The relative quantity of mixing water, which will bleed from fresh concrete mix can be determined by the test for bleeding of concrete.
Test for Bleeding of Concrete
Apparatus and accesory required for bleeding test of concrete are as follows:
- Cylindrical container
- Weighing scale
- Tamping bar
- Graduated cylinder
1. Cylindrical Container
2. Weighing Scale
Digital weighing scale of accuracy up to 0.005 is required for weighing specimen samples.
Pipette is used to draw off the bleed water from specimen.
4. Tamping bar
5. Graduated Cylinder
Graduated cylinder of 100 cm3 is required to measure the water quantity.
- Firstly, take
sufficientquantity of freshly mixed concrete of known water content.
- Fill the Cylindrical container with
concretemix in 5 layers of each 50 mm.
- Each layer should be tamped or compacted by giving minimum 60 strokes using tamping bar after filling,
- After compacting the final layer,
topsurface is leveledand smoothed by troweling.
- Immediately after troweling, note down the time and weigh the container.
- After weighing, place the container in a
leveledsurface which should be free from vibrations.
- Top of the container should be closed with
lidor covered to prevent evaporation of bleed water.
- This test should be conducted at a temperature of 25oc to 29oC.
- For every 10 minutes, draw off the water accumulated on the top surface of concrete using
pipetteand collect it in graduatedcylinder. This should be done for first40 minutes.
- After 40 minutes, collect water for every 30 minutes and continue until bleeding stops.
- If it is hard to draw off water on
flattop surface, slightly tilt the container and collect it. Finallynote the weight of water collected in graduatedjar.
Bleeding water % = (B/W) X 100 ——— Equation (1)
Where B = Total quantity of bleeding water
W = Total quantity of water in the concrete mix
Bleeding water percentage of net mixing water contained with in the test specimen is,
Where, D = Total mass of bleeding water, Kg
w = Net mass of water (total water – water absorbed by aggregates)
S = Total mass of concrete mix
W = Total mass of water in the mix
Equation (2) is more accurate than equation (1), since water absorbed by aggregates is considering here.
Bleeding water percentage for the given concrete mix = _______ %