Using Fly Ash in Concrete

Long before the invention of portland cement, the Romans created impressive concrete structures using lime and a volcanic ash (with properties that were first discovered in Pozzuoli, Italy) that reacted with the lime and hardened the concrete. Coal fly ash, which is the particulate matter collected by pollution-control equipment from the smokestacks of coal-burning power plants, has a similar pozzolanic effect because of its silica and alumina content. Other widely used pozzolans are blast-furnace slag and silica fume.