Influence of Internal and External Seawater on Properties of Cement-Stabilized Marine Clay Slurry

Cement stabilization enhances the undesirable properties of dredged marine clay slurry, converting this waste material into suitable fill for land reclamation. However, seawater may be present both internally during mixing and externally during service life of cement-stabilized slurry, which would affect cement hydration and, subsequently, the engineering properties. Therefore, this work intended to elucidate the internal and external seawater effects on cement-stabilized marine clay slurry. Cement-stabilized clay slurries were prepared using deionized water and seawater, and then the hardened specimens were exposed to different curing conditions, including deionized water immersion, seawater immersion, and an airtight environment. Results show that internal seawater posed minor effect on the 28-day strength but reduced the strength of cement-stabilized specimens by 6%–30% at 180 days. For comparison, specimens subjected to external seawater effect achieved a 28-day strength 22%–41% higher than those cured in bags or distilled water but lowered the strength by 7%–33% at 180 days, and visual physical deterioration was only observed on specimens exposed to external seawater. In addition, specimens mixed with and cured in seawater showed the highest strength reduction, indicating the synergy effect of internal and external seawater attack. Microstructure analysis revealed that seawater exposure led to the formation of Friedel’s salt and ettringite in cement-stabilized specimens, contributing to their relatively higher porosity. Moreover, magnesium ions in seawater promoted portlandite dissolution and converted calcium silicate hydrate to magnesium silicate hydrate with low binding capacity, which was primarily responsible for the surface softening and strength reduction. The findings advance a comprehensive understanding of synergy seawater effects on cement-stabilized clay for application in marine environments.