The initial and final setting time durations for ordinary Portland cement, respectively, are:
🔬 Understanding Setting Time of Cement
The setting time of cement is a critical property that defines the period during which concrete can be mixed, transported, placed, and compacted. It is measured in two distinct phases:
- Initial Setting Time: This is the time when the cement paste begins to stiffen and lose its plasticity after water is added. It marks the start of the hardening process. A sufficient initial setting time is necessary to ensure the concrete can be properly handled and placed before it becomes too rigid.
- Final Setting Time: This is the time when the cement paste has hardened sufficiently to attain a certain shape and can resist a defined pressure. After this point, the concrete continues to gain strength over a long period.
For Ordinary Portland Cement (OPC), the most common type of cement, these times are strictly specified by national standards (like the Indian Standards) to ensure quality and predictability in construction.
📝 Detailed Analysis of the Options
(d) 30 minutes and 10 hours
This is the correct answer. According to Indian Standard IS 269 for Ordinary Portland Cement (grades 33, 43, and 53), the standard specifications are:
• Initial Setting Time: Should not be less than 30 minutes.
• Final Setting Time: Should not be more than 600 minutes (which is equal to 10 hours).
This pair correctly represents the standard minimum initial setting time and the standard maximum final setting time for OPC.
(a) 15 minutes and 30 minutes
This is incorrect. An initial setting time of 15 minutes is too short for general construction, and a final setting time of 30 minutes is characteristic of Quick Setting Cement, not OPC.
(b) 1 hour and 3 hours
This is incorrect. While an initial setting time of 1 hour (60 minutes) is acceptable (as it's more than 30 minutes), a final setting time of 3 hours (180 minutes) is much shorter than the allowed maximum of 10 hours for OPC.
(c) 2 hours and 24 hours
This is incorrect. An initial setting time of 2 hours is acceptable, but a final setting time of 24 hours (1440 minutes) is far too long and exceeds the maximum permissible limit of 10 hours for OPC.
📊 Summary: Setting Times for Common Cements
| Type of Cement | Initial Setting Time (Min) | Final Setting Time (Max) |
|---|---|---|
| Ordinary Portland (OPC) | ≥ 30 minutes | ≤ 600 minutes (10 hours) |
| Rapid Hardening (RHC) | ≥ 30 minutes | ≤ 600 minutes (10 hours) |
| Low Heat Cement | ≥ 60 minutes | ≤ 600 minutes (10 hours) |
| Quick Setting Cement | ≥ 5 minutes | ≤ 30 minutes |
💡 Study Tips
- The "30 and 600" Rule: For OPC, the most important numbers to remember are 30 minutes (minimum for initial set) and 600 minutes or 10 hours (maximum for final set).
- "Not Less Than" vs. "Not More Than": Be careful with the wording. The initial time is a minimum (it must be at least 30 minutes). The final time is a maximum (it must be no more than 10 hours).
- Identify the Outlier: The main exception to the 10-hour rule is Quick Setting Cement, which has a very short final setting time of just 30 minutes.