Optimizing the Dose of Warm-Mix Asphalt Additives by Maximizing the Asphalt-Aggregate Adhesion Measured via Surface-Free Energy

Warm-mix asphalt (WMA) is a group of technologies focused on reducing the viscosity of the asphalt binder (or binder) to produce asphalt mixtures at a reduced temperature compared with that specified for conventional hot-mix asphalt mixtures. The WMA technologies include two main groups: foaming and additives. The additives can be classified as synthetic-chemical or natural-based. This study aims at assessing the feasibility of optimizing the WMA additives dose by maximizing the adhesion between the asphalt binder and the aggregate at their interface in WMA mixtures. Adhesion is quantified using energy parameters derived from surface-free energy measurements (SFE), including three WMA additives (Carnauba wax, a natural-based warm-mix additive, Sasobit, and Evotherm). Accomplishing this objective required measurements of SFE for four different asphalt binders, and corresponding WMA-modified asphalt binders were performed. The results suggest the possibility of identifying a WMA-additive dose that maximizes adhesion at the binder-aggregate interface in terms of resistance to fracture (i.e., adhesive failure) and moisture damage, and the wettability of the binder. In addition, the results showed that the inclusion of Carnauba wax as a warm-mix additive yielded equivalent adhesion at the binder-aggregate interface compared with the response of the other commercially available WMA additives evaluated (i.e., Sasobit and Evotherm). Additional studies at the mixture level are recommended to validate further the conclusions obtained in this study.