Segregation and Bleeding Phenomena:

Segregation

Segregation is defined as separation of ingredients, particularly the coarse and fine aggregates, of concrete mix to the cement water paste or mortar. Generally, large size/heavy particles have a tendency to settle down/separate out from the paste. Because of segregation concrete mix looses its homogeneity and as non-homogeneous mix cannot be fully compacted the strength of such concrete in hardened state gets reduced. It is one of the undesirable characteristic of fresh concrete, which should be prevented in all circumstances, as it is very harmful to concrete. The segregation can be observed on the exposed surface of the tall concrete members like, wall, column, etc. after erasing the formwork. The various factors, which are responsible for segregation of concrete, are as follows:

(a)        Huge quantity of water along with insufficient mixing that reduces the consistency of the mix.

(b)       Improper grading of aggregates or large difference in aggregate sizes.

(c)        Under-sanded concrete mix, that leads to less cohesive mix.

(d)       Huge difference of specific gravity of different fractions of aggregates.

(e)        Dropping of concrete from greater height.

(f)        Overcompaction of concrete.

(g)       Lesser quantity of cement, that leads to harsh and less cohesive mix.

(h)       Maximum size of aggregate is very large.

(i)        Complicated formwork along with sharp corners.

(j)         Too vibratory or too long transporting methods of concrete.

(k)       Leakage of mortar by formworks.

By taking a few cares of the above declare factors the segregation can be avoided.