Honeycomb is the space or void inside the concrete.

Causes

• Improper compaction as well as mixing of ingredients.
• Due to too stiff (Hard) concrete.
• When large size aggregate is used.
• Due to Segregation of ingredients of concrete
• Caused if there is not adequate gap between steel rods to enter concrete mix into it.

Effects

• Reduce Strength of Concrete
• Generally, occur in beam, slab, column etc. which may cause collapse of whole structure.
• Dangerous for earthquake structure
• Easy corrosion of Rebar.

Remedies

• Mix concrete materials properly.
• Use standard size aggregate
• Use vibrator for compaction of concrete. (Too much compaction of concrete with vibrator leads to segregation in concrete)

For more details:

Top 5 Cause of Honeycomb in Concrete – Remedies of Honeycomb