Bacterial Concrete or Self-Healing Concrete
Self-healing concrete could solve the problem of concrete structures deteriorating well before the end of their service life. Concrete is still one of the main materials used in the construction industry, from the foundation of buildings to the structure of bridges and underground parking lots. Traditional concrete has a flaw, it tends to crack when subjected to tension.
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. Since the costs involved for maintenance and repair of concrete structures are usually high, this research focuses on the development of self-healing concrete. Self-healing of cracks in concrete would contribute to a longer service life of concrete structures and would make the material not only more durable but also more sustainable.
Concrete has an autogenous healing capacity as unhydrated cement is present in the matrix. When water contacts the unhydrated cement, further hydration occurs. Furthermore, dissolved CO2 reacts with Ca2+ to form CaCO3 crystals. These two mechanisms, however, may only heal small cracks.
Concrete can withstand compressive forces very well but not tensile forces. When it is subjected to tension it starts to crack, which is why it is reinforced with steel to withstand the tensile forces.
Why we need self healing concrete?
Concrete will continue to be the most important building material for infrastructure but most concrete structures are prone to cracking. Tiny cracks on the surface of the concrete make the whole structure vulnerable because water seeps in to degrade the concrete and corrode the steel reinforcement, greatly reducing the lifespan of a structure. Concrete can withstand compressive forces very well but not tensile forces. When it is subjected to tension it starts to crack, which is why it is reinforced with steel to withstand the tensile forces. Structures built in a high water environment, such as underground basements and marine structures, are particularly vulnerable to corrosion of steel reinforcement. Motorway bridges are also vulnerable because salts used to deice the roads penetrate into the cracks in the structures and can accelerate the corrosion of steel reinforcement.
In many civil engineering structures, tensile forces can lead to cracks and these can occur relatively soon after the structure is built. The repair of conventional concrete structures usually involves applying a concrete mortar which is bonded to the damaged surface. Sometimes, the mortar needs to be keyed into the existing structure with metal pins to ensure that it does not fall away. Repairs can be particularly time-consuming and expensive because it is often very difficult to gain access to the structure to make repairs, especially if they are underground or at a great height.
Who Developed Self-Healing Concrete ?
Self-healing concrete was developed by microbiologist Hendrik Jonkers of the Delft University of Technology in the Netherlands. It was largely inspired by natural body processes in which bones heal through mineralization, and Jonkers explored the idea of whether this could be replicated in concrete.
The common problem found in Concrete is Crack
- Concrete expands and shrinks due to temperature differences
- Settlement of structure
- Due to heavy load applied
- Due to loss of water from concrete surface shrinkage occurs
- Insufficient vibration at the time of laying the concrete
- Improper cover provided during concreting
- High water cement ratio to make the concrete workable
Various Types of Bacteria Used in Concrete
There are various types of bacteria were used in bacterial concrete construction are:
- Bacillus sphaericus.
- Escherichia coli.
- Bacillus subtilis.
- Bacillus cohnii.
- Bacillus balodurans.
- Bacillus pseudofirmus.
ADVANTAGES AND DISADVANTAGES OF SELFHEALING CONCRETE
The use of self-healing concrete significantly enhances the strength of concrete.
- It has lower permeability when compared to conventional concrete.
- It has also lower water absorption when compared to conventional concrete. It offers great resistance against freeze and thaw attacks.
- The chances of corrosion of reinforcement are reduced to negligible. Redressing of cracks can be done efficiently.
- Overall maintenance cost of this concrete is low
- There is no design of bacterial concrete is mentioned in IS codes or any other codes.
- Cost of this concrete is comparatively higher than conventional concrete; it’s about 10-30% more than conventional concrete.
- The germination of bacteria is not suitable in every environment.
- The investigations involved to observe calcite precipitation are costly.
- Bacteria that are used in concrete are not good for human health; hence its usage should be limited to the structure.
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Founder & Admin of civilengineeringsolution.com, I am a civil engineer working as a Assistant Engineer (QA/QC).