Optimization of Enzyme Induced Carbonate Precipitation (EICP) as a Ground Improvement Technique

Enzyme induced carbonate precipitation (EICP) is a bio-cementation technique and is a new area of Geotechnical Engineering. In this paper, a parametric study was conducted to evaluate and optimize the effect of concentration and activity of urease enzyme and concentration of other chemical constituents (urea and calcium chloride) on EICP process. pH, electrical conductivity (EC), and micro-structure analysis using scanning electron microscope (SEM) imaging were performed. Results indicate that, the precipitation ratio (PR), which is defined as the ratio of mass of precipitated CaCO3 in test tube and theoretical mass of CaCO3 is a function of the concentration of urea-CaCl2 (mol/L) and urease enzyme (kU/L). Rate of change in pH and EC during urea hydrolysis is influenced by urea and urease enzyme concentration. SEM images of CaCO3 precipitates from solution containing low active urease enzyme (3,500 U/g) showed a disordered and anhedral calcite crystals whereas the high active urease enzyme (40,150 U/g) showed euhedral and agglomerated rhombohedral calcite morphology.