Comparison of Wilhelmy Plate and Sessile Drop Methods to Evaluate Moisture Susceptibility of Asphalt Mixes

The present study evaluates moisture damage susceptibility of twelve different asphalt mixes based on interfacial energy of aggregate-asphalt binder system estimated using Wilhelmy plate (WP) and Sessile drop (SD) methods. The present study aims to compare both the methods based on contact angle, surface free energy (SFE) components, bonding energy, and compatibility ratio (CR). Three asphalt binders (unmodified, polymer, and crumb rubber modified), and four aggregates (basalt, limestone, granite, and sandstone) were selected in this study. The results show that both the methods are successful in measurement of contact angle. The SD method showed a high variability in measurement of contact angle compared to the WP method. The SD method found to be less sensitive to capture acid nature of asphalt binders. Both the methods showed that PMB40-basalt, VG30-basalt, PMB40-limestone mixes can have the best performance. However, in majority of the cases (9 out of 12 mixes, excluding PMB40-basalt, VG30-basalt, PMB40-limestone), both the methods give different ranking of mixes. The CR threshold value of 0.5 based on the WP method may not be applicable to the SD method. This study develops a correlation between the CR estimated from the WP and SD method. The present study indicates that a caution should be taken while using a selected method for measurement of contact angle of binders and ranking the asphalt mixes.