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Until recently, engineers either ignored or neglected the role of microorganisms in geotechnical engineering. The microbially induced calcite precipitation (MICP) research technique is an innovative and relatively green technology which consists in a biological process through which microorganisms react with minerals (calcium source and cementation reagent) to produce calcite (CaCO 3 ) as a byproduct that modifies and improves the engineering properties of soil. Laboratory and field results obtained from various studies are promising and viable, suggesting potential for various engineering applications. This research technique has also been considered to be useful in many engineering applications such as improvement of construction materials, cementation of porous media, improvement in strength and stiffness of engineering soils, hydraulic control of engineering facilities (waste containment), liquefaction, and erosion mitigation. In this review, the various methods of production of calcium carbonates (calcite), the role played by bacteria, various state-of-the-art procedures that have evolved in this research area, as well as ongoing studies are reported. Furthermore, the use of the MICP technique in remediation of contaminants and other environmental concerns is also presented. The advantages and challenges (in form of undesired byproducts) of this research technique are highlighted herein.

The plasticity characteristics of lateritic soil with varying Sporosarcina pasteurii (S. pasteurii) suspension density and compositional variables were evaluated in microbial-induced calcite precipitation (MICP) application. The liquid limit value of the natural lateritic soil was used to prepare samples with three mix proportions of the bacteria and cementation reagent (i.e., 25% bacteria-75% cementation reagent, 50% bacteria-50% cementation reagent and 75% bacteria-25% cementation reagent). The S. pasteurii suspension densities used to trigger the MICP process are 0, 0.5, 2.0, 4.0, 6.0 and 8.0 McFarland standards (i.e., 0, 1.50 × 10 8 , 6.0 × 10 8 , 1.20 × 10 9 , 1.80 × 10 9 and 2.40 × 10 9 cells/ml, respectively). Tests carried out on the treated specimens include Atterberg limits and linear shrinkage as well as calcite content using the acid wash method. Results obtained showed a general decrease in the Atterberg limit values with higher S. pasteurii suspension density. The best improvement of plasticity index was achieved for lateritic soil prepared with 75% S. pasteurii and 25% cementation reagent at S. pasteurii suspension density of 2.40 × 10 9 cells/ml with a corresponding peak 6.0% calcite content. Also, a maximum 4% contaminant concentration of a synthetic leachate produced the best S. pasteurii growth pattern.

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