Influence of calcium chloride and urea in self-healing concrete using Bacillus subtilis, Bacillus megaterium and Bacillus licheniformis

Concrete is a non-flexible and breakable material that is widely used in building construction. Concrete cracking may affect the strength of buildings. Due to difficulties of concrete fixing processes, this research focuses on developing a self-healing concrete by using a biocementation process of bacteria. As bacteria have a property of producing calcium carbonate from calcium chloride, urea, and water, Bacillus licheniformis, Bacillus megaterium and Bacillus subtilis were chosen. In this research, the concentration of calcium chloride and urea were varied from 0.1 - 0.7 M and 0.6 - 1.2 M, respectively to find the optimal concentrations which potentially yield the most calcium carbonate precipitate from bacteria. Bacterial cultures were monitored by observing growth, pH and urea consumption. The results indicated the number of bacterial cells showed slightly increasing trends with the decrease in pH and urea consumption, which confirming the usage of substrates. The results of investigating optimal substrates concentration showed that concentration of calcium chloride in the range of 0.1 M - 0.7 M and concentration of urea in the range of 0.1 M - 0.7 M did not significantly affect the biocementation of bacteria. This could be because the usage of substrates affected pH level in solution, resulting in sub-optimal bacterial growth. However, the rates of biocementation from bacteria culturing with various substrate concentrations were obtained. It was found that Bacillus subtilis produced the highest amount of calcium carbonate, followed by Bacillus licheniformis and Bacillus megaterium, respectively. This indicates the potential for developing self-healing concrete by using bacteria.

Keywords: Biomineralization, Self-healing Concrete, CaCO₃, Calcium Chloride, Urea, Bacillus licheniformis, Bacillus megaterium and Bacillus subtilis