Definition of Honeycomb in Concrete
Concrete is required as per the structural design in various structural elements like columns, beams, foundations, slabs etc. When concrete is poured into the formwork, the concrete starts flowing like water. But I didn’t reach. It looks like a bee’s nest. If it is not vibrated properly it can leave spaces exposed to aggregates. A concrete honeycomb not only reduces strength but also provides passage for water which in turn corrodes the reinforcement bars. Corrosion is a process that continues through reinforcement rods even in good concrete, resulting in the loss of grip between the rods and the concrete, which is very dangerous for the safety and life of concrete structures.
In other words, honeycomb refers to the voids in the concrete that are caused by the mortar not filling the spaces between the coarse aggregate particles.
A concrete honeycomb is commonly seen at the column and beam junction because of the overcrowding of the reinforcement bars as poor concrete fills.
Honeycombing in Concrete due to the following reason
1. Unsuitable workability of concrete.
2. Hardened concrete is used or laid before the concrete is set.
3. Improper vibration of concrete in the formwork.
4. Provide reinforcement more than required.
5. The use of large-sized aggregates in large quantities.
6. The formwork is not rigid and watertight.
7. Concrete is poured from above the allowable height.
8. The amount of steel in the concrete also affects the honeycomb. Heavy reinforcement in concrete does not allow the concrete to flow easily.
9. Poor workmanship.
10. Adding more water than is designed on-site to achieve workability.
Repair Honeycombing in Concrete
The following are some tips for honeycomb concrete repair
(1.) Mark this affected area of the honeycomb and remove all loose aggregates and mortar from the concrete surface using a wire brush and a chipping hammer.
(2.) Clean the concrete surface with a brush to remove fine particles and then flush the surface with water.
(3.) Wait 2-3 hours for the surface to dry and apply Chemi-Fix glue on the area.
(4.) Prepare a grout mix with white cement and add the required amount of water (as per the specification recommended by the manufacturer).
(5.) Fill the affected area of the concrete surface properly. In case of a large area affected by honeycomb, make a patched hole before applying the grout for proper bonding.
(6.) Remove formwork if applicable and allow the surface to cure properly for at least 24 hours
The remedial measure to avoid Honeycomb
1. Concrete falls should be kept to a minimum (not more than 1.5 m).
2. Use a mixture of suitable working capacity for the condition in which it is to be kept.
3. Make sure the mixture has enough granularity to fill in the gaps between the coarse aggregates.
4. Ensuring that the concrete is fully compacted and placing methods reduce the risk of separation.
5. Ensure that the formwork is rigid, that the joints are waterproof and that the entry through the formwork is properly sealed.
6. At the places of the junction of columns and beams, concrete with a strictly 20 mm and down aggregate should be used with a little more water and cement to avoid a honeycomb.
7. Taping out the edges of the shuttering with a wooden hammer during concreting and vibrating will help reduce the honeycomb substantially in the case of columns and beams.
8. The use of a thin needle of 25 mm or less with a vibrator at complex concreting sites will also help reduce honeycombs to a great extent.
9. During concreting, taping the edges of the shuttering from the outside with a wooden hammer will help reduce the hive to a great extent.
A Civil Engineer’s Opinion on Honeycombing in Concrete
Honeycomb in concrete is not a serious concern when it covers a small area. But, if it covers a large area and depth of concrete, it becomes a big issue for any structure.
You know that care is better than cure, honeycomb can be avoided by using good workability of concrete and applying proper compaction to the concrete when the concrete is in the liquid state.
Special care should be taken of the corners of the member while compacting the concrete. Honeycombing mainly occurs at the corner or where a compacting needle is inaccessible. Also when repairing this defect use a rich mortar mix for proper bonding to the concrete surface.