Waste Plastic in Asphalt Mixtures via the Dry Method: A Bibliometric Analysis

Although waste plastic (WP) application as a paving material has drawn increasing attention from scholars, there is a lack of studies that summarize the latest development of WP research. Considering there is no standard procedure to incorporate WPs in asphalt mixtures, it is important to document the major findings from the available literature to identify knowledge gaps to tackle in future research and advance knowledge on this subject. Using a bibliometric analysis method, this study carries out a holistic review of WP articles published from 2003 to 2023, focusing on incorporating WP in asphalt mixtures via the dry method. This study particularly focused on identifying and evaluating individual types of WP mostly used in asphalt mixtures via the dry method and how their most common characteristics (size, shape, and melting point) affect the mixing procedure and the overall mixture's performance. The analysis highlighted China, the USA, and India as leading countries in WP-related publications. Typically, low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polyethylene terephthalate (PET) were the most utilized WPs in the dry method. Smaller WP particle sizes (<2.36 mm) were considered more suitable in asphalt mixtures. In general, studies employing procedures involving WP melting, typically by introducing WP to pre-heated aggregates at temperatures surpassing its melting point, resulted in improved asphalt mixtures with enhanced resistance to rutting, cracking, and moisture damage. In this context, positive performance outcomes were notably observed in studies using HDPE or LDPE, potentially because of their low melting point. The key knowledge gaps identified were the lack of a consistent procedure applicable across studies, a feasibility assessment for scaling laboratory-based procedures to field applications, and laboratory evaluations utilizing advanced performance tests as suggested in the Balance Mix Design (BMD) approaches.