Fly Ash, Pozzolans, and SCMs

Pozzolans are siliceous or siliceous aluminous materials that alone possess little or no cementitious value that will, in a finely divided form and with water, chemically react with cement at ordinary temperatures to form compounds with hydraulic cementitous properties. Supplementary cementitous materials (SCMs) are finely divided, non-crystalline or poorly crystalline materials similar to pozzolans. They possess latent cementing properties that become active in the presence of portland cement and water (Malhotra and Mehta, 1996). Pozzolans can be natural or artificial; primarily artificial pozzolans are those formed as a byproduct of some industrial process such as fly ash, but can include calcined shales and clays. SCMs include ground, granulated blast furnace slag (GGBFS), and high-calcium fly ash. Although Class F fly ash and silica fume are not strictly supplementary cementitious materials, but they are often grouped with GGBFS and Class C fly ash in industry literature as SCMs. Pozzolans and SCMs are called mineral admixtures when added to concrete or blended cements.