Experimental study on the engineering characteristics of expansive soil improved conjointly using enzyme induced carbonate precipitation and eggshell powder

[Display omitted] •A feasible solution for using agro-waste eggshell powder to alleviate the geotechnical problems is determined.•Enzyme induced calcium carbonate precipitation (EICP) is a sustainable method of problematic soil.•A novel technique of using EICP in conjunction with ESP is adopted to enhance the geotechnical characteristics of expansive soil.•The stabilizing process was investigated in terms of changes in mineralogical and microstructural properties. Enzyme induced carbonate precipitation (EICP) is gaining more and more recognition that can be utilized on-site to enhance the quality of the weak soil. In this experimental study, a novel approach that combines EICP and eggshell powder (ESP) to strengthen the engineering characteristics of natural expansive soil has been implemented. The engineering properties of expansive soil were examined using the environmentally friendly method EICP with an optimal 0.75 mol/L concentration and 14% ESP optimal content, with varying curing durations. ESP serves as a filler between particles and also a nucleation site to promote the precipitation of calcium carbonate. A thorough examination of the soil’s microstructure development after treatment was additionally executed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The findings demonstrated that combining EICP and ESP decreases the swelling pressure about 25 times, compared with the individual treatment that yielded 5 and 1.5 times reduction for EICP and ESP, respectively. Additionally, the combined treatment led to an increase in the unconfined compressive strength, cohesion, internal friction angle, unsoaked CBR, and soaked CBR by 3, 1.6, 1.8, 8.0, and 9.5 times, respectively, indicating better enhancements than the individual treatments of EICP and ESP. Moreover, at the microstructural level, SEM imagery demonstrated a highly reinforced soil composite. The XRD analysis unveils distinct mineralogical changes, predominantly characterized by enhanced calcite formation and a refined microstructural composition. This study highlights the synergistic potential of combining EICP and ESP as stabilizing additives to enhance the engineering properties of expansive soil. Beyond soil enhancement, this innovative blend offers a sustainable solution by repurposing agrowaste. The mutual incorporation of EICP and ESP emerges as a promising strategy for advancing sustainable civil infrastructure development.