SIEVING METHOD
Principle: The fineness of cement is measured by sieving it on standard sieve. The proportion of cement of which the grain sizes are larger than the specified mesh size is thus determined. A reference sample having a known proportion of
material coarser than the specified mesh size is used for checking the specified sieve.
Apparatus:
a) Test Sieve: 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 pm mesh sieve cloth of woven stainless steel, or other abrasion-resisting and non-corrodible metal wire. 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.
b) Balance: Capable of weighing up to 10 g to the nearest 10 mg.
c) Brush: A nylone or pure bristle brush, preferably with 25 to 40 mm bristle, for cleaning the sieve.
Material for Checking the Sieve:
A Standard reference material of known sieve residue shall be used for checking the sieve. The material shall be stored in sealed, airtight containers to avoid changes in its characteristics due to absorption or deposition from the atmosphere. The containers shall be marked with the sieve residue of the reference material.
Procedure:
a) Determination of the Cement Residue
Agitate the sample of cement to be tested by shaking for 2 min in a stoppered jar to disperse agglomerates. Wait 2 min. Stir the resulting powder gently using a clean dry rod in order to distribute the fines throughout the cement.
Fit the tray under the sieve, weigh approximately 10 g of cement to the nearest 0.01 g and place it on the sieve, being careful to avoid loss. Disperse any agglomerates. Fit the lid over the sieve. Agitate the sieve by swirling, planetary and linear movement until no more fine material passes through it. Remove and weigh the residue. Express its mass as a percentage, R1, of the quantity first placed in the sieve to the nearest 0.1 percent. Gently brush all the fine material off the base of the sieve into the tray.
Repeat the whole procedure using a fresh 10 g sample to obtain 5. Then calculate the residue of the cement R2 as the mean of R1 and R2 as a percentage, expressed to the nearest 0.1 percent. When the results differ by more than 1 percent absolute, carry out a third sieving and calculate the
mean of the three values. The sieving process is carried out manually by a skilled and experienced operator.
NOTE - Alternatively a sieving machine may be used provided that it can be shown to give the same results as the manual operation.
b) Checking the Sieve
Agitate the sample of cement to be tested by shaking for 2 min in a stoppered jar to disperse agglomerates. Wait 2 min. Stir the resulting powder gently using a clean dry rod in order to distribute the fines throughout the cement.
Fit the tray under the sieve. Weigh approximately 10g of the reference material to the nearest 0.01 g and place it in the sieve, being careful to avoid loss. Carry out the sieving procedure as above including the repeat determination of residue to yield two values p1 and P2 expressed to the nearest 0.1 percent. The two values of P1 and P2 for a satisfactory sieve should differ by not more than 0.3 percent. Their mean P characterizes the state of the sieve.
Given the known residue on the 90 m mesh of the reference material, R0 calculate R0/P as the sieve factor, F, expressed to the nearest 0.0 1. The residue, R determined as in 1 step shall be corrected by multiplying by F, which may have a value of 1.00+-0.20.
EXPRESSION OF RESULTS
Report the value of R, to the nearest 0. I percent, as the residue on the 90 pm sieve for the cement tested. The standard deviation of the repeatability is about 0.2 percent and of the reproducibility is about 0.3 percent.
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