HONEYCOMBS

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HONEYCOMBS

HONEYCOMBS

HONEYCOMBS

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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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.

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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

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.

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Effects of Honeycombs

Water and air enters inside

Rusting and corrosion of reinforcement

Reduce durability

Less structural strength

Reduces the load bearing capacity

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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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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

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

Improper cover & placement of rebar

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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.

Movement of Formwork & Grout leak

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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.

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.

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Practices to minimize Honeycombing in

concrete

Use a mix with appropriate workability for the situation in which it is to beplaced.

Ensure the mix has sufficient fines to fill the voids between the coarseaggregate.

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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

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 ofelements where possible.

Ensure the reinforcement layout and the

section shape will permit the concrete to

flow around the reinforcement andcompletely fill the forms.

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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.

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Repairing HoneycombsFor 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.

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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

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Before

After