ASTM C989/C989M
Standard Specification for Slag Cement for Use in Concrete and Mortars
Ground granulated blast-furnace slag used as a supplementary cementitious material, and the Grade 80/100/120 designations that describe its reactivity.
Who needs it
Batch plants, mix designers, and specifiers targeting sulfate resistance, reduced permeability, lower heat, or lower embodied carbon.
What the test involves
It classifies slag cement by how much strength it contributes relative to a straight portland reference, which is what the grade numbers communicate — higher grade means more reactive. Slag is a byproduct of iron production that, when rapidly cooled and ground fine, behaves as a cementitious material in its own right rather than an inert addition. The specification also covers fineness, sulfate content, and air-content behavior.
Common misconceptions
- Slag concrete's characteristic light color is a curing and appearance factor, not a strength indicator, and it evens out with age and exposure.
- Higher grade is not automatically the right pick. Grade selection is matched to the replacement level and the strength schedule the job actually needs.
- Like fly ash, slag generally trades early strength for long-term strength and lower permeability, so testing at an early age understates what the concrete will become.
Official source
We summarize scope and purpose only. The full text belongs to the issuing body — read it at the official source. ASTM International