Effect of Low-Density Polyethylene and Crumb Rubber Blends with Different Ultraviolet Aging Degrees on the Storage Stability of Bitumen Based on Molecular Dynamics Simulation

Abstract

Although crumb rubber (CR) modified bitumen has been widely used in bitumen pavement, the issue of storage stability has not been resolved. Waste low-density polyethylene (LDPE), a new modifier, has been introduced to improve the performance of CR-modified bitumen. However, the interaction behavior among LDPE with different ultraviolet (UV) aging degrees, crumb rubber, and bitumen is not clear, depending on the environment and source. In this study, virgin LDPE (LDPE-0)/CR blends, LDPE with 8 days UV aging (LDPE-8)/CR blends and LDPE with 64 days UV aging (LDPE-64)/CR blends were prepared by melt compounding using a twin-screw extruder and mixed with bitumen. The samples were evaluated by various tests such as dynamic shear rheometer (DSR) tests, storage stability, fluorescence microscopy, and scanning electron microscope (SEM). Then, molecular dynamics (MD) simulation was used to explore the interaction behavior between LDPE/CR blends with different UV aging degrees and bitumen. The virgin bitumen model was validated by density, radial distribution function (RDF), and glass transition temperature (Tg). The interaction behaviors were characterized based on diffusion coefficient and concentration distribution. The results showed that LDPE/CR blends were able to improve the rheological properties and storage stability, especially in LDPE-8/CR-modified bitumen. From the microscopic analysis, it was also observed that a network of LDPE/CR blends in the modified bitumen was well dispersed. Furthermore, the addition of LDPE/CR blends inhibited the aggregation behavior of the light component and slowed down the diffusion rate of bitumen molecules. The research findings provide insights for improving the storage stability of bitumen.