Field Performance of Warm Mix Asphalt Technologies

Abstract

This report compares material properties and field performance of warm mix asphalt (WMA) and control hot mix asphalt (HMA) pavement sections constructed at 14 locations across the United States between 2006 and 2010. The specific objectives of the project were to (1) compare the short-term performance of WMA and control HMA pavements, (2) examine relationships among engineering properties of WMA binders and mixes and the field performance of pavements constructed with WMA technologies, (3) compare production and laydown practices between WMA and HMA pavements, and (4) provide relative emissions measurements of WMA technologies and conventional HMA technologies. Performance and material property data were obtained from 14 field projects. Each of the 14 projects included single- or multiple-WMA technology pavement sections and an HMA control section. A total of 12 WMA technologies were investigated. All projects used “drop in” WMA mix designs where the WMA technology was used with an existing HMA mix design with no significant changes to the binder content or other aspects of the mix design. Except for the reduced mixing and compaction temperatures for WMA, there were no substantial differences in the production and laydown practices of WMA and HMA. In-service performance of WMA and HMA in all projects was virtually identical, with little or no rutting, no evidence of moisture damage, and very little indication of transverse or longitudinal cracking. Energy use, plant and paver emissions, and worker exposure to fumes were extensively measured at three multiple-WMA technology projects. Compared to HMA, the reduced temperatures used in WMA production and laydown yielded lower energy consumption and emissions and reduced worker exposure to respirable fumes. Overall, then, no penalties and some potential benefits were observed in the short term when WMA replaced HMA. The key finding of laboratory testing of WMA binders and mixtures from the projects sampled at construction was the expected lower stiffness of the WMA materials that would have potential effects on pavement rutting and cracking. However, the equivalent performance of the WMA and HMA pavement sections over several years of service suggests that these differences in material properties, when present, were not great enough to affect the relative performances of HMA and WMA. This report fully documents the research in two parts bound in one report. Part 1 includes an appendix on Falling Weight Deflectometer Testing; Part 2 includes an appendix on Documenting Emissions and Energy Reductions of WMA and Conventional HMA During Plant and Paving Operations.