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Self-healing concrete also called bioconcrete is a type of concrete which possesses the ability to repair and fill its cracks and thus increasing its service life. This healing action is caused by the embedded particular type of bacteria which feeds on nutrients in the concrete and converts it to limestone which in turn seals off the cracks.

When concrete subjected to tensile stresses, it tends to crack and thereby reducing its strength. Furthermore, cracks allow water to seep into the concrete and causes the corrosion of steel reinforcement.

Fig-1: Sample of Self-healing concrete

Self-healing process:

Self-healing concrete is composed of a selected type of bacteria called genus Bacillus and nutrition such as calcium lactate, nitrogen, and phosphorus. These are mixing during the process of making concrete.

When cracks form and water start to seep in, the bacteria activates and begins feeding on the calcium lactate and takes up all the oxygen from it. Hence, the calcium lactate converted to limestone which hardens and closes the cracks.

The two main ingredients of this concrete( bacteria and calcium lactate) are separated by two clay pellets (2mm to 4mm wide) which ensure that there is no contact between them. When cracks open up the pellets, the two components will come in contact due to the seeping water, and the bacteria becomes and activated, and the healing action will be initiated.

Genus Bacillus is a very suitable type of bacteria since it can withstand harsh alkaline environments such as the mixture of cement and water which has a pH value of approximately 13. This type of bacteria is found in alkali lakes in Russia, carbonate-rich soils in desert areas of Spain and soda lakes in Egypt.


Disadvantages of Self-healing concrete:

1-Almost 20% of this concrete is comprised of clay-pellets which separate the bacteria from the calcium lactate. In other words, it has less amount of coarse aggregate than conventional concrete, and for this reason, it has a lower compressive strength.

2-It is much more expensive than traditional concrete.


REFERENCE:-

1- INGENIA, ISSUE 46 MARCH


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Writer Profile

Mohammad Barzan

BSc- Geotechnical Engineering- Koya University.


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