Urease active bioslurry: a novel soil improvement approach based on microbially induced carbonate precipitation

This paper presents a novel approach for soil stabilization by microbially induced carbonate precipitation (MICP) using a new urease active catalyzer, named herein as “bioslurry”. The bioslurry, which was produced from the reaction between bacterial culture and 400 mmol/L of CaCl 2 and urea, is pre-formed urease active crystals consisting of CaCO 3 plus imbedded urease active bacterial cells. By mixing the bioslurry with sand, more than 95% of the bioslurry was retained in the soil matrix as a result of the mechanical trapping mechanism, leading to high resistance to flushing with a low-salinity solution. The retained urease activity of bioslurry was uniformly distributed along the sand matrix, resulting in a rather uniform CaCO 3 precipitation. Through repeated treatments with a cementation solution, the unconfined compressive strength of bioslurry treated sand was significantly improved due to the effective CaCO 3 precipitation at the contact points of soil grains. Scanning electron microscopy analysis carried out on the bioslurry treated sand revealed that the induced large rhombohedral CaCO 3 crystals were localized around the bioslurry spherical fine crystals. The overall outcome of this work is that soil biocementation using the new bioslurry approach is controllable, reproducible, and homogeneous.