Effect of Sasobit and Aspha-Min on Wettability and Adhesion Between Asphalt Binders and Aggregates

The influence of natural wax in asphalt binders and hot-mix asphalt has been studied for decades, with consideration of both negative and positive effects. Recent advances in warm-mix asphalt (WMA) have spurred interest in the use of commercial waxes such as Sasobit and Asphaltan B as additives in asphalt binders to achieve certain positive effects. Despite a number of previous studies, the effect of Sasobit on wettability and adhesion between asphalt binders and aggregates is not fully understood. Likewise, the effect of water vapor released from Aspha-Min, another WMA additive, at production temperatures is not adequately understood, although such water may negatively influence the behavior of WMA. In the present study, the effect or Sasobit and Aspha-Min on wettability and adhesion was investigated using the surface free energy (SFE) method. Dynamic advancing-wetting contact angles were measured for wettability (coating) and dewetting-receding contact angles were measured to evaluate adhesion. It was observed that Sasobit increases the wettability of asphalt binders over aggregates, as indicated by the change in the spreading coefficient. Conversely, a general trend is that Sasobit reduces the adhesion (free energy of adhesion) between asphalt binders and aggregates. In this study, moisture susceptibility is defined as the amount of spontaneously released free energy due to the breaking of the binder-aggregate bond with water. For PG 64-22, a small or no reduction in moisture susceptibility was observed; for PG 70-28, an increase in moisture susceptibility was observed. In case of the Aspha-Min, the overall SFE results are insignificant.