The effect of waste plastic on the high-temperature performance of bitumen for pavement applications

This study investigates the feasibility of utilizing mixed industrial waste plastic (W.P.) from packaging and sealing industries as a sustainable modifier for bitumen binders. Fourier transform infrared (FTIR) spectroscopy confirmed that the waste plastic is composed of high-density polyethylene (HDPE). Bitumen was modified with 3, 5, 7, and 10 wt% W.P., and the effects of the modifier on the physical, rheological, and thermal properties of the binder were comprehensively evaluated. The incorporation of W.P. significantly enhanced the binder performance by reducing penetration by 20–54%, increasing the softening point from 49 °C for the base bitumen to 85 °C at 10 wt% W.P., and increasing the kinematic viscosity at 135 °C by up to 47.6%, indicating improved stiffness and reduced temperature susceptibility. Dynamic mechanical analysis (DMA) showed that the modified binders exhibited a higher complex modulus and lower phase angle than the base binder, reflecting improved stiffness and a greater elastic contribution to the rheological response. Furthermore, the Superpave rutting factor (G*/sin δ) after short-term aging increased substantially, with the critical temperature rising from 58 °C for the base binder to 76–78 °C for the 5 and 7 wt% formulations and to 98–100 °C for the 10 wt% formulation, demonstrating markedly improved resistance to permanent deformation. Thermogravimetric analysis (TGA) revealed enhanced thermal stability for the modified binders, particularly at 7 wt% W.P., while differential scanning calorimetry (DSC) confirmed effective thermomechanical interaction between the HDPE-rich waste plastic and the bitumen matrix. Considering the combined physical, rheological, and thermal performance, the binder containing 7 wt% W.P. provided the optimum balance of stiffness, elasticity, rutting resistance, and thermal stability, highlighting its potential as a sustainable and high-performance bitumen modifier.