Seawater-based bio-cementation of natural sea sand via microbially induced carbonate precipitation

Seawater-based microbially induced carbonate precipitation (MICP) method is proposed to improve the physical and engineering properties of siliceous sea sand. A series of comparative MICP treatments and siliceous sand experiments using seawater-based cementation and freshwater-based cementation were conducted. The results revealed that the growth of Sporosarcina pasteurii was affected by seawater, whereas after incubation, the biomass and urease activity of S. pasteurii in the seawater environment were not much different from those in the freshwater environment. Although the dry density, carbonate content, ultrasonic velocity, and permeability of the sand columns treated using seawater-based cementation were lower than those of the sand columns treated using freshwater-based cementation, the unconfined compressive strengths of the former were higher than those of the latter when using the optimal concentration solution after four grouting batches. One reason for this is that the metal ions contained in the seawater played a role in transporting and fixing bacteria during the MICP process, resulting in a more uniform distribution of carbonates in the sand columns. Another reason could be that the calcite and magnesium carbonate generated in the seawater samples had a better material strength compared with the calcite generated in the freshwater samples. In addition, the failure patterns and computed tomography analysis of the sand columns indicated that the distribution of the carbonates was more homogeneous in the seawater columns than in the freshwater columns. This new exploration indicates that the MICP technique has a high potential for use in construction projects in seawater environments.