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Concrete Honeycombs

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Honeycombing is a very common defect found in concrete structures

Published in: Education
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Concrete Honeycombs

  1. 1. HONEYCOMBS HONEYCOMBS 1 HONEYCOMBS HONEYCOMBS HONEYCOMBS
  2. 2. Group Members (G4)  2013/123 K.N.D.CHATHURANGA  2013/125 C.U.UDAGE  2013/127 M.A.R. AMEERUTHEEN  2013/128 M.H.A.S.D HETTIARACHCHI  2013/135 G.M.G.S. TILAKARATHNE  2013/136 P.M.C.S. BANDARA  2013/137 K.W.K.R. HELITHA  2013/138 I.P.S.C. KITHSIRI  2013/143 H.M.M. ROUSHEN  2013/147 M.W.M. IZMY HONEYCOMBS 2
  3. 3. 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. HONEYCOMBS 3
  4. 4. Types of Honeycombs HONEYCOMBS 4 Small Size Honeycombs Depth is less than 25mm Moderate Size Honeycombs Deeper than 25mm but steel bars have not exposed Larger Size Honeycombs Deeper than 25mm & bars have come out
  5. 5. Where can we find Honeycombs?  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. HONEYCOMBS 5
  6. 6. Effects of Honeycombs  Water and air enters inside  Rusting and corrosion of reinforcement  Reduce durability  Less structural strength  Reduces the load bearing capacity HONEYCOMBS 6
  7. 7. Causes for Honeycombs Poor workability Poor grading of aggregate Grout leak Movement of formwork Improper compaction Improper cover & placement of rebarHONEYCOMBS 7
  8. 8. Poor Workability8  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
  9. 9. Improper compaction9  The purpose of compacting concrete by vibration is the elimination of entrapped air and forcing the particles in to a closer configuration that will definitely build the more strength.  Over vibration would make the concrete segregated while under vibrated concrete would have honeycombs in it.  Poor concrete compaction occurs due to ineffective vibration or rebar congestion. Over vibration Under vibration Inserting at angles Touching reinforcement Touching formwork
  10. 10. Improper cover & placement of rebar HONEYCOMBS 10  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 & 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, honeycombs might occur.
  11. 11. Movement of Formwork & Grout leak HONEYCOMBS 11  When joints of formwork are loose there can be leakage of grout through these joints. Honeycombs occur.  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.
  12. 12.  Presence of more percentage of bigger size of aggregate in concrete also prevents concrete to fill narrow spaces between the reinforcement rods.  Voids often occur because aggregate is too large to pass through a condensed area of reinforcement. HONEYCOMBS 12 Poor grading of aggregate
  13. 13. Practices to minimize Honeycombing in concrete  Use a mix with appropriate workability for the situation in which it is to be placed.  Ensure the mix has sufficient fines to fill the voids between the coarse aggregate. HONEYCOMBS 13
  14. 14. Insert vertically Vibrate by layers Vibrate the whole depth of layer Insert at intervals HONEYCOMBS 14  Use proper methods of compacting and ensure concrete is fully compacted  Use proper methods of placing concrete  Avoid segregation  Avoid delays  Pour by layers
  15. 15.  Proper cover block thickness should be maintained for particular concrete structures.(Eg : walls, columns, staircases – 25mm, slabs- 40mm, beams- 50mm, pile caps- 75mm)  Sufficient cover blocks should be provided  Rebar congestion can be minimized by having larger (that is, lesser) rebar or by increasing the sectional dimensions of elements where possible.  Ensure the reinforcement layout and the section shape will permit the concrete to flow around the reinforcement and completely fill the forms. HONEYCOMBS 15
  16. 16. Practices to minimize Honeycombing in concrete  Check that the formwork is rigid and well braced, the joints are watertight and any penetrations through the formwork. e.g.: form ties are properly sealed.  Provide enough supports to formwork  Defective formworks and accessories should be repaired or replaced to prevent grout leakage during concreting. HONEYCOMBS 16
  17. 17. Repairing Honeycombs For small & 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. HONEYCOMBS 17
  18. 18. For large Honeycombs  Hack & 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 is cleaned  Barra emulsion is used as a bonding agent.  Over the wet surface barra emulsion is applied and before drying, 1:2 cement mortar is applied  After mortar has set sufficiently, final surface is prepared by trowel.  Texture and colour is matched for aesthetic finish.  Curing is done. HONEYCOMBS 18 Before After

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