Workability and Microstructure Properties of Calcium Bentonite Slurry with Polyanionic Celluloses Mixed in High-Salinity Seawater

The seawater preparing slurries in this region of freshwater shortage has excellent environmental benefits. Slurries of calcium bentonite (CaB) in seawater have low viscosities, high filtrate losses, and poor stabilities, so they cannot maintain the stability of the stratum during the excavation of a cutoff wall trench. The salinity of the seawater along the Persian Gulf coast is 4.08%, and the preparation of bentonite slurries using the high-salinity seawater is more challenging. In this study, three cellulose modifiers, including polyanionic cellulose (PAC), sodium carboxy methyl cellulose (CMC), and hydroxy propyl mehyl cellulose (HPMC), were used to improve the workability of CaB high-salinity seawater slurries. A series of slurry workability tests were conducted, including the Marsh viscosities and filtrate losses. Among the three celluloses, PAC has the best modification effect. With the CaB content of 12% and PAC dosage of 0.20%, the filtrate losses and the Marsh viscosities of the seawater slurry are 18.0 mL and 36.1 s, respectively, which meets the requirements of the DL/T 5199-2019 standard for a cutoff wall trench. Further analyses, including optical microscopy (OM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), were conducted to investigate the microstructure and molecular structure of filter cakes formed by different slurries. The results revealed that PAC (polyanionic cellulose) is tightly bound to CaB (calcium bentonite) through cationic bridging and hydrogen bonding, leading to enhanced modification of the slurry properties. This study provides both theoretical insights and experimental evidence for the preparation of high-salinity seawater slurries, offering valuable guidance for applications in ocean geotechnical engineering.