Honeycombs in Concrete | Their Causes | Remedies

Honeycombs in Concrete

Concrete is made into various structural elements such as columns, beams, foundations, slabs, stairs, etc. as required by the structural design. 

When concrete is poured into the formwork, the concrete begins to flow like water, sometimes they form cavities/voids in the concrete when the concrete does not reach all the places. It looks like a honeycomb. 

If not properly vibrated, it can leave gaps that expose the aggregate. 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 reinforcing rods even in good concrete, resulting in 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 caused by the mortar not filling the gaps between the coarse aggregate particles. Concrete honeycomb is typically seen at the junction of column and beam due to crowding of the reinforcement bars leading to poor concrete fill.

Causes of Honeycombing in Concrete

• Insufficient compaction to concrete.
• Less rebar coverage.
• Inadequate workability in concrete
• Concrete already set before laying.
• Large concrete free fall during the pouring
• Non-watertight / rigid formwork.
• Aggregates thicker than designed mix ratios and oversized aggregates.
• Incorrect placement of bars at the junction of column and beam.
• Adding more water than designed on-site to achieve workability.
• The congestion of the steel does not allow the concrete to flow to all corners.

Remedies of Honeycombing in Concrete

• A concrete drop should be kept to a minimum.
• Use a mix of suitable workability for the situation in which it is to be placed.
• Make sure the mixture has enough fines to fill the gaps between the coarse aggregate.
• Ensure that the concrete is completely compacted and the placement methods minimize the risk of segregation.
• Make sure the formwork is rigid, gaskets, and penetrations through the formwork are properly sealed.
• In the places of joining columns and beams, concrete with aggregate strictly 20 mm and down with a little more water and cement should be used to avoid honeycombs. Hitting the sides of the formwork from the outside with a wooden hammer during concreting and vibration will help minimize honeycombs to a great extent in the case of columns and beams. Using a thinner needle says 25mm or less with vibrator in intricate concreting spots will also help reduce honeycombs to a great extent.
• Tapping the sides of the formwork from the outside with a wooden hammer during concreting will help minimize honeycombs to a great extent.