Bleeding in concrete is the movement of water to the surface of the concrete after manipulation. Bleeding is more prominent on the surface of concrete, when water to cement ratio is higher and it occurs when ingredients of concrete are not in good proportions, bad mix proportion etc.…
Segregation is the cause of bleeding in the fresh concrete mix. Segregation is the phenomenon in which heavy aggregate particles settle down at the bottom of the slab and light particle moves to the surface top.
Due to settling of heavy particles, water travels to the surface of concrete and form a water layer on the top surface of concrete. That upward movement of water also carries fine particles of cement too and that creates a deficiency of cement within the concrete. Therefore, when amount of cement is less than concrete will not form a proper bond with the reinforcement bars. If proper bond doesn’t develop, then strength distribution will not remain the same throughout the cross section.
Effect Of Bleeding On Workability
There are two types of bleeding in fresh concrete depending upon the amount of water loss.
- Normal bleeding
- Excessive bleeding
Normal bleeding in concrete is quite good for properties of concrete, because it enhances the workability of concrete. The rise in workability gives concrete a good finishing properties and easiness during manipulation of concrete.
If the bleeding rate is very high then it is not good for the workability of concrete as well as on later strength related properties of concrete. When bleeding happens in excess, then it carries most of the water and fine particles of cement from freshly laid concrete.
Due to this a resulting concrete will be weaker in strength, strength will not be uniform throughout the cross section, carry a large number of air voids and diminish durability of concrete.