Transforming waste into value: Advancing sustainable construction materials with treated plastic waste and foundry sand in lightweight foamed concrete for a greener future

Abstract This study presents a significant advancement in the development of sustainable construction materials by utilizing treated plastic waste and foundry sand to produce lightweight foam concretes and investigates the performance of lightweight foamed concrete premixed with a new composite of plastic waste pre-treated with polyester polymer and covered with waste foundry sand as a sand replacement material with different dosages of 10, 20, 30, 40, and 50 by weight of sand. The mechanical properties, including compressive, tensile, and flexural strengths, were evaluated at ages of 7, 14, 28, 56, and 180, in addition to their fresh properties. Durability aspects such as porosity, shrinkage, and water absorption ensure long-term resilience. The thermal properties, including conductivity and diffusivity, were examined to enhance the energy efficiency, and microstructural analyses were conducted. The results showed a significant increase in initial and final setting times by 6.3 and 30%, respectively, with a 6.4% improvement in workability with 20% sand replacement. Compared to the reference mix, the dry density decreased by 9.4%, and the compressive increased by 76.1, 70.4, 84.2, 84.4, and 83% at 7, 14, 28, 56, and 180 days, respectively. Moreover, splitting strength increased by 99%, and flexural strength increased by 84.7, 91.3, 115, 111.9, and 110.9% compared to the reference mix at 7, 14, 28, 56, and 180 days, respectively. The dry shrinkage decreased by 56.48% after 28 days for all replacement ratios. Notably, replacing sand with 50% waste plastic reduced thermal conductivity to 0.28 W·m −1 ·K −1 and decreased specific heat capacity by 18.7%. Scanning electron microscopic analysis revealed a dense microstructure with smaller voids. These findings demonstrate that incorporating treated plastic waste and foundry sand as sand replacements in lightweight foamed concrete significantly enhances the mechanical strength, durability, and thermal efficiency, making it a promising material for sustainable and energy-efficient construction in the future.