Honeycombs in Concrete and its Remedies
Honeycombs are hollow spaces and cavities left in concrete mass on a surface or inside the concrete mass where concrete could not reach. These look like honey bees nest. When concrete is poured into the formwork it does not just flow in like water and fill up the forms to the top. The concrete has to be vibrated for ease of flow and to form a uniform surface. If it is not vibrated properly it may leave voids exposing the aggregate. The surface on concrete appears as a rough, pitted with voids in concrete resulting in incomplete filling with the gap between the aggregates of the concrete against the formwork. Such type of surface and texture on concrete resemblance like a Honeycomb in a beehive of Honey Bee.
Honeycomb is due to non-reaching of concrete to all places due to which cavities and hallow pockets are created, the main reasons are:
1) Improper vibration during the concrete.
2) Less cover to reinforcement bars
3) Use of very stiff concrete (this can be avoided by controlling water as per slump test).
4) Places like the junction of the beam to beam to column and to one or more beams are the typical spots where honeycombs are observed. This is due to the jumbling of reinforcement of beams and column rods at one place; special attention is required at such place during concreting and vibrating.
This scenario can happen on any structural element- Columns, Beams, Lift Walls, Foundation of any type, etc. Honeycombs which are on sides are visible to naked eyes and can be detected easily as soon shuttering is removed. Honeycombs that are inside the mass of concrete can only be detected by advanced techniques like ultrasonic testing etc.