Solidification of loess using microbial induced carbonate precipitation

Abstract

Microbial-induced carbonate precipitation (MICP) is a relatively innovative and environmentally-friendly soil reinforcement technology, primarily used on sand, but its application in loess has rarely been studied. This paper explores the viability of the MICP technique for improving the engineering properties of typical loess. Sporosarcina pasteurii was used to trigger carbonate precipitation. Factors such as reaction temperature, pH of the media, and the inoculation ratio were adopted to determine the optimum conditions. Different concentrations of Sporosarcina pasteurii and cementation reagent were selected for combination to treat the loess samples with a self-designed vacuum test device. The unconfined compressive strength and calcium carbonate content of the treated samples were tested and Scanning Electron Microscopy (SEM) was carried out to evaluate the improving effect. The results showed that the optimum conditions are reaction temperature of 30°C, pH of the media of 9, a higher inoculation ratio can produce higher enzyme activity and monomer enzyme activity. The engineering properties of the MICP-treated loess are significantly improved. The obtained unconfined compressive strength increases nearly 4 times when the OD600 is 1.5 and cementation reagent concentration is 1 mol/L. The test results of calcium carbonate content are consistent with unconfined compressive strength. Finally, the microstructure of loess samples was quantitatively analyzed by Pore (Particle) and cracks analysis system (PCAS). It was showed that MICP has a great influence on the surface porosity, followed by the pore fractal dimension and the probability entropy, but has little influence on the pore average form factor.