SEGREGATION IN CONCRETE AND ITS TYPES

Segregation refers to separation of different concrete phases. It happens when concrete mix is not cohesive enough.Slump Test in Conventional concrete and Flow test in Self Compacting Concrete can give a good picture of segregation of concrete. If concrete is not cohesive larger particles will separate out.

Segregation is the separation of an individual or group of individuals from a larger group. It sometimes happens to apply special treatment to the separated individual or group. Segregation can also involve the separation of items from a larger group. For example, a brokerage firm might segregate the handling of funds in certain types of accounts in order to separate its working capital from client investments.

Types of Segregation of Concrete

1. The coarser and the heavier particles tend to separate out or setting down from the rest of the mix because they tend to travel faster along a slope or settle more than finer materials. This type of segregation may occur if the concrete mix is too dry
2. Grout (water + cement) separating out from the rest of the material because of lowest specific gravity. This type of segregation may occur if the concrete mix is too wet. A well-designed concrete does not segregate if rightly mixed and batched.

Causes of Segregation in Concrete

Following are the major causes :

• The difference in the specific gravity of the mix constituents i.e fine aggregates and coarse aggregates.
• The difference in the size of aggregate.
• Improper grading of aggregates.
• Improper handling of aggregates.
• Bad practices and handling and transporting of concrete.
• Too much vibration of concrete.
• Concrete that is not proportioned properly and not mixed adequately for 2 workable mix.
• Placing of concrete from a greater height.
• Concrete is discharged from a badly designed mixer or from a mixture with worn-out blades.

How to Prevent Segregation of Concrete

• At the time of construction, especially while using transit mixers care should be taken that the concrete is not poured from a height greater that 1.5 meter.
• Aggregates should be properly graded as it will prevent the segregation.
• To improve the viscosity of concrete which prevents the segregation, air entertaining agents can be used.
• In case of mass concreting where mechanical vibrators are used care should be taken that they are not used for longer period.

PRECAUTIONS TO TAKE

• The concrete mix should be properly designed with optimum quantity of water to make a cohesive mix. Such concrete will not exhibit any tendency for segregation.
• Field quality control must be maintained while handling, transporting, placing & compacting and finishing concrete.
• If at any stage segregation is observed, then remixing should be done to make the concrete again homogeneous.
• Admixtures, such as pozzolanic materials or air entertaining agent should be used to avoid segregation. Air entertainment permits a reduction of the mixing water with no loss of slump which increases workability and decreases segregation and bleeding.
• Concrete should not be allowed to fall from greater heights. It should be placed as near its final position as possible.