Investigating the impact of zeolite on reducing the effects of changes in runoff acidity and the moisture sensitivity of asphalt mixtures

Abstract

Most studies evaluating the performance of asphalt mixtures against moisture damage use distilled water or drinking water to create wet conditions. However, the main part of the moisture entering the asphalt layers in the pavement is the rainfall runoff that contains dust, soot, and other pollutants absorbed by the pavement surface, which affect the acidity of rainfall runoff. Accordingly, the impacts of water acidity and Zeolite as an environmental pollutant absorbent, as well as a pH moderator of the water entering the asphalt layers, were investigated on the moisture sensitivity of different asphalt mixtures with mechanical and surface free energy (SFE) tests. The results of the mechanical methods revealed that the change in the runoff acidity increases the moisture damage potential of asphalt mixtures. Asphalt cement modification with Zeolite reduced the drop in the tensile strength ratio (TSR) as a result of changing the pH. The application of Zeolite increased the base component of SFE and reduced the acid component of the asphalt cement. The use of Zeolite caused the formation of amorphous chains in the asphalt cement structure, which increased the nonpolar component of SFE. The polar SFE component of the asphalt cement was slightly improved with the incorporation of Zeolite. The utilization of Zeolite increased the free energy of cohesion, thereby increasing the resistance of the asphalt cement film to cohesive failure. In addition, the debonding energy calculations indicated a decrease in this component due to asphalt cement modification. The results of both mechanical and thermodynamic methods illustrated that asphalt cement modification with Zeolite has a positive effect on decreasing the debonding energy and, thus, reducing moisture damage.