Next-Generation Australian Roads: Characterizing Waste Plastic as a Sustainable Bitumen Modifier

As the demand for resilient transport infrastructure grows alongside rising environmental concerns, integrating recycled materials into pavement engineering has become a critical priority. Australia generates vast quantities of plastic waste, presenting both an environmental challenge and a unique opportunity to advance circular economy principles in civil infrastructure. This study evaluates the viability of post-consumer waste plastic as a sustainable bitumen modifier for Australian roads.

A targeted laboratory testing program was conducted to characterize waste plastic-modified bitumen. Physical evaluations—specifically Penetration and Softening Point tests—determined baseline consistency, temperature susceptibility, and modifier dosage. Flow behavior was evaluated using Brookfield Viscometer testing, while short-term oxidative aging was simulated using the Rolling Thin Film Oven Test (RTFOT) to analyze binder degradation during production and placement. Viscosity–temperature analysis revealed exponential viscosity growth beyond ~6% low-density polyethylene (LDPE) or ~4% high-density polyethylene (HDPE), establishing these as practical upper limits for workability under standard Hot Mix Asphalt (HMA) production (< 180 °C). Equivalent mixing and compaction temperatures increased by 10–25 °C relative to neat binders, highlighting constructability constraints for highly modified systems. Overall, incorporating waste plastic increased binder stiffness and elevated-temperature stability, indicated by reduced penetration values and higher softening points. Post-RTFOT analysis confirmed improved short-term aging resistance, provided dosage controls are maintained to prevent excessive embrittlement. Ultimately, this research defines clear performance bounds and constructability limits for plastic-modified binders. These empirical metrics support the safe, scalable adoption of waste plastics, advancing the transition toward longer-lasting, circular, and climate-resilient Australian road infrastructure.