Which of the following properties of concrete is determined using a compaction factor test?
Correct Answer: D. Workability of concrete
📚 Detailed Explanation: Compaction Factor Test
The compaction factor test was developed by the Road Research Laboratory in the UK to provide a more sensitive measure of workability than the slump test, especially for stiff mixes (low workability) where the slump test gives unreliable results.
Why D (Workability) is correct: The compaction factor (CF) = mass of partially compacted concrete / mass of fully compacted concrete. This ratio measures how easily the concrete consolidates under its own weight — which is a direct measure of workability. High CF (close to 1.0) = highly workable. Low CF (~0.80) = low workability. The test does not directly measure density (A), porosity (B), or strength (C) — though all are related to workability indirectly.
Workability vs. Compaction Factor
| Compaction Factor | Degree of Workability | Equivalent Slump |
|---|---|---|
| <0.75 | Very low | 0–25 mm |
| 0.75–0.85 | Low | 25–75 mm |
| 0.85–0.92 | Medium | 50–100 mm |
| >0.92 | High | 100+ mm |
- Compaction factor test is most sensitive for stiff mixes (CF 0.75–0.92) where slump test is unreliable.
- For very stiff mixes (CF <0.75), the Vee-Bee test is preferred.