Upcycling of low-density polyethylene and multilayer plastic waste into sand-plastic paving blocks: Material characterization and mechanical properties

This study investigates the upcycling of low-density polyethylene (LDPE) plastic bags and multilayer plastic (MLP) wastes into sand-plastic paving blocks and evaluates the influence of plastic type and plastic-sand ratio on their physicochemical and mechanical properties Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (DSC/TG/DTG) showed that LDPE behaves as a single-polymer system with higher crystallinity, distinct melting behaviour, and greater thermal stability, whereas MLP exhibits multiple polymer phases and inorganic residues that reduce melt compatibility. Paving blocks were produced at plastic-sand ratios ranging from 100:0 to 40:60 and characterized for density, porosity, water absorption, and compressive strength. LDPE composites achieved the best performance at a 60:40 ratio, reaching a compressive strength of 25.7 MPa with water absorption below 0.4%. MLP-based blocks showed higher porosity and lower compressive strength, with a maximum value of 18.4 MPa, attributed to immiscible polymer layers and metallic impurities. Nevertheless, all samples exhibited excellent water resistance, with water absorption below 1%, outperforming conventional cement-based paving materials. These findings demonstrate that both mono-material and complex plastic wastes can be effectively upcycled into durable paving products, providing a sustainable waste valorization route that links physicochemical characteristics to engineering performance for the minimization and utilization of difficult-to-recycle plastic waste.