Crystal clusters in clinker

Published 13 December 2017

With increasing use of alternative fuels, short homogenisation times in precalciner kiln systems and the requirement for high alite cement, the presence of crystal clusters is not expected to be a thing of the past. While the impact of crystal clusters in clinker on quality is not always clear, some effects can be seen. 

Figure 1: brown and lighter blue belite crystals surrounding liquid phase

Cement clinker for general-purpose Portland cement is composed essentially of four compounds known as alite, belite, aluminate and ferrite. When mixed with water, alite and belite provide the calcium silicate hydrates necessary to produce strength for a cement and the other phases play their part either in the process of making alite crystals or in controlling the hydration characteristics of cement. 

It is commonly asserted that in an ideal clinker the crystals would all be uniformly dispersed through the clinker but in practice this is rarely if ever the case. The influence of crystal clusters of any of the clinker compounds on quality are not always clear although some effects can be demonstrated.

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