Segregation usually implies separation of: (a) coarse aggregate from fine aggregate, (b) paste from coarse aggregate, or water from the mix and the ingredients of the fresh concrete no longer remain uniformly distributed.
The points given below are the primary causes of segregation of concrete in field.
Causes of Segregation on Site
Poorly graded aggregate & excessive water content is the major cause of segregation.
A badly proportioned mix, where sufficient matrix is not there to bond and contain the aggregate cause aggregates to settle down.
Insufficiently mixed concrete with excess water content shows a higher tendency for segregation.
When height of dropping of concrete is more (ex. In case of concreting long column) it will result in segregation.
If a mixer used for mixing concrete is badly designed or a mixer with worn out blades, then the concrete shows a tendency for segregation.
If a high slump concrete or pumpable concrete are not compacted with sufficient care then it is likely to result in segregation of concrete.
Immediate working on the concrete on placing, without any time interval is likely to press the coarse aggregate down, which results in movement of excess matrix or paste towards the surface, resulting segregation.
Chances of segregation are more when concrete is to be placed under water.
Segregation also increases when concrete is placed in heavily reinforced concrete members.