According to IS 456, the number of grades of standard concrete mixes are:
Correct Answer: D. 7
📚 Detailed Explanation: IS 456 Standard Concrete Grades
Why D (7) is correct per the standard answer: IS 456:2000 classifies concrete grades into three groups. The “Standard” concrete group covers multiple grade designations. Per Indian civil engineering textbook convention for this question, the number of standard concrete grades is 7. The IS 456 Table 2 lists grades from M10 through to M55, with various sub-groupings in different editions.
IS 456 Concrete Grade Groups
| Category | Grades | Count |
|---|---|---|
| Ordinary Concrete | M10, M15 | 2 |
| Standard Concrete | M20, M25, M30, M35, M40, M45, M50 | 7 |
| High Performance | M55, M60, M65, M70, M75, M80 | 6 |
Key Points
- Standard concrete grades (per this question's textbook): 7 grades (M20 through M50).
- Ordinary concrete = 2 grades (M10, M15) used with nominal mixes only.
- For M25 and above, IS 456 mandates design mix (IS 10262) rather than nominal mix proportioning.