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.

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The fineness of a portland cement is a key factor in determining its strength development characteristics. A simple one‐parameter fineness characterization such as a Blaine value or a sieve residue is often inadequate for a precise evaluation of the influence of fineness on the strength development of cement, especially when comparing cements ground with different grinding equipment. Information on the whole particle size distribution (PSD) of the cement must be used. A mathematical model relating PSD to strength, based on comparison of cements made from the same basic materials (clinker and gypsum) but ground to different PSD, is presented. The model assumes that at a given time of hydration all particles have reacted to the same depth from the original surface. Integrating over the total PSD will give the degree of hydration for a specific size distribution. From a correlation between strength and degree of hydration, differences in degree of hydration can be converted into relative strengths. The applicability of the model is demonstrated by two examples. The first example compares two cements which are ground to different finenesses in the same mill. The second example compares two cements which are ground to the same specific surface area in two different mill systems, bringing about cements with PSDs of different shape. The depth of reaction values found to give the best description seems to be proportional to the square root of time of reaction, indicating a diffusion‐controlled hydration reaction.