Influence of using waste plastic as coarse aggregates-based sustainable concrete

This study investigates the feasibility of utilising shredded waste plastics as a controlled alternative for coarse aggregate in structural concrete. In most previous studies, the use of waste plastics was limited to non-load-bearing or lean concrete due to concerns regarding their compressive strength. However, this study proposes using shredded waste plastics in conventional structural concrete. Crushed plastic granules were incorporated at varying substitution rates (0%–20% by volume content) into a standard concrete mix of 25 MPa grade. The experimental investigation consisted of 20 cubes, 10 cylindrical specimens, 5 beams, and four mixes with different % of shredded plastic waste: 5%, 10%, 15%, and 20% replacement of coarse aggregate by weight, as well as a control mix. A comprehensive suite of mechanical and microstructural evaluations was conducted for all specimens. The findings show that workability decreases as the plastic material content increases. Compressive, split tensile, and flexural strengths increased slightly up to 5% and slightly reduced beyond 5% replacement level. Specifically, concrete beams with waste plastic aggregates exhibited higher ductile failure performance. A scanning electron microscopic study revealed that shredded plastics improved the reduction of microcracks, at the expense of the concrete’s density and weight. This study is vital for determining how to utilise shredded plastic waste as a partial replacement for coarse aggregate in structural concrete applications.