What is segregation?
A mixture of cement, water, fine and coarse aggregate is called the concrete. In engineering, segregation meanings to “separation of constituent materials in concrete.” So, the segregation of concrete is the tendency of coarse aggregate to separate from the concrete mix.
It can generally be observed in the plastic stage of the concrete. Problems like porous layer, honeycomb, sand streaks, rock pockets, etc. arise due to the segregation of concrete.
Types of segregation
- Separation of grout (water + cement) from the rest of the particles due to lower specific gravity.
- Separation of coarse aggregates from the concrete mixture.
- Separation of water from the concrete mix (bleeding of concrete).
Causes of segregation of concrete
- The difference in the specific gravity of the constituents used in the concrete mix.
- Vibrating concrete for a long period of time or over the vibration of concrete.
- Improper mixing in the concrete, which might include: use of poorly graded aggregates, excessive use of water in the mix, etc.
- Storing concrete mix for a long period of time or transporting concrete mix for longer distances.
- Improper or insufficient compaction of concrete.
- The insufficient mixing time of concrete. Either the concrete is mixed for a lower duration or longer duration. They both cause segregation of concrete.
- When the concrete mix is dropped from more than 1.5 meters, large aggregates get separated from the mixture due to differences in weight causing segregation.
Effects of segregation of concrete
- Problems of leakage, corrosion, carbonations.
Since segregation causes the formation of pores in the concrete, there is leakage of water or water permeability in the concrete causing leakage of water from the slab or column. Due to leakage in the column, the reinforcement forms corrosion. Also, there won’t be a bond between reinforcement and concrete in RCC, which directly affects the durability of the structure.
- Develops the crack in the concrete
Because of segregation, the strength of concrete is poor in slab or beam or column, which causes the development of cracks in the structure.
- The lower strength of concrete
Lack of compaction and bond formation in concrete due to segregation lowers the strength of the concrete.
How to prevent segregation?
- The water-cement ratio should be used in the limit. It’s best to have w/c from 0.4 to 0.6.
- Proper handling of water content in the concrete. Concrete shouldn’t be too dry or too wet.
- Concrete mixing should be done for a sufficient time period.
- The aggregates and other binding materials used in the concrete mix should be of high quality.
- Never pour or place concrete from more than 1.5m height.
- The shortest route should be chosen for concrete transportation.
- Vibrating concrete for a limited period of time. Vibration should not be done for a long time or too little time.
- Formwork should be made watertight to prevent leakages.
- Proper handling and placing of freshly prepared concrete.
- Using Air entraining admixtures to enhance the viscosity in concrete.
Water permeability and leakage of water have major effects and disadvantages in the structures like a dam, water tank, etc.
So, the segregation should never be underestimated in concrete. Columns and beams play a significant role in preventing the structure from collapse due to later or vertical loads. If segregation is detected in these columns and beams, then they are already weakened, which jeopardizes our whole structure.
I hope this article remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Mohan Khadka