Precipitation of calcium carbonate (CaCO3) crystals via bioinspired pathways is a promising method and, in recent years, has gained significant attention as a ground improvement technique. The location, amount, structural and compositional features of the finally precipitated bio-minerals must be controlled precisely to obtain the desired improvement. Microbially induced calcium carbonate precipitation (MICP) and enzymatically induced calcium carbonate Precipitation (EICP) are two extensively explored bioinspired techniques. Due to the elimination of bacterial cells, which adds to the technique’s diversity, EICP is said to be more practically possible from a field deployment standpoint. However, despite recent advancements in the EICP method, such as understanding the role of chemical conditions, including enzyme, substrate concentrations, pH, temperature, etc., and different treatment strategies, the degree of control over the CaCO3 remains inadequate to achieve all the aforementioned mineralization characteristics. This is mainly attributed to the elimination of microbial cells, which otherwise acted as nucleation sites and provided morphological control over the crystal formation.

To address the limitations of the conventional EICP process, the current study envisages the application of carbonate-responsive, biomimetic, calcium alginate beads as a modification in EICP to introduce a nucleation template and gain spatial control over the location of precipitation within the porous skeleton. Calcium alginate beads were synthesized by two different concentrations of CaCl2 cross-linker to incorporate the effect of gel strength, and formed spherical beads were allowed to collapse without and within soil environment by exposing them to carbonate (CO32-) rich solution obtained by urease-driven urea hydrolysis. Free carbonate ions in the solution combined with alginate-entrapped calcium ions and calcium carbonate mineralization were confined to the bead surface.
The morphological evolution due to the inclusion of alginate and the distribution of the formed precipitates within the soil domain were assessed through the SEM imaging technique. The type of polymorph and compositional features of the CaCO3 were identified with XRD and EDX, respectively. Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA) revealed the interplay between organic polymeric and inorganic mineral phase. Based on the obtained results from microstructural testing, a mechanism of bead dissolution and resulting mineralization incorporating the effect of concentration of cross-linker solution used during bead synthesis is proposed. Experimental results demonstrated the feasibility of using synthesized biomimetic beads to foster a template for crystal nucleation and localize the formation of CaCO3 crystals, preferably at intergranular pore throats, making biogenic treatment more effective.