Impact of Sand Particle Size on the Mechanical and Thermal Properties of Sand/PET Composites

Abstract

ABSTRACT Plastic waste continues to pose serious environmental challenges in developing countries, where recycling systems are often weak or non‐existent. Transforming waste plastics into construction materials offers a sustainable alternative, both reducing pollution and providing low‐cost building solutions. In this study, recycled polyethylene terephthalate (PET) was blended with river sand of different particle sizes to produce sand/PET composites for potential use in roofing and wall cladding. The composites were prepared by melting shredded PET and mixing it with pre‐sieved sand in a fixed 50:50 weight ratio before molding and testing. Three sand particle size ranges—coarse, medium, and fine—were examined. The results demonstrate that sand particle size has a decisive impact on both the mechanical and thermal behavior of the composites. Coarse and fine sand composites achieved higher compressive strengths (7.17 MPa and 7.19 MPa, respectively) compared to 4.64 MPa for medium sand. Fine sand composites also displayed the best flexural strength (2.98 MPa) and superior insulation properties, with a thermal conductivity of 0.164 W/m·K. In contrast, coarse sand composites exhibited the lowest thermal conductivity (0.072 W/m·K), making them attractive for lightweight applications. Variations in density, thermal effusivity, and volumetric heat capacity across the particle sizes further highlight how gradation governs composite performance. Overall, the study shows that optimizing sand particle size is critical for achieving balanced strength, durability, and insulation in sand/PET composites. These findings not only underline the potential of particle‐size engineering in composite design but also demonstrate a practical pathway for reusing waste plastics in sustainable, low‐cost construction, particularly in regions like Cameroon, where plastic pollution and affordable housing remain pressing concerns.