Hello welcome to Just Learn Civil. Please
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in concrete
let's begin with segregation in concrete
 
Definition of segregation. Separation of
constituent materials in concrete
Constituent materials in concrete are
cement, sand, coarse aggregate and water
types of segregation
Separation of  coarse aggregate from concrete mixer
separation of cement paste from concrete
during its plastic States. Separation of
water from concrete mix-This is also
called Bleeding.
Primary cause of segregation. Primary
cause of segregation
is difference in specific gravity of
constituent. Different constituents of
concrete have different specific gravity
 
for example: specific gravity of
cement is 3.1 to 3.6
and that of aggregate is 2.6 to 2.7 and water is
is 1. Lighter particle tends to move
upward and heavier particle tends to move
downward due to the specific gravity and
hence segregation occurs, that is,
separation occurs.
Other causes of segregation are: dropping
concrete from more than one meter height
vibrating in vibrator; mechanical
vibrator or others for very long time
similarly, poorly proportioned mix may
also cause segregation.
How to minimize segregation? By
proportioning the mix. By handling that
concrete carefully; placing, transporting,
compacting and finishing. This process
should be carried out carefully
Air entraining agent, Admixtures and
pozzolanic materials can also be used to
be minimize segregation
 
This is a figure depicting segregation of
concrete.
 
 
Now, bleeding. Generally it occurs in wet mix of concrete. It is also a form of
segregation. Water present in concrete is
pushed upward due to settlement of
cement and aggregates and bleeding occurs. Specific gravity of water is
low so it tends to move. Cause of
bleeding. High water cement ratio: if
water amount is more, that is, water
cement ratio is more then bleeding occurs
in concrete
Control of bleeding. Air entraining
admixtures can be used. Water cement
ratio should be controlled, that is,
minimum amount of water. Bleeding is not
harmful if the rate of evaporation is
equal to the rate of bleeding.
Normal bleeding is quite good and it
enhances the workability, that is, it makes
the concrete workable. By enhancing the
workability of concrete mean the
concrete can be placed/laid easily.
Friction is less and there is not much
problem in laying the concrete.
This figure shows the Bleeding in concrete. You can see the water of mix paste at the
surface of the concrete. This is how the
concrete looks after it has bled.
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