Blast-furnace slag and steel slag are by-products released during the making of iron and steel. They are stony materials that, after processing, are reused in construction — as a raw material for cement, as aggregate in concrete and as a base material in road construction. These are two different slags from two steps of the production process.
The difference
- Blast-furnace slag arises when making pig iron in the blast furnace. Rapidly cooled (granulated) and finely ground, it gains latent-hydraulic properties: it behaves as a binder and is the basis for blast-furnace cement (CEM III).
- Steel slag arises later, when converting pig iron into steel. This slag is harder and heavier and is used mainly as crushed aggregate in road bases, asphalt and hydraulic engineering.
| Blast-furnace slag | Arises when making pig iron in the blast furnace; granulated and finely ground it behaves as a binder; basis for blast-furnace cement (CEM III) |
|---|---|
| Steel slag | Arises when converting pig iron into steel; harder and heavier; used mainly as crushed aggregate in road bases, asphalt and hydraulic engineering |
Why reuse
Reusing slag saves primary raw materials (clinker, gravel, stone) and lowers the COâ‚‚ emissions of construction. Slag therefore fits into the circular economy and sustainable building.
Points to note
Slags must meet the correct standards and environmental quality requirements; some steel slags can still expand when wet, which in road and hydraulic engineering applications is managed with processing and handling regulations.
Related terms
- Blast-furnace cement
- Cement
- Concrete
- Aggregate
- Circular economy
- Binder
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