Abstract Two main formation routes for thaumasite exist below 15 °C. One is the direct route from C–S–H reacting with appropriate carbonate, sulfate, Ca2+ ions and excess water. The other route is the woodfordite route from ettringite reacting with C–S–H, carbonate, Ca2+ ions and excess water, in which thaumasite arises through the intermediate formation of the solid solution woodfordite. The woodfordite route for thaumasite formation appears to be relatively quicker (although still slow) than the direct route, presumably because with the former the ettringite already has the octahedral [M(OH)6] units that can facilitate the critical change from [Al(OH)6]3− to [Si(OH)6]2− groupings. Both routes are mutually dependent on each other. The presence of magnesium salts can modify the path to thaumasite formation. High pressure might be able to stabilise [Si(OH)6]2− groupings and allow thaumasite to become formed above 15 °C. This possibility is discussed.
[1]
A. A. Colville,et al.
Efflorescent mineral assemblages associated with cracked and degraded residential concrete foundations in Southern California
,
1989
.
[2]
J. Bensted.
Thaumasite — background and nature in deterioration of cements, mortars and concretes
,
1999
.
[3]
R. Swamy,et al.
Thaumasite formation in Portland-limestone cement pastes
,
1999
.
[4]
H. Strunz.
Die Beziehungen der Isotypie zwischen Sillikaten und Germanaten. Versuch einer Germanat-Klassifikation
,
2004,
Naturwissenschaften.
[5]
S. J. Barnett,et al.
Solid solutions between ettringite, Ca6Al2(SO4)3(OH)12·26H2O, and thaumasite, Ca3SiSO4CO3(OH)6·12H2O
,
2000
.
[6]
John Bensted.
Scientific background to thaumasite formation in concrete
,
1998
.
[7]
G. Menzer.
Mineralogische Tabellen. 3.
,
1958
.