Eco-Construction from the sea: assessment of mollusk shells by-products as sustainable building materials

This paper describes the development of novel bio-composite mortars made by reusing waste from the fish canning industry, namely mussel, clam, and oyster shells, as recycled aggregates to achieve a complete (100%) replacement of conventional sand. For each shell type, different granulometric fractions (0.00–1.00 mm, 1.00–2.00 mm, 2.00–4.00 mm, and a calibrated 0.00–4.00 mm blend) were investigated. Several waste-based cement mixes were tested and compared with conventional OPC mortar. Chemical-physical properties and the functional and engineering performance of the new bio-composite mortars were evaluated to explore their potential for construction applications. Main results indicated a strong dependence of mortar performance on both shell type and particle size distribution. In particular, oyster- and clam-shell mortars significantly improved the mechanical properties, achieving increases of up to 120% in flexural strength and 60% in compressive strength compared with the reference mortar, whereas mussel-shell formulations generally exhibited lower mechanical performance; opposite behaviours were observed for the mussel shell. Nevertheless, developed mixes were analysed in light of EN 998-1 and EN 998-2, for plastering and masonry application respectively, demonstrating potentials for uses in construction, including ordinary and lightweight structures and plasters. In addition, with an average 30% reduction in bulk density and a 40% increase in energy behaviour, the bio-composite mortars resulted particularly suitable for improved energy-saving applications. Finally, accelerated aging tests based on salt (4% NaCl) crystallization and exposure to high thermal loads (up to 800 °C), permitted to simulate exposure to prolonged stress and preliminary investigate the evolution of degradation phenomena, suggesting long life span. In conclusion, the use of sole bio-waste aggregate offers a sustainable alternative to conventional landfill disposal of the waste and makes these mortars promising candidates for Minimum Environmental Criteria certification, in line with the European Green Deal and Circular Economy principles.