Supplementary cementitious materials (SCMs) are byproducts of processes that improve concrete properties while reducing ordinary Portland cement usage. Also called mineral admixtures, they replace a portion of the cement in a mix and react chemically with the calcium hydroxide released from the hydration of cement to form various cement compounds. The use of SCMs provides a double benefit – it enhances the performance of concrete while reducing its carbon footprint. Typical supplementary cementitious materials include fly ash, slag, silica fume, and other natural pozzolans.

SCMs make concrete mixtures more economical, reduce permeability, increase strength, and can influence other concrete properties. Most of these are byproducts from coal-fueled power generation, steel production, and the manufacture of silicon that would otherwise end up in landfills. Since SCMs reduce greenhouse gas emissions, the use of these materials can help garner LEED credits for green building projects.