224 TESTS ON CEMENT 



ness of the product. The fineness of cement is determined 

 by passing it through a series of sieves of different mesh and 

 then measuring the amount retained on each. Three sieves 

 are commonly employed, namely, those having 50, 100, and 

 200 wires to the linear inch. Sieves for cement testing should 

 never be used until they have been carefully examined and 

 found to conform to the following standard specification: 



1. Cloth for cement sieves shall be of woven brass wire 

 of the following diameters: No. 50, .0090 in.; No. 100, 

 .0045 in.; and No. 200, .00235 in. 



2. Mesh to count on any part of the sieve as follows: 

 No. 50, not less than 48 nor more than 50 per lin. in.; No. 100, 

 not less than 96 nor more than 100 per lin. in.; and No. 200, 

 not less than 188 nor more than 200 per lin. in. 



3. Cloth to be mounted squarely and to show no irregu- 

 larities of spacing. 



Method of Making the Fineness Test. The method of using 

 the sieves in the fineness test is to weigh out 50 g. of cement 

 on a scale sensible at least to & g. and to place it on the 

 No. 200 sieve, on which it is shaken until not more than rV g- 

 passes the sieve at the end of 1 min. of shaking. The arrival 

 of this stage of completion can be watched either by using a 

 pan under the sieve or by shaking over a piece of paper. 

 The residue remaining on the sieve is weighed, placed on the 

 No. 100 sieve and the operation repeated, again weighing the 

 residue. The amount remaining on the No. 50 sieve is then 

 determined similarly. The process of sifting can be acceler- 

 ated by placing a small quantity of coarse shot or pebbles 

 on the sieves with the cement during the shaking. These 

 may be separated from the cement by passing the residue 

 with the shot through a coarse sieve, such as the No. 20. 



Results of Fineness Tests. Portland cement should be 

 ground to such a fineness that it will leave a residue of not 

 more than 25%, by weight, on the No. 200 sieve, and not 

 more than 8% on the No. 100 sieve. Of these two require- 

 ments, the first is the more important, because it is only that 

 part of the cement passing the finest sieve that is active in 

 the setting and hardening of the material. The amount 

 remaining on the No. 100 sieve is also important, because this 



