Concrete can be severly damaged by sulfate attack due to the formation of ettringite, thaumasite and gipsum. In Switzerland, this is mainly a problem in tunnels, where an interaction between concrete and sulfate bearing groundwater can take place and sewage systems. The damage occurring depends on the chemical composition of the cement, its physical properties and the chemical composition of the attacking solution. These factors determine the kind and amount of secondary products formed and thereby the extent of damage to the structure.
We study the influence of different sulfate solutions on systems with various cements experimentally. The results are used for thermodynamic modelling permitting a better understanding of the reactions present. One of this results, it was shown that ettringite forms at an initial state of sulfate attack. Thaumasite is only formed at a latter stage when molar SO3/Al2O3 ratio exceeded 3. A prerequesite for thaumasite formation is the presence of carbonates that can be provided by fillers or the aggregates.
Thaumasite veins in concrete damaged by sulfate attack
As a way of validation we compare the results of the laboratory experiments with the phenomena on real structures. Furthermore, we look for possibilities to test the sulfate resistance of concrete.
Residual anhydrous cement and ettringite in thaumasite matrix
Schmidt, T./Lothenbach, B./Scrivener, K. L./Romer, M./Rentsch, D./Figi, R. Conditions for Thaumasite formation. 12th International Congress on the Chemistry of Cement, Montréal, Canada, July 8-13, 2007, 12 pp. /CP
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