Evaluation of the use of automotive shredder residue plastics in concrete: physical, mechanical, and durability properties

The increasing generation of automotive shredder residue (ASR) from scrap vehicle recycling presents a significant environmental burden. Mixed plastics, a major heterogeneous ASR component, are difficult to recycle using conventional methods. This study evaluates the use of ASR plastics as a partial replacement for natural sand in concrete. ASR samples sourced from an Australian metal recycler were characterised, showing that rigid plastics constitute a significant fraction (13.8 wt%) suitable for sand substitution. Concrete mixes were prepared by replacing natural sand with ASR plastic aggregates at various volumetric percentages, and their physical, mechanical, and long-term durability properties were evaluated. The results showed that the reductions in all mechanical properties were significantly lower than those reported in previous mixed plastic studies. At a maximum replacement rate of 45%, the slump was 40 mm, and the fresh and dry densities were 2200 and 2019 kg/m³, respectively. Compared with control groups, the compressive strength (36.79 MPa), flexural strength (6.06 MPa), splitting tensile strength (4.64 MPa), and modulus of elasticity (27.64 GPa) were reduced by 35%, 25%, 24%, and 36%, respectively. Microstructural analysis identified fibrous features and glass fibre-reinforced composites within the ASR plastics, which may account for the relatively moderate declines in performance. Durability testing under one year of acid and sulphate exposure showed that ASR-modified concretes performed comparably or slightly better than controls. These findings demonstrate the potential of ASR plastics as a sustainable fine aggregate alternative, offering a viable upcycling route for plastic-rich waste streams in concrete production.