Pozolans

Pozolans are a type of siliceous or siliceous and aluminous material which, when mixed with lime and water, forms a cementing compound. They are primarily used in the production of Portland cement and other hydraulic cements. The term "pozzolan" is derived from the town of Pozzuoli in Italy, where volcanic ash was used as a cementing material.

Pozolans are typically classified into two main types: natural pozzolans and artificial pozzolans. Natural pozzolans are found in volcanic rocks and soils, such as volcanic ash, pumice, and diatomaceous earth. Artificial pozzolans are produced through industrial processes, including fly ash from coal combustion, silica fume from the production of silicon and ferrosilicon alloys, and metakaolin from the calcination of kaolin clay.

The pozzolanic reaction occurs when pozzolans are mixed with lime (calcium hydroxide) and water. This reaction produces calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H), which are the main binding phases in Portland cement. The pozzolanic reaction is slower than the hydration of Portland cement, but it contributes to the long-term strength and durability of concrete.

Pozolans are widely used in the construction industry due to their ability to improve the properties of concrete, such as workability, strength, and durability. They are also used in the production of other hydraulic cements, such as blast furnace slag cement and limestone-filled cement. The use of pozzolans in cement and concrete production has significant environmental benefits, as it reduces the carbon footprint of the construction industry by lowering the amount of Portland cement required.