The impact of multi-marine intertidal service on the durability of concrete repair materials

This study investigates the impact of different marine environments on the durability of four common repair materials, which were exposed to a one-year real sea service test at the intertidal zones of Zhoushan and Sanya. The methods employed to investigate the causes of durability degradation after exposure included Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and microscopy. After one year of exposure at Sanya (a tropical marine climate), the materials’ mechanical properties showed only a slight overall decline. In contrast, at Zhoushan (a subtropical marine climate), the properties of all four materials significantly declined due to factors such as large tidal range, high flow velocity, and high sediment concentration, with flexural strength being particularly affected. Although XRD analysis revealed the dissolution of struvite in the surface layer, magnesium phosphate cement (MPC) maintained the highest compressive strength and lowest chloride penetration depth. EDS detected the reaction between sulfoaluminate crystals and chloride ions in sulfoaluminate cement (SAC), which resulted in a high chloride penetration depth at Sanya. Epoxy mortar (EM) and acrylic-modified mortar (AMM), due to their low initial strength and high pore volume, showed significantly poorer performance after exposure at Zhoushan. This study provides a framework for evaluating the durability of repair materials in various marine environments, offering valuable insights for material selection under similar conditions.