The mineralogy and petrology of cement clinker and its influence on the quality of Portland cement
The relationships between the mineralogical, chemical and petrological characteristics of cement clinker minerals and the quality of the resultant Portland cement, is of great interest to producers and users of cement and concrete. To examine these relationships, different types of cement clinkers from wet,semi-dry and dry process production kilns were analysed and then tested for quality using British Standard tests. The mineralogical and petrological properties of the calcium silicates, aluminates, ferrites and alkali sulphates were studied. From several thousand mineral analyses performed with an electron microprobe analysis unit, the substitution systems for the different minerals and polymorphs have been determined. The mineral analyses of the various cement clinkers have been plotted on ternary phase diagrams. The different mineral assemblages of the clinkers have been used to assess the effects of composition and production process on the cement clinkers. All the analyses of the characteristics of the minerals and the quality of the cement have been compared using a trend analysis, developed by the author. This analysis establishes which characteristics have a significant effect on the strength of the Portland cement. The role of potassium in the cement clinker and particularly its substitution into the belite phase, is crucial. The reasons for this influence and a relationship between the potassium substitution in the belite and the 28 day compressive strength of the cement is presented.