13 Proven Ways to Avoid Honeycombing in Concrete : Causes & Preventive Methods

What Is Honeycombing in Concrete?

Honeycombing in concrete refers to the hollow spaces or cavities left in the concrete by the mass of the material due to the mortar not filling the spaces between the coarse aggregate particles.

If the depth of the honeycomb is less than 25 mm, then it is called a small-sized honeycomb. If the depth of the honeycomb is 25 mm or deeper but the steel bars have not been exposed, then it is called a moderate-sized honeycomb. If the depth of the honeycomb is 25 mm or deeper and steel bars are exposed, then the honeycomb is known as a large-sized honeycomb.

Defects due to honeycombing on the outer surface of the structure can be detected after the removal of shuttering, and the defects due to honeycombing on the inside of the concrete mass can only be detected by advanced techniques such as ultrasonic testing, etc.

Causes of Honeycombing in Concrete

The main causes of honeycombing in concrete are:

• Poor workability
• Poor grading of aggregate
• Grout leak
• Movement of formwork
• Improper compaction
• Improper cover and placement of rebar

Also read: Concrete Blocks

1. Poor workability

The slump test is used for testing workability. If the slump is less, workability is less. The reasons for poor workability are:

• Low water content
• High temperature
• Fine cement particles
• Ratio of fine to coarse aggregate

2. Poor grading of aggregate

If the presence of bigger-sized aggregate in concrete is at a higher percentage, it can prevent the concrete from filling in the narrow spaces between the reinforcement bars. The voids may occur because the aggregate is too large to pass through the narrow area of reinforcement.

3. Grout leak and movement of formwork

If the joints of the formwork or structure are loose, there can be leakage of grout, i.e., cement slurry, which forms the honeycomb. An increase in water content is the main reason for this leakage.

4. Improper Compaction

Compaction is very important in concrete work. Poor concrete compaction occurs due to improper vibration during casting or rebar congestion. The compaction of concrete is done by vibration, which eliminates the entrapped air and forces the concrete particles into every corner of the formwork or structure. Over-vibration of concrete during casting can segregate the concrete, while under-vibrated concrete has a honeycomb.

5. Improper cover and rebar placement

If the concrete cover’s thickness is insufficient, a honeycomb may occur. Also, if the rebar is placed too close and the concrete mixture is unable to pass through it, there is a chance of honeycombing.

Effects of Honeycomb on Concrete

The effects of honeycomb on concrete are as follows:

• Reduce the durability
• Reduce the structural strength of the formwork
• Reduces the load-bearing capacity of the structure.
• Rusting and corrosion of the reinforcement bars
• Water and air enter the structure through the honeycomb.

How to Repair Honeycomb Concrete?

Repairing small and moderate honeycombs in concrete as follows:

1. Remove the loose particles from the surface around the honeycomb.
2. Clean the surface with a water jet to make it dust-free.
3. Grout for construction is applied.
4. The color and texture of grout are matched to get the desired aesthetic appearance.
5. Grout is applied in a proper layer
6. Curing is done Repair of large honeycombs in concrete
7. Remove the weak concrete from the surface around the large honeycomb.
8. Clean the surface properly and make it dust-free.
9. Make the surface wet.
10. On a wet surface, the emulsion is applied, and the required mortar is applied before it dries.
11. A proper layer of mortar is placed all over the required surface.
12. The texture and color of the mortar should be the same as the structure for aesthetic appearance.
13. Finally, the curing is done.

How to Avoid Honeycomb in Concrete

There are some practices by which we can minimize honeycombing in concrete. Some of them are:

1. Use the proper concrete mix for the workability required for the structure.
2. Make sure that the mix has proper fine aggregates to fill the voids between the coarse aggregates.
3. Use the proper method of compacting the concrete.
4. Use the proper method for placing the concrete and avoid segregation, delays, and pouring in layers.
5. A proper thickness of concrete cover should be maintained for a particular concrete structure.
6. Sufficient cover blocks should be provided.
7. Rebar congestion should be minimized.
8. Make sure that the reinforcement layout and structure, or section shape, will allow the concrete to flow around the reinforcement and fill the complete section.
9. The formwork should be rigid and well-braced, and ties should be properly sealed.
10. Provide enough support for the structure.

How to fill Honeycomb in Concrete

The procedure for filling the honeycomb in concrete has the following steps:

1. Remove the loose concrete and aggregate by hammering or using a wire brush.
2. Clean all dirt and dust from the honeycomb area.
3. Wet the cleaned area properly before applying the material to it.
4. Fill the honeycomb with the required material.
5. If the honeycomb covers a large area, we have to make the patch hole for proper bonding.
6. If there is a need for formwork, then place the formwork first and pour the grout over it.
7. If there is no need for formwork, apply the material directly to the wet surface.
8. The filling process should result in a 15-mm-thick layer.
9. The material mix for repairing or filling the honeycomb should have a strength equal to the strength of the virgin concrete of the structure.
10. Provide texture and color for the aesthetic appearance of the structure.
11. At last, the curing is done.

Also read: Five Reasons to Waterproof Concrete Construction Projects

Frequently Asked Questions (FAQs)