As a cheap alternative, the fineness of cement is tested by using:
🧪 Measuring Fineness: Why and How?
The fineness of cement refers to the size of its particles. It's a critical property because finer cement has a larger surface area, which leads to a faster rate of hydration, quicker strength development, and more heat generation. While the most accurate way to measure fineness is the air permeability test (which measures specific surface area), a simpler and cheaper method is often used for basic quality control: the sieve test.
The sieve test directly measures particle size by checking how much of the cement is retained on a standard fine sieve.
📝 Detailed Analysis of the Options
(a) IS 90 μ sieve where at least 95% (by weight) should pass
The sieve size (90 μ) is correct, but the passing percentage is not. 95% passing (or 5% retained) is a stricter requirement, typically associated with Rapid Hardening Cement, not Ordinary Portland Cement.
(b) IS 100 μ sieve where at least 90% (by weight) should pass
The sieve size is incorrect. The standard sieve for this test is 90 μ, not 100 μ.
(c) IS 100 μ sieve where at least 90% (by weight) should be retained
This is incorrect on two counts. The sieve size is wrong, and the requirement is for material to *pass*, not be *retained*. Retaining 90% would mean the cement is extremely coarse and unusable.
(d) IS 90 μ sieve where at least 90% (by weight) should pass
This is the correct answer. According to IS 4031 (Part 1), the standard sieve test for fineness of Ordinary Portland Cement (OPC) is conducted using an IS 90 micron sieve. The procedure involves sieving a known weight of cement for 15 minutes. For OPC, the weight of the residue left on the sieve should not be more than 10% of the original weight. This is equivalent to saying that at least 90% of the cement by weight must pass through the 90 micron sieve.
📊 Sieve Test Fineness Requirements (for OPC)
| Parameter | Standard Specification (IS 4031) |
|---|---|
| Sieve Size | IS 90 micron (μm) |
| Maximum Residue Retained | ≤ 10% by weight |
| Minimum Passing | ≥ 90% by weight |
💡 Study Tips
- Remember "90-90": The standard test uses a 90 micron sieve, and at least 90% must pass through it. This is a simple way to remember the key numbers.
- Retained vs. Passing: Pay close attention to the wording. The code specifies the maximum *retained* (10%), but questions often ask for the minimum *passing* (90%). They are two sides of the same coin.
- Cheap but Coarse: The sieve test is called a "cheap alternative" because it's simple but only measures the coarsest particles. It doesn't give a full picture of the particle size distribution like the air permeability test does.