Structural features of C-S-H(I) and its carbonation in air - A Raman spectroscopic study. Part II: Carbonated phases

BLACK, L., BREEN, C., YARWOOD, J., GARBEV, K., STEMMERMANN, P. and GASHAROVA, B. (2007). Structural features of C-S-H(I) and its carbonation in air - A Raman spectroscopic study. Part II: Carbonated phases. Journal of the American Ceramics Society, 90 (3), 908-917.

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The effects of carbonation of mechanochemically prepared C-S-H samples under ambient conditions for upto 6 months have been investigated by Raman spectroscopy and X-ray diffraction. The type and extent of carbonation are strongly dependent on the initial CaO/SiO2 (C/S) ratio of the samples. Amorphous calcium carbonate hydrate is formed within minutes upon exposure to air. It crystallizes, over time, to give primarily vaterite at C/S >= 0.67 and aragonite at C/S <= 0.50. Calcite was not observed as a primary carbonation product within the time frame investigated. Decalcification upon storage also initiates silicate polymerization. The dimeric silicate units seen in the calcium-rich phases polymerize rapidly to yield Q(2) silicate moieties. After 6 months, broad bands are seen in most spectra, ascribed to poorly ordered silica. C-S-H phases with C/S ratios of 0.75 and 0.67 are the most resistant to carbonation, and even after 6 months of storage, Q(2) silicate units still dominate their structures. The ability of Raman spectroscopy to probe the short-range order of poorly crystalline materials is ideal for investigations of C-S-H structure. Additionally, the technique's sensitivity toward the various calcium carbonate polymorphs illuminates the sequence of carbonation and decalcification processes during aging of C-S-H. Of particular importance is the identification of amorphous calcium carbonate as the first carbonation product. Additionally, the formation of aragonite as a carbonation product is related to the presence of SiO2 gel in the aged samples.

Item Type: Article
Research Institute, Centre or Group - Does NOT include content added after October 2018: Materials and Engineering Research Institute > Advanced Coatings and Composites Research Centre > Polymers, Composites and Spectroscopy Group
Identification Number:
Page Range: 908-917
Depositing User: Jill Hazard
Date Deposited: 14 May 2010 10:41
Last Modified: 18 Mar 2021 21:15

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