In the last two spectra of the NaOH-activated paste, at 108 J/g and 184 J/g, a second octahedral resonance was visible at 5.4 ppm. Some authors consider that this Al is part of another amorphous aluminate phase, called the third aluminate hydrate (TAH) , made of Al(OH)6 3-or OxAl(OH)6-x (3+x)-units, and which precipitates either as a separate phase or on the surface of C-S-H. However, in some more recent work , using DNP-enhanced 27 Al CP MAS NMR and 2D 27 Al- 29 Si DNP-enhanced correlation spectra, the authors assigned this resonance to [AlO2(OH)4] 5-units linked to silicates and therefore proposed that this peak corresponds to the octahedral Al substituting the bridging Si in C-A-S-H. This hypothesis might explain why the relative intensities of the tetrahedral pairing Al were higher than those of the tetrahedral bridging Al and could suggest that the assignment of the 75.7-and 68.3 ppm resonances to Al in pairing and bridging positions is not as far-fetched as initially assumed.