In situ laboratory X-ray powder diffraction (LXRPD) is widely used for studying cement hydration at
early ages. However, this approach has limitations due to the intrinsic characteristics of the main
methodologies (flat sample and capillary) and their blindness to the amorphous phases and
microstructures. In addition, laboratory X-ray microtomography (μ-CT) is being used for several
applications but the accuracy of the obtained results is not established. Here, we present an innovative
approach where LXRPD and μ-CT data are taken in the same volume of the same hydrating paste within
a thick capillary with time. The results from both techniques should agree, resulting in more reliable
information. The methodology developed here is based on capillaries of 2 mm of diameter to minimize
self-drying and to have very good powder averaging. In this proof-of-principle investigation, μ-CT data
have been collected for a PC-42.5R paste, w/c=0.50, at 12 hours and 1, 3 and 7 days, and for LXRPD at
1, 3 and 7 days. Powder diffraction data have been analysed by the Rietveld method and the results have
been verified by mass balance calculations. μ-CT data have been segmented. The results indicate that the
developed methodology is accurate. The long-term aim of this research is to be able to monitor the
reaction of the amorphous components of widely-used supplementary cementitious materials (SCMs) like
the amorphous silica in fly/volcanic ashes or the metakaolin in calcined clays.