Honeycombs in concrete and remedies
Honeycombs are cavities left in concrete s where concrete could not reach. These look like honey bees nest.
Honeycombs which are on sides are visible to naked eyes as soon shuttering is removed. Honey combs which are inside concrete can be detected by ultrasonic testing etc.
Honeycomb is due to non-reaching of concrete to all places due to which cavities are created
main reasons are:
1) Improper vibration during concrete.
2) Insufficient cover to main reinforcement
3) Use of stiff concrete
4) Places like junction of beam to beam to column are the typical spots where honey combs are noticed.. This is due to conjuctivity of reinforcement; special attention is required at such place during concreting .
5) Presence of bigger size of aggregates prevents concrete to fill narrow spaces between the reinforcement rods.
Remedies :
Strictly speaking wherever honeycombs are observed concrete should be broken and should be re concreted after applying bonding epoxy(like nito bond)to the old surface.
Honeycombs not only reduces the load bearing capacity but provide a gateway for water to reinforcement rods resulting rusting and corrosion . Corrosion is a process in which reinforcement corroded even in good concrete, this result in loosing grip between rods and concrete, which is a dangerous aspect to life of concrete on structures. R.C.C. structures have failed with in 20 or 30 years even though the life span of structure is 60 years ( min) as defined due to corrosion in reinforcements.
In case of honey combs on surface pressure grouting with non shrink grout. can be adopted after due consultation with the structural designer.
It will not be out of context to point out that contractors and their supervisors are in the habit of hiding honey combs by applying cement plaster on the honey combs. hence site engineer should be very cautious on these subjects.
At places of junction of columns and beams concrete with strictly 20mm and down aggregates should be used with proper water cement ratio in concrete. 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.
Honeycombs are cavities left in concrete s where concrete could not reach. These look like honey bees nest.
Honeycombs which are on sides are visible to naked eyes as soon shuttering is removed. Honey combs which are inside concrete can be detected by ultrasonic testing etc.
Honeycomb is due to non-reaching of concrete to all places due to which cavities are created
main reasons are:
1) Improper vibration during concrete.
2) Insufficient cover to main reinforcement
3) Use of stiff concrete
4) Places like junction of beam to beam to column are the typical spots where honey combs are noticed.. This is due to conjuctivity of reinforcement; special attention is required at such place during concreting .
5) Presence of bigger size of aggregates prevents concrete to fill narrow spaces between the reinforcement rods.
Remedies :
Strictly speaking wherever honeycombs are observed concrete should be broken and should be re concreted after applying bonding epoxy(like nito bond)to the old surface.
Honeycombs not only reduces the load bearing capacity but provide a gateway for water to reinforcement rods resulting rusting and corrosion . Corrosion is a process in which reinforcement corroded even in good concrete, this result in loosing grip between rods and concrete, which is a dangerous aspect to life of concrete on structures. R.C.C. structures have failed with in 20 or 30 years even though the life span of structure is 60 years ( min) as defined due to corrosion in reinforcements.
In case of honey combs on surface pressure grouting with non shrink grout. can be adopted after due consultation with the structural designer.
It will not be out of context to point out that contractors and their supervisors are in the habit of hiding honey combs by applying cement plaster on the honey combs. hence site engineer should be very cautious on these subjects.
At places of junction of columns and beams concrete with strictly 20mm and down aggregates should be used with proper water cement ratio in concrete. 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.
