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What is Honeycombing of Concrete? Prevention and Repair: 8 Important Points

Honeycombing of Concrete 01

You must have seen the poorly appeared structure surface with exposed reinforcement or aggregates, it is known as Honeycombing of Concrete. Do you know what exactly Honeycombing of Concrete is, why it happened, how to prevent it to happen and how to repair it?

Please read this blog for details

What is the Purpose of Cement Concrete in Structure Elements?

In simple terms, cement concrete is a mix of adhesive (cement) and small grits or aggregates. The adhesive is made from a mix of cement and water in the desired ratio.

When added together (cement, water and aggregate), a chemical rejoinder takes place and it hydrates the mix and gradually the mix begins to harden. Once settles, it increases its strength and becomes a solid mass concrete.

The durability and strength of cement concrete is the key driver to consider it as indispensable material for all type structures such as bridges, building, highway, railways, etc.

What is Honeycombing of Concrete?

When cement concrete is dispensed into the structure casing or formwork, the mix flows like a very concentrated liquid. In an ideal situation, it should gradually flow in all direction within the casing or formwork, but sometimes it doesn’t happen.

When it doesn’t happen means, when the mix doesn’t reach all the places within the formwork, it creates voids. Once the concrete settles and formwork is removed, it appears like a nest of the honeybee and as a result, the structure loses its full expected strength.

What are the reasons for Honeycombing of Concrete?

After removing the Formwork, when settled concrete surface displays small pockets of air void and or exposed aggregate without mortar (cement mix), it is called honeycombing of concrete.

Honeycombing could be present on the top surface or it could be present deep inside.  As a result, it significantly impacts the strength of the structure. Honeycombing of concrete also allows seepage of water through it and as a result, the steel reinforcement begins to corrode, which is a serious risk to the integrity of the structure.

Following are the key reasons for Honeycombing of Concrete:

  • Inadequate compaction to concrete-mix.
  • Settlement of concrete-mix before full placement within the formwork
  • Improper placement of concrete around steel reinforcement
  • Inappropriate placement of steel reinforcement within formwork and blockage for water to flow to all the corners.
  • Inappropriate use of a vibrator to mix and place concrete within the formwork.
  • Poor workmanship.

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The Consequence of Honeycombing of Concrete:

  • Poor appearance of the surface finish of the structure
  • It worsens the structure strength and integrity
  • Honeycombing makes the concrete mix very weak
  • It leads to corrosion of steel reinforcement
  • It provides easy passage to water to flow within and makes the structure week.

How to Repair Honeycombing of Concrete/ Remedial Works?

  • Clearly identify the affected area and mark it up. Extract out all honeycombed area and aggregate plus concrete mix.
  • Apply chemical glue across the cleaned-up area.
  • Apply Grout Mix.
  • Apply concrete mix across the whole surface and set the formwork
  • Remove the formwork after 24 hours.

What are the Commonly known Grouting Methods?

  • Permeation Grouting
  • Vacuum Grouting
  • Jet Grouting
  • Compaction Grouting
  • Fracture Grouting

Permeation grouting

  • Permeation grouting is a well-known and widely used grouting method.
  • In this method, all joints, void and honeycombed area are filled back with new concrete mix.
  • It strengthens the new formation and provides a clean surface to the structure.

Vacuum Grouting

  • Vacuum grouting is a very effective method and it places concrete mix very precisely across the surface.
  • In this method, concrete is placed vacuum pressure and if any location found to create a void (which could result in further honeycombing) again, it extracts out the material by reverse vacuuming.

Jet Grouting 

As the name suggests, Jet grouting means grouting with the high-pressure jet. The jet pressure removes the unwanted material first and then applies grout to the surface.

Compaction Grouting

  • In compaction Grouting the mix in injected through pressure and compacted within the formwork.
  • Compacting Grouting is carried out in phases.

 Fracture Grouting

Fracture grouting uses a low viscosity cement grout and injects it under high pressure. In this grouting method, the concrete mix and the chemical mix is injected through hydraulic pressure.

Grout is pushed down the casing or formwork and spread over the fractured area.

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How to Eliminate or Mitigate Honeycombing in the first place / Repair Works:

  • Check the Framework is firmly placed. All the steel reinforcements, braces and joints are tightly placed. There are no gap or opening left within the formwork
  • Cement and aggregate are properly mixed and when placing the concrete within the framework, make sure it is compacted adequately and there are no voids left anywhere within the framework.
  • Ensure that the mix has flowed in all areas within the formwork and formwork is totally filled.

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