Slag cement is a hydraulic cementitious material produced by rapidly cooling molten blast-furnace slag, drying the granules, and grinding them. It is used with portland cement or as part of a blended hydraulic cement; it is not the same thing as unprocessed blast-furnace slag.
Terminology
| Term | Meaning |
|---|---|
| Granulated blast-furnace slag | Glassy granules produced by rapid cooling |
| Slag cement or GGBFS | Finely ground granulated slag meeting the applicable specification |
| Portland blast-furnace slag cement | Factory-blended hydraulic cement containing slag |
| Slag concrete | Concrete whose cementitious system includes slag cement |
Effects on concrete
Slag cement can reduce heat development, refine pore structure, and improve resistance to chloride penetration and some sulfate exposures when the mixture is properly proportioned and cured. Early strength may develop more slowly, especially in cool weather, while later-age strength can remain strong.
Selection cautions
- Set the proportion from performance trials rather than a universal replacement percentage.
- Check finishing and curing time in cold weather.
- Verify air-void performance where freezing and deicing salts govern.
- Match the cementitious system to sulfate, alkali-silica, chloride, and heat-control requirements.
Specification and quality control
Use the current project specification for slag cement, blended cement, concrete performance, and curing. Environmental comparisons should use product-specific declarations and an equivalent concrete-performance basis, not a generic percentage claim.