Plasticizers are admixtures that are added to concrete to increase the fluidity or workability of a cement paste or concrete. It is also called as workability aids, that are added to fresh or early stage concrete to change its workability characteristics.
Plasticizers are also called as water-reducers as they produce a concrete with the same workability at a lower water/cement ratio. Plasticizers hence help to manufacture a concrete mix with high durability with the same water content.
|Concrete With and Without plasticizer|
Action of Plasticizers in Concrete
Plasticizers have plasticizing action due to the presence of polymer molecules present in it. These molecules when mixed with concrete absorbs on the surface of the cement grains that would create a ionic group that points outwards. This would finally give a negative charge to the cement particles.
|Action of Plasticizers On Concrete|
These negatively charged cement particles cause mutual repulsion. This repulsion between the particles breaks the flocs of particles in the water/cement system that would result in entrapped air as shown in the figure below.
|Plasticizer Action on Concrete Steric Hindrance|
Other than the repulsion caused, these cement particles will be surrounded by sheath of oriented water molecules which also prevent close approach of the cement grains. This phenomenon is called as steric hindrance. This overall effect causes the greatest lubrication and fluidity for the concrete paste.
Classification of Plasticizers on Concrete
Based on the principle of working, plasticizers are classified as:
1. Hydrophilic Plasticizers
2. Hydrophobizing Plasticizers
Advantages of Plasticizers in Concrete
The main advantages of using plasticizers are:
- Improves workability of concrete without the addition of extra water.
- Improves the strength of concrete without increasing the cement content.
- Increase the strength characteristics of the finished concrete foundation by twenty five percent.
- Plasticizers make the compaction easy without the use of vibrators.
- Improves flowability and good adhesion to the surface.
- Concrete with high density is achieved using plasticizers.
- Plasticizers reduce the moisture content in concrete, making it frost resistant and prevents cracking.