## 10 Bacteria-Activated Self-Healing Cementitious Materials
### Effect of Bacteria on Concrete Performance  
Table 7 shows the variation in the CS values, bacterial concentrations, and bacterial strains when different types of calcium sources are given to the bacteria. The calcium source supplied to the bacteria indeed determined rapidity or slowness of the setting times of the concrete upon the incorporation of the bacteria spore powder. The nutrients, such as calcium formate, calcium nitrate, and calcium lactate, were provided to the bacteria. The setting time of concrete was improved upon adding the calcium nitrate and calcium \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Autotrophic Bacteria** & \multicolumn{3}{c}{**Heterotrophic Bacteria**} \\ \hline Non-methylotrophic methanogenesis & Assimilatory pathways & Dissimilatory pathways \\ \hline \multicolumn{3}{c}{Urea decomposition} & Organic carbon oxidation \\ \hline Anoxygenic photosynthesis & & Aerobic & Anaerobic \\ \hline \multicolumn{3}{c}{Processes/e-acceptors} & Processes/e-acceptors \\ \hline Oxygenic photosynthesis & Ammonification of amino acids & Respiration & O\({}_{2}\) & NOx reduction & NO\({}_{3}\)/NO\({}_{2}\) \\ \hline \multicolumn{3}{c}{Methane oxidation} & CH\({}_{4}\)/O\({}_{2}\) & Sulphate reduction & SO\({}_{4}\)\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Various metabolic pathways for the precipitation of bacterial CaCO\({}_{3}\). formate, while it was slowed down due to the addition of calcium lactate [112; 128]. Calcite precipitation served as the basis for a biotechnological approach to enhance the strength of the concrete structures. Due to the permeability of the cement mortar, the initial curing period was highly nourishing for the microbial cells acclimatizing to a novel environment. During the curing period, the high pH level of the cement helped the bacterial cells to grow gradually. Multiple ions located in the media led to form the calcite precipitates in the cement mortar matrix and surface of the cell, while the cells continued to grow. Consequently, the cement mortar experienced a reduction in the permeability and porosity. The simultaneous filling of multiple pores in the matrix led to the halting of the flow of oxygen and nutrients into the bacterial cells, causing endospores or death of these cells. This clearly explicated the interaction of the microbial cells to enhance the CS of the mortar [129]. Lower grade concrete achieved less strength than higher grade concrete, as the calcite precipitation was greater in the latter after the addition of Bacillus Megaterium bacteria at the concentration of 30 \(\times\) 10\({}^{5}\) cfu/mL. In another study, the highest-grade concrete showed an increase in the strength by almost 50 MPa, indicating the possibility of the highest rate of strength development in such concrete [117]. Sparcious Pasteurii bacteria of concentration 10\({}^{5}\) cells/mL were included in FA-based concrete by substituting 10% of cement. The microorganism cell surface that was covered by the deposition of CaCO\({}_{3}\) led to an improvement of the concrete's structural strength by 20% [118]. Additionally, the CaCO\({}_{3}\) precipitation was responsible for the enhancement in the CS value of the silica fume-added concrete following the incorporation of the bacteria. The SEM and XRD microstructure analysis revealed the presence of calcium carbonate in the concrete matrix [130]. Over a period of 28 days curing, concrete prepared without Sparcina Pasteurii bacteria was found to have 20% less CS than the one designed with the bacteria [131]. Compared to the control specimen, the CS of the mortar containing bacterial cells was increased by 10, 14, and 19% with the substitution of cement by fly ash (FA) contents of 40, 20, and 10%, respectively [64]. Optimal efficacy in the cracks self-healing was due to the presence of GNP that served as an ideal carrier compound for the uniform distribution of bacteria in the concrete matrix.