Circular Gypsum-Based Composites Incorporating Recycled PET from Bottle Preforms: Mechanical, Thermal and Environmental Performance

The growing volume of plastic waste is one of the major environmental problems of this century. Among the plastics discarded each year, polyethylene terephthalate (PET) waste accounts for a significant proportion, making it increasingly urgent to establish new methods for its recovery and recycling. This study addresses the manufacture and characterisation of new gypsum composites incorporating PET waste from bottle preforms. Specifically, different series were produced by partially replacing the original gypsum with rPET at 7.5%, 15.0%, and 22.5% by volume. The resulting composites were then subjected to mechanical, thermal and environmental characterisation. All the materials analysed exceeded the minimum mechanical strength values set by the regulations, achieving flexural and compressive strengths of over 2 MPa and 8 MPa, respectively. Furthermore, thermal conductivity was reduced by up to 10%, resulting in a thermal resistance of 0.77 (m2·K)/W when employed as prefabricated blocks for interior partition walls in residential buildings. Furthermore, the environmental impact analysis, covering the cradle-to-site life cycle, showed a reduction in impact across all assessed categories, including up to 22% in CO2 eq. emissions. These results support the suitability of using plastic waste in the manufacture of gypsum-based prefabricated elements and demonstrate that this alternative constitutes a technically and environmentally viable solution.