Concrete Honeycombs

Honeycombing is a very common defect found in concrete structures

1. HONEYCOMBS
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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
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3. What are honeycombs?
Honeycombs arethehollowspacesandcavitiesleftin
concretemassonsurfaceorinsidetheconcretemasswhichis
causedbythemortarnotfillingthespacesbetweenthe
coarseaggregateparticles.
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4. Types of Honeycombs
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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. Where can we find Honeycombs?
Honeycombswhichareonsidesandbottomsarevisibletonakedeyesand
canbedetectedwhenshutteringisremoved.Honeycombswhichareinside
massofconcretecanonlybedetectedbyadvancedtechniqueslike
ultrasonictestingetc.
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6. Effects of Honeycombs
Water and air enters inside
Rusting and corrosion of reinforcement
Reduce durability
Less structural strength
Reducestheloadbearingcapacity
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7. Causes for
Honeycombs
Poor
workability
Poor grading of
aggregate
Grout
leak
Movement of
formwork
Improper
compaction
Improper cover
& placement
of rebar
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8. Poor Workability8
SlumpTestcanbeusedtofindouttheworkabilityofconcrete.Iftheslumpis
lessworkabilityisless.
Workabilitymightbelessbecause
Lowwatercontent
Finercementparticles
Hightemperature
Ratiooffine-to-coarseaggregatebeinglow

9. Improper compaction9
Thepurposeofcompactingconcretebyvibrationis
theeliminationofentrappedairandforcingthe
particlesintoacloserconfigurationthatwill
definitelybuildthemorestrength.
Overvibrationwouldmake theconcrete
segregatedwhileundervibratedconcretewould
havehoneycombsinit.
Poorconcretecompactionoccursduetoineffective
vibrationorrebarcongestion.
Over vibration
Under vibration
Inserting at angles
Touching reinforcement
Touching formwork

10. Improper cover & placement of rebar
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Rebarcongestion-Ifrebarisplacedtooclose
togetherortooclosetoformworkitwilltrapthe
largerpiecesofaggregatewhilethemortarin
themixturemaynotpassthrough&interfere
withconcreteflowandvibration.
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. Movement of Formwork & Grout leak
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Whenjointsofformworkareloosetherecanbeleakageofgroutthroughthese
joints.Honeycombsoccur.
Increasedwatercontentalsoresultsinbleeding,hence,increasedwater
contentcanalsomeanthatcementslurry(grout)willescapethroughthejoints
oftheformwork.

12. Presenceofmorepercentageofbiggersizeofaggregatein
concretealsopreventsconcretetofillnarrowspacesbetweenthe
reinforcementrods.
Voidsoftenoccurbecauseaggregateistoolargetopassthrough
acondensedareaofreinforcement.
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13. Practices to minimize Honeycombing in
concrete
Useamixwithappropriateworkabilityforthesituationinwhichitistobe
placed.
Ensurethemixhassufficientfinestofillthevoidsbetweenthecoarse
aggregate.
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14. Insert vertically
Vibrate by layers
Vibrate the whole depth of layer
Insert at intervals
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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. Propercoverblockthicknessshouldbe
maintained forparticularconcrete
structures.(Eg:walls,columns,staircases–
25mm,slabs-40mm,beams-50mm,pile
caps-75mm)
Sufficientcoverblocksshouldbe
provided
Rebarcongestioncanbeminimizedby
havinglarger(thatis,lesser)rebarorby
increasingthesectionaldimensionsof
elementswherepossible.
Ensurethereinforcementlayoutandthe
sectionshapewillpermittheconcreteto
flowaroundthereinforcementand
completelyfilltheforms.
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16. Practices to minimize Honeycombing in
concrete
Checkthattheformworkisrigidandwell
braced,thejointsarewatertightandany
penetrationsthroughtheformwork.e.g.:
formtiesareproperlysealed.
Provideenoughsupportstoformwork
Defectiveformworksandaccessories
shouldberepairedorreplacedtoprevent
groutleakageduringconcreting.
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17. Repairing Honeycombs
For small & moderate honeycombs
Hackandremovethelooseparticlesinorderto
appearsoundsurface.
Surfaceiscleanedbywaterjettoobtaindust
freesurface.
Constructiongroutisapplied.
Textureandcolorshouldthenbematchedfor
aestheticfinish.
Curingisdone.
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18. For large Honeycombs
Hack&removetheweakconcretetoexpose
soundconcretesurface.
Tokeepclearancearoundreinforcement12mm
thickconcretelayerisremoved.
Byusingwaterjetsurfaceiscleaned
Barraemulsionisusedasabondingagent.
Overthewetsurfacebarraemulsionisapplied
andbeforedrying,1:2cementmortarisapplied
Aftermortarhassetsufficiently,finalsurfaceis
preparedbytrowel.
Textureandcolourismatchedforaestheticfinish.
Curingisdone.
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Before
After