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The Effect of Alkali Ions on the Incorporation of Aluminum in the Calcium Silicate Hydrate ( C – S – H ) Phase Resulting from Portland Cement Hydration Studied by 29 Si MAS NMR
Author(s) -
Skibsted Jørgen,
Andersen Morten D.
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12024
Subject(s) - alkali metal , calcium silicate hydrate , silicate , hydrate , ion , anhydrous , chemistry , phase (matter) , tobermorite , mineralogy , inorganic chemistry , crystallography , analytical chemistry (journal) , materials science , cement , organic chemistry , metallurgy
The incorporation of aluminum in the calcium–silicate–hydrate ( C – S – H ) phases formed by hydration of three different white Portland cements has been investigated by 29 Si MAS NMR . The principal difference between the three cements is their bulk Al 2 O 3 contents and quantities of alkali ( Na + and K + ) ions. 29 Si MAS NMR allows indirect detection of tetrahedral Al incorporated in the silicate chains of the C – S – H structure by the resonance from Q 2 (1 Al ) sites. Analysis of the relative 29 Si NMR intensities for this site, following the hydration for the three cements from 0.5 d to 30 weeks, clearly reveals that the alkali ions promote the incorporation of Al in the bridging sites of the dreierketten structure of SiO 4 tetrahedra in the C – S – H phase. The increased incorporation of Al in the C – S – H phase with increasing alkali content in the anhydrous cement is in accord with a proposed substitution mechanism where the charge deficit, obtained by the replacement of Si 4+ by Al 3+ ions in the bridging sites, is balanced by adsorption/binding of alkali ions in the interlayer region most likely in the near vicinity of the AlO 4 tetrahedra. This result is further supported by similar 29 Si MAS NMR experiments performed for the white Portland cements hydrated in 0.30 M Na OH and NaAlO 2 solutions.