In a slump test, each layer of concrete is compacted by a steel rod 60 cm long and of 16 mm diameter for:
Correct Answer: B. 25 times
📚 Detailed Explanation: Slump Test Procedure — Tamping
Why B (25 times) is correct: IS 1199 specifies: fill the slump mould in 3 equal layers, each approximately 1/3 of the mould height. Rod each layer 25 times uniformly distributed over the cross-section. The bottom layer must be rodded throughout its depth; upper layers are rodded just through into the layer below. 25 strokes provide sufficient compaction without over-compacting.
Slump Test Step-by-Step (IS 1199)
| Step | Detail |
|---|---|
| Mould dimensions | Top 100 mm, Bottom 200 mm, Height 300 mm |
| Number of layers | 3 equal layers |
| Strokes per layer | 25 times |
| Tamping rod | 16 mm dia, 600 mm long, bullet nose |
| After rodding | Strike off excess, lift mould vertically |
| Slump measurement | 300 mm minus height of slumped concrete |
- 3 layers × 25 strokes each = 75 total strokes for the complete specimen.
- The tamping rod must penetrate each layer fully but not into the previous layer (except bottom layer).