Pozzolans

Part of speech: noun

Definitions

1. A category of materials, either natural or synthetic, that combine with lime or cement to improve concrete's strength and longevity
2. These substances, used in construction, react with lime to enhance the durability and mechanical properties of cement-based mixes
3. Materials that, when mixed with lime, undergo a chemical reaction to form compounds that strengthen and protect cement structures

Etymology: Pozzolans take their name from Pozzuoli, a town on the Bay of Naples. The volcanic ash found in the surrounding hills was prized by Roman builders, who mixed it with lime to make mortars that hardened even under seawater. Italian speakers came to call the material "pozzolana," after the town, and that Italian name is the source of the English word. "Pozzolans" is simply the plural of "pozzolan," so it refers to several such materials. Modern versions include fly ash from coal power plants and silica fume, which are added to cement mixes for the same reason the Romans used volcanic ash: they react with lime to produce a denser, tougher binder.