Evaluation of Sasobit® for Use in Warm Mix Asphalt

Abstract

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. One of these processes utilizes Sasobit®, a synthetic long chain Fischer-Tropsch wax. Sasobit® can be blended with the binder at a terminal or in the contractor’s tank, introduced in a molten form, added with the aggregate, or pneumatically blown into a drum plant. A laboratory study was conducted to determine the applicability of Sasobit® 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 Sasobit® may lower the optimum asphalt content, so it should be added during the mix design process. Sasobit® was 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). The addition of Sasobit® does not affect the resilient modulus of an asphalt mix nor does it 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 as well as from the anti-aging properties of Sasobit. There was no evidence of differing strength gain with time for the mixes containing Sasobit® 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 with Sasobit® or any such similar Warm Mix additive may increase the potential for moisture damage. Overall, Sasobit® appears to be a viable tool 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 specialized applications, such as airport runway construction, where rapid opening to traffic is essential.