As this picture shows the honeycomb happened at the bottom of column.
Reasons:
1. Due to heavy reinforcement, concrete can't travel till the end.
2. If we are doing proper vibration by vibrator also, external tamping is needed for settling the aggregates with slurry.
3. Insufficient slurry passed till bottom. For this we need to pour at least 1:1 or 1:2 cement sand mortar initially before pouring concrete.
4. Water cement ratio is less than required/designed.
5. Due to heat temperature, it is better to pour cement slurry by at least every 2 to 3 pans (Ghamelas) of concrete simultaneously.
6. COVER IS NOT AVAILABLE, SO THE CONCRETE GOT OBSTRUCTED AT STIRRUPS.
7. Fine aggregate and 10mm down aggregates not seen in this concrete.
8. Slurry leakage may have happened because not providing foam sheets at corners of shuttering.
9. Improper supervision.
10. Normally we should avoid pouring concrete in columns directly from first outlet from transit mixers. (1st ring of concrete at millars should be avoided for column concrete).
11. 20 mm aggregate over size may cause this issues.
12. All in aggregate and combined aggregate grading may not satisfied for this particular mix.
13.
