Binder-Level Rheological Evaluation of Virgin HDPE, LDPE, and PP as Asphalt Binder Modifiers: Baseline Assessment for Plastic Waste Recycling Applications

Increasing plastic waste and limited recycling rates underscore the need for value-added recycling applications. Polymers commonly present in plastic waste streams, including packaging films, bottles, caps, and rigid containers, may provide a practical pathway for developing plastic-modified asphalt binder (PMAB) systems. In this study, virgin high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) were selected as reference modifiers to evaluate their intrinsic effects on performance grade (PG) 58-28 and PG 67-22 base binders. Conventional high-, intermediate-, and low-temperature gradings were complemented by ΔTc, the Christensen–Anderson R-value (R-value), the Glover–Rowe (G-R) parameter, Linear Amplitude Sweep (LAS) fatigue analysis modeled via Viscoelastic Continuum Damage (VECD), rheological master curves, and extended Bending Beam Rheometer (BBR) testing. Modification improved high-temperature grading and LAS-based fatigue response while increasing master-curve stiffness. However, ΔTc, G-R parameter, and extended BBR results indicated increased low-temperature cracking susceptibility. High-temperature grades increased by 3.4 °C, 2.8 °C, and 2.3 °C per percent HDPE, LDPE, and PP, respectively, whereas low-temperature grade losses reached 7.8 °C; HDPE produced the highest high-temperature grade improvement, while LDPE showed the greatest extended BBR grade loss, and PP exhibited the fastest physical hardening rate. These results provide a controlled binder-level baseline for evaluating HDPE, LDPE, and PP as modifiers for future PMAB development.