Stratification of concrete

In relation to concrete, the term 'stratification' refers to the formation of horizontal, layered lines that can sometimes be found in cured cast-in-place concrete. This is the result of the pouring of successive concrete batches that may differ slightly in appearance.

Stratification generally only occurs in wetter concrete, rather than those that are of medium or drier consistencies. Concrete that is over-wet or over-vibrated can separate into horizontal layers, with the lighter material tending to form towards the top, and heavier material moving towards the bottom. This can have a detrimental effect on the durability of the concrete.

To remedy stratification, the concrete can be re-vibrated, as long as the concrete has not become stiff to the point where plasticity will not be restored after re-vibration.

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