Effect of Magnesium Incorporation in Enzyme-Induced Carbonate Precipitation (EICP) to Improve Shear Strength of Soil

Abstract

AbstractEnzyme-induced carbonate precipitation (EICP) is a novel, bioinspired soil stabilization technique in which calcium carbonate (\({\text{CaCO}}_{3}\)) crystals are enzymatically precipitated to cement and link the soil grains, thereby improving the shear strength of the soil. This work aims to analyze the effect of incorporating \({\text{Mg}}^{{2+}}\) ions on crystal morphology and their direct influence on the mechanical properties of the soil. A beaker experiment conducted by mixing urea, urease enzyme and \({\text{MgCl}}_{2}\)/\({\text{CaCl}}_{2}\) in different molar ratios revealed that the increase in the \({{{\text{Mg}}^{{2+}}} \mathord{\left/{\vphantom {{{\text{Mg}}^{{2+}}} {{\text{Ca}}^{{2+}}}}} \right. \kern-0pt} {{\text{Ca}}^{2 + } }}\) molar ratio decreases the amount of precipitated mass. The soil specimens for unconfined compressive strength (UCS) test were prepared as per its maximum dry unit weight (\(\gamma_{\text{dmax}}\)), and an optimum solution content (\({\text{w}}_{\text{opt}}\)) consisting of urea, urease enzyme and \({\text{MgCl}}_{2}\)/\({\text{CaCl}}_{2}\) at various \({{{\text{Mg}}^{{2+}} }\mathord{\left/{\vphantom {{{\text{Mg}}^{2+}} {{\text{Ca}}^{2 + } }}} \right. \kern-0pt} {{\text{Ca}}^{2 + } }}\) molar ratio. Field-emission scanning electron microscopy (FESEM) and X-ray powder diffraction (XRD) tests performed on precipitated mass verify the influence of \({\text{Mg}}^{{2+}}\) ions on crystal morphology and the occurrence of other carbonates (dolomite) and polymorphs of \({\text{CaCO}}_{3}\). The results of the UCS tests show that the lower molar ratio of \({\text{Mg}}^{{2+}}\)/\({\text{Ca}}^{2 + }\) can significantly improve the undrained shear strength of the soil.KeywordsEICPPrecipitationMorphologyShear strength