Therefore, these results were in agreement with the previous analysis of the 29 Si NMR spectra. Indeed, they also showed the formation of a C-A-S-H gel when NaOH was used, while an amorphous cross-linked N-A-S-H gel first formed in Na2Si1.7O4.4-and Na2CO3-activated pastes. Moreover, the changes in intensity and position of the N-A-S-H resonance suggest again that this gel was progressively turning into a more ordered C-A-S-H gel. However, the lower resolution of these spectra and the number of contributions used led to more uncertainty on the parameters used for the fits and thus on the MCL and Al/Si calculated (see Characterization of the hydrates by 27 Al NMR 27 Al MAS NMR experiments were also conducted in order to study the aluminum incorporated in the C-A-S-H gels and other aluminates which could be formed during the hydration reaction (Figures . The spectra were normalized with respect to the total surface area under the curve between 150 and -90 ppm. Here also, the spectra of the most hydrated samples were fitted first as they are the most resolved.