The “mica crisis” in Donegal: A case of internal sulfate attack?
During a current project, the concrete blocks of four affected homes are investigated by microstructural and chemical analysis combined with thermodynamic modelling.
High sulfur content
Apart from mica, the aggregates contain iron sulphides mainly in the form of pyrrhotite. The sulfur content of the aggregates considerably exceeds the limit value defined by the European standard for concrete aggregates (EN 12620). The results of the microstructural analysis coupled with thermodynamic modelling demonstrate that the concrete suffers from internal sulfate attack triggered by pyrrhotite oxidation. The comparison of the results of this investigation with the data collected by chartered engineers on almost hundred damaged homes shows that the four investigated cases are representative of the situation in Donegal.
The work has been published in Cement and Concrete Research, Volume 168, June 2023.