➤Bleeding
Bleeding
is sometimes referred as water gain. It is a particular form of segregation, in
which some of the water from the concrete comes out to the surface of the concrete,
being of the lowest specific gravity among all the ingredients of concrete.
Bleeding is predominantly observed in a highly wet mix, badly proportioned and
insufficiently mixed concrete.
Due
to bleeding, water comes up and accumulates at the surface.Sometimes, along
with the water; certain quantity of cement also comes to the surface. When the
surface is worked up with in the towel and floats, the aggregates goes down and
the cement and water come up to the top surface.
➤Method of Test for Bleeding of Concrete
A
cylindrical container of approximately 0.01meter cube capacity, having an
inside diameter of 250 mm and height 280 mm used. A tamping bar similar to the
one used for slump test is used. A pipette for drawing off free water from the surface,
a graduated jar of 100 centimeter cube capacity is required for test.
A
sample of freshly mixed concrete is obtained. The concrete is filled in 50 millimeter
layer for a depth of 250±3 millimeter (5 layers) and each layer is tamped by
giving stokes, and the top surface is made smooth by toweling.
The
test specimen is weighed and the weight of the concrete is noted. Knowing the
total water content in 1 meter cube of concrete quantity of water in the
cylindrical container is also calculated.
The
cylindrical container is kept in a level surface free from vibration at a
temperature of 27⁰C ± 2⁰C; it is covered with a lid. Water accumulated at the
top is dawn by means of pipette at 10 minutes interval for the first 40 minutes
and at 30 minutes interval subsequently till bleeding ceases. To facilitate collection
of bleeding water the container may be slightly titled. All the bleeding water
collected in a jar.
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