Honeycomb in concrete | effects of honeycomb in concrete | solution for honeycomb in concrete

 What are Honeycombs

Honeycombs are the hollow spaces and cavities left in concrete mass on surface or inside the concrete mass which is caused by the mortar not filling the spaces between the coarse aggregate particles.

Types of Honeycombs:-

1.Small size Honeycombs: in which the depth of hollow spaces are less than 25mm. 

2.Moderate Size Honeycombs: the depth of hollow spaces are deeper than 25mm but steel bars have not exposed. 

3.Larger Size Honeycombs: the depth of hollow spaces are deeper than 25mm and bars have come out. 

   

Where can we find Honeycomb?

• Honeycombs which are on sides and bottoms are visible to naked eyes and can be detected when shuttering is removed. Honeycombs which are inside mass of concrete can only be detected by advanced techniques like ultrasonic testing etc.  

  👉Walls

  

  👉Columns

  

  👉Beams

  

  👉Slabs

  

  👉Footings

  

  
  

  Effects of Honeycombs

  👉Water and air enters inside

  👉Rusting and corrosion of reinforcement

  👉Reduce durability

  👉Less structure strength

  👉Reduce the load bearing capacity

   

  Causes of Honeycombs

  1.Poor Workability: 

  Slump test can be used to find out the workability of concrete. If the slump is less workability is less.

  Workability might be less because

  👉Low water content

  👉Finer cement particles

  👉High Temperature

  👉Ratio of fine to coarse aggregate being low
  

  2.Poor grading of aggregate:

  👉Presence of more percentage of bigger size of aggregate in concrete also prevents concrete to fill narrow spaces between the reinforcement steel bars.

  👉Voids often occur because aggregate is too big to pass through a small gap of reinforcement.
  

  3.Grout Leak:

  When joints of formwork are loose there can be leakage of grout through these joints and honeycomb occurs.
  

  3.Movement of Form-work:

  Increased water content also results in bleeding, hence increased water content can also mean that cement slurry(grout) will escape through the joints of the formwork
  

  4.Improper compaction:

  👉The purpose of the compacting concrete by vibration is the elimination of entrapped air and forcing the particles into a closer configuration that will definitely build the more strength.

  👉Over vibration would make the concrete segregated while under vibrated concrete would have honeycomb in it.

  👉Poor concrete compaction occurs due to ineffective vibration or rebar congestion.
  

  5.Improper cover and replacement of rebar:

  👉Rebar congestion: If rebar is placed too close together or too close to formwork it will trap the larger pieces of aggregate while the mortar in the mixture may not pass through and interfere with concrete flow and vibration.

  👉Insufficient cover: When number of cover blocks to rebar is less or the size of the cover blocks is not sufficient then honeycomb might be occurs.
  

   

   Practices to minimize Honeycomb in concrete

  1.Use a mix with appropriate workability for the situation in which it is to be placed.

  2.Ensure the mix has sufficient fines to fill the voids between the coarse aggregate.

  3.Use proper method of compacting and ensure concrete is fully compacted.

  4.Use Proper methods of placing concrete:

  👉Avoid segregation

  👉Avoid delays

  👉Pour by layers

  5.Proper cover block thickness should be maintained for particular concrete structure i.e.

  Slab-40mm

  Beams-40mm

  Column-40mm or 25m

  Staircase-20mm

  6.Sufficient cover blocks should be provided.

  7.Rebar congestion can be minimized by having larger (i.e. lesser) rebar or by increasing the sectional dimensions of elements where possible.

  8. Ensure the reinforcement layout and the section shape will permit the concrete to flow around the reinforcement and completely fill the forms.

  9. Check that the formwork is rigid and well braced, the joints are water tight and any penetration through the formwork. e.g. form ties are properly sealed.

  10.Provide enough supports to formwork.

  11.Defective formwork and accessories should be repaired or replaced to prevent grout leakage during concreting.

  
  

  REPAIRING HONEYCOMBS

  For small and moderate honeycombs 

  👉Hack and remove the loose particles in order to appear sound surface.

  👉Surface is cleaned by water jet to obtain dust free surface.

  👉Construction grout is applied.

  👉Texture and color should then be matched for aesthetic finish.

  👉Curing is done. 
  

   
  

  For large Honeycombs

  👉Hack and remove the weak concrete to expose sound concrete surface.

  👉To keep clearance around reinforcement 12mm thick concrete layer is removed.

  👉By using water jet surface for cleaning.

  👉Barra emulsion is used as a binding agent.

  👉Over the wet surface barra emulsion is applied and before drying 1:2 cement mortar is applied.

  👉After mortar has set sufficiently then final surface is prepared by trowel.

  👉Texture and color is matched for aesthetic finish.

  👉Curing is done.

  
  
  

   

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