The ratio of various ingredients (cement : sand : coarse aggregates) in concrete of grade M20 is:
Correct Answer: C. 1:1.5:3
📚 Detailed Explanation: Nominal Mix Ratios per IS 456
Why C (1:1.5:3) is correct: IS 456 specifies nominal mix proportions (cement : fine aggregate : coarse aggregate by volume) for standard concrete grades. These are approximate mixes for ordinary concrete. For M20 the nominal proportion is 1:1.5:3.
IS 456 Nominal Mix Proportions
| Grade | Nominal Mix (C:FA:CA) | Target Strength (N/mm²) | Use |
|---|---|---|---|
| M10 | 1:3:6 | 10 | Lean concrete, PCC |
| M15 | 1:2:4 | 15 | Foundation, mass concrete |
| M20 | 1:1.5:3 | 20 | General RCC (beams, slabs, columns) |
| M25 | 1:1:2 | 25 | Pre-stressed, high-strength RCC |
- M20 = 1:1.5:3 (cement : sand : CA by volume).
- For M25 and above, IS 456 recommends design mix (IS 10262) rather than nominal mix.