Two statements: 1. As the compaction factor increases, slump decreases. 2. Slump test helps qualitatively understand the setting time of concrete. Select the correct option.
Correct Answer: C. Statement 1 and Statement 2 are false
📚 Detailed Explanation: Compaction Factor and Slump — Two False Statements
Why C (Both false) is correct:
Statement 1 — FALSE: Compaction factor (CF) and slump are both measures of workability. As workability increases, both CF and slump increase together — they are positively correlated, not negatively. A mix with CF = 0.95 (high workability) will also have a high slump (100+ mm). A mix with CF = 0.80 (low workability) will have a low slump (25–50 mm). So “CF increases → slump decreases” is completely wrong.
Statement 1 — FALSE: Compaction factor (CF) and slump are both measures of workability. As workability increases, both CF and slump increase together — they are positively correlated, not negatively. A mix with CF = 0.95 (high workability) will also have a high slump (100+ mm). A mix with CF = 0.80 (low workability) will have a low slump (25–50 mm). So “CF increases → slump decreases” is completely wrong.
Statement 2 — FALSE: The slump test measures consistency and workability of fresh concrete. It has no relationship with setting time. Setting time is measured by the Vicat needle apparatus (IS 4031 Part 5): initial setting time ≈ 30 min; final setting time ≈ 600 min for OPC.
Workability Tests and Their Purposes
| Test | What It Measures | Unit |
|---|---|---|
| Slump test | Workability (medium range) | mm |
| Compaction factor test | Workability (low–medium) | Ratio (0–1) |
| Vee-Bee test | Workability (very low) | Seconds |
| Vicat needle test | Setting time of cement | Minutes |
- CF and slump are positively correlated — higher workability = higher CF and higher slump.
- Slump test = workability. Vicat needle = setting time. Never confuse the two.