SEGREGATION IN CONCRETE AND ITS TYPES
Segregation refers to the separation of the different phases of concrete. This happens when the concrete mix is not cohesive enough. Slump test in conventional concrete and flow test in self-compacting concrete can give a good picture of concrete segregation. If the concrete is not cohesive, the large particles will separate.
Segregation is the separation of an individual or a group of individuals from a larger group. Sometimes special treatment is given to the individual or the separated group. Segregation can also involve the separation of elements from a larger group. For example, a brokerage firm may separate the management of funds in certain account types to separate its working capital from client investments.
Types of concrete separation
- Coarser and heavier particles tend to separate or settle from the rest of the mix because they tend to move faster down a slope or settle more than finer materials. This type of segregation can occur if the concrete mix is too dry
- Grout (water + cement) separating from the rest of the material due to the lower density. This type of segregation can occur if the concrete mix is too wet. Well-designed concrete will not separate if properly mixed and proportioned.
Causes of segregation in concrete
Here are the main causes:
- The difference in specific gravity of the constituents of the mixture, i.e. the fine aggregates and the coarse aggregates.
- The difference in the size of the aggregate.
- Incorrect classification of aggregates.
- Improper handling of aggregates.
- Bad practices and the handling and transport of concrete.
- Too much concrete vibration.
- Concrete that is not properly proportioned and poorly mixed for 2 feasible mixes.
- Placing concrete from a greater height.
- Concrete is discharged from a poorly designed mixer or mixed with worn blades.
How to Prevent Concrete Segregation
- At the time of construction, especially when using transit mixers, care should be taken that concrete is not poured from a height greater than 1.5 meters.
- Aggregates must be properly graded as this will prevent segregation.
- To improve the viscosity of the concrete which prevents segregation, air entertainment agents can be used.
- In the case of mass concreting where mechanical vibrators are used, care should be taken that they are not used for a longer period.
PRECAUTIONS TO TAKE
- The concrete mix must be properly designed with an optimum amount of water to make a consistent mix. Such concrete will show no tendency to segregation.
- Field quality control must be maintained during the handling, transportation, placing, compacting and finishing of concrete.
- If at any stage segregation is observed, then remixing should be done to make the concrete homogeneous again.
- Adjuvants, such as pozzolanic materials or an air diverting agent, should be used to prevent segregation. Air entertainment allows for reduction of mix water without loss of slump, which increases workability and decreases segregation and bleeding.
- Concrete should not be able to fall from greater heights. It should be placed as close as possible to its final position.