Blast Furnace Slag Characteristics

General Characteristics

Blast furnace slag is the co-product of molten iron production in a blast furnace.

The chemistry usually has a narrow ratio of basic to acid components.

Calcium and magnesium content, reported as equivalent oxides, normally results in a 1.25 to 1.55 basicity ratio.

The total basic elements, reported as equivalent CaO plus MgO divided by silica results in slag chemistry such as:

CaO 38% MgO 10% SiO2 36%

with minor elements such as:

Iron Oxide (FeO &Fe2O3)<1% Sulfur (S) 1%± Alumina (Al2O3) 6-12%

          Physical Characteristics and Uses

	Slag Type		Physical Characteristics		Uses
	Air Cooled		Molten slag poured into pits in layers, allowed to solidify, and cooled either by external temperatures or by water addition after solidification, then crushed and screened.		General aggregate use in base, concrete, asphalt applications, rail ballast, roofing, shingle coating, glassmaking, and rockwool raw material.
	Expanded or Lightweight		Produced by rapidly pouring molten slag into sloping pits, moist on the bottom to allow steam penetration while still viscous, causing many small voids.		Concrete blocks.
	Granulated		Rapidly cooled by a high velocity mixing of molten slag flow with water jets in a ratio of one part slag to 6-10 parts water by mass.		Cement replacement in concrete making, or as an ingredient in making a blended cement.  May also be used as a lightweight fill and as a sand replacement in concrete.
	Pelletized		A variation of granulating in which less water is used with violent impelling of the viscous, but rapidly cooling slag through the air.		Cement replacement in concrete making, or as an ingredient in making a blended cement.  May also be used in some lightweight concrete applications or products.