Segregation of Concrete: Types and Causes
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A workable concrete is a concrete which will not easily segregate. More specifically, concrete segregation means separation of concrete ingredients from each other resulting in the non-uniform mix, leading to weak and porous concrete.
The segregation of concrete is primarily caused due to the differences in the size of particles and in the specific gravity of the mix constituents. But it can be controlled by doing the grading of concrete and by handling the concrete in proper way.
Addition of higher water in dry concrete mix leads to downward movement of the heavier aggregates which also results into segregation in concrete.
Also Read: Importance of Water-Cement Ratio in Concrete
Courtesy - 123rf
Generally, segregation occurs when we don’t mix concrete ingredients in correct proportion or do not take care while handling, transporting, or placing of concrete. Segregation creates porous concrete which reduces the strength of the concrete. It also leads to the voids in concrete, which causes leakage in house and accelerate the process of corrosion. Sometimes, it can become the reasons of building failure due to corrosion.
If you are constructing your own house, you have to understand segregation in concrete.
Types of Segregation in Concrete
There are two forms of segregation in concrete:
01. Segregation due to the Separation of Aggregates
The coarser and the heavier 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. 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.
02. Segregation due to the Separation of Cement Slurry
Cement slurry (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. i.e. Addition of water in concrete dry-mix is higher than that is specified in concrete mix design.
Workability is a very important virtue of fresh concrete 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.
Know more about the Workability of Concrete.
Causes of Segregation in Concrete
A well-designed and workable concrete does not segregate, if proper care is taken during the pouring of concrete. You can prevent segregation by knowing the exact cause of segregation in concrete. Hence,know the causes of segregation in concrete.
01. Uneven Proportion of Concrete Ingredients
To make the durable concrete, first, the proportion of concrete ingredients are decided by doing the concrete mix design. Concrete mix design specifies the exact quantity of waterand weight of the concrete ingredients like aggregates, cement, etc. which are required to make concrete. At the time of concrete mixing, if the ingredients of concrete are not mixed in proportion specified in concrete mix design, then it results into the poor workability of concrete. Poor workability of concrete may be the cause of segregation.
Hence, to avoid segregation, it is advisable to use the batching machine and carry out weigh or volumetric batching of concrete to get the proportion which is specified in predesigned mix.
02. Insufficient Mixing Time of Concrete
During the mixing of concrete at site, many times concrete workers do not mix the ingredients in a proper manner. Sometime the concrete is mixed for the lower duration or for longer duration. In both the cases, the aggregates may separate from the mix and it may be the reason of the segregation.
In case of drum mixture, dry concrete should be mixed for at least one minute and then the ingredients should be mixed one more minute after mixing the water in drum mixture. Hence, consider mixing time of at least two or two and half minutes to make the one batch of concrete.
When you are mixing ingredients manually, first mix dry ingredients properly and later add water to the dry mixture. Mix the ingredients for a duration at which it become homogeneous.
If you buy 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.
Know how to order RMC (Readymade concrete).
03. Handling of Concrete Mix
Once the concrete is mixed, the concrete has to be handled properly and it is to be poured on site. Sometimes poor handling of concrete while pouring also leads to the segregation in concrete. Make sure the concrete is transferred directly from the skip or bucket to the final position in the form.
Sometimes the poring of concrete is done manually and it is to be transferred through longer distance. In such cases, the heavierparticles are set at the bottom of ghamela and ultimately segregation happens.
04. Placing of Concrete Mix
It is observed that the bad construction practices followed during the placing of concrete mostly result into the segregation.
- Concrete always segregates, if it falls from height more than one mater 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. Sometime 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. Testing of aggregates is an important activity. If aggregates are not tested frequently during the construction, it may lead to improper proportion of concrete which may also cause segregation in concrete.
Sometimes ghamelas are used to batch the concrete ingredients. This type of batching is just like volumetric batching of concrete. But the measurement of concrete ingredients by ghamelas increases the chances of error in batching of concrete.
- Every important activity and construction machineries requires skilled person or operator to complete the work in suitable quality. Sometime unskilled worker operates machines like drum mixture, vibrator, etc. In most of the case, unskilled worker cannot operate the machineries like drum mixture and vibrators properly, which may cause the segregation of concrete. Sometimes, the poor performance of construction machineries i.e. faulty vibrator, miller, drum mixture, etc. may also be the cause of segregation of concrete.
Concrete should be compacted well at the time of placing. Over vibration or poor vibration also cause segregation in concrete.
Also Read: Methods of compaction and types of vibrator
- Sometimes the poor quality of shuttering material is used to form the concrete members. Generally, cement slurry gets out from the hole of formwork or broken corner/side of formwork, which will result into the honeycombing of concrete. Honeycombing of concrete is the result of segregated concrete.
- Sometime concrete admixtures are added to improve the workability of concrete, but extra use of admixture may lead to the segregation in concrete.
Nowadays most of the houses are made from the concrete. Concrete is a material which provides long service life to house. But, the segregation of concrete results into the porous or honeycombed structure. It leads to the other problems like leakages, cracks, corrosion in concrete. It ultimately leads to early repair of the house. By knowing the causes of segregation, you can easily avoid the segregation of concrete, and increase the life of your house.