Rheological Properties and Modification Mechanism of OLDPE–SBS High-Viscosity Modified Asphalt

To enhance the compatibility of waste plastic [low-density polyethylene (LDPE)] with asphalt, waste cooking oil was used to pretreat the LDPE, resulting in oil-based LDPE (OLDPE). This OLDPE was then combined with styrene–butadiene–styrene (SBS)-modified asphalt to create a high-viscosity modified asphalt. Currently, research on the rheological properties and modification mechanisms of low-density polyethylene in high-viscosity asphalt is limited. This study first examines the basic physical properties and zero shear viscosity of the modified asphalt through orthogonal experiments. A dynamic shear rheometer and bending beam rheometer (BBR) were subsequently employed to analyze rheological characteristics, using Tafpack Super high-viscosity modified asphalt as the control group. Fluorescence microscopy (FM) was used to evaluate the dispersion and compatibility of the polymer in the modified asphalt, while Fourier transform infrared spectroscopy (FTIR) was employed to study changes in chemical structure and modification mechanisms. The results indicate that a combination of 5% OLDPE and 6% SBS is optimal for enhancing high-temperature rutting resistance, while 4% OLDPE and 6% SBS is the best combination for improving high-temperature creep recovery and intermediate-temperature fatigue performance. BBR tests reveal that adding OLDPE reduces the low-temperature performance of asphalt, but the low-temperature performance of the 4% OLDPE and 6% SBS group is comparable to the control group. FM analysis reveals that under the uniform distribution of OLDPE particles, the modified asphalt forms a denser network structure, indicating good compatibility. FTIR analysis shows that the interactions among OLDPE, SBS, and asphalt are physical, with no new chemical functional groups formed. A comprehensive performance analysis suggests that 4% OLDPE and 6% SBS is the optimal material combination, particularly suitable for high-temperature regions.