Effect of Salt Water on the Process of Microbially Induced Carbonate Precipitation

Abstract

Microbially induced carbonate precipitation (MICP) is a bio-cementation process using microbes to hydrolyze urea and form carbonate-based minerals with the presence of Ca ion. This reaction produces bonding among soil grains and improves stiffness and strength of soils. The MICP implementation in offshore construction would gain a significant benefit from use of sea water owing to its abundance. However, the effect of various chemical constituents in sea water, such as Na+, Cl-, Ca2+, and Mg2+, on the MICP process remains poorly understood. This study investigates the effect of artificial salt water on the MICP process through batch tests, soil column tests, and microscopic analyses. The batch tests revealed that the level of urea hydrolysis with the salt water was higher than that with the deionized water. We also confirmed that the MICP-treated sand with salt water showed the greater improvements in small-strain shear modulus and unconfined compressive strength than the one treated with deionized water. Microscopic imaging showed that use of salt water results in different morphology of precipitated minerals though most precipitates still consisted of CaCO3. The experimental results provide clear evidence that various cations in salt water facilitates MICP treatment of soils, and the MICP can be effectively implemented using salt water.