Strength and Workability Characteristics of Concrete Using Recycled Plastic Waste for Sustainable Construction

The increasing amount of recycled plastic waste and the extensive use of construction materials both contribute significantly to CO 2 emissions, a major global concern. This study investigates the use of recycled plastic waste (PW) as a partial replacement for natural 4/10 mm coarse aggregates in concrete mix design, aiming to promote sustainable construction practices. Concrete mixes were prepared with varying levels of plastic replacement—0%, 15%, 30%, 45%, and 60% by volume—and evaluated for workability, compressive strength, tensile strength, water absorption, and microstructural properties. Results indicated that replacing aggregates with PW increased slump values, suggesting improved workability, particularly at 30–45% replacement. However, both compressive and tensile strengths exhibited a declining trend as the replacement level increased. The standard strength was maintained only at 15% replacement, achieving 35.3 MPa at 56 days compared to 37.3 MPa for the control mix. Durability tests showed reduced water absorption at low replacement levels but significant porosity and microcracking at higher percentages. Scanning Electron Microscopy (SEM) revealed weak interfacial transition zones (ITZs) between plastic waste and cement paste, with bonding weakening and micro voids increasing as replacement levels rose. A simplified life cycle assessment (LCA) suggests that while CO 2 emissions remain largely unchanged due to cement dominance, incorporating recycled plastic waste provides sustainability benefits through resource conservation and waste diversion rather than direct carbon reduction. These findings highlight that limited aggregate replacement with plastic waste can be practical, cost-efficient, and environmentally advantageous. This research underscores the potential of recycled plastics in sustainable construction, contributing to waste management and reducing reliance on natural aggregates.