WARM MIX: THE WAVE OF THE FUTURE?

Technologies for lowering mix temperatures for Hot Mix Asphalt (HMA) are being met with success in Europe and are enabling countries to respond to European Union mandates calling for reductions in greenhouse gases. The technologies are beginning to make their way to the U.S., with the hope that benefits such as reductions in plant emissions, energy consumption, and plant wear can be realized. This article discusses four different processes that are being actively marketed. These include the use of foamed asphalt, mineral additives, organic additives, as well as a chemically based method. Foamed asphalt reduces the stiffness of the asphalt mix, leading to an increase in its workability and allowing for the lower production temperature. Mineral additives can also have the same effects, while organic additives lower the viscosity at construction temperatures and maintain the necessary stiffness at service temperatures. The article notes that even with the obvious reductions in fumes, emissions, and energy consumption afforded by these new techniques, issues regarding their costs and benefits still remain.