Optimizing mechanical performance and water absorption behavior of silica-reinforced recycled thermoplastic composites for rooftile applications

This investigation was conducted to synthesize and characterize sustainable composite materials for construction applications—specifically roof tiles—by utilizing recycled thermoplastics (HDPE, PP, PET) reinforced with silica sand microparticles. This methodology offers the dual advantage of mitigating plastic-waste accumulation and providing a cost-effective alternative to conventional, resource-intensive construction materials. Employing a Taguchi L9 orthogonal array, the study systematically optimized the effects of thermoplastic type, filler weight fraction (30–50 wt.%), and particle size (150–450 µm) on mechanical performance and moisture-ingress resistance. Experimental analysis revealed that the composite comprising HDPE, 30 wt.% silica, and 150 µm particles (A1B1C1) exhibited superior energy-absorption capacity (impact strength: 5.83 J) and minimal water absorption (0.15%). Conversely, the most favorable mechanical integrity was achieved with the PET, 50 wt.% silica, and 300 µm particle configuration (A3B3C2), which maximized hardness (60.8 HRB), compressive strength (57.9 MPa), and flexural strength (49.56 MPa). Multi-response optimization via Grey Relational Analysis (GRA) confirmed that the A3B3C2 combination provided the most robust overall solution, yielding a maximum Grey Relational Grade of 0.833. Consequently, the successful fabrication of these optimized recycled thermoplastic composites demonstrates their strong potential for real-world use in roof-tile production, thereby supporting a more sustainable and resource-efficient construction industry.