Nanomechanical Experiments and Molecular Dynamics Explorations for the Deterioration Evolution of Asphalt Driven by Chloride Salt Erosion

Abstract

The salt erosion environment will lead to the deterioration of asphalt pavement performance and seriously restrict the service life and sustainability of asphalt pavement. In this research, the evolution mechanism of asphalt performance induced by chloride salt erosion was explored by atomic force microscopy (AFM) and molecular dynamics (MD) simulation from the nanoscale. The AFM test results demonstrated that with increasing chloride salt concentration and erosion time, the adhesion force, adhesion energy, surface free energy, and dissipated energy of asphalt binder decreased significantly. The fitted modulus of the four contact mechanics models all decrease with increasing chloride erosion time. It is recommended to use the Cone Sphere or Johnson-Kendall-Roberts (JKR) model to fit the Young’s modulus of asphalt binder. The MD simulation results show that the tensile strength and shear strength of asphalt binder in the three directions decreased after chloride salt erosion, and there are differences in the magnitude of reduction in different directions. Chloride salt erosion not only inhibits the translational migration behavior of SARA fractions [saturates (S), aromatics (A), resin (R), and asphaltenes (A)] but also limits the rotational migration behavior. Although chloride salt erosion has little effect on the aggregation behavior of asphaltene, it still affects the degree of molecular entanglement of SARA fractions. The distribution of asphalt molecules becomes heterogeneous after chloride salt erosion. This research not only presents the erosion damage mechanisms of the asphalt binder but also helps to promote the sustainability of the asphalt pavements exposed to a chloride salt environment.