Evaluation of the Treatment Processes for MICP- and EICP-Treated Sands

Abstract

Bio-cementation, notably microbial induced calcite precipitation (MICP), and Enzyme induced calcite precipitation (EICP), binds soil particles together through calcium carbonate (CACO3) precipitation (cementation). Both MICP and EICP have significant potential for many scientific and engineering applications including improvement of strength, reducing soil liquefaction potential, surface erosion control, reducing permeability, and heavy metal contaminant remediation. However, the catalytic mechanism and the precipitation of CACO3 in MICP and EICP mainly depends on the source of urease enzyme and the treatment process used. This study evaluates the mechanical and microstructural behaviour of bio-cementation using the standard MICP and EICP treatment process. The results indicate that, for the same number of treatment cycles (NTC), a higher amount of precipitated CACO3 was achieved for MICP than EICP which affects the strength. For similar average CACO3 content (AC), the standard treatment method used in EICP produced a higher chemical efficiency (defined as the amount of CACO3 precipitated relative to the quantity of urea-CaCl2 used) than in MICP. The results from scanning electron microscopy (SEM) imaging shows that the morphologies of the precipitated CACO3 in MICP and EICP are similar, however, a high amount of vaterite was found in EICP than MICP. The outcome of this study indicates that the standard treatment processes used in MICP and EICP may influence the chemical efficiency, the amount, distribution, and polymorph of the precipitated CACO3 which may directly affect the strength.