Effect of chloride salt migration at interfaces on asphalt-aggregate adhesion: A molecular dynamics study

Asphalt pavements can be damaged by moisture and salt, and the bond strength between asphalt and aggregate is related to the erosion of the salt solution. In this study, considering the migration and diffusion of the solution at the interface, a molecular dynamics modeling method was used to simulate the process where the salt solution erodes the asphalt-aggregate interface, and results show that the solution invades the asphalt-aggregate interface, gradually squeezing the asphalt away from the aggregate surface in a wedge shape, and the interaction force between the asphalt and the aggregate is gradually reduced to 0. The diffusion rate of the solution at the interface is related to the position of the solution. If the solution is farther away from the aggregate, it will be less restricted by the aggregate. NaCl affects the diffusion of water molecules. The greater the concentration of NaCl solution, the lower the height of the wedge formed by the solution at the interface. Compared to quartz, calcite has a stronger limiting effect on the solution, which is manifested by a greater resistance to water damage. Under the attraction of NaCl solution, the polar components are more likely to move toward the solution surface, while the less polar components show different distribution and diffusion states. In this study, we observed the conformational changes in the erosion process of different concentrations of NaCl solutions and calculated the change rule of interaction force, which helps understand the erosion process of salt solutions and provides a new idea for the study of chloride on asphalt pavement spalling.