[en] Full text: The expected increase in world-wide cement consumption in the years to come along with society's demands for new construction materials with low embodied CO₂ emission promote research in new cement blends where a significant part of Portland cement is replaced by supplementary cementitious materials (SCM's). The high abundance of clay minerals in the Earth's crust makes these materials potential candidates as new SCM's. Clays contain aluminium and silicon cations in layered structures and a pozzolanic material can be achieved by thermal treatment, which results in dehydroxylation of the aluminate and silicate species and the introduction of disordered structural sites. Solid-state NMR spectroscopy represents a strong tool for structural analysis on the nanoscale of a wide range of inorganic materials. The main advantages of the method are the nuclear-spin selectivity, where one spin-isotope (e.g. 1H, 11B, 19F, 23 Na, 27Al, 29Si ...) is detected at a time, and the fact that crystalline as well as amorphous phases are detected in an equal manner. The latter is very important in studies of cementitious materials as the principal hydration product, the calcium silicate hydrate (C-S-H) phase, and most SCM's (including calcined clays) are amorphous phases. Generally, rather simple NMR spectra can often been achieved for complex materials, for example reflecting minor constituent phases or guest-ion incorporations in the dominating phases. The lecture will present recent studies where solid-state NMR has been used to explore the thermal activation, structural changes, and pozzolanic activities of montmorillonite and kaolinite-based SCM's (see for example: Garg and Skibsted, J. Phys. Chem. C (2014) 118, 11464). This includes the impact of the SCM on the composition of the C-S-H phase and the degree of reaction for SCM's in hydrated Portland cement blends. The results are compared with the phase assemblages obtained by thermodynamic modelling for the hydrated systems. (author)