Sustainable Fire-Resistant Materials: Thermal, Physical, Mechanical, and Environmental Behavior of Walls with Waste from the Aquaculture Industry

The aquaculture industry generates large amounts of shell waste, with limited recycling options at the industrial scale. This study explores the feasibility of substituting 20% of gypsum with seashell waste to produce sustainable, fire-resistant panels for non-load-bearing walls on a semi-industrial scale (2.4 × 2.2 × 0.1 m). The new composite exhibits high density (≈1500 kg/m³) and mechanical performance comparable to commercial gypsum. Thermal and fire tests confirmed its excellent insulation and stability: after 4 h of standard fire exposure, the non-exposed surface temperature remained below 80 °C, meeting European fire-resistance criteria. The incorporation of shell waste slightly reduced density and thermal conductivity (0.23 W/mK at 500 °C) without affecting strength or surface hardness. Environmental characterization revealed leaching and radionuclide levels well below regulatory limits, confirming its safety for building use. Overall, this work demonstrates, for the first time at a semi-industrial scale, the technical and environmental feasibility of reusing seashell waste as a gypsum substitute for fireproof materials. The proposed approach advances circular-economy strategies for aquaculture residues, providing an innovative pathway toward sustainable and low-impact construction products.