Identify the correct pair(s) from the following based on the types of cement and their respective IS specifications.
| 1. | Initial setting time of ordinary Portland cement | Not more than 30 minutes |
| 2. | Initial setting time of sulphate resistant Portland cement | Not less than 45 minutes |
| 3. | Final setting time of sulphate resistant Portland cement | Not more than 600 minutes |
🔬 Understanding Cement Setting Times
The setting time of cement is a critical property that dictates the time available for mixing, transporting, and placing concrete before it begins to harden. It's divided into two stages:
- Initial Setting Time (IST): This is the time elapsed from the moment water is added to the cement until the paste starts to lose its plasticity. It marks the beginning of the hardening process. The IST must be long enough to allow for concrete placement and finishing.
- Final Setting Time (FST): This is the time from when water is added until the cement paste has completely hardened and can sustain some load. After the final set, the concrete continues to gain strength over time.
These times are determined using the Vicat's apparatus and are strictly defined by Indian Standards (IS) for different types of cement.
📝 Detailed Analysis of the Pairs
Pair 1: Initial setting time of ordinary Portland cement - Not more than 30 minutes
This statement is false. According to IS 269, the initial setting time for Ordinary Portland Cement (OPC) shall be not less than 30 minutes. This minimum time is required to ensure there is sufficient time for mixing and placing the concrete. "Not more than 30 minutes" is the specification for the final setting time of Quick Setting Cement.
Pair 2: Initial setting time of sulphate resistant Portland cement - Not less than 45 minutes
This statement is false. According to IS 12330, the initial setting time for Sulphate Resisting Cement (SRC) is the same as for OPC: it shall be not less than 30 minutes. While 45 minutes is technically "not less than 30 minutes," it is not the specified minimum limit in the IS code, making the pairing incorrect.
Pair 3: Final setting time of sulphate resistant Portland cement - Not more than 600 minutes
This is the correct statement. As per IS 12330, the final setting time for Sulphate Resisting Cement shall be not more than 600 minutes (or 10 hours). This is a standard requirement for most common types of cement, including OPC, PPC, and SRC, to ensure the concrete hardens within a reasonable timeframe.
Conclusion: Since only Pair 3 is correctly matched with its IS specification, the correct option is (d).
📊 Summary: Setting Times for Different Cements (as per IS Codes)
| Type of Cement | Initial Setting Time (IST) | Final Setting Time (FST) |
|---|---|---|
| Ordinary Portland (OPC) | Not less than 30 min | Not more than 600 min |
| Sulphate Resisting (SRC) | Not less than 30 min | Not more than 600 min |
| Rapid Hardening (RHC) | Not less than 30 min | Not more than 600 min |
| Portland Pozzolana (PPC) | Not less than 30 min | Not more than 600 min |
| Low Heat Cement | Not less than 60 min | Not more than 600 min |
| Quick Setting Cement | Not less than 5 min | Not more than 30 min |
💡 Study Tips
- The "30/600" Rule: Remember that most common cements (OPC, PPC, RHC, SRC) share the same standard: IST ≥ 30 minutes and FST ≤ 600 minutes. This covers the majority of cases.
- Memorize the Exceptions: Focus on what's different. Low Heat Cement needs more time to start setting (IST ≥ 60 min). Quick Setting Cement is the complete opposite, setting very fast (IST ≥ 5 min, FST ≤ 30 min).
- "Not Less Than" vs. "Not More Than": For IST, "not less than" (≥) means it needs at least that much time. For FST, "not more than" (≤) means it must be finished within that time.