Laboratory Investigation of High-Temperature Rheological and Mechanical Properties of HDPE-Modified Bitumen

This study addresses the critical challenge of permanent deformation in asphalt pavements under high-temperature conditions by developing recycled high-density polyethylene (HDPE)-modified bitumen. Through systematic laboratory investigation, we quantified the dose-dependent effects of HDPE (2–9% wt.) on rheological and mechanical properties. Dynamic shear rheometry revealed a 472% increase in rutting resistance (G*/sinδ = 6.48 kPa) at 6% HDPE versus unmodified bitumen (1.13 kPa), alongside an 18–32% reduction in phase angle (58–88 °C). Rotational viscosity surged by 240% at 135 °C (1170 cP vs. 344 cP). Mechanically, Marshall Stability peaked at 19,000 N (46% enhancement) with 6% HDPE, while flow values minimized at 2.3 mm (15% reduction). Complementary tests confirmed superior temperature susceptibility control: penetration decreased by 50% and softening point increased by 43% (72.3 °C) at 9% HDPE, with Penetration Index shifting from −0.4 to +2.18. SEM microstructural analysis validated optimal polymer dispersion at 6%, forming a continuous reinforcing network, whereas agglomeration at higher doses induced defects. Statistical modeling identified a robust linear relationship for Marshall Quotient (Adjusted R2 = 0.8383). The study establishes 6% HDPE as the optimal dosage, delivering synergistic high-temperature performance enhancement while utilizing recycled plastic. Future work should address long-term aging and field validation for sustainable pavement applications in tropical regions.