Molecular Dynamics Simulation on Original and Polymer Modified Asphalt Mixtures

Asphalt is complicated viscous liquid originally coming from crude oil distillation. It is widely applied on road pavement and roof patching. In order to improve its performance on road pavement, different modifiers such as polymers have been applied to improve its physical and mechanical properties at different temperatures. In order to study the polymer modification effect on asphalt in molecular detail, 4 kinds of polymer modified model asphalt mixtures were built, each with 1 kind of polymer, including polystyrene, polyethylene, polystyrene-butadiene, and poly(styrene-butadiene-styrene). Based on all-atom LAMMPS molecular dynamics simulation trajectories, different physical properties including heat capacity, isothermal compressibility, expansion coefficient, diffusion coefficients of components, radial distribution function of components, and density were calculated on both polymer modified asphalt mixtures and original asphalt mixture. It was found that the diffusion coefficients, isothermal compressibility, expansion coefficient, and the heat capacity of the overall mixture at different temperatures were not affected significantly by the addition of the modifier. However, the model asphalt density increases with the addition of the polymer except polyethylene. The distribution of molecules in mixture system changed during the simulation. This research helped to predict the modification effect of different polymers on the physical properties of asphalt mixtures and can help to design optimum asphalt mixtures on road pavement.