Portland cement clinker (abbreviated k in the European norms) is ground to a fine powder and used as the binder in many cement products. A small amount of gypsum (less than 5 wt.%) must be added to avoid the flash setting of the tricalcium aluminate (Ca3Al2O6), the most reactive mineral phase (exothermic hydration reaction) in Portland clinker. It may also be combined with other active ingredients or cement additions to produce other types of cement including, following the European EN 197-1 standard:European cement standard EN 197-1 Cement – Part 1: "Composition, specifications and conformity criteria for common cements" which defines 27 distinct common cement products and their constituents.
