Segregation In Concrete – Definition, Causes, Effects, Types and Prevention. (Civil Engineering Blog By Khazran)

Definition of Segregation:

The simple definition of Segregation in concrete is the separation of aggregate and concrete paste from each other due to handling and placing. Due to compaction or over the vibration of concrete Segregation of concrete occurs and in which the cement paste comes to top and aggregate at the bottom.

We know that Concrete is a mixture of Cement, fine, and coarse aggregates. The good form of concrete is the one in which all the constituents are properly categorized to form a homogeneous mixture. Specific gravities’ differences in of the constituents is the key cause of Segregation in concrete. The Specific gravity of Cement is in between 3.1-3.6g/cc, and for aggregate it lies between 2.6-2.7g/cc due to this difference, the aggregate separates from the matrix and causes segregation in concrete.

Some factors causing segregation in concrete:

01.   Irregular Proportion of Concrete Ingredients

The mixed design of concrete specifies the exact quantity of water and weight of the concrete ingredients like aggregates, cement, etc. to make the durable concrete, which is required to make concrete. During the time of concrete mixing, Poor workability of concrete may be the cause of segregation.  So the best advice is to use to avoid segregation is to use the batching machine and carry outweigh or volumetric batching of concrete to get the proportion which is specified in predesigned mix.

02. Poor  Mixing Time of Concrete

During the mixing of concrete at site, many times concrete workers do not mix the ingredients in a proper manner.  We know that the concrete sometimes is mixed for the lower duration or for a longer duration. In both the cases, the aggregates may separate from the mix and it may be the reason for the segregation.

Dry concrete should be mixed for at least one minute in case of drum mixing and then the ingredients should be mixed one more minute after mixing the water in the drum mixer. Hence, consider mixing time of at least two minutes to make the one batch of concrete.If you will do RMC (ready mix concrete), Consider the time of transportation, it should be as minimum as possible. Higher the time of transportation it will increase the chances of segregation of concrete.

    03. Handling of Concrete Mix

One another cause of segregation is when the concrete is mixed, the concrete has to be handled properly and it is to be poured on-site. Poor handling of concrete while pouring sometimes also causes segregation in concrete. Make sure the concrete is transferred directly from the bucket to the final position in the form.

In manually poring of concrete and when it is to be transferred through long distance, the heavier particles are set at the bottom of ghamela and ultimately segregation happens.

    04. Placing of Concrete Mix

The Concrete is always segregating if it falls from a height more than 3.28 feet or 1meter at the place of casting. When concrete falls from more than one meter, the large aggregates separate from the mixture which results in segregation of concrete. Sometimes pouring of concrete through the chute also creates the problem of segregation. If you use non-graded aggregates to make concrete, there may be chances of segregation in concrete. And alsoIf aggregates are not tested frequently during the construction, it may lead to the improper proportion of concrete which may also cause segregation in concrete.

Effects on Concrete:

• It affects concrete and it will become difficult to compact it properly.
• 2.      Segregated concrete does not give a homogeneous mass throughout the structure
• 3.      Porous, Rock pockets, sand streaks layers in hardened concrete are the result of segregation.
• 4.      Segregate also affects the strength of concrete.
• 5.      Due to segregation after placing, the concrete in the lower part of a pour of any significant depth can be stronger than that in the upper part.
• 6.     Due to segregation excess mortar comes to the top of the surface, which causes plastic shrinkage cracks.

Two types/forms of segregation in concrete:

1.             1. Segregation due to the Separation of Aggregates

The Coarse particles tend to separate out or setting down from the rest of the matrix because they tend to travel faster along a slope or settle more than finer materials just because of more weight or size. This type of segregation may occur if the concrete mix is too dry. i.e. addition of water in concrete dry-mix is lower than that is specified in concrete mix design.

2.            2. Segregation due to the Separation of Cement Slurry

Cement slurry Which is a mixture of water and 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. i.e. Addition of water in concrete dry-mix is higher than that is specified in concrete mix design. The important worthiness of fresh concrete is workability and water content of mix is a prominent factor which majorly affects the workability. Good workability of fresh concrete always results into the durable concrete and ultimately leads to higher service life of house.

How to minimize segregation in concrete:-

·       Mix segregation can be controlled to some extent by adding air-entraining agents, admixtures and pozzolanic materials.

·       Segregation can be controlled by maintaining proper proportioning the mix.

·     Segregation can be controlled by peculiar handling, placing, transporting, compacting,and finishing of concrete.

·       Concrete should be placed through  inclined chutes If the depth  of concrete is more than 4.92ft.