Quantitative phase analysis of ordinary Portland cements using synchrotron radiation powder diffraction

High-resolution synchrotron X-ray powder diffraction data have been analysed using the Rietveld methodology to obtain the mineralogical composition of four commercial and NIST RM-8488 Portland clinkers. Alite phase coexistence has been observed in four patterns. White Portland clinkers show a single alite or a very small amount of a second alite phase with smaller unit cell volume likely due to a higher magnesium content. Grey Portland clinkers show a much more pronounced alite phase coexistence. This effect is not so pronounced or even negligible when low resolution data, i.e. laboratory X-ray powder diffraction data are used. Moreover, the full mineralogical composition (including the non-diffracting content) has been determined from the overestimation of the added standard, alpha-Al2O3, in the Rietveld analyses. White clinkers contain similar to 15 wt% of non-diffracting content while this fraction is much smaller in grey clinkers, similar to 7 wt%.