SEGREGATION OF CONCRETE
![]() |
What do you mean by Segregation OR what is Segregation of Concrete?
·
In
simple word segregation means separation of one from another.
·
The
term Segregation of Concrete in Civil Engineering means the separation of constituents
of concrete from each other.
·
Segregation
of concrete is also defined as the separation of some size groups of aggregates
from cement mortar in isolated location resulting in to deficiencies of those
materials in other locations because of differences in size, density shape and
other properties of ingredients in which they are composed.
Causes of Segregation or What are
the causes of segregation in Concrete?
The causes and conditions due to
which the segregation in concrete occurs are as follows –
a) The main reason of segregation in
concrete is the differences in size of particles and sometimes the specific
gravity of the mix constituents differs from each other.
b) Use of poorly graded aggregate, for
example flakiness.
c) Bad proportioned of concrete mix.
d) Using high water cement ratio
(happens when concrete mixed by unskilled worker at site)
e) Transportation of concrete for long
distance.
f) Poor compaction of concrete after
placing.
g) Over compaction of concrete.
h) Specific gravity of aggregate is in
between 2.6-2.7 g/cc and for cement it is in between 3.1-3.6 g/cc, due to these
differences, the aggregate separates from the matrix and loose its homogeneous
nature.
i)
Dropping
of concrete more than 1 m height in case of underground foundations like and
rafts etc.
j)
If
concrete conveyed through conveyor belts, wheel barrow, long distance haul by
dumper promoting segregation of concrete.
Types of Segregation or Forms of
Segregation:
There are two types or forms of
segregation,
·
In
case of first one, (Segregation due
to the separation of aggregate) the coarser and the heavier particle tens to separate
out or settling down from the rest of the surrounding substances since they
travel further along a slope or settle more than the finer particle. This type
of segregation occurs when the concrete mix is too dry i.e. the mixing of water
in the dry mix is lower than its design aspects.
·
In
case of second one, (Segregation due
to the separation of cement slurry), generally occurs in wet mixes, is
manifested by the separation of cement slurry or grout (cement + water) form
the mix. This type of segregation occurs when the concrete mix is too wet i.e.
addition of water to the concrete mix is higher than its specified mix design.
Effect of segregation in Concrete:
Following’s are some effect of
segregation in concrete –
a) The segregation in concrete will
affect the strength of the concrete. When segregation occurs in concrete the
strength of concrete decreased as compared to it’s designed / target strength.
b) It is very difficult to compact a
segregated concrete.
c) When segregation occurs in concrete
sometime the excess mortar comes to the top of the surface resulting in plastic
shrinkage cracks.
d) A homogeneous mass throughout the
structure cannot obtain when the concrete becomes segregate.
e) As a result of segregation after
pouring of concrete, the lower portion of the concrete pour of any significant
depth is stronger than the upper portion.
f) Segregation results the porous
layers, rock pocket, sand streaks in hardened concrete.
g) Honey combing, high permeability of
concrete, poor finishing of surface are also some harmful effect of segregation
in concrete.
How to prevent or minimize or
control Segregation in Concrete:
To control Segregation –
a) The concrete mix should be properly
designed with most favorable quantity of water i.e. not too wet or not too dry.
b) If the concrete does not have far to
travel and transferred directly from skip or the wheelbarrow to the final
position of in the formwork, the danger of segregation is small.
c) During placing of concrete more than
a height of 1.50 m it is possible to avoid the dropping of concrete by passing
the concrete through a inclined chute, keeping the inclination between 1:3 to
1:2 for the smooth travel of concrete from top to bottom, and particularly with
changes of direction or by discharging concrete through an obstacles reduce the
possibility of segregation.
d) By using a correct method of
handling, transporting and placing of concrete the chances of segregation can
be minimized.
e) The segregation in concrete can be
controlled by using air entrain agents, admixtures and pozzolanic material in
the concrete mix.
f) The formwork in which concrete
should be poured should be air tight so that leakage of slurry prevented which
leads to the control of segregation.
g) If any segregation is observed in
concrete, remixing should be done to make it homogeneous again.
h) Proper compaction of concrete
prevents the segregation in concrete.
i)
Some
field quality tests should conducted to control the segregation of concrete.
Moreover, you should look for sealers with rubber compound, which are more flexible and water-resistant, or insist that your asphalt repair contractor use such a sealer. asphalt
ReplyDelete