Segregation of concrete refers to the separation of the different components of concrete, such as cement, sand, aggregate, and water, that can occur during the mixing, transportation, or placing of concrete.
When concrete segregates, the different components separate from each other, resulting in a non-uniform mixture that can have a negative impact on the strength and durability of the concrete.
For example, when the larger aggregates settle at the bottom of the mix, leaving a layer of cement and water at the top, it results in coarse aggregate segregation. Similarly, when lighter materials such as cement and sand float to the top, it leads to fine aggregate segregation.
Types of segregation
Coarse aggregate segregation: This occurs when the larger aggregate particles settle and separate from the rest of the mix.
Bleeding: This occurs when the water in the mix rises to the surface of the concrete and evaporates, leaving behind a layer of cement paste that is weaker than the rest of the mix.
Plastic settlement: This occurs when the heavier particles in the mix settle to the bottom, leaving a layer of water on the surface.
Causes of Segregation of Concrete
Improper mix design: The mix design of concrete plays a crucial role in preventing segregation. If the mix is not designed properly or the correct proportions of different components such as cement, water, sand, and aggregates are not maintained, it can lead to segregation.
Poor placement techniques: Improper placement techniques can lead to the separation of the different components of concrete. For example, if the concrete is poured from a height, it can cause the larger aggregates to settle at the bottom, leading to coarse aggregate segregation.
Excessive vibration: Over-vibrating the concrete can cause the aggregates to settle at the bottom of the mix, leading to segregation.
Inadequate compaction: Inadequate compaction of concrete can cause lighter materials such as cement and sand to float to the surface, resulting in segregation.
Use of unsuitable aggregates: The use of unsuitable aggregates such as those with poor grading, shape, or size can also lead to segregation.
High water content: If the water content in the mix is too high, it can cause the cement and aggregates to separate, leading to segregation.
Prevent Segregation of Concrete
Proper mix design: The mix design should be done carefully, and the correct proportions of cement, water, sand, and aggregates should be maintained to create a uniform mix that resists segregation.
Adequate compaction: Adequate compaction should be done during placement to ensure that the different components of the mix are well bonded and prevent any segregation.
Proper placement techniques: The placement of concrete should be done carefully to prevent the larger aggregates from settling at the bottom. The concrete should be placed at a lower height to avoid any separation of materials.
Note: As per the Indian Standard Code of Practice IS 456:2000 clause 13.2, the free fall of concrete during its placement should not exceed 1.5 meters (5 feet). This limit is specified to prevent the segregation of concrete, as excessive free fall can cause the larger aggregates to settle at the bottom, leading to coarse aggregate segregation.
Avoidance of over-vibration: Over-vibration of concrete can cause the aggregates to settle at the bottom of the mix and result in segregation. Hence, proper vibration techniques should be used.
Use of appropriate aggregates: Suitable aggregates should be used in the mix to prevent segregation. The aggregates should have proper grading, shape, and size to create a uniform mix.
Maintaining the correct water content: The water content of the mix should be maintained carefully. The excess water in the mix can cause the separation of the cement and aggregates, leading to segregation.
Also read: Bleeding in concrete, causes, remedies
