chapter  2
20 Pages

- Blast Furnace Slag

The American Society for Testing and Materials (ASTM) denes blast furnace slag (BFS) as “the non-metallic product consisting essentially of calcium silicates and other bases, developed in a molten condition simultaneously with pig iron in a blast furnace” [1]. Normally 1 ton of pig iron generates 250-350 kg of slag. In the blast furnace, the process is optimized to maximize the production of pig iron, that is, with effective removal of slag. The smooth ¤ow of molten slag out of the furnace is ensured by adding a basic agent such as lime to reduce its viscosity. When the blast furnace is tapped to release molten iron, it ¤ows from the furnace, with molten slag ¤oating on its upper surface. These two materials are separated using a weir, the molten iron being channeled to a holding vessel and the molten slag to a point where it is to be treated further. The slag consists of, principally, silicates and aluminosilicates of lime and magnesia. The BFS produced from the blast furnace in the integrated steel plant is also called ferrous slag; the nonferrous varieties are the byproducts of copper, nickel, and lead melting. The BFS from different plants differ in chemical, mineralogical, and physical constitution. The nal form of the BFS depends upon the method of cooling and can be produced in the following forms:

Air-cooled: The molten slag solidied under ambient conditions in pits near the furnace. It is crystalline in nature. It has very limited cementitious properties and is used as an aggregate for all types of construction.