Evaluation of New Technologies for Use in Warm Mix Asphalt
Type of DegreeThesis
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Several new processes have been developed with the goal of reducing the mixing and compaction temperatures of hot mix asphalt without sacrificing the quality of the resulting pavement. Three potential Warm Mix Asphalt processes were evaluated in this study. They were Aspha-min®, Sasobit®, and Evotherm®. A laboratory study was conducted to determine the applicability of these processes to typical paving operations and environmental conditions commonly found in the United States, including the performance of the mixes in quick traffic turn-over situations and high temperature conditions. Superpave gyratory compactor (SGC) results indicated that Aspha-min®, Sasobit®, and Evotherm® increase the density of lab compacted samples. Therefore, it is currently recommended to determine the optimum asphalt content with a typical PG binder and then substitute in the Warm Mix Asphalt additive. All three processes were shown to improve the compactability of mixtures in both the SGC and vibratory compactor. Statistics indicated an overall reduction in air voids with the Warm Mix Asphalt processes. Improved compaction was noted at compaction temperatures as low as 190?F (88°C). The addition of Aspha-min®, Sasobit®, or Evotherm® did not affect the resilient modulus of an asphalt mix nor did they increase the rutting potential measured by the Asphalt Pavement Analyzer. The rutting potential did increase with decreasing mixing and compaction temperatures, which may be related to the decreased aging of the binder resulting from the lower temperatures. There was no evidence of a difference in indirect tensile strength over different age times for the mixes containing Aspha-min® and Evotherm® when compared to the control mixes, indicating that a prolonged cure time before opening to traffic is not an issue. Regarding the Sasobit®, statistical analysis conducted on the laboratory data indicated that a cure may be beneficial before opening to traffic. However, field data pertaining to Sasobit® indicated that traffic could be opened quickly with no negative effects. A second potential problem area that was observed deals with moisture susceptibility. The lower mixing and compaction temperature used when producing Warm Mix Asphalt may increase the potential for moisture damage. Overall, Aspha-min®, Sasobit®, and Evotherm® appear to be viable tools for reducing mixing and compaction temperatures that can be readily added to hot mix asphalt mixtures in the United States. Reductions in the mixing and compaction temperatures are expected to reduce hot mix asphalt (HMA) plant fuel costs, reduce plant emissions, extend the paving season, and facilitate specialized paving applications, such as airport runway construction, where rapid opening to traffic is essential.