Microbial-Induced Calcite Precipitation


Figure 4: (a) Fracture surface of processed Ottawa sand after four MICP treat- ments, and (b) the same specimen at a higher magnification.


Discussion Aſter a single MICP treatment, many CaCO3


hemispheres


were found on the surface of the sand particles, reducing the possible bonding area of the calcium carbonate to the sand par- ticles (Figure 2b). Multiple treatments increased the CaCO3 tent and enhanced the CaCO3


con- bonding (Figure 4). Conventional


SEM can only analyze the surface of the sample. Aſter ion-beam milling a small cross section at the surface, SEM imaging could reveal deeper layers of carbonate (Figure 5). An automated mill- ing process along with simultaneous SEM observation allowed study of the interior structure of MICP-treated soil specimen.


28


Figure 5: Cross-sectional analysis of calcite-sand boundary. (a) SEM image of internal boundaries exposed by ion-beam milling after four MICP treatments, and (b) the same region of specimen at higher magnification.


More CaCO3 precipitated aſter each additional treatment cycle, (Figure 5b).


Careful imaging at the fracture surface and the milled surface allowed imaging of remnant bacteria.


Conclusion Conventional SEM and FIB/SEM have been used to inves-


tigate mineral bond formation in sandy soil treated by the pro- cess of microbial-induced calcite precipitation. SEM images


www.microscopy-today.com • 2019 January


and the milling function of the FIB exposed a cross section that showed the layer-by-layer deposition of CaCO3


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