Formation of magnesium silicate hydrates (M-S-H)

Ellina Bernard , Barbara Lothenbach (1) , Daniel Rentsch (2) , Isabelle Pochard (3, 4) , Alexandre Dauzeres (5, 6)

1 Laboratory for Concrete & Construction Chemistry
2 Swiss Federal Laboratories for Materials Testing and Research
3 ICB - Laboratoire Interdisciplinaire Carnot de Bourgogne
4 UTINAM - Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
5 IRSN/PRP-DGE/SRTG/LETIS - Laboratoire d'Etude et de recherche sur les Transferts et les Installations dans les Sols
6 IRSN/PSE-ENV/SEDRE/LETIS - Laboratoire d'étude et de recherche sur les transferts et les interactions dans les sous-sols

The formation of magnesium silicate hydrates (M-S-H) with MgO to SiO2 ratios from 0.7 to 1.6 has been studied at 20, 50 and 70 C. TGA and XRD data reveal that initially brucite and M-S-H are formed while amorphous silica is still present as indicated by FT-IR and 29Si MAS NMR experiments. In this first step M-S-H with Mg/Si ~1 with pH values ~9.4 is formed independently of the total Mg/Si. Investigations by FT-IR and 29Si MAS NMR detail that the structure of that initial M-S-H evolved with time and M-S-H formed with Mg/Si ranging from ~0.8 to ~1.3 after 2 years at 20 °C and after 1 year at 50 and 70°C. This implies that the composition of synthetic M-S-H depends strongly on temperature and equilibration time. At 50 and 70°C the M-S-H formation occurs faster although it is thermodynamically slightly less stable. The solubility of M-S-H, talc and antigorite after 1 year or longer shows comparable trends.

Domaines: Chimie

Ellina Bernard, Barbara Lothenbach, Daniel Rentsch, Isabelle Pochard, Alexandre Dauzeres. Formation of magnesium silicate hydrates (M-S-H). Physics and Chemistry of the Earth. Parts A/B/C, 2017, 99, pp.142-157. ⟨10.1016/j.pce.2017.02.005⟩. ⟨hal-02066520⟩