In fineness test of rapid hardening Portland cement the residue on I.S. sieve No. 9 should not be more than:
🔬 Understanding Fineness and Its Importance
Fineness is a measure of the particle size of cement. Finer cement has a larger surface area available to react with water, which leads to a faster rate of hydration. This results in quicker strength development and a higher rate of heat evolution. Rapid Hardening Cement (RHC) gets its properties primarily from being ground much finer than Ordinary Portland Cement (OPC). The fineness test, using an I.S. Sieve No. 9 (which has a 90-micron mesh opening), measures the proportion of coarse particles in the cement by weighing the residue left on the sieve after a sample has been passed through it.
📝 Detailed Analysis of Fineness Limits
(b) 0.05
This is the correct answer. According to Indian Standards (IS 8041 for RHC), the cement is required to be much finer than OPC. The standard specifies that when tested on an I.S. Sieve No. 9, the weight of the residue left on the sieve should not be more than 5% of the original weight of the cement sample. The value 0.05 is the decimal equivalent of 5%.
(c) 0.1
This is incorrect for RHC, but correct for OPC. A residue of 10% (or 0.1) is the maximum permissible limit for Ordinary Portland Cement (OPC). Since RHC must be finer than OPC, its limit must be stricter (lower).
(a) 0.01 & (d) 0.15
These are incorrect. A residue of 1% (0.01) would be extremely fine and likely uneconomical to produce for general RHC. A residue of 15% (0.15) would be too coarse even for OPC and would not provide the rapid hardening properties required.
📊 Fineness Limits (Residue on I.S. Sieve No. 9)
| Cement Type | Maximum Permissible Residue | Reason |
|---|---|---|
| Rapid Hardening Cement (RHC) | 5% (or 0.05) | Must be very fine for fast hydration. |
| Ordinary Portland Cement (OPC) | 10% (or 0.10) | Standard fineness for general use. |
💡 Study Tips
- Finer = Faster: Remember this simple rule. To make cement react faster (rapid hardening), you must grind it finer.
- Finer = Less Residue: A finer cement means fewer coarse particles will be left on the sieve, so the percentage of residue will be lower.
- Know the Two Key Numbers: Memorize the two standard limits for the sieve test: 10% for OPC and a stricter 5% for RHC.