In a 1:3:6 concrete mix, the actual quantity of sand per unit volume of cement, if bulking of sand is 15%, is:
Correct Answer: B. 3.45
📚 Detailed Explanation: Bulking Correction for 1:3:6 Mix
Why B (3.45) is correct: The mix specifies 3 parts dry sand per 1 part cement. With 15% bulking, the moist sand occupies more volume. To deliver 3 dry-volume units of sand, we must measure an increased (bulked) volume.
Specified dry sand per unit cement = 3 volumes
Bulking = 15% = 0.15
Bulking = 15% = 0.15
Measured moist sand volume = 3 × (1 + 0.15)
= 3 × 1.15 = 3.45 volumes
General Bulking Correction Table
| Mix | Specified Sand | Bulking | Measured Volume |
|---|---|---|---|
| 1:2:4 | 2 | 20% | 2 × 1.20 = 2.40 |
| 1:3:6 | 3 | 15% | 3 × 1.15 = 3.45 |
| 1:1.5:3 | 1.5 | 25% | 1.5 × 1.25 = 1.875 |
- For 1:3:6 with 15% bulking: measure 3.45 volumes of moist sand per unit cement.