Ordinary Portland Clinker
Portland cement clinker is ground to a fine powder and used as the binder in many cement products. A little gypsum is sometimes added. It may also be combined with other active ingredients or chemical admixtures to produce other types of cement including: ground granulated blast furnace slag cement.
Clinker is the first stage in making cement. Clinker is ground (usually with the addition of a little calcium sulfate) to become Portland cement