According to the classification of ordinary portland cement by Indian Standard Bureau. Which of the following is not a grade of cement?
🔬 Understanding OPC Classification in India
The Bureau of Indian Standards (BIS) classifies Ordinary Portland Cement (OPC) into different grades based on its strength. The grade number directly corresponds to the minimum compressive strength the cement mortar is expected to achieve after 28 days of curing, measured in N/mm² (or MPa). This system allows engineers to select the appropriate cement for the required structural strength. For many years, three main grades have been standardized and are widely used in the Indian construction industry.
đź“ť Detailed Analysis of the Grades
(c) Grade 63
This is the correct answer because it is NOT a standard grade. The Bureau of Indian Standards has only standardized OPC in three grades: 33, 43, and 53. There is no official "Grade 63" for Ordinary Portland Cement in the Indian Standards. While some special cements might achieve such high strengths, it is not a recognized grade for OPC.
(a) Grade 53, (b) Grade 33, and (d) Grade 43
These are incorrect because they are all standard, recognized grades of OPC.
• Grade 33 (IS 269): This was the most common grade for general construction for many years but is less used now. It achieves a minimum 28-day strength of 33 N/mm².
• Grade 43 (IS 8112): This is now the most popular general-purpose cement, used for plastering, non-structural works, and concrete of lower grades. It achieves a minimum 28-day strength of 43 N/mm².
• Grade 53 (IS 12269): This is a high-strength cement used for high-strength concrete, precast elements, and structures requiring rapid strength gain. It achieves a minimum 28-day strength of 53 N/mm².
đź“Š Summary: Standard OPC Grades and Strength Development
| OPC Grade | Min. 3-Day Strength (N/mm²) | Min. 7-Day Strength (N/mm²) | Min. 28-Day Strength (N/mm²) |
|---|---|---|---|
| Grade 33 | 16 | 22 | 33 |
| Grade 43 | 23 | 33 | 43 |
| Grade 53 | 27 | 37 | 53 |
đź’ˇ Study Tips
- The Magic Trio: Remember the three standard grades of OPC in India: 33, 43, and 53. Any other number is likely not a standard grade.
- Grade = 28-Day Strength: The grade number itself is the easiest thing to remember – it's the minimum compressive strength in N/mm² after 28 days.
- Higher Grade, Faster Strength: Notice from the table that a higher grade not only means higher final strength but also higher strength at earlier stages (3 and 7 days).