According to IS 10262 : 1982, what should be the compressive strength of OPC of grade C?
🔬 Understanding Cement Grading Systems
The grading of cement is crucial for concrete mix design, as it indicates the cement's strength potential. Before the current system of grades 33, 43, and 53 was widely adopted, an older version of the Indian Standard for concrete mix design, IS 10262:1982, used a letter-based grading system (A to F). This system also classified cement based on its 28-day compressive strength, but grouped the strengths into different ranges. This question refers to that older, letter-based classification system.
📝 Detailed Analysis of Grade C Strength
(a) 42.5 to 47.5 MPa
This is the correct answer. According to the table in IS 10262:1982, Grade C corresponds to a 28-day characteristic compressive strength range of 41.7 to 46.6 MPa. The option (a) "42.5 to 47.5 MPa" is the closest available range to this official specification. This grade is roughly equivalent to the modern OPC 43 Grade cement, as 43 N/mm² (MPa) falls within this range.
(d) 37.5 to 42.5 MPa
This is incorrect. This range most closely corresponds to Grade B in the 1982 code, which has an official range of 36.8 to 41.7 MPa.
(c) 32.5 to 37.5 MPa
This is incorrect. This range corresponds to Grade A in the 1982 code, which has an official range of 31.9 to 36.8 MPa. This is equivalent to the modern OPC 33 Grade.
(b) 47.5 to 52.5 MPa
This is incorrect. This range corresponds to Grade D in the 1982 code, which has an official range of 46.6 to 51.5 MPa. This is roughly equivalent to the modern OPC 53 Grade.
📊 Summary: OPC Grades as per IS 10262:1982
| Grade | Compressive Strength Range (MPa) | Modern Equivalent (Approx.) |
|---|---|---|
| A | 31.9 – 36.8 | OPC 33 |
| B | 36.8 – 41.7 | - |
| C | 41.7 – 46.6 | OPC 43 |
| D | 46.6 – 51.5 | - |
| E | 51.5 – 56.4 | OPC 53 |
| F | 56.4 – 61.3 | - |
💡 Study Tips
- Know Both Systems: While the 33/43/53 system is current, questions on the older A-F grading can still appear. It's useful to know the approximate equivalents.
- Link C to 43: A simple way to remember is that Grade C is the third letter, and it corresponds to the middle numerical grade, 43.
- Check the Code Year: Always pay attention to the IS code year mentioned in the question. IS 10262:1982 refers to the old letter system, while later revisions use the numerical system.