Mechanisms of interface electrostatic potential induced asphalt-aggregate adhesion

The electrostatic potential at the interface of the asphalt molecular and aggregate oxides is the primary factor generating the adhesion between the asphalt-aggregate contact surfaces. However, the route of electrostatic potential affecting the asphalt-aggregate adhesion is yet to be determined at the molecular level. This study proposed that the electron accumulation at the interface of the asphalt molecular and aggregate oxides generates a significant electrostatic potential hence to induce the adhesion between the asphalt and aggregate in asphalt pavement. A microscopic molecular dynamics (MD) simulation incorporated with macroscopic adhesion work experiments is conducted to analyze the interface adhesive performance between the asphalt and aggregate. The adhesion work experiment demonstrated the effect of aggregate surface oxides on asphalt adhesion at the macro level and further verified the simulation results. The result demonstrated that a notable electron accumulation can be observed by MD at the interface of asphalt molecular and multiple oxides which generates the electrostatic potential. The strong electrostatic attractions and hydrogen bonds between alkaline oxides (MgO, CaO, CaCO3) and asphalt molecules enhance the relative concentration distribution, diffusion coefficient, and adhesion of asphalt on the aggregate surface. The significant electrostatic potential difference at the interface of the asphalt molecular and the oxide enables a strong adhesion between them due to the near-surface failure potential. Besides, the negative charge accumulation on both the benzene ring structure and oxygen atoms in the asphalt molecules results in poor adhesion at the interface of asphalt molecules and multiple oxides. It was found that a high correlation exists between the MD prediction and experimental testing results. Thus, this research provides a valuable tool for guiding the pairing and selection of asphalt with various minerals for pavement design, construction, and maintenance agencies.