Investigation on the Impact of Cementation Media Concentration on Properties of Biocement under Stimulation and Augmentation Approaches

Biomediated soil improvement has been established as a promising solution for improving soil engineering properties in the last decade. The primary factor determining the efficacy of biocementation is the material properties of the precipitated crystals, which are highly impacted by the concentration of cementation reagents. In the present study, the biocementation potential of specific microbes liable for the augmentation and stimulation approaches are investigated at different concentrations of cementation media (CM) ranging from 250 to 2,000 mM. An indigenous soil microbe (BS3) and a consortium (C), both obtained from a natural riverbank environment, are analyzed for their potential to improve the soil strength in comparison with the standard biocementing microbe Sporosarcina pasteurii (SP). The soil strength improvement is investigated by conducting the needle penetration test on the biocemented soil samples. Maximum needle penetration resistance was observed at 500 mM concentration of CM for all the microbes. The isolated soil microbe (BS3) exhibited 30% more penetration resistance than SP at the optimal concentration (500 mM) of CM. The needle penetration resistance decreased at the higher concentrations of CM. The biochemical properties of the microbes were evaluated via a laboratory shake-flask batch test to determine the potential reasons behind the variation in the penetration resistance. Their biochemical properties, including the urease activity, urea hydrolysis rate, calcium depletion rate, and carbonate precipitation potential are compared at different concentrations of CM. The findings revealed that the microbes respond distinctively to different concentrations of CM. A detailed microstructure analysis on the precipitated CaCO3 crystals suggested that the morphology, texture, and quantity are possibly the major strength influencing parameters. The present study unravels the potential reasons for the distinct responses of the augmentation and stimulation-inducing microbes at the different concentrations of CM.