Homogeneity and mechanical behaviors of sands improved by a temperature-controlled one-phase MICP method

Microbially induced carbonate precipitation (MICP) has been actively investigated as a promising method to improve soil properties. A burning issue impeding its wide application is the severe spatial inhomogeneity of the CaCO3 distribution. Inspiring by the temperature sensitivity of the bacteria activity, a temperature-controlled one-phase MICP method is proposed consisting of two major steps: (1) grouting the specimen with the mixture of cementation and bacteria solutions in a low temperature; (2) inducing CaCO3 precipitation by exposing the specimen to room temperature. A series of experiments are conducted to demonstrate the advantages of the proposed method over the normal two-phase MICP method. Specimens treated with the proposed temperature-controlled method present higher CaCO3 contents with a roughly uniform distribution along the height of the specimen; the strength of those specimens are substantially improved with apparent dilatancy due to the effective bond network formed by the homogeneously distributed CaCO3 precipitation. SEM images indicate that the temperature-controlled method tends to form small crystals distributing uniformly on the grain surface, which may increase the roughness of the grain and the residual stress more effectively.