What is Honeycomb in concrete. Types, Causes, Effect, Prevention & Repair
Honeycomb in
Concrete – Types, Causes, Prevention & Repair
By Mohammad
Izhar / 18 February, 2023
Honeycomb in concrete means the cavities and
voids on the surface of the concrete or inside the concrete. It is caused due
to less clear cover or improper vibration and sometimes due to bleeding of
concrete.
Here in this post we will discuss about what
is honeycomb in concrete, types of honeycomb in concrete, causes of honeycomb
in concrete, effect of honeycomb in concrete, how to prevent honeycomb in
concrete and how to repair Honeycomb in concrete.
What is Honeycomb in
Concrete?
Honeycomb refers to the cavities and voids on
the surface of the concrete or inside the concrete. The pattern of the cavities
and voids looks similar to a bee nest so it is named as honeycomb.
Just after the removal of the formwork of the
concrete member or structure the surface honeycomb can be detected, but the
honeycombs which are inside the concrete can only be detected by advanced
techniques such as ultrasonic tests and others.
Honeycomb is a very serious issue in
construction. It reduces the concrete strength and also makes reinforcement
concrete structure vulnerable to water and moisture and as a result
corrosion takes place on the bars.
Corrosion or rusting is the process which
takes place in the steel bars and as a result the steel bars start losing its
bond with the concrete which makes the structure very dangerous in its life
expectancy.
When honeycomb occurs the coarse aggregates
are seen on the surface of the structure with less bonding of mortar due to
which it leaves cavities and voids.
Honeycomb generally occurs in columns and beams,
and sometimes it is seen on the slab because of bleeding of concrete. So, it is
necessary to use proper vibration in beams and columns.
Types of Honeycomb in Concrete
Broadly there are three types of honeycomb in
concrete, such as,
- Small
sized honeycomb
- Medium
sized honeycomb
- Large
sized honeycomb
Small Sized Honeycomb:
This type of honeycomb structure in concrete,
the depth of cavities or voids are less than 25mm and as a result the strength
of structure is not so compromised.
Medium Sized Honeycomb:
The depth of cavities or voids is more than
25mm in this type of honeycomb, but the steel bars are not exposed. And hence,
the strength of structure is not fully compromised and the steel bars are
vulnerable to water and moisture.
Large Sized Honeycomb:
The depth of
cavities or voids is more than 25mm same as in case of medium sized honeycomb but
the steel bars are exposed in this case. As a result the strength of structure
is compromised. The exposure of steel bars to water and moisture promotes
corrosion on the steel bars. This type of honeycomb in concrete is vulnerable
during earthquake and other natural hazards.
Causes of Honeycomb in Concrete
There are many reasons for the occurrence of
honeycomb in the concrete structures. Here some of the important causes have
been discussed below;
1.Honeycomb causes
because of improper ratio of mix design of concrete.
2.It also causes
when the workability of concrete is not good and it is poorly supervised.
3.The honeycomb
generally occurs when the casting of any structure is done and the vibration process
is not managed properly.
4.It also takes
place in the concrete structure if the clear cover is not manages properly
during placing of formwork.
5.It also
causes when there is improper grading of aggregates.
6. Plenty use of water than the water-cement ratio causes honeycomb as it
wash away the fine aggregates and cement from the concrete mix.
7.Less use of
water than the water-cement ratio also causes honeycomb in concrete due to bad
workability.
8.If wooden/plywood
formwork is used for the concreting and the joints of the formwork are not
properly closed then honeycomb may caused due to bleeding of concrete.
9.Honeycomb
also causes at the time of concrete casting if the concrete is not poured
partly and giving less settling time.
10.
Excess amount of large coarse aggregates in a
concrete mix which makes hard for the smaller particles to penetrate also
causes honeycomb.
11.
Use of over reinforcement is also one of the causes
of honeycomb.
12.Pouring of concrete from an excess height i.e., more than allowable
height i.e. 1.5 m causes honeycomb.
Effect of Honeycomb in Concrete
Honeycomb in concrete causes the following
effects:
- Reduction in bearing capacity and
strength of structure.
- Air, water and moisture enters into the
concrete.
- Corrosion and rusting of steel bars.
- Decreases the life expectancy of the
structure.
- Makes a bad aesthetic of the structure.
How to Avoid Honeycomb in Concrete?
Some points below have been discussed,
following which Honeycomb in concrete can be avoided;
1.The grading
of Aggregate should be properly done.
2.Vibrator must
be used in the supervision of an engineer/foreman/supervisor.
3.The ratio of
mix design concrete should be followed accurately as provided by the Q.C. Engineer
or the manufacturer.
4.Workability
of the concrete must be tested before the work.
5.Desired clear
cover should be provided from the steel bars to the formwork.
6.Use of water
content should be done as mentioned in the water-cement ratio.
7.The wooden formworks
or plywood formwork should be water tight and joints should be fully covered. There
should be no gap.
8.Over
reinforcement should not be used.
9. The pouring of concrete should be from an allowable height, which is
less than 1.5m of height.
Honeycomb Concrete Repair
We can repair Honeycomb in concrete by the
following steps:
1.First of all
clean the area where honeycomb appears by brushing the loose fine aggregates
with a wire brush and clearing the loose coarse aggregates by a chipping
hammer.
2.Then spray
water to the affected area to wash away the dusts present on it.
3.Apply
chemi-fix glue on the area after the area gets dry. The glue attach properly
when the surface is in dry state.
4.Then mix the
concrete grout properly with white cement and add water to it as directed by
the manufacturer.
5.Lastly, paste
the mixture to the honeycomb in the concrete. In large sized honeycomb, make a
pocket by the chipping hammer and pour the mixture and then jam the poured
mixture with piece of wood or any other formwork material to apply pressure.
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Very very important and impressive article. Keep up the good work.
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