Magnesia in clinker
Magnesia is often present in clinker as periclase, which is formed of free MgO. However, periclase does not always provide a welcome part of the clinker’s composition and can lead to significant volume expansion of the concrete that is made with cement manufactured from such clinkers.
Figure 1: periclase inclusions in belite. The belite crystal with two inclusions is 12µm across
In cement clinker magnesia (MgO) can be present as a substituent in each of the primary clinker minerals alite, belite, aluminate and ferrite. However, the degree of substitution is not large and varies depending on the environment in which the clinker is produced and on the presence of other substituents within the clinker minerals. Periclase is the name given to crystals formed of free MgO. Therefore, it is not always simple to predict the amount of periclase present on the basis of chemical composition alone.
