What is gypsum, and what role does it play in cement production?
Gypsum is a mineral (specifically, CaSO4…2H2O – hydrated calcium sulfate). Many Lehigh plants use gypsum that is quarried from a major reserve in Nova Scotia. Some plants are able to recycle industrial by-products with a similar chemical composition as natural gypsum. During the cement making process, after the clinker has been cooled, a small amount of gypsum–up to 5%–is added during the final grinding process. The clinker and gypsum are then interground, producing the super-fine powder called portland cement. Gypsum is a critical ingredient that helps to control the setting time of the cement when it is mixed into concrete. Without gypsum, the cement would begin to set immediately.