Durability of PA-assisted MICP-reinforced sand in marine environment

Coastal erosion leads to land loss and can drastically alter coastlines over time. Microbially induced calcite precipitation (MICP) technology offers an eco-friendly reinforcement method by leveraging microbial metabolism to precipitate calcium carbonate, thereby improving soil resistance to coastal erosion. However, prolonged exposure to the marine environment may degrade the reinforcement. This study introduces polycarboxylic acid (PA) as an additive and investigates its impact on the durability of MICP-reinforced sand. A series of samples with varying PA concentrations was prepared and subjected to in situ marine exposure tests to evaluate variations in strength, mass, and calcium carbonate content (CCC). Results indicate that the addition of 10% PA significantly improves the compressive strength and durability of the sand samples. After 21 d of seawater immersion, the strength and CCC of the group with 10% PA remained at 74.24% of the pre-exposure strength. Secondary reinforcement tests further demonstrated that samples subjected to erosion recovered strength effectively after re-treatment, with a maximum recovery exceeding the initial strength after exposure by 4807 kPa. PA not only increases the total amount of calcium carbonate but also improves its distribution uniformity within the sand, thereby reducing localized abrasion. Overall, the use of PA shows strong potential for enhancing the durability of MICP-reinforced sand, while secondary reinforcement provides an effective means to extend the service life of engineering applications.