微生物沉积优化与混凝土自修复条件的相关性研究

Study on the Correlation Between the Optimum Conditions of Microbially-induced CaCO_(3) Precipitation and the Prerequisites for Self-healing Concrete

本研究旨在探索基于脲解反应的微生物诱导碳酸钙沉积的最优条件与实现自修复混凝土的先决条件之间的联系。首先针对影响微生物诱导碳酸钙沉淀过程的实验条件设计正交试验。结果表明,初始菌密度和钙离子浓度分别为影响微生物诱导碳酸钙沉淀效果的极显著因子和显著因子,且高初始菌密度(1×10^(8) cells/mL)和相对较低的钙离子浓度(50 mmol/L)更有利于微生物碳酸钙沉积。因为自修复剂在裂缝中的溶解被认为是自修复的必需条件,所以本研究的第二部分通过溶出实验来模拟尿素和钙离子在混凝土裂缝中的溶出情况。当混凝土中加入的尿素和硝酸钙的质量比为2∶3时,裂缝中溶出的最高估计尿素浓度(345 mmol/L)和钙离子浓度(44 mmol/L)接近正交试验所得出的最优值。虽然尿素和硝酸钙的加入不会对混凝土的力学性能产生负面影响,但是由于直接掺入自修复剂的利用率较低,不建议自修复剂不采用任何负载方法而直接掺入混凝土基体中。

This paper aimed at correlating the optimum conditions of ureolytic type microbially-induced CaCO_(3) precipitation(MICP)with the prerequisites for self-healing concrete.Orthogonal experiments of a combination of factors contributing to the MICP process were firstly designed and performed.Results show that initial cell density and Ca^(2+) concentration were highly significant factor and significant factor respectively.Besides,high initial cell density(1×10^(8) cells/mL)together with relatively lower Ca^(2+) concentration(50 mmol/L)favored microbial precipitation.The se-cond part of this study was associated with dissolution tests to simulate the dissolving behavior of urea and calcium in the concrete crack solution,since the dissolving of healing agents in crack is the prerequisite for self-healing concrete.By an addition of urea and Ca(NO_(3))_(2) with constant mass ratio of 2∶3 in concrete,the highest values of the estimated urea concentration(345 mmol/L)and Ca^(2+) concentration(44 mmol/L)dissolved in cracks were close to the optimum values found by orthogonal experiments.Although the addition of urea and Ca(NO_(3))_(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 incorporated healing agents for self-healing concrete.