Honeycombing (a gravel pocket) is a local defect in cast concrete where the coarse aggregate is not fully surrounded by cement mortar, leaving open voids between the stones. At that spot the concrete is porous, weaker and vulnerable to moisture.
How does honeycombing occur?
Honeycombing mainly results from poor compaction or from segregation of the concrete. Common causes are:
- Insufficient vibration — the concrete is not properly compacted, so air and voids remain
- Too stiff a mix — low workability fails to fill the formwork completely
- Segregation — dropping the concrete from too great a height separates the aggregate from the mortar
- Congested reinforcement — the aggregate cannot pass between the bars
- Leaking formwork — cement paste leaks away and leaves bare aggregate behind
Consequences and repair
Honeycombs are weak spots in the structure. They reduce the compressive strength and the cover to the reinforcement, inviting corrosion and concrete decay. Small pockets are cut out and patched with repair mortar; large defects may lead to rejection of the work.
Prevention starts with good workability, careful compaction and tight, clean formwork.
Related Terms
- Concrete
- Concrete mix
- Compaction
- Concrete cover
- Concrete rot
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