Segregation in Concrete

Segregation is a process by which large aggregates separate small aggregates and is normally caused by pouring concrete from heights of more than one meter.

To obtain a good concrete all the ingredients must be properly distributed so that a homogeneous mixture is achieved. There is considerable difference in the sizes and specific gravities of the constituent ingredients of concrete making it natural that the materials show a tendency to fall apart.

A concrete that is well mixed by taking into consideration various parameters such as grading, size, shape and surface texture of aggregate with optimum quantity of water will result into a good cohesive mix thus limiting the chances for segregation. The cohesive and fatty characteristic of the concrete mix does not allow the aggregate to fall apart and at the same time it plays a crucial role in containing the aggregate by denying water an easy way to drain out freely from the rest of the ingredients.

The conditions that make concrete prone to segregation include;

• Badly proportioned mix with absence of sufficient matrix to bind and contain the aggregates. 

• Insufficiently mixed concrete with excess water content. 

• Dropping of concrete from high heights as in the case of placing concrete in column concreting. 

• When concrete is discharged from a badly designed mixer, or from a mixer with worn out blades. 

• Conveyance of concrete by conveyor belts, wheel barrow, long distance haul by dumper, long lift by skip and hoist are the other situations promoting segregation of concrete. 

• Lack of sufficient vibration. Vibration of concrete is one of the important methods of compaction. It should be remembered that only comparatively dry mix should be vibrated. It should be noted that vibration is continued just for required time for optimum results. If it is overdone particularly in a too wet mix, it is likely to result in segregation of concrete due to settlement of coarse aggregate in matrix.

Segregation can be avoided by; 

•     Properly following the right concrete mix-design. 

•     Mixing concrete ingredients properly. 

•     Maintaining the correct water-cement ratio. 

•     Not dropping concrete from too high heights during placing. 

•     Avoiding over vibration of the concrete.