Have you ever noticed cracks on concrete? Are there any methods to remove cracks? I know you will answer only a few external methods of repairing the cracks, Is there any way that we can repair cracks internally? Have you ever heard about self healing concrete?
There are a lot of questions to be answered, it takes only 5 minutes to read this article, so you will understand clearly about self healing concrete and its various properties.
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To understand properly we divided this into following sections;
Introduction
Definition: Filling of the cracks is a biological reaction or in other words, a product i.e, limestone is produced within the concrete with the help of bacteria and after hardening it fills the crack known as self healing of concrete, It is also known as bacterial concrete.
The bacteria which is present inside the concrete will be in a dormant state for over 200 years under dry conditions and when there will be a crack, moisture enters inside the concrete, and bacteria act as a catalyst in the process of crack healing.
The cracks which are in the range of 0.05 to 0.1 mm are completely sealed in repetitive dry and wet cycles.
Types of Bacteria used in self healing concrete?
Various bacteria used in the production of bacterial concrete are;
- Bacillus pasteurizing
- Lysinibacillus sphaericus
- Escherichia coli
- Bacillus subtilis
- Bacillus cohnii
- Bacillus halodurans
- Bacillus pseudofirmus
Self healing concrete Preparation
Bacterial concrete is prepared in two ways;
- By direct application method.
- By encapsulation method
By direct application method: In this direct method, the bacterial spores and calcium lactate are directly added into the concrete after the mixing process.
By encapsulation method: In this method, the bacterial spores and calcium lactate are placed together in clay pellets and these are mixed in the concrete at 6% of the total concrete mixture.
Mechanism of bacteria in concrete
When the cracks are formed in the concrete, the moisture will comes in contact with the calcium and bacteria in the concrete.
This bacteria reacts with the calcium lactate i.e, Nutrient for bacteria, and produces limestone.
The chemical reactions for the above mechanism is;
From the above chemical reaction, it is clear that calcium oxide when reacts with water releases calcium hydroxide and when calcium hydroxide reacts with carbon dioxide, it will produce calcium carbonate which is a solid substance that fills the cracks in concrete.
Advantages of self healing concrete
- Self-repairing of concrete without any external applications.
- The flexural strength and compressive strength of self healing concrete are greater than the normal concrete.
- Bacterial concrete acts as a resistance to freeze-thaw attacks.
- The permeability of concrete is reduced.
- It also reduces the corrosion of steel reinforcement and improves durability.
- Bacillus bacteria are harmless and can be used for the repairing of the concrete.
Disadvantages of self healing concrete
- The cost of bacterial concrete is double that of conventional concrete.
- The growth of the bacteria is not the same in all weather conditions and media.
- The clay pellets which are holding the bacterial spores and calcium lactate will comprise at least 20% of the volume of the concrete and this may become a shear or faulty zone in the concrete.
- Design Standards of self healing of concrete are not available in any IS codes or other code.
- The investigation is costlier and time-consuming.
Conclusion
- From these studies, it is clear that we can implement this technology to improve the properties of concrete.
- When we compare the cost with sustainability, for long term solution, the self healing of concrete is dominating the conventional one.
- In the future, self healing concrete is going to revolutionize the construction industry.
From this discussion, What are your thoughts on self healing of concrete? comment below!
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