Slag cement (GGBFS)
Ground granulated blast-furnace slag, a byproduct of iron production used to replace part of the portland cement. It lowers permeability and improves sulfate resistance.
What does slag cement (ggbfs) mean?
Slag is cementitious in its own right rather than merely pozzolanic, and it is graded by how much strength it contributes relative to plain cement. Replacement levels can be high, which makes it a major lever for reducing embodied carbon. Slag concrete sets more slowly, generates less heat, and produces a characteristically light, almost blue-white color that evens out with exposure.
In practice
If a fresh slab looks noticeably paler than the last one and the mix changed, slag content is usually the explanation.