The main object of compaction of concrete is:
Correct Answer: D. All options are correct
📚 Detailed Explanation: Objectives of Compaction
Why D (All options correct) is correct:
(a) Eliminate air holes: Un-compacted concrete can contain 5–20% entrapped air. Vibration releases this air, reducing voids and improving density/strength.
(b) Achieve maximum density: As air is expelled and particles pack closer together, bulk density increases towards the theoretical maximum. Each 1% air void reduces strength by ~5%.
(c) Intimate contact with embedded materials: Vibration flows concrete into every corner of formwork and around all reinforcement bars, anchor bolts, and inserts — ensuring full encasement and bond.
(a) Eliminate air holes: Un-compacted concrete can contain 5–20% entrapped air. Vibration releases this air, reducing voids and improving density/strength.
(b) Achieve maximum density: As air is expelled and particles pack closer together, bulk density increases towards the theoretical maximum. Each 1% air void reduces strength by ~5%.
(c) Intimate contact with embedded materials: Vibration flows concrete into every corner of formwork and around all reinforcement bars, anchor bolts, and inserts — ensuring full encasement and bond.
Effect of Adequate Compaction
| Benefit | Result |
|---|---|
| Air void elimination | Each 1% void removed → ~5% strength gain |
| Maximum density | Denser matrix = lower permeability, higher durability |
| Intimate contact | Full rebar bond, no honeycombing |
- All three objectives of compaction are equally important — the answer is always “all correct.”
- Under-compaction = voids and honeycombing. Over-vibration = segregation. Both are defects.