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

Abstract

Microbial induced calcite precipitation (MICP) using ureolytic bacteria have been investigated to improve engineering properties of soil. Urease, produced by the ureolytic bacteria, can hydrolyze urea to drive the biogeochemical reaction in MICP. The goal of this study was to use EC and pH change value of urea hydrolysis test as an indicator to monitor ureolytic activities of bacteria before 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 value and unconfined compression strength (UCS) of MICP-treated soil. The EC and pH value of the mixed solution were measured after adding bacterial suspension into urea solution. Then, the bacterial suspension was mixed with sand sample and cementation media to drive MICP process. The results showed that once the bacterial suspension was mixed with urea, the EC and pH value of the mixed solution increased immediately due to the urea hydrolysis. The optimum EC and pH value at 60 minutes were found to be 1.50 to 1.80 mS/cm and 8.82 to 9.02, respectively, to achieve consistent UCS performance of MICP treated specimens with 0.25 M Ca cementation media.