Quantitative phase analysis of Portland cements from reactive powder concretes by X-ray powder diffraction

As part of a Cooperative research programme between Bouygues, Lafarge and Rh6ne-Poulenc, X-ray powder diffraction has been used to study the effects of heat treatments on very high strength concretes (‘reactive powder concretes’). Three methods of X-ray quantitative analysis have been developed, and the paper reports on the advantages and limits of each. Method A (area measurement) is the fastest and does not require high-speed computers. However, it requires pure reference materials and does not work for belite whose peaks overlap with those of alite. Method B (a Rietveld analysis using structural models) allows good accuracy, although the quality of refinement is affected by the lack of alite crystal models. Method C (a Rietveld analysis using full pattern matching for alite and a structural model for other phases) gives high-quality refinements but is not adequate to determine the alite content, because of the poor accuracy of the Bogue composition. The three methods give nonconflicting data and they can be used to follow the various stages of hydration of cement phases, in particular alite and belite, and to investigate (i) xonotlite formation, and (ii) pozzolanic activity, which is associated with a portlandite decrease.