The test most suitable for concrete of very low workability is ……………..
Correct Answer: C. Vee-Bee test
📚 Detailed Explanation: Vee-Bee Test for Very Low Workability
Why C (Vee-Bee test) is correct: Very stiff mixes (very low w/c, lean mixes, roller-compacted concrete) have near-zero slump and near-zero CF difference — both other tests become insensitive. The Vee-Bee test measures time in seconds for concrete to remould under vibration, and it remains sensitive for VB times from 2 to 40+ seconds. Slump test (A) = 0 for all very stiff mixes, indistinguishable. Compaction factor test (B) is better than slump but still limited for CF < 0.75. Vee-Bee (C) = always the best for very stiff mixes.
Test Selection by Workability Level
| Workability Level | Best Test | Sensitivity Range |
|---|---|---|
| Very low (CF <0.75) | Vee-Bee test | VB >10 s |
| Low to medium (CF 0.75–0.92) | Compaction factor test | CF 0.75–0.92 |
| Medium to high | Slump test | 25–150 mm |
| Very high / SCC | Slump flow / flow table | >500 mm spread |
- Very low workability = Vee-Bee test is most suitable.
- VB test is standard for dry-lean mixes, precast under pressure, and roller-compacted concrete (RCC dams).