For an ordinary Portland cement .............
📋 Key Specifications for Ordinary Portland Cement (OPC)
To ensure quality and consistency, IS codes specify several key properties that OPC must meet. This question tests your knowledge of four of these fundamental requirements: Fineness, Soundness, Setting Time, and Compressive Strength.
📝 Detailed Analysis of the Options
(a) Residual does not exceed 10% when sieved through IS Sieve No. 9
This statement is factually correct. The fineness test for OPC requires that the residue left on a 90-micron sieve (IS Sieve No. 9) must not be more than 10%. However, in questions with multiple correct statements, we must find the most accurate or the one with no ambiguity.
(b) soundness varies from 5 to 10 mm
This statement is incorrect. The IS code specifies that for the Le Chatelier soundness test, the expansion must not exceed 10 mm. It does not specify a range. A value of 2 mm is perfectly acceptable. The wording "varies from 5 to 10 mm" is wrong.
(c) initial setting time is not less than 30 minutes
This is the correct answer. This is a direct and unambiguous statement of a fundamental IS code requirement for OPC. It ensures that there is a sufficient window of time to mix, transport, and place the concrete before it begins to stiffen. This statement is universally true for OPC.
(d) compressive stress after 7 days, is not less than 175 kg/cm²
This statement is incorrect. 175 kg/cm² is equal to 17.5 N/mm². The minimum 7-day compressive strength for the lowest grade of OPC (33 Grade) is 22 N/mm² (approx. 220 kg/cm²). The value given is too low.
📊 Key IS Code Requirements for OPC (33 Grade)
| Property | Requirement | Status of Option |
|---|---|---|
| Fineness (Sieve Test) | Residue on 90µ sieve ≤ 10% | Option (a) is a correct statement. |
| Soundness (Le Chatelier) | Expansion ≤ 10 mm | Option (b) is worded incorrectly. |
| Initial Setting Time | ≥ 30 minutes | Option (c) is a correct statement. |
| 7-Day Compressive Strength | ≥ 22 N/mm² (≈ 220 kg/cm²) | Option (d) states an incorrect value. |
💡 Study Tips
- Precision Matters: In competitive exams, pay close attention to wording. "Varies from 5 to 10" is very different from "shall not exceed 10". This made option (b) incorrect.
- Know Your Numbers: Memorize the core values for OPC: 10% (fineness), 10mm (soundness), 30 mins (initial set), 600 mins (final set), and the strengths for common grades.
- Handling Multiple Correct Options: When two options seem correct (like 'a' and 'c' here), re-read them carefully. Both are fundamental properties, but often one is considered more universally defining or is presented without any potential for misinterpretation. In this case, both are strong contenders, but the provided answer key selects (c).