Mechanical Characterization of a Composite Material Made from Recycled Plastic and Sand under Compression and Bending Loads

Abstract

This study is part of an initiative to valorize plastic waste for use in sustainable construction materials. Indeed, despite the growing interest in plastic-sand composites, a significant research gap remains regarding the optimization of plastic content to achieve a balance between mechanical performance and material durability. This study therefore hypothesizes that an optimal proportion of recycled plastic can improve interfacial adhesion and overall strength, while introducing an innovative approach for the formulation of eco-efficient composites for non-structural civil engineering applications. The main objective is to evaluate the compressive and flexural mechanical properties of a composite material made from recycled plastic and sand, to analyze the influence of the plastic content on these properties, and to identify an optimal formulation suitable for civil engineering applications. The methodology adopted is based on the production of three composite formulations containing 15%, 20%, and 25% recycled plastic by mass, respectively, combined with sand. Cylindrical and parallelepiped specimens were prepared and subjected to standardized mechanical tests using a Controlab hydraulic press. The tests performed included uniaxial compression and three-point bending, allowing the determination of the maximum stresses σC and σf, respectively. The results show that in compression, the strengths obtained are 10.76 MPa, 11.66 MPa, and 9.36 MPa. The strengths obtained in the flexural test are 5.35 MPa, 7.80 MPa, and 7.13 MPa. These different strengths represent the maximum compressive and flexural stresses of the composites containing 15%, 20%, and 25% recycled plastic by mass, respectively. The analysis highlights an optimal formulation with 20% recycled plastic, for which the material exhibits the best mechanical performance, thanks to improved interfacial cohesion and compactness. Beyond this threshold, a degradation of properties is observed, linked to an increase in porosity and a decrease in sand-sand contact. These results confirm the potential of plastic-sand composites as an alternative material for non-structural applications in civil engineering.