Segregation of concrete will adversely affect the properties of hardened concrete, it will significantly reduce the strength and durability, the separation of aggregate and cement paste know as segregation, cohesiveness is an important characteristic of concrete, cohesiveness determine the ability of concrete to hold all ingredient together during placing and compacting, a proper cohesive concrete will not segregate during placing and compacting, concrete will segregate due to following reasons:
- using high W/C, the increase of water content in the concrete mix above the acceptable limit will result in a downward movement of aggregate. as a result, aggregate will accumulate at the bottom and cement paste at the top.
- pouring concrete from height such as for foundation, this will lead to concrete segregation.
- over-vibrating of concrete could cause segregation.
- improper proportions of concrete mix will cause concrete particles to segregate.
Preventing segregation is the duty of designer and engineer at the field, the following measures will prevent the segregation of concrete:
- W/C ratio should be maintained within the acceptable range, W/C usually range from 0.35 to 0.40, superplasticizer can be used to increase concrete workability.
- pouring concrete should be done at a height less than 1.5 m
- adding water at the field should not be allowed, adding water could lead to segregation.
- improper grading of aggregates and using elongated aggregate will lead to unworkable concrete and this will to segregation of concrete, therefore aggregate should be graded properly and elongated aggregate should not be used.