Evaluation of MICP treatment through EC and pH tests in urea hydrolysis process

Abstract

Microbially induced calcite precipitation (MICP) using ureolytic bacteria has been investigated to improve the engineering properties of soil. Urease, produced by ureolytic bacteria, can hydrolyse urea to drive the biogeochemical reaction in MICP. The goal of this study was to use changes in electrical conductivity (EC) and pH values from the urea hydrolysis test as an indicator to monitor the ureolytic activities of bacteria before the MICP process and using this indicator to maintain a consistent MICP treatment. Laboratory experiments were conducted to establish the relationship between the EC and pH values and unconfined compression strength (UCS) of MICP-treated soil. The EC and pH values of the mixed solution were measured after adding bacterial suspension into urea solution. Then, the bacterial suspension was mixed with a sand sample and cementation medium to drive the MICP process. The results showed that, once the bacterial suspension was mixed with urea, the EC and pH values of the mixed solution increased immediately due to urea hydrolysis. The optimum EC and pH values at 60 min were found to be 1·50–1·80 mS/cm and 8·82–9·02, respectively, to achieve consistent UCS performance of MICP-treated specimens with 0·25 M calcium (Ca) cementation medium.