Pozzolane
Pozzolane, or pozzolana, refers to siliceous or siliceous and aluminous materials that, in the presence of moisture, react with calcium hydroxide released during cement hydration to form cementitious compounds. The term originates from Pozzuoli, Italy, where ancient Romans used volcanic ash in concrete. Natural pozzolane include volcanic ash and pumice, diatomaceous earth, and certain clays; artificial pozzolane include fly ash from coal combustion, silica fume, metakaolin, and calcined clays. Pozzolane are not cementitious on their own but gain binding properties when combined with lime or Portland cement.
In modern concrete, pozzolane are typically used as supplementary cementitious materials (SCMs) to partially replace Portland
Standards classify pozzolanic materials for cementitious use and set limits for silica, alumina, and other properties.