242 



REIBLING AND REYES. 



powder and found that it still retained a rather slow normal set. These facts 

 are shown more specifically by the figures given in Table XXXIII: 



Table XXXIII. — The effect of fineness of grinding upon brand L cement. 



Average results of cement L tested per 

 request No. 74109 



Average results of cement L tested per 

 request No. 74272 



Mixture of cement L as received 



Same as above reground 



Fineness. 



200- 

 mesh. 



74.7 



83.7 

 73.8 

 89.5 



100- 

 mesh. 



95.6 



97.3 



94.2 



100.0 



Speci- 

 fic 

 grav- 

 ity. 



3.10 



3.10 

 3.10 

 3.09 



Initial set. 



Hours. 



Min- 

 utes. 



Final set. 



Hours. 



Min- 

 utes. 



16 



20 

 20 

 00 



Although the data in Table XXVII and figure 17 show that the effects of 

 plaster on the non-seasoned cement L were in general similar to those on cement 

 Oij it is also evident that L produced a cement which comparatively was slower 

 setting than Oi and that it required less plaster (1.0 per cent) to prevent regaug- 

 ing and to retard the set to normal requirements. 



Accordingly, it was found that the addition of 1.0 per cent of plaster to 

 cement L was sufficient not only to insure the practical control of its setting 

 properties, but also to obtain a slower setting cement than a similar mixture 

 with Oj. Therefore, the characteristic slow set of the commercial product whicli 

 L represents seems to have been duly accounted for. 



Cement K introduces more complicated considerations, because the 

 practical control of its set necessitates a preliminary process of seasoning. 



Formerly, all Portland cement clinkers had to be seasoned, as otherwise 

 the cement would be unsound. Now, the best rotary practice yields a 

 clinker which is sound when fresh. Therefore, it being very often 

 desirable to use the material as soon as possible, the packing of fresh 

 cements is of more and more frequent occurrence. Samples 0^ and L 

 are characteristic of cements the setting properties of which can be put 

 under control even though the clinker is plastered, ground and packed 

 without previously having been seasoned. 



However, it sometimes happens that the nature of a cement is such 

 that it must be seasoned before the plaster is added, or otherwise the set 

 can not be controlled. This was found to be especially true of cements 

 which contain a considerable percentage of anhydrous free lime, or whose 

 setting properties are greatly influenced by thermal conditions. 



Table XXVII and figure 17 show that the addition of 3.5 per cent of 

 plaster to the non-seasoned cement made from K produced a maximum 

 retardation of the initial set of 32 minutes. On the other hand, figure 

 19 shows that it was possible so to season the K clinker, that when 

 ground, the addition of 1.5 per cent of plaster gave a maximum 

 retardation of the initial set of 135 minutes. Therefore, we thought 

 that 2.5 per cent of plaster would keep this cement normally slow setting 

 under all conditions of ordinary storage. Accordingly, we aerated a 



