Effect of carbonation on eco-friendly binders for marine infrastructures

This research examines the effects of carbonation on various binders— CEM I (Ordinary Portland Cement), CEM III (a slag cement containing ground granulated blast furnace slag), and calcium sulfoaluminate (CSA) cement— focusing on their potential as sustainable materials for artificial reefs. Mechanical properties, leaching, and mineralogical changes were evaluated under accelerated carbonation and subsequent exposure to artificial seawater for 91 days. Results show that carbonation significantly reduces the surface pH of the binders, indicating alterations in chemical properties. X-ray Diffraction (XRD) analysis reveals that carbonation transforms Ca(OH)₂ by forming CaCO₃, enhancing material durability and reducing Ca(OH)₂ content. Compressive strength tests indicate that CEM III with 25 % recycled concrete fines achieved the highest strength of 69.9 MPa after carbonation, outperforming CEM I and CSA. Despite having the lowest compressive strength (42.5 MPa), carbonated CSA samples demonstrated the highest oyster settlement density (0.0408 oysters/cm²), likely due to the breakdown of ettringite during carbonation, forming carbonates, calcium sulfates, and alumina. Additionally, CEM I and CEM III exhibited significant calcium leaching over time, resulting in strength loss, which surface carbonation mitigated. The surface carbonation-induced pH reduction and calcium carbonate formation suggest a favorable environment for optimal oyster settlement. These findings highlight the potential of carbonated eco-friendly binders as sustainable solutions for artificial reefs, offering environmental and structural benefits. • Carbonation improves eco-friendly binders for marine infrastructures. • Calcium sulfoaluminate cements promote faster oyster settlement. • Carbonized binders enhance marine biodiversity in artificial reef construction. • Sustainable materials demonstrated superior mechanical and ecological performance. • Novel insights bridge material science and marine ecology for coastal management.