Evaluation of Potential Processes for Use in Warm Mix Asphalt (With Discussion)
2006
Several new processes have been developed to reduce 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. 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. Improved compaction was noted at temperatures as low as 190°F (88°C). Superpave gyratory compactor results indicated that Aspha-min®, Sasobit®, and Evotherm® may lower the optimum asphalt content. 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 of an asphalt mix as 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 differing strength gain with time for the mixes containing the three processes as compared to the control mixes indicating that a prolonged cure time before opening to traffic is not an issue. The lower compaction temperature used when producing warm 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. Reductions in mixing and compaction temperatures are expected to reduce fuel costs, reduce emissions, widen the winter paving window and facilitate niche applications such as airport runway construction where rapid open to traffic is essential.
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