Pozzolan Cement

a general name for a group of cements containing not less than 20 percent active mineral additives. The term “pozzolan cement” is derived from the name of a friable volcanic rock—pozzolana—used in ancient Rome as an additive to lime in the production of hydraulic cement.

In modern construction, the major type of pozzolan cement is portland-pozzolan cement, produced by grinding together portland cement clinker (60–80 percent), an active mineral additive (20–40 percent), and a small amount of gypsum. It differs from ordinary portland cement in its higher resistance to corrosion (especially in soft or sulfate waters), reduced rate of hardening, and lower frost resistance. Pozzolan cement is used mainly to produce concretes used in underwater and underground structures.