EMINENTLY HYDRAULIC LIMES: GRAPPIER CEMENTS. 



175 



be sufficient to accomplish the disintegration of the entire mass, through 

 the force produced during its own slaking. Accepting this statement, 

 we can calculate the percentages of the various constituents which 

 should be present in an ideal hydraulic lime, both before and after 

 slaking, and also the composition of the limestone necessary to give, 

 in burning, this ideal product. The results of such a calculation are 

 shown in the following table. 



TABLE 69. 

 COMPOSITION OP IDEAL HYDRAULIC LIMESTONE AND HYDRAULIC LIME. 



In actual practice, however, it is found that these theoretical com- 

 positions cannot be worked up to advantageously. If, for example, a 

 limestone of the composition given above (SiC>2 13.2 per cent, CaCOa 

 86.8 per cent) is burned under the ordinary conditions of hydraulic-lime 

 manufacture, it is found that all the silica does not combine with three 

 fourths of the lime, as is required by the theory. What actually hap- 

 pens is that part of the silica will combine with part of the lime to 

 form tricalcic silicate, thus leaving a certain amount of uncombined 

 silica and entirely too much uncombined lime. Any increase in the 

 uncombined lime beyond the amount necessary to cause the clinker to 

 disintegrate by its slaking lessens the hydraulic value of the product. 



It is therefore necessary, in practice, to modify the ideal compositions, 

 these modifications being in the following directions: 



(a) Lower lime content. The limestones in actual use, as shown 

 by the analyses quoted in Tables 70 and 71, differ from the ideal 

 hydraulic limestone in carrying from 70 to 80 per cent of lime carbonate 

 in place of the 86.8 per cent of theory. This lowering in the original 

 lime carbonate content of the limestones decreases the amount of uncom- 

 bined lime in the product. 



(6) Presence of alumina and iron. Even the best hydraulic lime- 

 stones in actual use carry notable amounts of alumina and iron oxide. 



