350 



CEMENTS, LIMES, AND PLASTERS. 



cement either in the United States or in England. The effect on the 

 waste when a magnesian limestone is used in the alkali-plant is well 

 shown by analyses 3, 4 and 5, in all of which the magnesia is high for a 

 Portland-cement material. 



At the only American cement-plant which uses alkali waste the 

 materials (clay and waste) are mixed wet. The waste carries 90 to 95 

 per cent of lime carbonate, while the clay used gives the following 

 analysis : 



Silica (SiO 2 ) 63.54 



Alumina (A1 2 O 3 ) : j ^ QQ 



Iron oxide (Fe 2 O 3 ) J 



Lime (CaO) 1 .66 



Magnesia (MgO) 1.05 



Alkalies (K 2 O,Na 2 0) 0.78 



Carbon dioxide (CO 2 ) 2.47 



Water 7.05 



The clay is put through a rotary drier and ground in a dry -pan, 

 after which the waste and clay are mixed in a wet pug-mill and ground 

 in wet tube mills. The mix is made drier than at most of the plants 

 using marl and contains usually about 40 per cent of water. 



It is not, of course, necessary that wet mixing should be practiced 

 when alkali waste is employed as one raw material. The waste could 

 be dried, though it is possible that its physical properties might render 

 this more difficult than drying limestones or clays. 



List of references on alkali waste as a cement material. The follow- 

 ing brief list covers the few available references on this subject: 



Butler, D. B. [Alkali waste used in England.] Portland Cement: its Manu- 

 facture, Testing, and Use, pp. 25-27. 1899. 



Lathbury, B. B. The Michigan Alkali Company's plant for manufacturing 

 Portland cement from caustic-soda waste. Engineering News, June 7, 

 1900. 



Lathbury, B. B., and Spackman, H. S. The Michigan Alkali Company's plant, 

 Wyandotte, Michigan. The Rotary Kiln, pp. 110-119. 1902. 



Redgrave, G. R. [Use of alkali waste in England.] Calcareous Cements: 

 their Nature and Uses, pp. 182-184. 1895. 



Blast-furnace Slag. 



True Portland cements, which must be sharply distinguished from 

 the slag (or puzzolan) cements described in Part VII of this volume, can 

 be made from mixtures which contain blast-furnace slag as one ingredient. 

 In this case the slag is intimately mixed with limestone and the mixture 

 is finely powdered. It is then burned in kilns and the resulting clinker 

 pulverized. 



