29Si and 27Al MAS-NMR of NaOH-Activated Blast-Furnace Slag |
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Authors: | Paul J. Schilling Leslie G. Butler Amitava Roy Harvill C. Eaton |
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Affiliation: | Department of Mechanical Engineering, Department of Chemistry, and Department of Civil Engineering, Louisiana State University, Baton Rouge, Louisiana 70803 |
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Abstract: | b29Si and 27Al 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 29Si 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 29Si peaks with widths of ca. 2 ppm are formed at -78.5 Q 1, –81.4 [ Q 2(1Al)J, 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, 27Al MAS-NMR reveals the presence of aluminum in octahedral sites, which is attributed to the aluminate phase (C,M)4AH13. 29Si 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. |
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