The influence of water acidity and alkalinity on the adhesion properties of bitumen-aggregate interface

To examine the influence of water acidity and alkalinity on bitumen-aggregate interfacial adhesion, we measured interaction force between aggregate and bitumen using atomic force microscopy with a 1mmol/L KCl background solution at pH levels ranging from 2 to 10. Experimental materials included four types of aggregates (basalt, granite, limestone A, and limestone B) and two types of bitumen (Zhenhai 90# matrix and Styrene-Butadiene-Styrene modified). Results showed adhesion rankings: granite < basalt < limestone B < limestone A. Long-range forces increased with higher pH, in line with Derjaguin-Landau-Verwey-Overbeek theory. Acidic conditions reduced repulsive forces between bitumen and aggregates while increasing adhesive forces. Compared with the Zhenhai 90# matrix bitumen, Styrene-Butadiene-Styrene modified bitumen demonstrated superior adhesion. Zeta potential values for bitumen and aggregate consistently decreased with rising pH, reflecting the aggregate-bitumen interaction force, suggesting electrostatic forces' dominance. Boiling water method was used to assess bitumen spalling on different aggregates under varied acid-base conditions, finding a significant correlation between spalling rate and microscopic interaction force. This study offers theoretical support for minimizing water damage in bitumen pavements by shedding light on the adhesion process of bitumen and aggregates in wet settings.