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The most active part of cement is the material finer than 10-15 nanometer. Furthermore, a fine grind of cement clinker is able to coat the surfaces of aggregates more completely than coarse material enabling intimate contact of the resultant paste or mortar.
Generally, the fineness of the OPC cement should be up to 225 sqm per kg of cement.
As per IS code provisions, the fineness of cement is calculated by sieving 100 grams of the cement sample in a 90-micron sieve. The weight s the cement-retained on the sieve is taken.
Fineness of cement = Percentage retained = (Weight retained / weight taken) x 100
A good cement should have the percentage retained not more than 10%.
The same is applicable to OPC as well.
% fineness for OPC – <= 10% by seive analysis test for finding fineness of cement.
It shows % weight of residue left on 90 micron seive.(is seive no -9).
