What is Segregation of concrete? - Causes, remedies, and different types.

 1. What is the segregation of concrete?

The concrete is composed of different constituents. The main ingredients that form the concrete mix are cement, fine aggregates, coarse aggregates, and water. The separation of these constituents from one another while placing the fresh concrete in the formwork or in any mold is said as segregation of concrete.

2.  What causes the segregation of concrete?

The various constituents that are part of a concrete mix have different specific gravity. The water is the lightest among them having a specific gravity of 1. The sp. gravity of fine and coarse aggregates falls in the range of 2.3 to 2.8. The sp. gravity of cement is anything between 3.12 to 3.20 depending upon the type of cement. 

So each of these materials has a tendency to separate from each other as they carry different weights. The lighter materials form the top layer and the heaviest one settles at the bottom part of the concrete poured in the formwork.

This separation happens due to improper mixing of the constituents, and non-technical handling of the concrete, resulting in non-cohesive concrete.

3. What are the different types of segregation in concrete?

The segregation of concrete happens in the following three ways.

1. The segregation of water that comes over the top surface of the concrete, which is also known as the bleeding of concrete.

2. Segregation of the coarse aggregates at the bottom or at the corner of the formwork.

3. Segregation of the cement paste, that oozes out from the concrete mix.

4. What are the factors that make the segregation in concrete?

1. Improper water-cement ratio: 

Adding excess water to the concrete creates bleeding of the concrete. 

2. Excess vibration: 

Vibrating the concrete by an unskilled worker for a prolonged time gives a way to concrete segregation. 

3. Improper batching of concrete: 

The ingredients in the concrete have to be added proportionately to create a homogeneous concrete mix.

The ingredients that are added out of proportion in the concrete, lead to its segregation from the concrete mix.

4. Mixing time in the concrete mixer:

 Strictly you have to rotate the concrete mixer to its specified time for the proper blending of all the ingredients. Pouring the concrete in a hurry before its homogeneous mix leads to concrete segregation.

Mixing concrete.

5.  Pouring concrete height: 

While placing the concrete, the pouring height should be within 1.5m ( 5 ft.) to avoid segregation. You have to use a chute or hose, providing proper inclination for the smooth movement of the concrete when the height exceeds 5ft. 

Chute to place concrete.

 6. Non-technical use of admixtures and plasticizers: 

Adding the admixtures and other concrete chemicals above their specified limit is another way to make concrete segregation.

7. Transport distance of concrete: 

If the RMC is transported covering a larger distance over a rough surface road, it helps in creating segregation while placing them in the formwork.

RMC truck.

8. Improper mix design.

5. What are the side effects or problems created by the segregation of concrete?

1. Honeycombing in the structure.

2. Producing concrete of lower density with voids in it.

3. Lower life span of concrete.

4. Weak concrete, having a lower design strength.

5. Creates a lower binding strength with rebar. 

6. How to prevent segregation in concrete?

In question no. 4 above, I have explained the different factors that help in the segregation of concrete. So, controlling all those factors or doing the reverse of it will prevent the segregation of concrete.

For your convenience, I will rewrite it as follows.

1. Maintaining the specified w/c ratio.

2. Concrete vibration: 

Using the immersion needles of a specified size and vibrating them for the required time limit.

Concrete vibration.

3.  Batching of concrete: 

Weight batching is one step ahead of volume batching in preventing concrete segregation. You have to avoid random batching as far as possible to have cohesive concrete.

4. Concrete mixing time: 

Rotate the concrete mixer until you get a properly blended cohesive mix of uniform colors.

5. Height of the concrete:

 You will observe the honeycombing in columns at the bottom part, which is due to the excess height while placing the concrete. Avoid the direct pouring of concrete when you cross the formwork height above 1.5m. or while placing it in congested areas. Use a chute or concrete hose pipe in such conditions for the concrete flow. 

Honeycomb in structure.

6. Admixtures & plasticizers: 

Use these concrete chemicals as per the specified dosage when they are necessary, and avoid unnecessary usage of them.

7. Transport distance: 

You have to remix the RMC when it travels a longer distance until you are sure that it is blended properly. Make the RMC truck container rotation keep going, to achieve this cohesive mix.

8. Mix design: 

Make a proper mix design after testing the available raw materials on your site. Avoid blindly choosing any one grade of concrete for the preparation, without understanding the properties and specifications of the ingredients.

To get the answer to more such construction-related FAQs, click here.

Thank you for going through this article❤. Have a good day 😄.

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