396 



CEMENTS, LIMES, AND PLASTERS. 



addition to the expected loss of water, carbon dioxide, and other vola- 

 tile components, the cement has suffered other changes which prevent 

 it from having the exact composition calculated from the mixture. 

 During the process of burning, the clinker has taken up a certain amount 

 of material from the fuel ashes, the kiln linings, or the gases produced 

 in the kiln. The changes in composition thus caused will be briefly 

 discussed. 



The change in composition during burning is almost inevitably 

 in the direction of raising the Cementation Index of the cement, i.e./ 

 making it more clayey. This is due to the fact that the impurities 

 picked up during burning are all of a clayey character, the. kiln linings 

 and the fuel ash being predominantly composed of silica and alumina. 

 To partly counterbalance these additions of clayey matter, it is prob- 

 able that the dust blown out of the kiln is more clayey than the rest 

 of the mix; but this is not sufficient in amount to avail much against 

 the combined influence of the fuel ash and the kiln lining. Of the two 

 factors the fuel ash is by far the most important, because the kiln bricks 

 are pretty steadily covered by a skin of clinker. 



The variation in composition of the ash derived from different types 

 of fuel is shown by the following analyses made by Candlot.* 



TABLE 172. 

 ANALYSES OF FUEL ASH. 



The differences between the calculated and actual compositions of 

 a cement are well illustrated by the example given below. In this case 

 a marl and clay of determined composition were mixed in a known ratio. 

 The composition which a cement made from this mixture should show 

 was calculated and is given in column 3, while the composition of the 

 cement actually resulting is given in column 4. For these data the 

 writer is indebted to Prof. S. B. Newberry, who carried out the test 

 in question. 



* Bonnami. Fabrication et Controle des Chaux Hydrauliques et des Ciments, 

 p. 58. 



