SELF HEALING CONCRETE OR BACTERIAL CONCRETE

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SELF HEALING CONCRETE OR BACTERIAL CONCRETE

Self-healing concrete fills up the cracks developed in the structures by the help of bacteria in the concrete after hardening.

This common problem of cracking in the building has many remedies before and after the crack. One of the remedial processes is Bacterial Concrete or Self Healing Concrete.

The use of technology is on the next level or say higher level to taste different type of procedures, methods, and materials.

But due to some reasons like human mistakes, unskilled labours, and incorrect handling, it is hard to sustain its designed life.

SELF HEALING CONCRETE OR BACTERIAL CONCRETE
Figure 1; SELF HEALING CONCRETE
Source- THE CONSTRUCTOR

WHY SELF HEALING CONCRETE???

To overcome the problems which arises after the construction like weathering, cracks, leaks, and bending etc., self-healing concrete is taken into the account.

Another some reasons are given below-

  • Concrete expands and shrinks due to temperature differences
  • Settlement of structure
  • Due to the heavy load applied
  • Due to the 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
  • Due to corrosion of reinforcement steel
  • Many mixtures with rapid setting and strength gain performance have an increased shrinkage potential.

CRACK WIDTH WHICH CAN BE HEALED???

It can be observed that small cracks that occur in a structure of width in the range of 0.05 to 0.1mm gets completely sealed in repetitive dry and wet cycles. The mechanism of this autogenously healing is, the width of range 0.05-0.1mm act as capillary and the water particles seep through the cracks. These water particles hydrate the non or partial reacted cement and the cement expands, which in turn fills the crack.

But when the cracks are of greater width, need of other remedial work is required. One possible technique is currently being investigated and developed was based on application of mineral producing bacteria in concrete.

The bacteria used for self-healing of cracks are acid producing bacteria. These types of bacteria can be in dormant cell and be viable for over 200 years under dry conditions. These bacteria act as a catalyst in the cracks healing process.

TYPE OF BACTERIA USED???

There are various types of bacteria were used in bacterial concrete construction are:

  • Bacillus pasteurizing
  • Bacillus sphaericus
  • Escherichia coli
  • Bacillus subtilis
  • Bacillus cohnii
  • Bacillus balodurans
  • Bacillus pseudofirmus

MECHANICS OF BACTERIAL CONCRETE???

Self-healing concrete works on biological reactions of non-reacted limestone and a calcium-based nutrient with the help of bacteria to heal the cracks that appeared on the building.

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.

(Aide- अंगरक्षक, परिसहायक, an assistant to an important person, especially a political leader)

It also improves the durability of steel reinforced concrete due to consumption of the oxygen by the bacteria to convert calcium into limestone.

CHEMICAL PROCESS OF SELF-HEALING???

When the water comes in contact with the unhydrated calcium in the concrete, calcium hydroxide is produced by the help of bacteria, which acts as a catalyst. This calcium hydroxide reacts with atmospheric carbon dioxide and forms limestone and water. This extra water molecule keeps the reaction going.

CaO + H2O – Ca(OH)2

Ca(OH)2 + CO2 – CaCO3 + H2O

The limestone then hardens itself and seals the cracks in the concrete.

SELF HEALING CONCRETE v/s NORMAL CONCRETE

Test results for the self-healing concrete and normal concrete-

DAYSNORMAL CONCRETE (N/mm2)BACTERIAL CONCRETE (N/mm2)
720.8527.10
2830.0038.95
Table 1; Compressive Strength

DAYSNORMAL CONCRETE (N/mm2)BACTERIAL CONCRETE (N/mm2)
73.904.6
287.057.80
Table 2; Flexural Strength

From the test results this can be seen that the bacterial concrete is better than normal concrete in both ways.

Research Papers for the strength of bacterial concrete-

  1. STUDY OF COMPRESSIVE STRENGTH OF SELF HEALING CONCRETE
  2. Bio Concrete- The Self-Healing Concrete
  3. BACTERIAL CONCRETE AND EFFECT OF DIFFERENT BACTERIA ON THE STRENGTH AND WATER ABSORPTION CHARACTERISTICS OF CONCRETE: A REVIEW
  4. Bacterial concrete: Development of concrete to increase the compressive and split-tensile strength using bacillus sphaericus

ADVANTAGE OF BACTERIAL CONCRETE

  • Self-repairing of cracks without any external aide.
  • Significant increase in compressive strength and flexural strength when compared to normal concrete.
  • Resistance towards freeze-thaw attacks.
  • Reduction in permeability of concrete.
  • Reduces the corrosion of steel due to the cracks formation and improves the durability of steel reinforced concrete.
  • Bacillus bacteria are harmless to human life and hence it can be used effectively.

DISADVANTAGE OF BACTERIAL CONCRETE

  • Cost of bacterial concrete is double than conventional concrete.
  • Growth of bacteria is not good in any atmosphere and media.
  • The clay pellets holding the self-healing agent comprise 20% of the volume of the concrete. This may become a shear zone or fault zone in the concrete.
  • Design of mix concrete with bacteria here is not available any IS code or other code.
  • Investigation of calcite precipitate is costly.

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