Cracks in concrete are a common phenomenon due to the relatively low tensile strength. Durability of concrete is impaired by these cracks since they provide an easy path for the transportation of liquids and gasses that potentially contain harmful substances. If micro-cracks grow and reach the reinforcement, not only the concrete itself may be attacked, but also the reinforcement will be corroded.
Therefore, it is important to control the crack width and to heal the cracks as soon as possible.
The process of self-healing of cracks or self-filling up of cracks by the help of bacterial reaction in the concrete after hardening is known as Self-Healing Concrete.
Mechanism of Bacterial Concrete
Self-healing concrete is a result of biological reaction of non-reacted limestone and a calcium based nutrient with the help of bacteria to heal the cracks appeared on the building.
Bacteria known as Bacillus is used along with calcium nutrient known as Calcium Lactate. While preparation of concrete, these products are added in the wet concrete when the mixing is done. This bacteria can be in dormant stage for around 200 years.
When the cracks appear in the concrete, the water seeps in the cracks. The spores of the bacteria germinate and starts feeding on the calcium lactate consuming oxygen. The soluble calcium lactate is converted to insoluble limestone. The insoluble limestone starts to harden. Thus filling the crack, automatically without any external aide.
Advantage of this process is, as the oxygen is consumed by the bacteria to convert calcium into limestone, it helps in the prevention of corrosion of steel due to cracks. This improves the durability of steel reinforced concrete construction.
Self healing bacterial concrete can be used for sectors such as
The timber, brick, concrete, or steel supports erected in a tunnel to maintain dimensions and safe working conditions.
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Story Source: TheConstructor.org