Segregation of concrete – Causes and Remedies
Segregation means the partition of course materials (cement, sand, aggregates) from other mass. When the water quantity in the concrete mix is increased, the greater sized aggregates are detached thus results in segregation.
Therefore, concrete should be free from segregation as concrete not only gets weak but lack of consistency also brings unwanted properties in the hardened state. The segregation can be avoided with the choice of proper grading and careful handling.
Reasons for segregation :
Carrying concrete mixes for long distance.
Imperfectly proportioned mix where adequate matrix does not exist to unite the aggregates.
Dropping concrete from height places (underground foundation & rafts).
Vibrating concrete for long time.
Segregation is available in two types - Initially (in too dry mixes), the coarse aggregate is segregated or settling down from the rest of the matrix, secondly ( in too wet mixes ), the paste or matrix is detached away from coarse aggregate. In case of segregation, remixing for a short time may transform concrete again homogeneous.
The following precautions should be taken to get rid of concrete segregation :-
The concrete mix should be perfectly designed with best possible quantity of water i.e. not too wet nor too dry.
The proportion of the mix should be correct.
Ensure the concrete is mixed perfectly at the proper speed in a transit mixture for minimum two minutes.
Concrete should not become excessively wet or dry.
Refrain from arranging concrete from long height.
There should be proper transportation of concrete through shortest route.
Air entraining admixture and pozzolanic materials should be used in mix.
Select coarse and fine aggregate with approach specific gravity.
The vibrator should be used for exact time period (not too long or short).
Don’t permit concrete to flow.
The formwork should be firm.
The formwork should not be vibrated.
Video Source: Civil Engineers