Electric arc furnace carbon steel slag (EAF)

Electric arc furnace carbon steel slag is a by-product of the manufacture of steel by the electric arc furnace process (EAF). An EAF produces steel by the melting of recycled steel scrap, using heat generated by an arc, created by a large electric current (Figure 1). The slag is formed through the addition of lime, which is designed to remove impurities from within the steel. The slag has a lower density than steel and therefore floats on top of the molten bath of steel. Once the steel has been tapped into a ladle, the slag is either poured from the furnace onto the floor where it is cooled and removed for further processing, or into slag pots where specially designed vehicles are used to transport the slag to purpose built lagoons. Here it is tipped and cooled prior to onward processing. (Figure 2)

Figure 1

Steel slag contains quantities of un-combined (free) lime in the form of calcium and magnesium oxides, which expand in the presence of moisture. In order to reduce this potential expansion, the slag has to undergo controlled conditioning, generally termed weathering.

The test method to determine the level of expansion within the slag and the categories for various levels of acceptability can be found in the European specifications EN 1744-1 and EN 13042 respectively. Further guidance can be found in PD 6682-2 - guidance on the use of EN 13043 and also the Specification for Highway Works.

In addition to "weathering" the slag, it is processed to remove entrapped metal. It also undergoes crushing and screening in the same manner as for natural aggregates, to produce aggregate chippings for use in a variety of applications.

Properties

EAF steel slag is a strong, dense, none porous aggregate that is cubical in shape, has good resistance to polishing and has an excellent affinity to bitumen. This makes it an ideal aggregate for asphalt surface course materials and road surface treatments as it produces materials that are resistant to deformation (rutting), safe and durable.

Applications

The majority of EAF slag in the UK is used in road construction in both unbound materials and asphalt as a high specification aggregate, but worldwide has gained acceptance in a variety of other industries. Some of these more diverse applications are listed below.

For more information contact John Bullock

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