When NaOH was used as the activator (Figure ), the first resonance, not corresponding to the anhydrous slag, appeared at 0.5 J/g with a chemical shift of 63.7 ppm, corresponding to Al in tetrahedral environments. It has previously been assigned to Al substituting Si in Q3 environments in N-A-S-H gel . This chemical shift is similar to the small resonance at 63.0 ppm which was present in the anhydrous slag (Figure ). This phase could not be resolved in the 29 Si and { 1 H} 29 Si MAS NMR spectra at 0.5 J/g (Figure and 13), suggesting that its structure was very amorphous and that it was only present in very small quantities. Therefore, it is difficult to know exactly how much was already present in the On the right, the curves used to fit the spectra are shown in gray. The samples were prepared at a w/s ratio of 0.4 and with 4 wt% of Na2O, at 20 °C.