SLAG BRICKS AND SLAG BLOCKS. 687 



Middlesborough, England, have been somewhat extensively employed * 

 as street pavement in Rotterdam. Holland clay bricks, limestone 

 blocks, and porphyry bricks are employed in the same city, and will 

 be useful for comparison with the slag blocks. The foundation, in 

 all cases, is simply a bed of sand, carefully packed. The thickness or 

 depth of pavement laid on this varies, according to the paving mate- 

 rial, as follows: Clay bricks, 4 inches; slag blocks, 5 inches; limestone 

 or porphyry blocks, 6 inches. The cost of material and laying per 

 square yard is: Clay bricks, 62 cents; limestone blocks, 62 cents 

 to $1.25; slag blocks, $1.25; porphyry blocks, $1.56. No data as to 

 proportions of each pavement in use, or durability of the different types, 

 are available. The adjunct director of public works of Rotterdam 

 stated that for light traffic the clay-brick pavements were regarded 

 as the best; for medium traffic, slag blocks or limestone; for heavy 

 traffic, porphyry blocks. 



The manufacture of slag blocks from copper slags at Mansfeldt, 

 Saxony, has been described f in detail by Egleston. The industry, as 

 carried on in this locality, presents certain features of interest which 

 warrant a somewhat lengthy abstract of the paper cited. 



The slags used are high in silica, ranging from 40 per cent to 60 per 

 cent. When cooled rapidly, they form a dark colored brittle glass, 

 but if cooled with great slowness the product becomes gray and crystal- 

 line. These slowly cooled slags are both hard and tough, and there- 

 fore serviceable in the manufacture of structural material. The process 

 employed at Krug Hutte is as follows: 



The slag, as it comes from the furnaces, is carried in slag wagons 

 to the molding ground, where the bricks are cast. The bed of the 

 molds is sand, which has been sieved to remove coarse particles. 



The bed is then carefully gone over with a shovel, which is pressed 

 into it an inch or so to make the sand soft. It is then smoothed over 

 with the shovel, and into the corners a piece of iron 0.18 m. to 0.20 m. 

 long, and 0.15 m. wide is laid, inclined so as to facilitate the passage 

 of the slag in the slag-runners which go round the whole space. 



The molding-bed is then so divided by iron partitions pushed down 

 into the sand as to give the size of blocks required. These partitions 

 have several round holes, about 0.05 m. in diameter, near their tops, 

 to permit the entrance of slag. Previous to use, the partitions are 

 washed with clay and sprinkled with sand to prevent the slag from 



* Streets and Highways in Foreign Countries. Special Consular Report, vol. 

 3, p. 190, Washington, 1897. 



f School of Mines Quarterly, vol. 12, pp. 112-117. 



