Which of the following is/are the reason(s) for honeycombing? (i) Insufficient vibration to remove entrapped air (ii) Too little sand/cement in the mix or using too much water or too little water. (iii) Pouring concrete from an excessive height (more than 1.5 meters)
- AOnly (i)
- B(i) and (ii)
- C(i) and (iii)
- D(i), (ii) and (iii)Correct
Solution
Concept
Honeycombing causes and concrete compaction
Formula
NONE
Step-by-step solution
1. Inadequate mechanical vibration leaves entrapped air pockets and voids between aggregate pieces; factor (i) causes honeycombing. 2. Harsh mixes with insufficient sand/cement paste cannot fill voids, while excessive or deficient water promotes segregation or poor flow; factor (ii) causes honeycombing. 3. Free-fall pouring from excessive heights (> 1.5 m) causes coarse aggregates to rebound and separate from mortar paste; factor (iii) causes honeycombing. 4. Therefore, all three conditions (i), (ii), and (iii) cause honeycombing. Answer: D
Explanation
Honeycombing in concrete is the formation of hollow pockets and exposed coarse aggregates resulting from incomplete compaction or grout loss. It is caused by inadequate vibrator consolidation, harsh or incorrectly proportioned mix designs lacking adequate fines, and segregation triggered when dropping concrete from heights exceeding 1.5 meters without tremie chutes.
Why the other options are wrong
A) Incomplete because mix proportions (ii) and pouring height (iii) are also major contributors to honeycombing. B) Incomplete because pouring from excessive height (iii) directly induces severe aggregate segregation. C) Incomplete because incorrect sand/cement proportioning or water control (ii) also creates honeycomb voids.
Shortcut
Honeycombing causes: under-vibration, harsh mix / improper paste content, and excessive free fall (> 1.5 m).
Common mistake
Believing only under-vibration causes honeycombing, ignoring aggregate segregation from high drops.
Correct answer: D) (i), (ii) and (iii)