Salt damage on asphalt surfaces under repeated dissolution at molecular scale

Abstract

Salt damage on asphalt surfaces is primarily attributed to migration of ions, with repeated dissolution exacerbating the degradation of asphalt performance. To investigate micro mechanism of salt corrosion on asphalt surfaces during repeated dissolution, this research uses molecular dynamics (MD) simulation and experiments to measure interactions among asphalt, salt, and water. Asphalt-salt systems and asphalt-water interfaces are built to calculate molecular damage behaviors by energies, mobilities, and distributions, along with micro-morphology and rheological properties of asphalt samples under salt corrosion. The interaction energies of salt with asphalt exhibit a hierarchy with Mg2+ ˃ Ca2+ ˃ Na+ and SO42- ˃ Cl-, predominantly governed by electrostatic energies. Repeated dissolution is a dynamic damage process. When water contacts on salt-eroded asphalt surfaces, salt ions migrate into water, forming solutions. Sulfates exhibit slower mobility and higher structural stability compared to chlorides, owing to smaller free volume, stronger interaction, and weaker water debonding. Rheologically, salt-eroded asphalt manifests as stiffer and tougher than water-eroded or base asphalt. These asphalt samples undergo softening and increased viscosity due to loss of salt ions. Consequently, compared to chlorides, sulfates demonstrate stronger interactions with asphalt and more difficulty in diffusing to water, resulting in severer damage on asphalt surfaces.