Progressively, the N-A-S-H gel turned into an amorphous C-A-S-H gel as evidenced from the progressive decrease of the Q3 resonances in the NMR spectra. As slag dissolved, more calcium was available explaining this progressive transformation of N-A-S-H into C-A-S-H gel. The contributions in the NMR spectra (Figure , 14, and 17) and the diffractograms (Figure ) remained broad. At the same time, a hydrated aluminate phase precipitated, but its low crystallinity or quantity could not allow us to characterize it properly. The formation of these two phases, C-A-S-H and the hydrated aluminate, was accompanied by a second heat flow peak (Figure ) and a strong increase of the mechanical strength and of the quantity of bound water (Figure ). Moreover, it appears that even if the same amount of bound water was measured in Na2Si1.7O4.4-and NaOH-activated pastes, probably mostly incorporated in the C-A-S-H gel, a higher mechanical strength was gained with Na2Si1.7O4.4. This could be due to the more amorphous structure and cross-linking of the C-A-S-H formed in this system, or, more likely, to denser structures and different pore size distribution as proposed in the literature .