Bleeding occurs when the water in a concrete mix rises to
the surface due to the fact it has a lower density than the cement and
aggregates in the mix.
The longer the concrete takes to set, the more time
there is for bleeding to take place.
Bleeding can be reduced by using very fine
aggregates and fine cement replacing materials, reducing the water content in
the mix or by using an air entraining agent.
- Bleeding can be beneficial for the following reasons:
- Lowers the water/cement ratio in the concrete
and densifies it.
- Hydrates dry-shake toppings.
Reduces the volume of water required for
Bleeding nearly always occurs in concrete floor slabs, it
is important to adequately control the rate of bleed to ensure it is neither
too fast nor slow. Bleeding may not be physically seen in hotter countries as
the water will evaporate at the rate it’s expelled.
can cause channels to form at the coarse aggregate surface which can lead to a
weaker paste-aggregate bond and if the surface of the concrete is finished
before bleeding is complete, delamination can occur.