29Si and 27Al MAS‐NMR of NaOH‐Activated Blast‐Furnace Slag

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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 [Q1], 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 Q1, –81.4 [Q2(1Al)J, and ‐84.3 [Q2]. 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. Copyright © 1994, Wiley Blackwell. All rights reserved

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Journal of the American Ceramic Society

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