Assessment of Eggshell Waste as a Sustainable Calcium Source for Biocementation-Based Soil Stabilization

Biological methods of soil stabilization are emerging as potential futuristic solutions for repair and maintenance of built infrastructure. However, development of a sustainable solution requires reliable supply of raw materials with added privileges in the context of circular economy. This study investigates the potential of waste egg shells as an eco-friendly source of calcium for microbially induced calcium carbonate precipitation (MICP) using Sporosarcina pasteurii MTCC 1761, with the aim of enhancing the geotechnical properties of Sea Shore Sand (SSS) and Dry Clayey Soil (DCS). The collection and utilization of the raw materials were administered with minimum processing steps. The mechanical and biochemical properties of SSS and DCS using Sporosarcina pasteurii were compared in the presence of two alternative calcium sources (eggshell powder (ESP) and calcium hydroxide (CH)). The results showed an increase in shear strength up to 0.35 kg/cm2 for SSS-CH and 0.29 kg/cm2 for SSS-ESP. Similarly, the unconfined compression strength for cohesive soil (DCS) reached up to 0.41 kg/cm2 under the test conditions. Further, an adaptive mechanistic framework is proposed for selecting an optimal implementation strategy for MICP using recycled materials such as ESP. For this, a correlation matrix is developed describing the relationship between cause, evidence and effect of soil stabilization based on biocementation. We propose that ESP can be a promising source of calcium for enhancing the sustainability of biocementation irrespective of the soil type.