Development and optimisation of sustainable recycled PET–sand composites for construction applications

Abstract The construction industry faces urgent sustainability challenges, with conventional materials such as cement, bricks, and concrete contributing significantly to CO 2 emissions. This study addresses these issues by developing polyethylene terephthalate (PET)-sand composites that use recycled PET as a binder rather than as an aggregate, thereby increasing plastic waste utilisation while eliminating cement. Composites were produced by blending PET with sand of varying particle sizes and ratios under controlled temperatures, systematically optimised using a Taguchi L25 design. Unlike previous studies that examined one variable at a time, this work introduces a comprehensive multi-parameter optimisation approach, simultaneously considering the effect of PET content, sand particle size, and processing temperature to achieve superior performance. Mechanical (compressive, flexural, tensile strengths) and physical (density, water absorption) properties were evaluated, and predictive models were established. Results showed that composite performance was strongly governed by the combined effects of processing parameters: smaller sand particles and higher PET content improved strength and durability, while processing temperature exhibited a threshold effect. The optimised composite achieved compressive strength of 39.9 MPa, flexural strength of 12.3 MPa, tensile strength of 1.0 MPa, density of 1735 kg/m 3 , and water absorption of 0.4%, comparable to or exceeding conventional masonry units. These findings demonstrate the potential suitability of PET–sand composites as sustainable masonry materials, contributing to plastic waste valorisation and advancing circular economy goals. Moreover, by transforming plastic waste into durable construction products, this research supports responsible consumption and production, promotes climate action through emission reduction, and helps protect aquatic ecosystems from plastic pollution, thereby aligning with global sustainability objectives.