WHAT IS SEGREGATION AND CAUSES OF SEGREGATION.

SEGREGATION

Segregation can be defined as separating out of the ingredients of concrete mix, so that the mix is no longer in a homogeneous and stable condition. Only a stable homogeneous mix can be fully compacted.

  • There are three types of segregation :
1. The course aggregate separating out from the mix, in case of dry mix.
2. The paste separating out from the mix, in case of wet mix.
3. Water separating out from the mix, being a material of lowest specific gravity, in case of excess water in the mix.

A homogeneous, stable and cohesive mix can be obtained by taking into consideration various parameters like grading of aggregate, size, shape and surface texture of aggregate with optimum water cement ratio. Such concrete will not exhibit any tendency for segregation. The cohesive and fatty characteristics of matrix do not allow the aggregate to separate out and matrix is sufficiently contained by the aggregate.


CAUSES OF SEGREGATION

1. Badly proportioned mix where sufficient matrix (paste) is not available to bind and contain the aggregates.
2. In sufficient mixing of concrete with excess water content.
3. Dropping the concrete in excess heights as in case of pouring the concrete in the column.This causes by variation in specific gravity in ingredients. The ingredients with the higher specific gravity fall first resulting in a segregation of concrete mix.
4. Discharging concrete against the reinforcement bars, formwork etc.
5. when concrete is discharging from a badly designed mixer, or from a mixer with wornout blades, concrete shows a tendency of segregation.
6. Conveyance of concrete by wheel borrow, conveyor belts, long distance haul by dumper, long lift by skip and hoist are also the situations promoting segregation of concrete.
7. If too wet concrete vibrated excessively it is results in a segregation of the concrete mix because when the vibrator is allowed to continue too long, segregation of course aggregate towards the bottom of the formwork and of the cement paste towards the top may result.
8. While finishing the concrete floors or pavement, with a view to achieve a smooth surface, masons are likely to work fast and rubbing the towel immediately on the wet surface resulting in course surface drops down and cement paste will be comes up.It is segregation.


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