMA are understood, the study needs to be extended to study additional variables. The use of WMA technologies in rubberized asphalt concrete (R-HMA) has been identified as the highest priority. Higher production and construction temperatures associated with R-HMA lead to more visible emissions (leading to shorter allowable production periods at some asphalt plants), poorer working conditions, and limited night and late season paving opportunities in cooler areas. The use of WMA technologies in R-HMA mixes could alleviate these problems thereby justifying increased use of R-HMA in paving projects.