The 29 Si NMR spectra of the NaOH-activated samples (Figure ) presented three resonances in addition to the one for the anhydrous slag: a Q1 contribution centered at -78.6 ppm, a Q2 contribution at -84.1 ppm, and a contribution at -81.5 ppm which can be assigned to a Q2(1Al) environment . This last resonance could also contain some signals from Si in Q2 B (bridging) environments, as they usually give a chemical shift in that range . The small widths used for these three contributions show that the C-A-S-H formed was quite ordered. Moreover, this gel seems to be constituted of small silicate chains since the MCL calculated is of about 4.