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
container used for this test is made of steel and has a capacity of 0.01 m3. The inside diameter and the inside height of the cylinder 250 mm and 280 mm respectively.
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
bar used in this test is a rounded steel bar of diameter 16 mm and 610 mm length.
5. Graduated Cylinder
Graduated cylinder of 100 cm3 is required to measure the water quantity.
- Firstly, take quantity of freshly mixed concrete of known water content.
- Fill the Cylindrical container with mix 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, surface is and smoothed by troweling.
- Immediately after troweling, note down the time and weigh the container.
- After weighing, place the container in a surface which should be free from vibrations.
- Top of the container should be closed with or 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 and collect it in cylinder. This should be done for 40 minutes.
- After 40 minutes, collect water for every 30 minutes and continue until bleeding stops.
- If it is hard to draw off water on top surface, slightly tilt the container and collect it.
- note the weight of water collected in jar.
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 = _______ %