Analytical study of silane-based and wax-based additives on the interfacial bonding characteristics between natural rubber modified binder and different aggregate types

The modification of asphalt binder with natural rubber latex (NR) significantly improves the rutting and fatigue resistance of asphalt mixtures. However, NR-modified binder is prone to low workability and wettability due to its high viscosity. Therefore, this research focuses on examining the influences of silane and wax-based additives on the wettability of natural rubber-modified binders and the binder-aggregates adhesion performances. In this study, experimental and analytical approaches were used. The contact angles of asphalt binder were measured using a goniometer through the sessile drop method with three solvents: deionised water, formamide, and glycerol. The C++ algorithm was adopted to compute the surface free energy (SFE) elements of the asphalt binder. Analytical methods were employed to analyse the results based on the Young-Dupre equation, followed by linear regression to establish a correlation between the compatibility ratio (CR) and the SFE components. The results inferred that modified asphalt binders with additives possessed improved moisture resistance, wherein dry work adhesion values were less than 210 ​mJ/m² under granite interfaces, whereas the limestone interface exhibited higher dry adhesion values of 340 ​mJ/m² and below. Similar performance results were observed under wet adhesion conditions; with granite wet adhesive values observed below 120 ​mJ/m², while limestone wet adhesion values were ascertained below 180 ​mJ/m² for all tested samples and conditions. According to the spread–ability coefficient results, the limestone interface has greater spread-ability than granite interfaces. Meanwhile, compatibility ratio values indicated better compatibility of 1.9 or higher for tested samples under granite interfaces, whereas compatibility values of 1.7 and below were observed under limestone interfaces. Among the SFE components studied for correlation with CR, the acidic SFE component demonstrated excellent correlations (with R² values greater than 0.91) under all ageing conditions. An inclusion of micro-level additive enhanced binder adhesion properties, resulting in a more resilient asphalt pavement.