Influence of acidity and alkalinity of water environments on the water stability of asphalt mixture: phase III—surface free energy testing and analysis

To accurately quantify the influence of acidity and alkalinity of water environments on the water stability of asphalt mixtures, a surface/interfacial tension test method was proposed in this study based on the Good-van Oss-Chaudhury surface free energy theory. Building upon traditional testing methods, the Wilhelmy plate method and vapor adsorption method were improved to enhance the accuracy of test results. The surface energy parameters of aqueous solutions with different pH values, base asphalt, and aggregates were measured and calculated, respectively. Furthermore, the water stability of asphalt mixtures under aqueous environments with different pH values was quantified and ranked. Finally, the water stability evaluation results obtained via the surface free energy approach were verified through the Strategic Highway Research Program net adsorption test, water-immersed pull-off test, and freeze-thaw splitting test. The findings indicate that in a water environment, the adhesion of asphalt-aggregate is significantly reduced, and the water stability of limestone-based asphalt mixtures is superior to that of granite-based asphalt mixtures. For acidic and alkaline solutions, the non-polar component of surface energy increases while the polar component decreases. The energy ratio index derived from surface energy effectively quantifies the water stability of asphalt mixtures under water environments with different pH values. The surface energy test results are consistent with the macroscopic water stability test results. This study accurately quantifies the water stability of asphalt mixtures under water environments with varying pH values, providing a reference for research related to the water stability of asphalt mixtures.