Supplementary cementitious material, the umbrella term for fly ash, slag cement, silica fume, natural pozzolans and calcined clays that replace part of the portland cement in a mix. The pozzolans react with the calcium hydroxide left by cement hydration and slag also hydrates on its own, so both form extra binding gel, which lowers permeability, heat and carbon at the cost of slower early strength. Replacement runs from 5 to 10 percent for silica fume up to 50 percent or more for slag.
With 40 percent SCM in that mix, don't plan on stripping the deck forms on day three.
Also heard as
- SCMs
- supplementary cementitious materials
Related terms
Fly ash
Fine powder captured from coal-fired power plant exhaust, used to replace part of the cement in concrete.
Slag cement
Ground granulated blast-furnace slag, an ironmaking byproduct that replaces part of the portland cement in a mix.
Silica fume
Ultrafine silica dust from silicon smelting that makes concrete much denser, stronger and less permeable.
w/cm
Water-to-cementitious-materials ratio: the weight of mix water divided by the weight of cement plus SCMs.
ASR
Alkali-silica reaction, a slow internal reaction between cement alkalis and certain aggregates that cracks concrete.