Cement-free composite brick from waste foundry sand and mixed post-consumer thermoplastic waste for sustainable construction

The emergence of environmentally conscious construction practices aligned with circular economy principles has become increasingly important due to the accelerating depletion of natural resources. Therefore, this study aims to develop a value-added pathway for the reutilisation of waste plastic and foundry sand to create a cement-free perforated composite brick using waste foundry sand (WFS) and mixed post-consumer thermoplastic waste (PTW). The PTW comprised polyethylene terephthalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), and multilayer plastic (MLP). The WFS, with a fineness modulus of 2.13, was combined with PTW at a 50:50 mass ratio and processed through melt mixing and compression moulding. Ten composite-brick specimens were fabricated and evaluated for their physical and mechanical properties. The developed perforated composite bricks exhibited a water absorption of 1.11% and a mean compressive strength of 5.32 N/mm². Microstructural observations revealed the mechanical encapsulation of WFS particles within a continuous polymer matrix, while the dense packing of the silica-rich WFS contributed to the compact composite structure. This compact structure reduced interconnected voids, resulting in low water absorption. Overall, the developed PTW–WFS composite brick demonstrated good compressive strength and low water absorption, indicating its technical feasibility and potential as a sustainable, environmentally friendly, cement-free alternative for low-load construction applications.