Clinker

Portland Cement Clinker is the essential ingredient of Portland Cement. Portland Cement is obtained by grinding Clinker with only minor amounts of a few other minerals, so its composition does not depart far from that of Clinker. Other Cements (i.e. non-Portland Cements, for example pozzolanic Cements, blast furnace slag Cements, limestone Cements and masonry Cements) contain larger amounts of other minerals and have a much wider composition range. Although the other potential ingredients may be cheap natural materials, Clinker is made in an energy-intensive chemical process. Between one and two billion tons a year of Clinker are made world-wide, and the details of its formation are therefore of great economic significance, since no viable alternative ingredients for making Cement-like materials currently exist.
Unlike many other thermal products (e.g. aluminium, pig-iron), Clinker is a fairly complex mixture of different minerals, and so its production depends on a multi-dimensional control of raw materials and a multi-staged heat treatment. It has been likened to a "man-made igneous rock", and an understanding of its structure and chemistry requires the application of many principles of geochemistry.

Portland Cement Clinker consists essentially of four minerals:

• Alite: approximately tricalcium silicate (typically about 65% of the total)
• Belite: approximately dicalcium silicate (typically about 15% of the total)
• Tricalcium Aluminate: Typically about 7% of the total
• Tetracalcium Aluminoferrite: Typically about 8% of the total

There are also many other non-essential minerals that occur in small quantities. The balance is made up of alkali sulfates and minor impurities. The typical mineral contents shown are subject to wide variation. Clinker consists of various calcium silicates including alite and belite. Tricalcium aluminate andcalcium aluminoferrite are other common components. These components are often generated in situ by heating various clays and limestone. Read more . . .