Waste-to-Construction Material Pathways: Recycling-Based Development and Characterization of PET–Foundry Sand Eco-Bricks

The increasing accumulation of plastic and industrial waste presents a major challenge for global recycling systems and sustainable resource management. In particular, post-consumer Polyethylene Terephthalate (PET) and industrial foundry sand (FS) are often underutilized due to limitations in conventional recycling pathways, resulting in significant material loss and environmental burden. This study proposes a recycling-oriented material valorization strategy by transforming PET and FS waste streams into high-performance Eco-Bricks for sustainable construction applications within a circular economy framework. Five composite formulations (100-P, 75-P, 50-P, 25-P, and 100-FS) were developed using compression molding, incorporating 5% Ordinary Portland Cement as a binder to enhance interfacial compatibility. The materials were systematically evaluated using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and mechanical testing to assess structural integrity, thermal behavior, and performance characteristics relevant to recycling-based applications. Results indicate that the 75-P composition exhibits optimal performance, achieving a flexural strength of 3.5 MPa, surpassing conventional construction benchmarks while maintaining enhanced ductility. FTIR analysis confirmed the preservation of PET’s chemical structure, demonstrating that the recycling process does not induce significant degradation. The incorporation of foundry sand improved mechanical stability while enabling the effective utilization of industrial byproducts. From a circular economy perspective, the developed Eco-Bricks enable the diversion of up to 85% of plastic waste and 90% of foundry sand from landfills. Lifecycle considerations indicate a reduction of approximately 60% in carbon emissions compared to traditional brick manufacturing, primarily due to the elimination of high-temperature processing. This study demonstrates a scalable waste-to-material pathway that integrates recycling, material engineering, and construction applications. The findings highlight the potential of combining polymer and industrial waste streams to develop value-added products, supporting sustainable material cycles, reducing environmental impact, and advancing circular construction practices.