Bleeding in Concrete

BLEEDING IN CONCRETE

What is Bleeding:

Bleeding in fresh concrete refers to the process where free water in the mix is pushed upward to the surface due to the settlement of heavier solid particles such as cement and water. Some bleeding is normal but excessive bleeding can be problematic.

The bleeding in concrete is not harmful if the rate of evaporation of water is equal to the rate of bleeding.

Causes of Bleeding:

The Prime factor for bleeding in concrete is the high dosage of Water cement ratio. Higher water-cement ratio weakens concrete and leads to excessive bleeding.

The cement type and fine aggregates can play a role in determining the bleed rate. The fewer fines you have in your mix, the more bleeding will occur.

Types of Bleeding:

• Normal bleeding refers to a uniform seepage of water over the entire surface of the structure.

• Channel bleeding refers to water rising through particular paths.

Effects of Bleeding:

• Concrete loses its homogeneity

• Due to bleeding, when the top surface is worked with trowel, the aggregate goes down and cement paste forms at the top surface forming Laitance which decreases the wearing capacity and decreases its life.

• This Laitance decreases the bond between successive concrete lifts

• Concrete becomes permeable

• Delays the surface finishing

• Decreases the pumping ability

Measures to reduce Bleeding:

• Reduce water content. Use lower slump mix

• Use finer cements

• Increase amount of fines in the sand

• Use supplementary cementitious materials

• Use air entraining admixtures