Recycled Waste Polypropylene in Asphalt Pavement: An Experimental Research of Adopting Two Modification Processes

Abstract

Incorporating waste materials in road construction will not only improve pavement performance but also significantly reduce road material cost and address the environmental challenges posed by hazardous waste disposal. This study explores the potential of using Recycled Waste Polypropylene (RWPP) as an asphalt modifier and an artificial aggregate to enhance the characteristics of the asphalt mixture. New recycling techniques are adopted in this work to produce RWPP with controlled dimensions. In addition, two modification processes were applied to prepare RWPP-modified mixtures: Wet Process (WP) and Semi-Wet Process (S-WP). The RWPP with a particle size of 0.075 mm was blended with base asphalt in WP at different ratios of 0.15%, 0.25%, and 0.35% by total mixture weight. Whereas, in S-WP, RWPP was used as a partial replacement of fine aggregate at three sizes of 2.36, 0.3, and 0.075 mm and dosages of 1%, 3% and 5% by the weight of the asphalt mixture. The asphalt tests, which included softening point, ductility, and penetration, were conducted to examine the tensile properties, consistency, and temperature sensitivity of base and RWPP-modified binders. Marshall and tensile strength tests were performed to evaluate the RWPP-modified mixtures' behaviour, and the storage stability test was performed to measure the segregation phase between RWPP and base binder. The outcome showed that the addition of RWPP significantly enhances the mechanical characteristics and resistance against moisture damage for the asphalt mixture. It is recommended to use 0.15% and 3% of RWPP for WP and S-WP, respectively, to achieve the optimal performance. Finally, S-WP is more effective than WP in terms of avoiding storage stability issues, incorporating large amounts of plastic in road pavement field, and reducing the carbon emissions and energy consumption during mixing and paving.