SEGREGATION
Definition
•
Separation of
constituent materials in concrete.
Types of
Segregation
•
Separation of
coarse aggregate from concrete mixture
•
Separation of
cement paste from concrete during its plastic stage
•
Separation of
water from the cement mix (Bleeding)
Primary
cause of Segregation
•
Difference in
specific gravity of constituent
•
Constituent of
Concrete = coarse aggregate + fine aggregate + cement + water
•
Specific gravity
of cement = 3.1 to 3.6
•
Specific gravity of
aggregate = 2.6 to 2.7
•
Specific gravity
of water = 1
•
Lighter particle
moves upward and heavier particle tends to move downward and hence segregation
occurs.
Other causes
•
Dropping concrete
from more than 1 metre
•
Vibrating for
long time
•
Poorly
proportioned mix
Minimizing
Segregation
•
By proportioning
the mix
•
By peculiar
handling, placing, transporting, compacting and finishing
•
Use air
entraining agent, admixture and pozzolanic materials in the mix
BLEEDING
Definition
·
Generally, occurs
in wet mix of concrete
·
form of
segregation
·
Water present in
concrete is pushed upwards due to settlement of cement and aggregate
·
Specific
gravity of water is low so it tends to
move upward
Cause of
Bleeding
·
High water cement
ratio
·
Not well compacted
or excess compaction
Control of
Bleeding
·
Air entraining
admixture
·
Control
water-cement ratio i.e. add minimum water
Note:
ü Bleeding is not harmful if the rate of evaporation is
equal to the rate of bleeding
ü Normal bleeding is quite good and it enhances the
workability of concrete
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