Blaine air permeability apparatus is used to determine the _______ of Portland cement.
- Apermeability
- Bspecific gravity
- Cgradation
- DfinenessCorrect
Solution
Concept
The Blaine apparatus measures the specific surface (fineness) of cement using air flow through a compacted cement bed.
Formula
Specific surface S ∝ √t (t = time for air to pass through the cement bed)
Step-by-step solution
1. A cement bed of known porosity is made in the Blaine cell. 2. Air is passed through the bed and the flow time is noted. 3. Finer cement gives more resistance, so air takes more time. 4. From this time, specific surface (cm²/g or m²/kg) is calculated. 5. Specific surface is a measure of fineness, so the answer is fineness.
Explanation
The Blaine air permeability apparatus gives the specific surface area of cement. A higher specific surface means finer cement. So it is used to find the fineness of cement.
Why the other options are wrong
A: It uses air permeability as a method, but the result is fineness, not the permeability of cement. B: Specific gravity is found with a Le Chatelier flask. C: Gradation is found by sieve analysis, mainly for aggregates.
Shortcut
Blaine = fineness (specific surface). Le Chatelier flask = specific gravity.
Common mistake
Choosing 'permeability' because of the word 'air permeability' in the apparatus name.
Correct answer: D) fineness