A one-phase injection method to improve the strength and uniformity in MICP with polycarboxylic acid added

The production and distribution uniformity of calcium carbonate plays a pivotal role in enhancing the effectiveness of microbially induced calcium carbonate precipitation (MICP). Various methods have been proposed to enhance the conversion rate of calcium ions and ensure uniform calcium carbonate distribution. These include multiphase injection methods and one-phase injection methods with environmental factors such as pH and temperature controlled. Polycarboxylic acid, a polymer organic substance rich in carboxylic acid groups, serves as a regulator for the initial precipitation time of calcium carbonate. It aids in increasing the total output of calcium carbonate by complexing calcium ions. This study introduces and investigates a one-phase injection method of MICP with the addition of polycarboxylic acid. The methodology is examined through bacteria growth tests, tube tests, sand column tests, and microscopic analyses. The results indicate that polycarboxylic acid does not exhibit any side effects on Sporosarcina pasteurii (S. pasteurii). When the urease activity of the bacterial solution is maintained at 15 kU/L and the concentration of the cement solution is 1 mol/L, incorporating a 3% solution of polycarboxylic acid delays the initial precipitation time of calcium carbonate by more than two hours. This delay significantly contributes to improving the uniformity of calcium carbonate distribution, with complete precipitation of calcium ions occurring within 24 h. After five treatment cycles, the unconfined compressive strength of the sand column reaches 2.76 MPa. This method demonstrates promising potential for application in enhancing reinforcement effects and streamlining the reinforcement process.