SLAG CEMENT: LIME, MIXING AND GRINDING. 663 



The specific gravity of this cement ranges between 2.80 and 2.90. 

 In all its properties it resembles other slag cements. 



Slag cement is made at the Cockerill plant * at Seraing, Belgium, 

 from blast-furnace slags ranging within the following limits: 



Per Cent. 



SiO 2 27 to 32 



A1 2 O 3 12 " 22 



CaO 49 " 55 



The slag is granulated and dried, the latter taking place at a tem- 

 perature of about 500 C., and requiring a fuel (coke) consumption of 

 about 9 per cent of the weight of slag dried. The slag is ground so as 

 to all pass a sieve of 76 meshes to the inch, and leave a residue of only 

 8 to 12 per cent on a sieve of 180 meshes to the inch. Grinding to this 

 fineness requires 25 to 30 H.P. for the production of 450 to 800 kilo- 

 grams per hour of powdered slag. Lime is burned, slaked by immer- 

 sion, and stored eight to ten days, at the end of which time it is screened 

 to pass a 76-mesh sieve. It is then mixed with the slag in the propor- 

 tion of 15 to 20 parts of lime to 100 parts slag. 



Costs of manufacture. Data regarding the cost of manufacture 

 of slag cement have been recently published. f The figures quoted are 

 said to have been the costs of actual manufacture some years ago at 

 the plant of the Maryland Cement Company. They are as follows, 

 being based on a production of 5000 barrels per month: 



Per Barrel. 



Mill force, labor and superintendence $0 . 160 



125 tons of coal at S3.05 per ton .076 



3000 bushels of lime at $0.16 per bushel . 100 



900 tons of slag at $0.50 per ton .090 



Repairs, $100 per month .020 



Oil and grease, $40 per month .007 



Contingencies O- 011 



$0.464 

 Cost of administration $0 121 



$0.585 







These figures seems rather high in some respects. For American 

 plants I should say that the average cost of manufacture should not 

 be over 35 cents per barrel. 



* Eng. and Min. Jour., vol. 64, pp. 515-516. 



f Boilleau and Lyon. Cost of making slag cement. Municipal Engineer 

 vol. 26, p. 321. May 1904. 



