The use of self-healing technology for sustainable infrastructural development
Mineral-producing bacteria mend micro-cracking in concrete. Properties of concrete vary with the addition of bacteria. There are micro cracks present in concrete. They cause the degradation of concrete and lead to the deterioration of the structure. So, we use the self-healing concrete bacteria technique worldwide. Self-healing concrete bacteria are is known as bio-concrete. It increases the strength and durability of concrete.
Which use bacteria to make self-healing concrete?
Self-healing concrete bacteria is new innovation. It leads to less maintenance cost and less decaying of structures. Micro-cracks developed during construction lead to leakage and corrosion of steel reinforcements. This results in billions of maintenance costs and eventually, the structure collapses.
By the addition of urease engendering bacteria along with calcium, sources result in calcite precipitation in concrete. The hydration process in concrete fills up freshly composed micro cracks. The bacteria (Bacillus Pasteurii or Bacillus Subtilis) give rise to urea. It is combined along with the calcium source to close up the freshly composed micro-cracks. It results in CaCO3 precipitation.
The Self-healing concrete bacteria remains unharmed throughout the mixing process. The two most commonly used bacteria are Bacillus or Sporosarcina. Sporosarcina is found in high alkaline volcanic lakes. It can survive for more than 200 years without any food, water, or oxygen. These Self-healing concrete bacteria become active when it comes in contact with water. Then, it shows healing properties.
Why we consider Bacillus bacterium right for the concrete?
Just like bones heal themselves through the mineralization process, we need Self-healing concrete bacteria. Concrete is an extremely alkaline, rocky, hard, and dry substance. It was challenging to find such a bacteria which can withstand the properties of concrete. Bacillus can survive such conditions. For bacillus to produce healing agents such a limestone, it needs some food such as sugar.
If we add sugar directly to our concrete mix, it would soften our concrete. So, Calcium lactate was added to bacteria and kept in capsules. These capsules are known as biodegradable plastic capsules. These capsules are added to the concrete mix and only open up when they come in contact with water. This entire process makes limestone. Limestone eventually shuts the cracks and makes the concrete “self-healing concrete”. This was all developed by microbiologist Jonkers, he said that,
“Nature is supplying us a lot of functionality for free – in this case, limestone-producing bacteria. If we can implement it in materials, we can really benefit from it, so I think it’s a really nice example of tying nature and the built environments together in one new concept.”
Now, will this Self-healing concrete bacteria be a beneficial future need?
Self-healing concrete is not in practice right at the moment. Professor Bob Lark said,
“Our vision is to create sustainable and resilient systems that continually monitor, regulate, adapt and repair themselves without the need for human intervention. These self-healing materials and intelligent structures will significantly enhance durability, improve safety and reduce the extremely high maintenance costs that are spent each year.”Professor Bob Lark
Also, one of the civil engineers said,
“We will be monitoring properties such as stiffness, permeability, and the mechanical damage recovery of the trial walls in comparison with conventional reinforced concrete walls.”
We apply Self-healing concrete bacteria, a repair mortar, and a liquid repair spray to existing concrete structures. They will be common in the market real soon. The real problem is its cost. It’s twice as conventional concrete. Jonkers said that we will work on it and find some other source for sugar to reduce the price.
What are the advantages of Self-healing concrete bacteria?
- It can last for decades
- Less maintenance cost. Self-healing of cracked concrete without any external aid
- Improved compressive strength and flexural strength. Reduction in permeability
- Reduction in corrosion of steel. Improves the durability of steel-reinforced concrete
- Bacillus bacterium is harmless to human life
What are the disadvantages of Self-healing concrete bacteria?
- Clay pellets holding the Self-healing concrete bacteria agent comprise 20% of the total volume of concrete. That 20% is normally a hard substance such as gravel (rocky). Clay is normally weaker than the rest of the aggregate. This weakens the concrete by 25% (reduction in compressive strength). This is a great problem when constructing high-rise buildings.
- The second disadvantage is the cost, as already discussed above. It’s double that of conventional concrete. Today, we use Self-healing concrete bacteria only at those sites where high quality is needed. Where we could face safety issues or places with less access for maintenance.
- Most of the contractors are not aware of the methodology of its use as it’s new in the market.
- The growth of Self-healing concrete bacteria can be dangerous
- Investigation of calcite precipitate is expensive
Types of Self-healing concrete bacteria
- Biotic: We use acid-producing bacteria. We use this where concrete stays in touch with water.
- Abiotic: We use chemical compounds. Such as cyanoacrylate, epoxy, polyurethane (PU), methyl methacrylate(MMA), dicyclopentadiene(DCPD), Na2Sio3). We use them when concrete is not in contact with any moisture.
Three prominent methods for Self-healing concrete bacteria
- Autogenous healing: This process of healing occurs when the continuity of two sides of cracks is restored without any external repair.
- Encapsulation of polymeric material
- Microbial production of calcium-carbonate (biotechnological approaches)
- Also, Calcium Carbonate is a versatile material we use in crack healing for the filling of voids. Bio-mineralization gives the best results in sealing the micro cracks. Also, keep in mind that the encapsulation method would give better results than the direct application method.
- Direct Application Method: Direct addition of healing agents to cement mixture.
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You can read some books about Self-healing concrete bacteria as well, here are some links: