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.

This study aims to systematically synthesize and critically evaluate the characteristics of electric arc furnace slag (EAFS) and ladle furnace slag (LFS) when applied as an alternative paving material. A systematic literature review was conducted following the PRISMA methodology, with research published between 2000 and 2024. Three major databases were searched, considering only Q1–Q2 and English articles. After independent, blinded screening by two reviewers, a total of 177 papers met the selection criteria. The results were qualitatively synthesized through bibliometric analysis, slag characteristics, and application type. Results show that asphalt concrete (AC) is the most common application of EAFS, representing 61% of studies, with many studies exploring 100% substitution of natural aggregates. Overall, EAFS and LFS demonstrate favorable mechanical properties, including high toughness, hardness, and adequate soundness, largely attributed to their iron-rich composition, supporting their use in base layers, AC, and Portland cement concrete (PCC). However, significant chemical and mineralogical variability influences swelling potential and reactivity, highlighting the need for case-specific characterization. While swelling concerns limit its use as an unbound base material, these issues are reduced when EAFS and LFS are used as a soil binder or encapsulated within AC or PCC matrices. Environmental assessments show that most EAFS and LFS samples meet the regulatory thresholds for their respective local leaching limits, though behavior varies with steel type (low-alloy vs. stainless), particle size and pH. Significant gaps remain in long-term performance and testing standards. This review proposes guidelines for selecting appropriate tests according to the intended pavement application, aiming to facilitate the safe and effective use of EAFS and LFS in road infrastructure.