The influence of natural wax in asphalt binders and hot mix asphalt (HMA) has been studied for decades, considering both negative and positive effects. Recent advances in warm mix asphalt (WMA) have spurred interests in the use of commercial waxes such as Sasobit® and Asphaltan B® as additives in asphalt binders to achieve certain positive effects. In spite of a number of previous studies, the effect of Sasobit® on wettability and adhesion between asphalt binders and aggregates are 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 of Sasobit® and Aspha-Min® on wettability and adhesion is 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 is observed that Sasobit® increases the wettability of asphalt binders over aggregates significantly, 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 binder-aggregate bond with water. For PG 64-22, small or no reduction in moisture susceptibility and for PG 70-28 an increase in moisture susceptibility were observed. In case of the Aspha-Min®, the overall SFE results are insignificant.
Abstract