Wednesday 15 November 2017

Fineness test of cement

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, (Figure). 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.
AIM:
To determine the fineness of cement.
Apparatus:
·         Sieve IS-90 microns, 
·         Balance, 
·         Brush, etc.
Procedure:
1.   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. Fit the lid over the sieve. Agitate the sieve by swirling, planetary and linear movement until no more fine material passes through it.
2.   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.
3.   Repeat the whole procedure using a fresh 10 g sample to obtain R2. Then calculate the residue of the cement R as the mean of R1, and R2, as a percentage, expressed to the nearest 0.1 percent.
4.   When the results differ by more than 1 percent absolute, carry out a third sieving and calculate the mean of the three values.

Percentage of fineness (%)= W1-W2/W1 X 100
Where, W1= Total weight of cement sample
 W2= Weight of residue

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