SELF HEALING CONCRETE


Self-healing concrete is a type of concrete which are recently used for construction purposes. Concrete is one of the most commonly used ingredients for construction projects. However concrete has minimal corrosion and weathering effects and cracks are formed due to thermal changes, shrinkage, etc. There has to found and cured. But in massive structures like bridges, high-rise buildings determining the cracks and their fixing is difficult. This lead to the invention of self-healing concrete. This concrete has the ability to heal itself. First, let us discuss Concrete. For more articles like this CLICK HERE

What is Concrete?

Concrete is made up of coarse aggregate, fine aggregate, and cement. Cement is called the binding material. Stone or brick ballast is used as coarse aggregate and fine aggregate sand is used.

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When the concrete mixes with water, a chemical reaction occurs called hydration. Concrete is durable and has high compressive strength. But these are liable to disintegrate by the attack of alkali, sulfur, etc. Thus cracks are developed. Concrete has another flaw, that it has low tensile strength. Therefore steel is used


These cracks are also formed due to concrete shrinkage, excess freezing and thawing, and due to heavy loads. Moisture from the atmosphere induces these cracks and causes corrosion of steel reinforcement.

AUTOGENOUS HEALING:-

Autogenous healing is the process in which the cracks formed are healed by themselves by some chemical reactions. Through the cracks water enters into the concrete and which causes hydration. Here the calcium hydroxide reacts with the carbon dioxide and forms calcium carbonate. This Calcium carbonate is formed as crystals in the gap and thus the cracks are healed. But this autogenous healing can heal only cracks up to 0.3mm wide.

MANUFACTURE OF SELF HEALING CONCRETE

Self-healing concrete is concrete that has the ability to repair its own crack by some microbial activities. These consist of capsules embedded with some materials which can release gel-like substances by rupturing the capsule.
Self-healing concrete is manufactured by different methods.

BY USING BACTERIA:-

Concrete has a hostile environment. Bacterias can easily survive in this hostel condition. These bacteria in high alkaline conditions are able to produce limestone. The bacteria which are used inside the concrete maybe of mineral producing power acid-producing bacteria

Some common type of bacterias which are used in self-healing concrete is
  • Bacillus colin
  • Escherichia coli
  • Bacillus sphaericus
  • Bacillus subtills
  • Bacillus pasteurizing
  • Bacillus baloduram
The lifetime of these microorganisms is 200 years under dry conditions. The oxygen inside the concrete is consumed by them. Thus corrosion is prevented. The spore produced by microorganisms is stored inside the concrete when the crackers healed. 

BY USING MICROFIBERS

A microorganism that has a size of less than 50 microns are used in concrete heal the cracks. During the crack occurs moisture enters in the concrete. This microfibers react with the the monster to form non hydrated clusters.Thus the cracked is healed.

BY USING ENCAPSULATED POLYMER

Hydrophobic nanoparticles are encapsulated inside a brittle ceramic glass tubes. This tubes are are mixing with concrete during its manufacture. During the formation of cracks hydrophobic nanoparticles is added to the polyline layer thus cracks are healed. The polymers which are commonly used for self healing concrete are
  • Methyl methacrylate
  • Water repellent agents
  • Poly urethane, etc
This encapsulated polymers are used in structures which are subjected under cyclic loads.

BY USING SUPER ABSORBENT POLYMER

In this type super absorbent polymers consisting of ionic monomers are used. This ionic monomers have self healing properties.

When they come in contact with water, they swell and repairs the crack. As the amount of super absorbent increases the workability also increases. The internal cracks are thus reduced by this method.

ADVANTAGES AND DISADVANTAGES


The main advantages of this concrete are
  • Makes the Concrete more resilient.
  • Increases the life span of concrete.
  • Reduces the emission of carbondioxide.
  • Corrosion is prevented.
  • Internal cracking can be reduced.
Some of the disadvantages of this Concrete are
  • The capsule in which the polymers are enclosed have high chances to break during the manufacturing process of concrete.
  • They occupy the 20 percentage of the volume and thus compression strength is reduced.
  • The cost of this concrete is twice the cost of conventional concrete


Although this concrete has many cons and pros they can used in areas where the repairing of cracks are difficult. These have an easy mechanism of healing  and no patching is needed.