A rock or artificial material composed of amorphous SiO2 (or silica and alumina), clay minerals, carbonate phases, iron compounds, and feldspars. Pozzolan forms a binder at ambient temperatures if mixed with Ca(OH)2 and water due to hydraulic reactions and the formation of calcium silicate hydrate (CSH) phases. Natural pozzolan is usually rich in clay minerals and soluble silica, commonly tuff with volcanic glass (silica) or sedimentary rocks with hydrated amorphous forms of silica (e.g., opal). Artificial pozzolan is often composed of milled bricks or fly ash. Pozzolan is a common additive for mortar and concrete.
Cf., calcium silicate hydrate (CSH) phases, brick, concrete, mortar