Comparison of Wilhelmy plate and Sessile drop methods to rank moisture damage susceptibility of asphalt – Aggregates combinations

• The CA measurement by SD method showed high variability compared to the WP method.
• The SFE of asphalt measured by the SD method had higher values than that of WP.
• SD method found to be less sensitive to capture acidic component of SFE of asphalt.
• CR value of 0.25 by SD method would be approximately equal to 0.5 by WP method.

The present study compares two techniques namely Wilhelmy plate (WP) and Sessile drop (SD) methods to rank moisture damage susceptibility of twelve different asphalt-aggregate combinations. Three asphalt binders: unmodified (VG30), polymer modified (PMB40), and crumb rubber modified (CRMB60) binders, and four aggregates (basalt, limestone, granite, and sandstone) were selected in this study. The contact angle of selected asphalt binders was measured using both WP and SD techniques. Thereafter, surface free energy (SFE) components of asphalt binders, bonding energy and compatibility ratio (CR) of selected asphalt-aggregate combinations were estimated. The results showed that the SD method showed a high variability in measurement of contact angle of asphalt binders compared to the WP method. The SD method found to be less sensitive to capture acid component of SFE of asphalt binders. Both the methods showed that PMB40-basalt, VG30-basalt, PMB40-limestone combination can have least susceptible to moisture damage. However, in majority of the cases (9 out of 12 asphalt-aggregates combinations, excluding PMB40-basalt, VG30-basalt, PMB40-limestone), both the methods resulted in different moisture damage ranking of asphalt-aggregates combinations. Currently set a minimum threshold value of CR as 0.5 based on the WP method for screening moisture damage susceptibility of asphalt-aggregate combination may not be applicable to the SD method. The present study develops a correlation between the CR of asphalt-aggregate combination estimated from the WP and SD methods.