Enhancing Bituminous Mix Performance Using Waste Plastics: Experimental Insights and Sustainability Considerations

Abstract

The dual challenge of managing the rising volume of plastic waste and improving the long-term performance of road pavements has become an important focus of research in sustainable infrastructure. Plastics, due to their non-biodegradable nature and extensive use across industries, contribute significantly to global environmental pollution, while flexible pavements are constantly exposed to increasing traffic loads, moisture damage, and climatic variations. These parallel issues create an opportunity to recycle waste plastics effectively by incorporating them into asphalt mixes, thereby addressing both waste management and pavement durability concerns.

This study evaluates the suitability of six categories of post-consumer thermoplastics—polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS)—for improving the performance of bituminous concrete. Each plastic type was introduced into a dense-graded bituminous mix at dosages of 5%, 7.5%, and 10% by weight of binder. A series of standard bituminous tests were conducted to assess their impact, including ductility, penetration, softening point, Marshall stability, and Marshall flow. Together, these properties provide a comprehensive view of the strength, stiffness, temperature susceptibility, and deformation resistance of the modified mixes.

The findings reveal that the inclusion of plastics generally enhances the high-temperature resistance and load-bearing capacity of the mixes, reflected by improvements in both softening point and Marshall stability. However, the effect on flexibility-related properties such as ductility and flow was observed to vary significantly with the type and proportion of plastic. HDPE at 10% and PP at around 7.5% produced the most balanced results, offering increased stability without severe compromise in ductility. PS at 10% dosage yielded the highest stability among all mixes, though it was accompanied by a moderate reduction in ductility. On the other hand, LDPE and PVC, while increasing stiffness, caused substantial decreases in ductility at the tested dosages, suggesting limited suitability under field conditions where flexibility is critical. PET demonstrated intermediate behaviour, with moderate improvements across most properties.

Overall, the study provides clear insights into the property interactions of commonly available waste plastics when blended with bitumen. By mapping the performance trade-offs across different plastic types and dosages, the research contributes practical guidance for selecting materials that achieve both engineering benefits and environmental sustainability. The outcomes reinforce the potential of plastic-modified bituminous pavements as a dual solution to waste recycling and infrastructure performance enhancement.