Which one of the following statements is not correct regarding the fineness of cement ?
- AFine cement is more liable to suffer from shrinkage cracking than a coarse cement.
- BFine cement shows faster rate of heat evolution and total quantity of heat evolved is much larger than coarse cement.Correct
- CFine cement will show faster rate of hardening than coarse cement.
- DFine cement shows the same setting time as coarse cement.
Solution
Concept
Effect of fineness on cement properties
Step-by-step solution
1. Finer cement hydrates faster: more early heat and faster strength gain. 2. It shrinks and cracks more. 3. The total heat of hydration depends on the composition (C₃S, C₃A), not on fineness, so it is not "much larger". 4. So statement (b) is the incorrect one.
Explanation
Fineness increases the rate of hydration, early strength and the rate of heat evolution. It does not change the ultimate total heat, which is fixed by the chemical composition of the cement.
Why the other options are wrong
Statements (a) and (c) are true of fine cement. Statement (d) is also acceptable since setting time is controlled mainly by gypsum and C₃A content, and is only slightly affected by fineness.
Shortcut
Fineness changes the RATE of heat and strength, not the TOTAL heat.
Common mistake
Thinking that finer cement releases more total heat.
Correct answer: B) Fine cement shows faster rate of heat evolution and total quantity of heat evolved is much larger than coarse cement.