Sustainable valorization of polyethylene and polystyrene wastes in lightweight mortars: performance optimization of...

The valorization of plastic waste is attracting increasing interest due to the scarcity of fossil resources and environmental concerns. In Algeria, 60 to 80% of plastic waste, primarily polystyrene from food packaging, is discarded into the environment, with its low profitability limiting its recycling. In this context, this study aims to propose a sustainable solution for the management and valorization of this waste through its integration into construction materials. It examines the co-valorization of polyethylene and polystyrene as partial substitutes for natural fine aggregates in mortars, using numerical optimization based on the response surface method. Formulations containing 0%, 10%, 20%, and 30% polymers were studied in terms of their physical and mechanical properties. The results show that incorporating plastic increases water absorption and porosity, while reducing fresh and dry densities, with more pronounced effects at high substitution rates, particularly for combined mixtures. Compressive and flexural strengths decrease with increasing plastic content, especially at 30%, but tend to stabilize after 28 days. Optimal performance is achieved with a formulation containing 20% polyethylene and 10% polystyrene. Furthermore, some optimized combinations achieve satisfactory mechanical performance, with coefficients of determination (R²) close to 1. This study is of direct interest to the fields of civil engineering and sustainable construction, particularly for the production of lightweight, non-structural, or insulating mortars. It contributes to reducing the environmental impact of plastic waste and preserving natural resources, while also offering potential applications in secondary building components and eco-friendly solutions. However, further adjustments to the formulations are still needed to ensure an optimal compromise between durability and mechanical performance.