Impact of Plastic Size and Texture Variability on Recycled-Plastics-Modified Asphalt Binder Performance

The incorporation of recycled plastics into asphalt binders presents a sustainable strategy for improving pavement performance while addressing plastic waste challenges. However, with increasingly varying sources and processing techniques of post-consumer plastics, understanding how polymer morphology influences binder behavior is critical to ensuring consistent performance. This study investigates the effects of recycled low-density polyethylene (LDPE) particle texture and size on the rheological and mechanical characteristics of asphalt binders. LDPE was processed into three textures—shredded, hand-cut, and melted-crushed. Each was further classified into three size ranges (2.36–4.75 mm, 1.18–2.36 mm, and <1.18 mm) and incorporated at 2% dosage into a performance grade (PG) 67-22 asphalt binder using high-shear mixing. Binder performance was evaluated through rotational viscosity, high-temperature stiffness, multiple stress creep recovery testing, and monotonic shear failure tests assessing peak stress, failure strain, yield energy, and monotonic cracking index. Results showed that both texture and particle size significantly influenced binder behavior. Melted-crushed LDPE at finer sizes led to the highest viscosity and stiffness, outperforming PG 76-22 in rutting resistance and elastic recovery, likely because of enhanced dispersion and binder interaction. Shredded LDPE showed higher viscosity at larger sizes but offered moderate mechanical improvements, while hand-cut LDPE produced more consistent, though less pronounced, effects. These findings emphasize the need to account for polymer morphology when designing recycled-plastic-modified asphalt binders, especially as plastic waste sources become increasingly heterogeneous.