Iron Slag:
Iron slag is a byproduct of iron smelting. When the blast furnace is tapped to release the molten iron, it flows from the furnace with molten slag floating 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.
Since slag is essentially a glass, there is a potential for alkali reactivity. On the other hand, slag in asphalt mix provides an excellent non-skid wearing surface.
Blast Furnace Slag
Blast furnace slag is an industrial byproduct of iron produced in a blast furnace. This slag consists primarily of silicates and aluminosilicates of lime and other bases.
The final form of the blast furnace slag is dependent on the method of cooling and can be produced in the following forms:
 |
Granulated (cement additive) |
|
Air-cooled (crushed for normal aggregate) |
|
Pelletized (lightweight aggregate) |
|
Expanded (lightweight aggregate) |
The details of slag production, properties, specifications and uses can be found at the LEVI site. Edw. C. Levy Co. is one of the foremost producers of slag in central US, with a base in Detroit, MI. Slag production in Ontario comes mostly from steel mills in Sault Ste. Marie and in Hamilton.
Table 3-1. Typical physical properties of blast furnace slag.
| Property | Slag Type and Value | ||
| Air-Cooled | Expanded | Pelletized | |
| Specific Gravity | 2.0 - 2.5 | — | — |
| Compacted Unit Weight, kg/m3 (lb/ft3) |
1120 - 1360 (70 - 85) |
(800 - 1040) (50 - 65) |
840 (52) |
| Absorption (%) | 1 - 6 | — | — |
Steel Slag
Steel slag, a byproduct of the steel making process, contains fused mixtures of oxides and silicates- primarily calcium, iron, unslaked lime, and magnesium. (1) Steel slag contains significant quantities of iron; its highly compressed void structure results in a very dense, hard material. At this time, however, its use as an aggregate is not cost-effective given its high asphalt absorption rate.
Nonferrous Slag:
Other smelting operations produce slag as well. However, there is little documented use of nonferrous slags as aggregate in embankments or fill, both air-cooled and granulated nonferrous slags are potentially useful for these applications. Nonferrous slag that is suitable for use as a granular base (copper, nickel, and phosphorus slags) will generally exceed specifications for embankment and fill construction. The high stability of nonferrous slag aggregates can be used advantageously to provide good load transfer to weaker subgrades
