Thermodynamics of Portland Cement Clinkering

The useful properties of cement arise from the assemblage of solid phases present within the cement clinker. The phase proportions produced from a given feedstock are often predicted using well-established stoichiometric relations, such as the Bogue equations. These approaches are based on a single estimation of the stable phases produced under standard processing conditions and so they are limited in their general application. This work presents a thermodynamic database and simple equilibrium model which is capable of predicting cement phase stability across the full range of kiln temperatures, including the effect of atmospheric conditions. This is termed a “reaction path” and benchmarks the kinetics of processes occurring in the kiln. Phase stability is calculated using stoichiometric phase data and Gibbs free energy minimization under the constraints of an elemental balance. Predictions of stable phases and standard phase diagrams are reproduced for the manufacture of ordinary Portland cement and validated against results in the literature. The stability of low-temperature phases, which may be important in kiln operation, is explored. Finally, an outlook on future applications of the database in optimizing cement plant operation and development of new cement formulations is provided.