THE INTERPKETATION OF CEMENT ANALYSES. 



271 



In the valuation of cements, however, it becomes necessary to 

 distinguish clearly between the essentials and non-essentials in its 

 composition, in other words to be able to discriminate between 

 the good and the bad constituents of the cement. 



The essentials may be enumerated as 

 Calcium orthosilicate Calcium aluminate Calcium ferrite 



The remaining constituents may be deemed non-essential 

 although some among them may be decidedly injurious, and will 

 if their quantity be excessive, sooner or latter bring about the 

 disintegration of the concrete. 



The possibility therefore of formulating an ideal cement from 

 purely theoretical considerations may be brought into practical 

 use and I would specify the type of a good cement to be one that 

 will prove on chemical analysis to be constituted in harmony with 

 the following scheme, the principle being, that there shall be the 

 correct proportion of lime present to make the combination com,, 

 plete occording to the demands of the law of chemical combination. 



Essentials. 



'Calcium orthosilicate 60-75 per cent. 

 Calcium aluminate... 18 — 20* „ 

 Calcium ferrite ... 2-5 „ 

 ^Calcium hydrate ... 2-10 „ 



'Insoluble silica 

 Sulphur trioxidef 

 Sulphur as sulphide 

 Free carbon 

 Non-Essentials.^ MagnesiaJ 

 Soda 

 Potash 

 Moisture 

 l Carbon di-oxide 



}2-8% 

 [not to exceed 10%] 



*The higher this figure appears, the quicker will be the cement in setting 

 f This and the magnesia together should not exceed 3 per cent. 

 X If the cement is to be used for harbours or submarine works, the 

 magnesia should not exceed 1 per cent. 



