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The prevention of honeycomb in concrete structures can save time and money, and help construct structurally sound concrete members. Therefore, undertaking preventive measures to avoid the occurrence of honeycomb is of utmost importance.

The measures include proper compaction, use of rigid and waterproofing formwork, clean placement of steel bars, adequate concrete cover, etc.

Honeycomb in at Junctions
Figure-1: Honeycomb at Junctions

Causes of Honeycomb in Concrete

Understanding the cause behind the formation of honeycomb in a structural element is the first step towards its prevention. Some of the causes are listed below:

  1. Low concrete workability, i.e., improper w/c ratio
  2. Over-vibration of concrete
  3. Inadequate concrete compaction
  4. Addition of extra water to concrete mixture to increase workability
  5. Pouring concrete from excessive heights
  6. Formwork lacks proper rigidity and water tightness; hence grouts leak out of poured concrete
  7. High aggregate content and oversized aggregates
  8. Congestion of steel bars
  9. Small concrete cover over steel bars
  10. Placement of concrete that has lost workability

How to Prevent Honeycomb in Concrete Structure?

  • Pour concrete from a suitable height, which should not exceed 1.5 m.
  • Perform sufficient concrete compaction and prevent over compaction, which causes concrete segregation and, ultimately, honeycombing.
  • Make sure to provide adequate concrete cover to facilitate concrete compaction.
  • Secure steels bars at their correct positions properly and maintain designated bar spacing to facilitate both flow and compaction of concrete.
  • If reinforcement congestion is inevitable, use self-compacting concrete or any other unique concrete formulation to ensure proper concrete pouring and compaction and consequently prevent honeycombing. Additionally, use a maximum aggregate size of 12.5 mm.
  • Make sure that the concrete around steel bars and other embedded objects is compacted adequately.
  • When big air bubbles come out of fresh concrete, the application of vibrators should be stopped.
  • Honeycomb is very likely to occur in the corners of concrete structural members. Therefore, compaction in the corners of structural members should be performed sufficiently.
  • Use adequately rigid formwork and seal joints to avoid leakage through them. The leakage may swell plywood, which may modify dimensions of the structural elements.
  • Make sure that concrete has suitable workability for the condition in which the structure is constructed. For instance, if a column is reinforced heavily, the concrete mix should have a slump value of around 15cm.
  • A concrete mix needs to be cohesive.
  • The concrete mix should have enough fines to fill spaces between coarse aggregates.
  • Apply tape outside of the formwork with a wooden hammer during concrete pouring to reduce the risk of honeycombing.
  • For column and beam junction, use a slightly higher water to cement ratio for concrete with a maximum aggregate size of 20 mm or smaller to decline the possibility of honeycombing.
  • Avoid the addition of extra water to concrete to increase workability because it increases the likelihood of honeycombing when vibration is applied.
Water tight formworks Prevent Leakage and in turn Avoid Honeycomb
Figure-2: Water tight Formworks Prevent Leakage and Avoid Honeycomb

FAQs

What are some preventive measures for avoiding honeycomb in concrete?

The measures include proper compaction, use of rigid and waterproofing formwork, clean placement of steel bars, adequate concrete cover, etc.

What are the causes of honeycomb in concrete?

1. Low concrete workability, i.e., improper w/c ratio.
2. Over-vibration of concrete
3. Inadequate concrete compaction
4. Addition of extra water to concrete mixture to increase workability
5. Pouring concrete from excessive heights
6. Formwork lacks proper rigidity and watertightness; hence grouts leak out of poured concrete
7. High aggregate content and oversized aggregates
8. Congestion of steel bars
9. Small concrete cover over steel bars
10. Placement of concrete that has lost workability

What is the maximum acceptable height for pouring concrete?

Pour concrete from a suitable height, which should not exceed 1.5 m.

What are the signs of adequate vibration in concrete?

When big air bubbles come out of fresh concrete, stop vibration When big air bubbles come out of fresh concrete, the application of vibrators should be stopped.

Read More

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