The fineness of cement has an important bearing on the rate of hydration and hence on the rate of gain of strength and also on the rate of evolution of heat. Finer cement offers a greater surface area for hydration and hence faster the development of strength. The fineness of grinding has increased over the years. But now it has got nearly stabilized. Different cements are ground to different fineness. The particle size fraction below 3 microns has been found to have the predominant effect on the strength at one day while 3-25 micron fraction has a major influence on the 28 days strength. Increase in fineness of cement is also found to increase the drying shrinkage of concrete.
Fineness of cement is tested in two ways :
(a) By sieving.
(b) By determination of specific surface (total surface area of all the particles in one gram of cement) by air-permeability apparatus. Expressed as cm2/gm or m2/kg. Generally Blaine Air permeability apparatus is used.
The samples of the cement shall be taken according to the requirements of IS 3535:1986 and the relevant standard specification for the type of cement being tested. The representative sample of the cement selected as above shall be thoroughly mixed before testing.
Balance be capable of weighing up to 10 g to the nearest 10 mg.
It comprises a firm, durable, non-corrodible, cylindrical
frame of 150 mm to 200 mm nominal diameter and 40 mm to 100
mm depth, fitted with 90 micron mesh sieve cloth of woven
stainless steel, or other abrasion-resisting and non-corrodible
The sieve cloth shall comply with the requirements of IS 460 (Part 1):1985 and IS 460 (Part 3):1985 and shall be free of visible irregularities in mesh size when inspected optically by the methods of IS 460 (Part 3):1985. A tray fitting beneath the sieve frame and a lid fitting above it shall be provided to avoid loss of material during sieving.
For cleaning of sieve.
IS 4031(Part 1):1996 Methods of Physical Tests for Hydraulic Cement: Determination of Fineness by Dry Sieving (second revision). Reaffirmed- May 2016