Residue from the waste: Post-industrial recycled plastic as an alternative coarse aggregate in lightweight concrete

The rapid increase in plastic consumption has resulted in serious environmental and human health concerns, driving the need for sustainable waste management strategies for this material. While plastic waste is conventionally classified into post-consumer and post-industrial streams, this study addresses a critical research gap by focusing on post-industrial plastic waste, which represents a significantly underexploited resource despite its high generation rate and superior material consistency compared to post-consumer alternatives. This research establishes the feasibility of developing lightweight concrete (LWC) incorporating post-industrial waste plastic lumps as a coarse aggregate replacement, thereby creating a novel pathway for industrial waste valorization. Five mixes were designed with recycled plastic aggregate (RPA) replacement levels ranging from 0% to 100% (at 25% intervals) to identify the optimum replacement ratio. A comprehensive performance evaluation framework was employed, encompassing equilibrium and oven-dry density measurements, compressive and splitting tensile strength tests, ultrasonic pulse velocity (UPV) assessment, stress-strain behavior, modulus of elasticity, and Poisson’s ratio. The results indicate that increasing RPA content led to a progressive reduction in concrete density, with mixes containing 50% RPA and above classified as LWC. Critically, although mechanical strengths decreased with higher RPA incorporation, the mix with 50% RPA satisfied the strength requirements for structural LWC in accordance with ACI PRC-213–14(23). Furthermore, RPA50 exhibited favorable UPV values, ductile stress-strain behavior, and balanced elastic properties, indicating adequate internal quality and structural integrity for load-bearing applications. This study makes a significant contribution by demonstrating that post-industrial plastic waste can be effectively utilized as a partial coarse aggregate replacement in structural LWC, with 50% RPA identified as the optimal replacement level. This work advances the circular economy agenda in construction by establishing a scalable waste-to-resource pathway that simultaneously addresses plastic waste accumulation, reduces virgin aggregate extraction, and delivers environmental benefits through lightweight structural solutions for sustainable construction.