The second tetrahedral resonance, at 75.7 ppm, has been assigned to different types of environments in the literature. It has hence been assigned to Q2 b bridging sites charge-balanced by Al in a pentahedral or octahedral environment . However, since no correlation could often be found between the quantities of Al in this tetrahedral environment and the pentahedral and octahedral Al, other hypotheses have been explored. Even though the substitution of bridging site is supposed to be favored compared to the incorporation of Al in pairing sites, it has been suggested that this contribution would indeed correspond to Al in pairing sites, which is said to be more plausible in C-A-S-H with small silicate chains . However, the relative intensities of these two contributions (see the Supporting Materials) suggest that there were more Al in the pairing than in the bridging position, which is contrary to the thermodynamic data . Some authors observed two C-A-S-H in SEM images of NaOHactivated slag and thus suggested that the two tetrahedral environments correspond to the substitution of Si bridging sites in each C-A-S-H. The peak at 75.7 ppm, with the smaller quadrupolar constants, corresponds to the more ordered phase.