Optimization of deposition process for a productive and cohesive bio-CaCO3 to repair concrete existing cracks.

Abstract

Microbial-induced carbonate precipitation (MICP) is being investigated to repair concrete cracks because of its good durability and compatibility with cementitious matrix. However, during the in-situ application, the repairing often lasts weeks, even months. And the strength regain is quite low. The repairing time is largely determined by the CaCO3 yield, and the strength regain after the repair is closely related to the cohesion and bonding strength of CaCO3 itself. Thus, the purpose of this paper is to obtain an efficient precipitation of bio-CaCO3 with both high yield and good cohesion to improve the in-situ repairing efficiency. Firstly, the most influential factors on urease activity were screened and the precipitation kinetics were detailly investigated. The results show that the CaCO3 with the largest yield and cohesion was obtained when the bacterial concentration was 107 cells/mL and the concentration of urea and calcium was both 0.5 M at 20 °C. This weight loss of bio-CaCO3 was 9.24% under ultrasonic attack. Secondly, two models were established to quantify or semi-quantify the relationship between the most influential factors and the yield and cohesion of precipitates, respectively. The results showed the order of contribution for bio-CaCO3 precipitation was calcium ions concentration > bacterial concentration > urea concentration > temperature > initial pH. According to these models, the required yield and cohesion of CaCO3 by engineering could be obtained by adjusting affecting factors. Models were proposed for guiding the application of MICP in practical engineering. KEY POINTS: • Screened the most affecting factors on urease activity and investigated the precipitation kinetics. • Obtained optimal conditions of bio-CaCO. • Established two models in order to give some guidance for practical civil engineering.