Journal
CEMENT AND CONCRETE RESEARCH
Volume 97, Issue -, Pages 61-72Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.cemconres.2017.03.012
Keywords
Low-pH cement; C-S-H; M-S-H; Si-29 MAS NMR; Thermodynamic modelling
Funding
- Swiss National Science Foundation (SNFS) [150638]
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The addition of MgCl2 to synthetic calcium silicate hydrate (C-S-H) with Ca/Si = 0.8 lowers the pH values below 10. Experimental observations and thermodynamic calculations show the destabilization of C-S-H and the precipitation of magnesium silicate hydrate (M-S-H). In contrast, the addition of MgO to C-S-H increases the pH values up to 11.5 and the Ca/Si in C-S-H from 0.8 to similar to 1.0. At high pH, the formation of M-S-H and brucite is observed experimentally. Less brucite is present at 50 than at 20 degrees C indicating a slow dissolution kinetic of brucite at 20 degrees C. Thermodynamic modelling is in good agreement with the changes in C-S-H and M-S-H formation in the presence of MgO although no brucite is predicted. M-S-H is observed in the presence of both MgCl2 and MgO, is stable from pH 7.5 to 11.5 and has a structure comparable to the structure of M-S-H prepared from MgO and SiO2 only. (C) 2017 Elsevier Ltd. All rights reserved.
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