Honeycombs details

Honeycombs are hollow spaces  left in concrete mass on the surface or inside the mass where concrete could not reach. These look like honey bees nest. Improper vibration and workability of concrete are main reason of Honeycombs in concrete.

Honeycombs are easily visible to naked eyes as soon shuttering removed. If It is not seen and we want to test then it  can be detected by advanced technology like ultrasonic testing machine.

   (Here the Mason concreting after                             remove of shuttering )


Causes of Honeycombs :-

Honeycombs are  non reaching of concrete to all places due to which cavities and hollow spaces are created.

Main reasons are :

1. Improper vibration during concrete.
2. Less cover to reinforcement bars.
3. Use of very stiff concrete.
4. Places like junction of beam and column ,or beam to beam, one or more then the typical spots the honeycombs are found.this is due to jumbling of reinforcement of beams and column rods at one place, special attention is required at such place during concreting and vibrating.
5. Presence of more percentage of bigger size of aggregates in concrete also prevents  concret to fill narrow spaces between the reinforcement rods.

Solution of Honeycombs :-

Whenever Honeycombs are observed in concrete, the affected area should be broken and the portion should be re-created after applying grouting chemical to the old surface.

Honeycombs as a defect not only reduces the load bearing capacity but water finds an easy way to reinforcement rods and rusting and corrosion starts.

Corrosion is a process which continues through reinforcement rods even in good concrete, this result in losing grip between rods and concrete, which is very dangerous to safety and life of concrete structures.

Reinforced concrete structure have failed within 20 or 30 years of their construction due to Honeycombs, which is less than half of their projected life. Especially no risk should be taken in case of columns, foundations, rafts,beams etc..., Where breaking and re-casting is the only best  way you have.

In case of Honeycombs on surface pressure grouting with cement based chemical which are non-shrinkable can be adopted after taking opinion of the designer and acting as per his advice.

It will not be out of context to point out that contractors and their supervisors are in the habit of hiding Honeycombs by applying super facially cement plaster on the honeycombs, hence site engineer must be very cautious.

At places of junction of columns and beams concrete with strictly 20mm and down aggregates should be used with slightly more water and cement to avoid honeycombs.

Taping with wooden hammer the sides of shuttering from outside during concreting and vibrating will help minimize the honeycombs to a great extent in case of columns and beams.

Use of thinner middle for example 25mm or less with vibrator at intricate places of concreting will also help to reduce the honeycombs in that structure.