Quantitative method of calcium carbonate in bio-grouting test under multiple treatment factors

Abstract

Bio-grouting is emerging as a sustainable technology for improving the mechanical properties of sand in which CaCO3 is the main product. Previous studies proved that the amount of CaCO3 affects the mechanical properties of bio-cemented sand, but few studies address CaCO3 quantification. In this paper, we describe a novel method to predict the amount of CaCO3 in the process of bio-grouting. A total of 25 bio-grouting tests were carried out with 6 treatment factors considered: bacterial suspension’s concentration, flow rate and retention time, cementing solution’s concentration, flow rate, and reaction time. Based on the mechanism of microbial-induced calcite precipitate (MICP), a theoretical solution to quantify the amount of CaCO3 was established by researching the effects of environmental substances on urea hydrolyzed rate in a liquid environment. This solution was developed by analyzing the difference between sandy and liquid environments. A series of time-dependent equations that evaluate the relationship between the amount of CaCO3 produced with bacterial concentration, the cementing solution’s concentration, and the reaction time, were derived. Moreover, it was found that the bacterial retention time and the flow rates of grouting solutions affect the distributions of reactants in sand. This can be captured by a residual coefficient in the CaCO3 quantification model. Finally, once the linkage between the improved strength of bio-cemented sand and the CaCO3 content is established, the proposed model can be applied to estimate the strength of bio-cemented sand in real time.