Compatibility-driven application of waste polypropylene in asphalt pavements: mechanistic insights and evaluation of VOC emissions and microplastic release

Waste polypropylene (WP) has the potential to enhance the performance of asphalt pavements. However, poor compatibility between WP and asphalt remains a major barrier to its large-scale application. This study examines the potential applications of WP in asphalt pavements from the perspective of compatibility, including performance evaluation, mechanisms of action, VOC emissions and microplastic(MP) release. Initially, the compatibility of WP with four representative asphalt types was analysed based on differences in solubility parameters, offering a comprehensive mechanistic analysis incorporating non-bonded energy, molecular conformational dynamics and spatial distribution characteristics. In this study, A-4 demonstrated the highest compatibility and performance. The results highlight the effect of asphalt composition (saturates) on the compatibility and performance. The molecular dynamics (MD) simulation results were validated using Cole–Cole plots and rheological experiments. Subsequently, emissions of VOCs and the MPs from WP-modified asphalt (WPMA) were evaluated. The WPMA prepared using A-4 exhibited the lowest emissions, with VOCs emissions and MPs release suppression reaching 9.4% and 49.7%, respectively. Finally, Pearson correlation analysis confirmed that enhanced compatibility is positively associated with improved asphalt performance and reduced VOC emissions and MP release. This study offers theoretical guidance for the efficient and scalable use of WP in asphalt pavements.