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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