Mechanistic study of graphene reinforcement of rheological performance of recycled polyethylene modified asphalt: A new observation from molecular dynamics simulation

The use of recycled polyethylene (RPE)-modified asphalt not only allows for significant consumption of waste plastics, but also enhances the performance of the asphalt matrix. However, storage stability is a major challenge for RPE-modified asphalt. The objective of this study was to investigate the enhancement mechanism of graphene on RPE-modified asphalt using molecular dynamics simulations based on a comprehensive evaluation of the temperature performance, storage performance and rheological properties of graphene/RPE-modified asphalt. The results showed that graphene enhanced the high-temperature rheological properties, medium-temperature fatigue resistance, low-temperature crack resistance and storage stability of RPE-modified asphalt to some extent. However, the self-aggregation phenomenon limits the enhancement effect of graphene, and the optimal laboratory admixture is 0.5 wt%. Molecular dynamics simulations revealed that graphene reduced the binding energy of asphaltenes to non-polar molecules (saturate and aromatic) from 64.28 kcal/mol and 51.39 kcal/mol to 53.12 kcal/mol and 41.73 kcal/mol, respectively, while the binding energy of RPE to non-polar molecules increased from 16.38 kcal/mol and 8.44 kcal/mol to 24.37 kcal/mol and 14.58 kcal/mol, respectively. In addition, graphene elevated the diffusion coefficient of non-polar molecules by about 8% and decreased the diffusion coefficient of polar molecules by about 2%. The concentration distribution results suggest that graphene disrupts the colloidal structure of the asphalt matrix, which may trigger changes in the asphalt properties. The results of molecular simulation adequately explain the enhancement mechanism of graphene, which can provide a reference for the performance enhancement of RPE-modified asphalt.