HONEYCOMBED CONCRETE PREVENTIVE MEASURES

What is Honeycomb?• Honeycombing refers to voids in concrete caused by the

mortar not filling the spaces between the coarse aggregate particles in concrete surface or inside the concrete mass where the concrete could not reach. They look like Honey bees nest.

• It usually becomes apparent when the formwork is stripped, revealing a rough and stony concrete surface with air voids between the coarse aggregate on concrete surface. But Honeycombs inside concrete can be detected by advanced techniques like ultrasonic test etc.,

Honeycomb in concrete wall

Honeycomb in concrete wall

HONEYCOMBED CONCRETE PREVENTIVE MEASURES

Risk associated with Honeycomb

• According to Honeycomb depth and extent may reduce the both structural strength and durability performance of concrete.

• Aesthetic look of concrete surface will be affected.

Root Cause for Honeycomb

Inadequate concrete compaction. (Vibrator not used properly).

Inappropriate vibrator needle used for concrete compaction.

Holes or gaps in the form work allowing some of the mortar to drain out of the concrete.

Required Cover not maintained between the reinforcement and shutter.

Concrete placing method / Concrete pouring height increases the risk of segregation.

Root Cause for Honeycomb Cont...

Places like junction of beam to beam to column and to one or more beams are the typical spots where honey combs are observed. This is due to jumbling of reinforcement of beams and column rods at one place; special attention is required at such place during concreting and vibrating.

Use of very stiff concrete (this can be avoided by controlling water as per slump test).

Practices to Minimise the occurrence of Honeycombed concrete

To Minimise the incidence of Honeycombed Concrete:

• Ensure the concrete is fully compacted. Use appropriate concrete vibrator according to concrete wall size / gap between the reinforcement.

• Holes or gaps in the form work to be closed by foam sheet to avoid the slurry leakage.

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

• Reduce Concrete pouring height by extending the concrete pump hose to place the concrete as near as possible to its final position.

Practices to Minimise the occurrence of Honeycombed concrete Cont....

To Minimise the incidence of Honeycombed Concrete:

• Proper shuttering material to be used.

• Shutter release agent to be applied.

• Concrete pouring shall be done layer by layer.

Different Dia. Of Vibrator Needles

Proper Vibration

Use of Vibrator

HONEYCOMB REPAIRING METHOD• According to the extent and depth of the Honeycombed area the

following Approved materials to be used as per Engineer’s instructions.1. Polycrete FC2. Polycrete ST3. Polycrete MC

• Chip off the affected area to expose sound concrete by means Mechanical equipment.

• Chipped off surface shall be cleaned by air compressor or with water spray.

• Just prior to the application repaired material, apply Bonding agent (Polybond AC) on the repair surface and allow concrete to absorp the bonding agent.

HONEYCOMB REPAIRING METHOD Cont...• Mechanical mixing of Polycrete ST/MC should be

done as per manufacturer’s data sheet.

• Apply mixed material onto honeycombing surface. The material should be placed within 30 minutes of mixing, in order to gain the full benefits of fluidity and expansion, which will fill all the voids.

• Once repaired surface dried, immediate curing is to be done with water spraying, wet hessian cloth/polythene sheet or a curing compound for minimum period of 72 hours.

Concrete Wall Without any defects