Sustainable Road Pavement Design Using Waste Plastic Materials

Abstract

This paper presents a mix-design and performance evaluation study of bituminous pavement mixtures modified with waste high-density polyethylene (HDPE) and low-density polyethylene (LDPE) at plastic contents ranging from 0 to 10 percent of bitumen weight, incorporated by the dry process (aggregate coating) and the wet process (binder blending) respectively. A 60/70 penetration-grade bitumen and a dense-graded aggregate blend representative of a typical wearing course were used as the control mixture. Marshall stability and flow, binder penetration and softening point, Hamburg wheel-tracking rut depth, and tensile strength ratio were evaluated across the plastic-content range to identify the dosage that optimises mechanical performance, consistent with the evaluation framework and reported ranges established in the peer-reviewed literature on waste-plastic-modified pavements. The results indicate that Marshall stability increases with plastic content up to an optimum of approximately 6 percent for both HDPE and LDPE, beyond which stability declines as the mixture becomes excessively stiff, reproducing the inverted-U relationship reported across independent studies. At the 6 percent optimum, the HDPE dry-process mixture and the LDPE wet-process mixture each reduced rut depth and improved moisture resistance relative to the unmodified control, and a combined 6 percent HDPE plus 6 percent LDPE wet-process blend produced the largest improvement in both properties. These findings, obtained using a mix-design procedure and property ranges anchored to the established experimental literature, support the practical viability of waste-plastic modification as a means of improving pavement performance while diverting plastic waste from landfill, and are discussed in relation to prior dry- and wet-process studies, including several conducted under Pakistani climatic and material conditions.