Segregation

Segregation in Concrete | Purposes, Types, Reasons, Effect and Prevention of Segregation in Concrete

In this article, we will discuss segregation in concrete.

 

  1. Introduction  

The segregation in concrete may be defined as the process of separation of cement paste and aggregates of concrete from each other at the time of handling and placement.

Segregation occurs due to over-vibration or compaction of concrete, in which cement paste advance to the top and aggregates sort out at the bottom. Coarse aggregates settle to the bottom with sand, fines, cement, and lastly water.

Concrete is a mixture of cement, fine and coarse aggregates. A mass of good concrete in which all the constituents are properly proportioned to prepare a homogeneous mixture.

The specific gravity of Cement is between 3.1-3.6gm/cc, and for aggregate it lies between 2.6-2.7gm/cc due to these differences, the aggregate separates from the matrix and causes segregation in concrete

A mass of good concrete is one in which all materials are uniformly distributed to make a homogeneous mixture.

Bleeding is one form of segregation, where water is seen coming out to the surface of the concrete, being the lowest specific gravity from whole the ingredients of concrete.  

 

segregation in concrete

 

  2. Purpose of Concrete Segregation  

1. To spill up or settle the coarse aggregate from the rest of the matrix.

2. The cement paste spilled from the coarse aggregates.

3. Water is different from the rest of the material being the lowest specific gravity content.

 

  3. Types of Segregation  

Segregation is as found two types –

Initially (dry mixes), the coarse aggregate is segregated or settling down from the rest of the matrix.

Secondly (wet mixes), the paste or matrix is separated from the coarse aggregate.

In the case of segregation, remixing for a short time may transform concrete again homogeneous.

 

  4. Reasons For Segregation  

a. Transporting concrete mixes for long-distance.

b. Imperfectly proportioned cement mix where insufficient matrix does not exist to combine the aggregates.

c. Dropping the concrete from height.

d. Using vibrator on a mass of concrete for a long time.

e . Badly proportion mixer or worm-out blades.

f. More vibration of concrete than needed.

 

  5. Effects Due To Segregation  

The harmful effects because of segregation of concrete are as follows:

1. Honeycombing of concrete is seen.

2. The risk of the high permeability of concrete.

3. Deceases the compressive strength of concrete.

 

  6. Prevention of Concrete from Segregation  

The preventions of segregation in concrete are as follows:

a. At first, make sure that the concrete is mixed properly; the concrete must be mixed at the right speed in the transport concrete mixer for at least two minutes quickly before discharging.

b. The concrete must be put down as soon as possible.

c. While transporting the concrete mixture, carry cautiously.

d. Regularly mix new concrete to the concrete prepared already.

e. Fixing the height from where the concrete has fallen.

f. The proper precautions should be taken during moving concrete.

g. To neglect segregation of concrete, don’t apply vibrator.

h. The utilizes of an air-entraining agent decreases isolation considerably.

i. The concrete mixes have to be proportionate nicely with the best amount of water i.e. neither too wet nor too dry.

j. Always measure the efficiency of the mixer concerning enough uniformity of distribution of parts in every matrix.

k. Utilize the vibrator sharply.

l. The formwork should be watertight so that the cement paste escapes from the foams; do not shake the formwork.

m. Shake the concrete only for a limited time; not too long, not too quick.

n. Utilize an air-entraining agent such as chemical penetration into the mixture because entered air decreases the chance of isolation.

o. If distinct is noticed in the concrete, the mixture must be expert to prepare it homogeneous again.

p. Do not let the solid flow.