Magnesium ion corrosion in subsea tunnel grouting: Insights, mechanisms, and optimization strategies for enhanced durability

In the construction of subsea tunnels, grouting reinforcement is crucial for enhancing tunnel strength, impermeability, and stability. This article investigates the impact of prolonged exposure to seawater, specifically magnesium ion corrosion, on the degradation of the C-S-H gel and the weakening of grouting compounds. Utilizing erosion acceleration theory, an experimental setup simulating seawater flow is designed to explore erosion patterns and mechanisms. Macroscopic and microscopic experiments and analyses reveal that magnesium ion corrosion products, Mg(OH)2 and M-S-H, lack cementation ability, leading to detachment from the grouting compound. This detachment results in increased porosity, crack formation, and reduced strength and impermeability. The study recommends reducing the water–cement ratio and increasing grouting pressure to enhance composite strength and impermeability, with attention to boundary effects and prevention of magnesium ion corrosion product shedding. These findings have significant implications for optimizing subsea tunnel construction by improving grouting reinforcement design and ensuring long-term durability.