29Si and "A1 MAS-NMR were performed on NaOHactivated 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 [el], with aluminum present exclusively in tetrahedral coordination. Upon reaction with 5M NaOH ( w / s = 0.4), three new *'Si peaks with widths of ca. 2 ppm are formed at -78.5 [el], -81.4 [Q'(lAl)], and -84.3 [Q']. 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, 27AI MAS-NMR reveals the presence of aluminum in octahedral sites, which is attributed to the aluminate phase (C,M),AH,,. *'Si 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.
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Approval does not signify that the contents necessarily reflect the views or policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
The effects of pH, time, valence, and radius of the activator cation on the reaction products and microstructure of ground granulated iron blast-furnace slag were studied by thermogravimetry and derivative thermogravimetry, X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray microanalysis. Blast-furnace slag was activated by alkali-metal hydroxides of Li, Na, and K (12.34 5 pH 5 14.71) and alkaline-earth hydroxides of Ca, Sr, and Ba (12.47 5 pH 5 13.53) using a water/slag ratio of 0.4 and curing for 1 day to 26 months. Reactivity of the slag was more strongly dependent on pH than on time.
The reaction products were mainly varieties of C-S-H, (C,M),AH,,, and minor amounts of Ca(OH), and C,ASH, (stratlingite). The nature of C-S-H was dependent on pH. A 1.2-nm peak appeared in X-ray diffractograms only when the activation pH was ~1 4 . 7 . Water was present in the C-S-H in a way similar to water in tobermorite and synthetic C-S-H.Leached Ca from unreacted blast-furnace slag was present around the glass particles as an amorphous layer which crystallized into Ca(OH), with time; Mg behaved similarly. The effect of the charge or ionic radius of the activator cation was insignificant.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.