Compatibility and Self-Healing Properties of Asphalt Binder with Polyethylene Plastics: Observations from Coarse-Grained Molecular Simulation

Abstract

Recycled polyethylene (PE) has been used in asphalt modification for sustainability benefits but shows complex interaction with asphalt matrix. This study investigated compatibility and self-healing properties of asphalt/PE blends using coarse-grained molecular simulation. The mesoscale model based on three-component asphalt binder was first built and validated by physical and thermodynamic properties in terms of density, glass transition temperature, diffusion coefficient of asphaltene, and viscosity. The compatibility of asphalt and PE with various molecular structures was then studied using interaction energy at different temperatures. The two-layer model was further used to explore self-healing characteristics of asphalt binder. The results show that medium-density PE (MDPE) presents the strongest compatibility with asphalt binder, followed by high-density PE (HDPE) and low-density PE (LDPE), respectively. This finding was consistent with the compatibility index (tube testing) results from the literature. The interaction energy between PE and asphalt decreases with the increasing temperature, while the relative trend among three PE-modified asphalts remains unchanged. The morphology and confirmation of PE molecules further indicate that MDPE has better interaction with asphalt binder, while LDPE shows an aggregation pattern. On the other hand, HDPE-, MDPE-, and LDPE-modified asphalt experience smaller diffusion and greater activation energy than neat asphalt binder, which indicates a higher barrier for self-healing. The study findings provide a fundamental understanding on the interaction mechanism of asphalt and PE from the molecular scale.