Abstract
Microbial induced CaCO3 precipitation (MICP) based upon enzymatic urea hydrolysis has been verified as an effective way for crack treatment, especially for self-healing of concrete cracks. This paper aimed at correlating optimum conditions of MICP with prerequisites for self-healing concrete. Orthogonal experiments on a combination of factors contributing to the MICP process were firstly performed. Initial cell density and Ca2+ concentration were highly significant factor and significant factor respectively. High initial cell density (1×108 cells·mL-1) together with relatively low Ca2+ concentration (50 mM) favored microbial precipitation. The second part of this study was associated with dissolution tests to simulate the dissolving behavior of urea and calcium, since the dissolving of healing agents in cracks is a prerequisite of self-healing. By an addition of urea and Ca(NO3)2 with constant mass ratio of 2:3 in concrete, the highest values of the estimated urea concentration (345 mM) and Ca2+ concentration (44 mM) dissolved in cracks were close to the optimal values found by orthogonal studies. Although the addition of urea and Ca(NO3)2 would not have a negative impact on the mechanical properties of concrete, direct mixing is not recommended due to the low utilization efficiency of incorporating healing agents for self-healing.
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