Honey combing in Concrete:
Concrete is made into various structural elements such as Columns, Beams, Foundations, Slabs etc. as required as per the structural design When concrete is poured into the formwork, concrete starts flow like water sometimes cavities/voids are formed in concrete when concrete does not reach all places. It appears like honey bee nest. If it is not vibrated properly it may leave voids exposing the aggregate. Concrete Honeycomb not only reduces the strength also provides passage for water which in turn corrodes reinforcement bars. Corrosion is a process which continues through reinforcement rods even in good concrete, this result in loosing grip between rods and concrete, which is very dangerous to safety and life of concrete structures.
In other words, Honey comb refers to voids in concrete caused by the mortar not filling the spaces between the coarse aggregate particles.
Concrete Honeycomb is normally seen at the column and beam junction due to overcrowding of reinforcement bars which leads to poor concrete fill.
Causes of honeycombing in Concrete:
- Insufficient compaction to concrete.
- Less cover to reinforcement bars.
- Improper Workability in concrete
- Concrete already set before placing .
- High concrete free fall while pouring
- Form work not watertight/rigid.
- More coarse aggrgegates than designed mix proportions and over sized aggregates.
- Improper placement of bars at column and beam junction.
- Addition of more water than designed at site for achieving workability.
- Steel congestion not allowing concrete flow to all corner.
Remedies of Honeycombing in concrete:
- Concrete fall should be be kept minimum
- Use a mix with appropriate workability for the situation in which it is to be placed.
- Ensure the mix has sufficient fines to fill the voids between the coarse aggregate.
- Ensuring the concrete is fully compacted and placing methods minimise the risk of segregation.
- Ensure that the formwork is rigid, the joints are watertight and penetrations through the formwork, are properly sealed.
- At places of junction of columns and beams concrete with strictly 20mm and down aggregates should be used with slightly more water and cement to avoid honeycombs. Taping with wooden hammer the sides of shuttering from outs side during concreting and vibrating will help minimizing honeycombs to a great extent in case of columns and beams. Use of thinner needle say 25mm or less with vibrator at intricate places of concreting will also help in reducing honey combs to a great extent.
- Taping with wooden hammer on the sides of shuttering from outside during concreting will aid in minimizing honeycombs to a great extent.
Important properties of Concrete
Segregation and Bleeding in concrete