Self Compacting Concrete is a highly flowable non-segregating concrete that can be placed in formworks without any external compaction. It gets compacted by means of its own weight.
Related Article: Types of Concrete
Advantages of Self Compacting Concrete
- Self Compacting Concrete can be placed at a faster rate with no need for mechanical vibration. It results in saving in placement costs, shortening the construction period and reducing the number of workers required.
- It can also be placed and self-compacted in restricted (hard to reach) areas.
- It makes more uniform concrete surface finish with minimum remedial surface work.
- Self Compacting Concrete makes better bonding with reinforcements.
- Since it is flowable. It can be pumped easily.
- It reduces the noise that might have resulted due to the use of mechanical vibrators.
Properties of Self Compacting Concrete
In the plastic state, Self Compacting Concrete should have two essential properties:
- Flowability: The flowability is achieved by using superplasticizers (high range water reducing admixtures) without adding extra water.
- Stability (Resistance to segregation): The stability is attained by increasing the amount of fines or by modifying the viscosity of the mixture.
Slump Flow Test
In the field, the properties of Self Compacting Concrete is tested by a modified slump test i.e. slump flow test.
The slump cone is completely filled without any compaction. The cone is then lifted and spread of the concrete is measured.
The flowability is measured by the spread of the concrete sample.
The stability is measured with the visual stability index (VSI). The VSI is established on the basis of whether bleed water is observed at the periphery of the spreading concrete. VSI values range between 0 for highly stable to 3 for unacceptable stability.
The viscosity of Self Compacting Concrete is can be measured by the rate at which the concrete spreads. The time taken by the concrete mix to reach a spread diameter of 50 cm (T50) is measured. The time varies from 2 to 10 seconds. The high T50 value is appropriate for concrete that has to travel long horizontal distances without much obstruction.
Uses of Self Compacting Concrete
It has been successfully used for
- Anchorage in bridges
- Filling joints
- Tunnel lining and construction
- Making concrete elements such as culverts, water tanks, slabs etc.