Warm-Mix Asphalt: European Practice

Warm-mix asphalt (WMA) is a group of technologies that allow a reduction in the temperatures at which asphalt mixes are produced and placed. These technologies tend to reduce the viscosity of the asphalt and provide for the complete coating of aggregates at lower temperatures. WMA is produced at temperatures 20 to 55 °C (35 to 100 °F) lower than typical hot-mix asphalt (HMA). In 2007, a team of U.S. materials experts visited Belgium, France, Germany, and Norway to evaluate various WMA technologies through the Federal Highway Administration’s International Technology Scanning Program. The scan team learned that the benefits of WMA technologies include reduced fuel usage and emissions in support of sustainable development, improved field compaction, which can facilitate longer haul distances and cool weather pavement, and better working conditions. A range of technologies is available to produce WMA. European agencies expect WMA performance to be the same as or better than the performance of HMA. Although several areas need to be addressed as these technologies are adapted to U.S. materials and production practices, the scan team believes that the United States has no long-term barriers to WMA use. With additional research and trials, the team expects that highway agencies will allow WMA as an alternative to HMA.