Ncat Evaluates Warm Mix Asphalt

In addition to lower emissions warm mix asphalt has several advantages over hot mix asphalt such as fuel energy savings, decreased binder aging and an extended paving season (Photo courtesy: Matthew Corrigan, FHWA) The National Center for Asphalt Technology (NCAT) is evaluating warm mix asphalt (WMA) technologies. WMA technology allows the mixing, lay down, and compaction of asphalt mixes at significantly lower temperatures compared to hot mix asphalt (HMA). The technology can reduce production temperatures by as much as 30 percent. Asphalt mixes are generally produced at 300°F (149°C) or greater temperatures in the U.S. depending mainly on the type of binder used. WMA mixes can be produced at temperatures of about 250°F (121°C) or lower. WMA offers the following significant advantages: • Reduced Fuel Consumption. The most obvious benefit of WMA is the reduction in fuel consumption. Fuel is used to dry and heat the aggregate. Studies have shown that lower plant mix temperatures associated with WMA can lead to as much as 30 percent reduction in energy consumption costs. • D e c r e a s e d emissions. WMA produces emissions (both visible and non visible) from the burning of fossil fuels at a significantly reduced level compared to HMA. This would permit asphalt plants to be located in and around areas such as large metropolitan areas that have air quality restrictions. The decrease in emissions may represent significant cost savings. • Decreased fumes and odor. WMA produces lower fumes and odor both at the plant and the paving site compared to HMA. This would also result in improved working conditions at both places. • Decreased binder aging. Short-term aging of liquid asphalt binder takes place when it is mixed with hot aggregate in the pug mill or mixing drum. This aging is caused by the loss of lighter oils from the liquid asphalt (continued on page 2)