Impacts of asphalt and mineral types on interfacial behaviors: A molecular dynamics study

In order to analyze the interfacial interaction mechanism between the types of mineral and asphalt at the molecular scale, molecular dynamics (MD) simulations were conducted to study the interfacial behavior of three asphalt binders (AS-1, AS-2, AS-3) with five minerals (SiO2, CaO, MgO, Al2O3, Fe2O3). Thermodynamic properties of asphalt binder were used to evaluate the rationality of MD simulations, such as density, glass transition temperature, cohesive energy density and solubility parameter. The mean square displacement (MSD), diffusion coefficient and relative concentration distribution were employed to analyze the diffusion regularity of asphalt SARA (saturate, aromatic, resin and asphaltene) components on the mineral surface, and the bonding strength between asphalt and different minerals was evaluated by calculating the adhesion work. The simulation results show that Van der Waals energy and Coulomb electrostatic energy play critical role in the adhesion of asphalt-mineral. The diffusivity of asphalt on the surfaces of five minerals was ranked as CaO > MgO > Al2O3 > Fe2O3 > SiO2. It is enhanced with the increase of alkaline strength of minerals, and then the adhesion work of asphalt-mineral increases. The interfacial adhesion strength of the asphalt binders and minerals are directly related to the proportion of asphaltene and resin components, and the molecular mass of asphalt will affect asphalt-mineral adhesion strength, which can also be reflected by the relative concentration distribution of SARA components on mineral surface.