SI-29 AND AL-27 MAS-NMR OF NAOH-ACTIVATED BLAST-FURNACE SLAG

Si-29 and Al-27 MAS.NMR were performed on NaOH-activated blast-furnace slag to better characterize the amorphous and poorly crystalline phases which occur in this system. The unreacted glass has a mainly dimeric silicate structure represented by a broad Si-29 peak (FWHM = 15 ppm) centered at - 74.5 ppm [Q(1)], with aluminum present exclusively in tetrahedral coordination. Upon reaction with 5M NaOH (w/s = 0.4), three new Si-29 peaks with widths of ca. 2 ppm are formed at -78.5 [Q(1)], -81.4 [Q(2)(1Al)], and -84.3 [Q(2)]. Relative peak areas indicate a mostly dimeric silicate structure for the tobermorite-like C-S-H layers, with roughly a third of the bridging sites occupied by aluminum, and less than 10% by silicon. In addition to the tetrahedrally coordinated aluminum substituted in the C-S-H structure, Al-27 MAS-NMR reveals the presence of aluminum in octahedral sites, which is attributed to the aluminate phase (C,M)(4)AH(13). Si-29 results indicate rapid initial consumption of the glass, with roughly a third of the glass reacting within the first day and another third consumed over the following 27 days.