These results allow us to assign the 9.8 ppm resonance of the 27 Al NMR spectra of the NaOH-activated slag (Figure ) to Al in hydrotalcite. This resonance was also present in the 27 Al NMR spectra of the most hydrated samples activated with Na2CO3 (Figure ) and Na2Si1.7O4.4 (Figure ), but none of the peaks of the diffractograms could be attributed to an aluminate phase. Nonetheless, hydrotalcite has been found previously in cements activated with sodium silicate, without it being noticeable on diffractograms, so it is most probably this phase that precipitated . A degree of hydration (DOH) was also defined using the results from the 29 Si and 27 Al NMR experiments (Table ). Equations ( ) and ( ), as proposed by Le Saoût et al. , were used to this end. Equation ( ) can be used for all the 27 Al NMR spectra and for the 29 Si NMR spectra.