The use of additives has generated significant attention due to their extensive application in the microbially induced calcium carbonate precipitation (MICP) process. This study aims to discuss the effects of Na-montmorillonite (Na-MMT) on CaCO3 crystallization and sandy soil consolidation through the MICP process. Compared with the traditional MICP method, a larger amount of CaCO3 precipitate was obtained. Moreover, the reaction of Ca2+ ions was accelerated, and bacteria were absorbed by a small amount of Na-MMT. Meanwhile, an increase in the total cementing solution (TCS) was not conducive to the previous reaction. This problem was solved by conducting the reaction with Na-MMT. The polymorphs and morphologies of the CaCO3 precipitates were tested by using X-ray diffraction and scanning electron microscopy. Further, when Na-MMT was used, the morphology of CaCO3 changed from an individual precipitate to agglomerations of the precipitate. Compared to the experiments without Na-MMT in the MICP process, the addition of Na-MMT significantly reduced the hydraulic conductivity (HC) of sandy soil consolidated.

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The adsorption of bacteria onto the Na-montmorillonite (Na-MMT) was studied as a function of time, bacterial concentration, temperature and pH with the introduction of the organic and inorganic calcium sources. The results indicated that albeit revealing the same adsorption mechanism, the organic calcium (i.e., Ca(CH3COO)2) proposed in this study is more beneficial and environmentally friendly than the inorganic calcium (i.e., CaCl2) in terms of the adsorption of bacteria onto the Na-MMT surface, which can be ascribed to the formation of the denser aggregates in the Na-MMT with Ca(CH3COO)2. Meanwhile, the adsorption kinetics and isotherms followed the pseudo-second-order kinetic model and Langmuir Equation for both two calcium sources. Meanwhile, the adsorption bands of the water molecules on the minerals were observed to shift significantly after the bacterial adsorption, showing that the hydrogen bonding on the Na-MMT surface played an important role during this process. A value of ΔH0 > 0 indicated that the bacterial adsorption was affected by van der Waals force and hydrophobic interaction. Finally, the negative zeta potentials of the Na-MMT increased with the addition of Ca2+ ions, and the experimental data also showed that the adsorption of bacteria onto the Na-MMT was mainly determined by the electrostatic and non-electrostatic forces.

This study proposed a novel bio-carbonation method to recycle water-based drill cutting (WDC) to prepare samples, which contains reactive magnesia (MgO) cement (RMC), ground granulated blast furnace slag (GGBS), and fly ash (FA), with the adoption of microbially induced carbonate precipitation (MICP). Through the investigation of some parameters (i.e., GGBS content, FA content, and curing time), the microstructures and strength development of bio-carbonated RMC-based WDC samples were evaluated. The preliminary results revealed that bio-carbonated RMC-based WDC samples outperformed the control group (i.e., without bio-carbonation) in terms of the 28-day strength (i.e., 9.8 MPa versus 4.4 MPa), which can be assigned to formation of the carbonates, that is, hydrated magnesium carbonates (HMCs). Further, in addition to the identification of HMCs, the microstructural analysis also revealed a continuous carbonate network due to the presence of HMCs, which accounts for the strength boost of samples.

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