Environmental benefits of reusing coastal expanded polystyrene waste as sand substitution in cement mortar

Waste Expanded PolyStyrene (EPS), accumulated in marine and coastal environments, poses a persistent environmental challenge due to its low density, high volume, and limited conventional recycling options. This investigation evaluates an integrated system for collecting, processing, and valorising waste EPS as an alternative fine aggregate in cement mortars, without chemical or thermal pre-treatment. The economic assessment shows that EPS processing is technologically mature and cost-efficient, with a manufacturing cost of 0.37 €/kg. Overall system costs are mainly driven by collection and transportation from natural environments. Life Cycle Assessment (EF 3.1) indicates a total climate change impact of 0.161 kg CO₂-eq per kg of processed EPS, with transportation and mechanical processing as the main contributors. The technical performance of EPS-based mortars demonstrates that incorporating waste EPS leads to a substantial reduction in density, improved thermal performance with thermal conductivity values as low as approximately 0.70 W/m·K, and compressive strength values of approximate 20 to 21 MPa at higher replacement levels. These properties meet RILEM Class II and III requirements for structural-insulating and lightweight insulating mortars. The results indicate that waste EPS can be transformed from an environmental burden into a functional construction material. While EPS processing is economically and technically viable, recovering EPS from marine and coastal environments requires institutional support, underscoring the need to integrate waste management, environmental protection, and construction material valorisation within a unified sustainability framework.