Alteration of nanocrystalline calcium silicate hydrate (C-S-H) at pH 9.2 and room temperature: a combined mineralogical and chemical study

Abstract : Calcium silicate hydrate (C-S-H) alteration was studied with flow-through experiments at 25°C and pH 9.2. Three materials with apparent Ca/Si ratios (C/S ratios) of 1.47, 1.38 and 0.86 were investigated. Physical (thermogravimetric analyses/differential thermal analysis), mineralogical (X-ray diffraction) and chemical (electron probe microanalysis, transmission electron microscopy/energy dispersive X-ray spectrometry) analyses were performed to characterize the reacting minerals. Initial stoichiometric C/S ratios were 1.22, 1.22 and 0.85, respectively. The excess of Ca is attributed mainly to the presence of calcium hydroxide intimately mixed in with C-S-H particles. The C-S-H chemical compositions were monitored during flow-through experiments in order to determine the mineral stoichiometry needed for reaction kinetics. Under our experimental conditions the stoichiometric C/S ratios decreased continuously with time. A close to stoichiometric dissolution was observed after 2 days of experiments. Using an integrated approach, the kinetics was found to be a function of the C/S. A decrease in layer-to-layer distance in the early stage of the alteration process is interpreted as interlayer Ca/Na exchange (Na being part of the pH buffering solution). A second dissolution step, marked by a close to stoichiometric release of Ca and Si, undoubtedly results from layer dissolution. The structural similarity of C-S-H and tobermorite was confirmed.
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Mineralogical Magazine, Mineralogical Society, 2015, 79 (2), pp.437-458. 〈10.1180/minmag.2015.079.2.20〉
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Soumis le : mardi 23 août 2016 - 13:05:51
Dernière modification le : jeudi 11 janvier 2018 - 06:27:31

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Nicolas C. M. Marty, Sylvain Grangeon, Fabienne Warmont, Catherine Lerouge. Alteration of nanocrystalline calcium silicate hydrate (C-S-H) at pH 9.2 and room temperature: a combined mineralogical and chemical study. Mineralogical Magazine, Mineralogical Society, 2015, 79 (2), pp.437-458. 〈10.1180/minmag.2015.079.2.20〉. 〈hal-01355446〉

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