The chemistry of Portland cement clinker

Technological developments in over a century of production of Portland cement clinker have greatly improved the homogeneity of the feed and clinker leading to much more favourable conditions for alite formation which remains the key chemical reaction in the process. This development is described along with the thermodynamic processes which either enhance the formation of alite by lowering its free energy, or inhibit the formation of alite by lowering the free energy of belite. These processes are always present to some extent depending on the concentrations of minor components in the raw materials and fuels, but can be specifically targeted by the controlled addition of effective mineralisers such as fluoride. This allows further increases in clinker output and reduction in fuel consumption, but perhaps more importantly allows higher contents of supplementary cementitious materials in composite cements for the same cement performance. The same approach can be used to produce new low temperature clinker types such as those based on the so-called Klein's phase.