CHAPTER XLIII. 







SLAG CEMENT: LIME, MIXING AND GRINDING. 



AFTER the slag has been granulated and dried, as described in the 

 preceding chapter, it must be mixed with a carefully slaked lime, in 

 proper proportions, and the mixture must be finely ground. These 

 points will be taken up first in the present chapter, after which data 

 on the general processes and costs of slag-cement manufacture will be 

 presented. 



Composition and selection of the lime. The lime used for admix- 

 ture with the slag may be either a quicklime (common lime) or a hydraulic 

 lime. In usual American practice, and also at most European plants, 

 a common or quicklime is used. At a few American, French, and 

 German plants, however, limes which have more or less hydraulic 

 properties are employed. Prost has carried on experiments touching 

 this point and decided that the use of a hydraulic lime did not notice- 

 ably increase the tensile strength of the resulting cement, but that it 

 did increase the value of the product in another way. This incidental 

 advantage is that slag cements made by using hydraulic lime are less 

 liable to fissure and disintegrate when used in air or in dry situations 

 than cement in which common quicklime is used. As above noted, 

 this method of improving the product has been tried, to the writer's 

 knowledge, at only a few of the American plants. At Konigshof, Ger- 

 many, the general practice at which plant is described on page 662, a 

 somewhat hydraulic lime is used, whose analysis will serve as fairly 

 representative of materials of this type, though most hydraulic limes 

 would run considerably higher in silica and alumina. 



ANALYSIS OF HYDRAULIC LIME, KONIGSHOF, GERMANY. 



Per Cent. 



Silica (Si0 2 ) , 12 .421 



Alumina (ALA) 2.620 



Iron oxide (FeA) ' 883 



Manganese oxide (MnO 2 ) tr. 



Lime (CaO) 81 .546 



Magnesia (MgO) 1-751 



Soda (Na.,O). . .211 



Carbon dioxide (CO 2 ) 0. 194 



Moisture (H 2 O) . 425 



653 



