What is Honeycombing of Concrete?
When finished concrete surface shows the air void in it or majority of aggregate with no mortar between them indicate honeycombing of concrete. Honeycombing is caused by the mortar not filling the spaces between the coarse aggregate particles.
It is seen on the concrete surface when the form-work is stripped, revealing a rough and ‘stony’ concrete surface with air voids between the coarse aggregate.
Honeycombing may be present on the surface or it can be extended deep into concrete member. It is one of major reason for strength reduction of concrete members. Generally, it creates bad outer appearance and depending on the depth and extent may reduce both the durability performance and the structural strength of the member.
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Causes of Honeycombing of Concrete:
- Inappropriate workability of concrete.
- Stiff concrete use or the concrete is already set before placing.
- Improper vibration of concrete in formwork.
- Over reinforcement.
- Use of larger size aggregates in excessive amount.
- Formwork is not rigid and watertight.
- Concrete is poured from more than allowable height.
- Amount of steel in concrete is also effect honeycombing. Heavy reinforcing in concrete does not allow concrete flow easily.
- Bad workmanship.
Effect of Honeycombing of concrete:
- Honeycombing makes concrete weak.
- It leads to open out reinforcement to the atmosphere, which may to corrosion problem in future.
- It provides easy entry of moisture in RCC.
- It makes a bad appearance
- Reduce structural strength of concrete Components.
- It shows the bad work of contractor or builders. It can spoil the reputation of them in market.
How to repair Honeycombing of concrete:
Honeycombing can be avoided if proper care is taken. Therefore, first try to avoid imperfection then go repair of it. Honeycombing can be repaired by following method.
1. Mark this affected area of honeycombing and remove all loose aggregate and mortar from the concrete surface by using a wire brush and a chipping hammer.
2. Clean the concrete surface with a brush to remove finer particles and then wash the surface with water.
3. Wait for 2 – 3 hour for drying out surface and apply Chemi-fix glue on the area.
4. Prepare Grout mix with white cement and add the required amount of water ( as per the specification recommended by the manufacturer).
5. Properly fill the affected area of the concrete surface. In the case of large-area affected by honeycombing make patch hole before applying grout for proper bonding.
6. Remove formwork if any applied and cure surface properly for at least 24 hours
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How to Avoid It:
To care is better than cure, so try to avoid this kind of defect in concrete.
- Ensure that the concrete mix has proper cement mortar gel to fill the voids between the coarse aggregate.
- As per the condition of concreting choose proper workability.
- Be sure about proper and sufficient compaction of concrete and the placing methods minimize the risk of segregation.
- Take care that concrete section shape and its reinforcement will allow the concrete to flow around the reinforcement and completely fill the forms.
- Before concreting check once that the formwork is rigid and well braced, the joints are watertight and any penetrations through the formwork eg form ties, are properly sealed.
Honeycombing is not a serious issue as soon as it covers the small area. But, if it covers large area and depth of concrete, it becomes major issue for any structure. You know that care is better than cure, honeycombing be can be avoided by using good workability concrete and applying proper compaction to the concrete while concrete in liquid state. While compacting concrete special care should be taken for corners of member. Honeycombing majorly occurs on corner or where there is compacting needle not reachable. Also while repairing this defect use rich mortar mix for proper bonding to the concrete surface.