10 a] Describe the concept of self healing bioconcrete and explain the role of bacillus spores calcium lactate nutrients and biomineralization processes in this technology
Bio-concrete is a self-healing form of concrete designed to repair its own cracks. To heal cracks in the concrete, Jonkers chose bacteria, that can produce limestone on a biological basis.
bacteria consume oxygen, which in turn prevents the internal corrosion of reinforced concrete. However, the bacteria do not pose a risk to human health since they can only survive under the alkaline conditions inside the concrete.
Self-healing concrete is nothing but concrete which can retain itself to the original state when it is subjected to cracks.” Bio-concrete is a material that will biologically produce minerals like limestone with the help of bacteria present in it, which will heal cracks that appear on concrete surfaces. Bacterial self-healing is an innovative technology that allows the repairing of open micro-cracks in concrete by CaCO3 precipitation. This biotechnology improves the durability of the structure. In this paper, peptone, yeast extract, and Bacillus Subtilis were added as microbial adjuvants in the concrete mix design.
- Bacillus Spores: Bacillus is a genus of bacteria commonly used in self-healing bioconcrete. These bacteria are typically spore-forming, which means they can encapsulate themselves in a protective spore when environmental conditions become unfavorable. In the context of self-healing bioconcrete, Bacillus spores are embedded within the concrete mixture. Their role is crucial because they remain dormant until cracks form in the concrete, providing the trigger for activation.
- Calcium Lactate: Calcium lactate serves as a source of calcium ions within the self-healing bioconcrete. Calcium ions are essential for the biomineralization process that facilitates crack repair. When cracks occur in the concrete, they expose the Bacillus spores to air and water. The presence of moisture triggers the spores to germinate, and the bacteria begin to consume the calcium lactate.
- Nutrients: In addition to calcium lactate, other nutrients such as nitrogen and phosphorous sources may be included in the bioconcrete mix. These nutrients are necessary for the bacterial metabolism and growth. As the bacteria consume the calcium lactate and nutrients, they produce calcium carbonate (CaCO3) as a metabolic byproduct.
- Biomineralization Process: The key to self-healing bioconcrete’s success lies in the biomineralization process. When the bacteria consume calcium lactate and nutrients, they produce urease enzymes as a part of their metabolic activity. These urease enzymes break down urea, which is naturally present in concrete and can be used as a source of nitrogen. As a result, the breakdown of urea releases ammonia (NH3) and carbonate ions (CO3^2-).
- Ammonia (NH3): The ammonia acts as a base, increasing the pH of the surrounding environment in the crack. This elevated pH triggers a chemical reaction between the carbonate ions and calcium ions that were released from the calcium lactate. The reaction leads to the formation of calcium carbonate (CaCO3), which precipitates in the cracks.
- Calcium Carbonate Precipitation: The calcium carbonate that forms is similar in composition to the naturally occurring minerals found in concrete. This newly formed calcium carbonate gradually fills the cracks and voids in the concrete, effectively repairing the damage and restoring the material’s structural integrity.
