Bleeding:
Bleeding may be defined as separation of cement paste from the concrete mix under troweling or compaction operation. Bleeding of concrete can be viewed as a special form of segregation. The bleeding phenomenon is more general for surface structures like, floors, slabs, etc. Because of bleeding, the cement paste comes out to the surface of the concrete member leaving rest of the concrete mass with lack of cement and water, along with the result the permeability of concrete increases and the strength and durability of concrete reduces. The cement paste, which comes out at the surface forms a layer and is popularly known as Laitance. It causes more shrinkage cracks. The several factors, which are responsible for bleeding of concrete, are as below:
(a) Highly wet mix along with bad proportion of ingredients or insufficient mixing.
(b) Overcompaction or overtroweling of concrete.
(c) High alkali or high C3A content.
(d) Thin sections of concrete members.