Microbial-Induced Calcite Precipitation
Figure 3: (a) Fracture surface of of processed Ottawa sand after four MICP treatments. (b) Energy-dispersive spectrometry X-ray spectrum of specimen region scanned in (a).
carbonate. Aſter four treatments, the CaCO3 layer expanded
and converged to a shell-like precipitation that wrapped around the sand particles. Cross sections of bonding. Figure 5 shows an SEM image
of the ion-beam sectioned inner core of a region of the quadru- ply treated sand specimen. Te leſt side of Figure 5a shows part of a bare sand particle, whereas the right side shows a portion of the CaCO3
Figure 2: SEM image of (a) untreated Ottawa sand and (b) fracture surface of processed Ottawa sand after single treatment of MICP.
and part of the oxygen peak in the spectrum originated from the Ottawa sand itself (known to be 98% SiO2
). MICP-treated four times. Fracture surfaces were
observed aſter samples were MICP-treated four times. Figure 4 shows the fracture surface in a quadruply treated sample and captures the exposed surface of a CaCO3
Tere were several interface lines between the CaCO3
bond-particle failure. and sand
during multiple treatments, particularly in Figure 4b. Te CaCO3 precipitated on the surface of sand particles first,
and carbonate formed in the next treatment attached to prior 2019 January •
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exposed on the fracture surface that illustrate the evolution of CaCO3
30 μm depth (yellow box). Figure 5b shows the milled region and an interface line between a sand particle and the calcium carbonate. It also shows three interfaces in the CaCO3 indicating that the CaCO3
tion through the CaCO3 (arrows) precipitation was accumulated layer-
by-layer with multiple treatments, with the final layer forming the precipitation shell that wraps around the sand particles. Tus, the CaCO3
contact surface area expanded, and the bond-
ing of the sand particles became stronger. Remnant bacteria. In each layer, there were some inactive bacteria surrounded by CaCO3 (see circled region in Figure 5b).
attracted to Ca2+
Images from other areas of the fracture surface provided insight into the remnant bacteria between the sand particles. Figure 6a shows inactive bacteria attached to the surface of the precipita- tion. Aſter FIB milling to 30 μm, the SEM image of the exposed section provided a much clearer image of inactive bacteria inside the CaCO3
precipitation. 27
layer on top of the sand particle. Te cross sec- layer was ion-beam milled to about a
(Figure 6b). Bacteria with negative surface charge were and were trapped by the CaCO3
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