The "mica crisis" in Donegal, Ireland – a case of internal sulfate attack?

Andreas Leemann, Barbara Lothenbach, Beat Münch, Thomas Campbell, Paul Dunlop

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In County Donegal, northwest Ireland, thousands of homes built with concrete blocks show an increasing degree of severe structural defects attributed to high mica content in the aggregates. Consequently, the problem is popularly known as the “Mica Crisis”. In this project the concrete blocks of four affected homes are investigated by microstructural and chemical analysis combined with thermodynamic modelling. 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.
Original languageEnglish
Article number107149
Pages (from-to)1-14
Number of pages14
JournalCement and Concrete Research
Issue numberJune 2023
Early online date15 Mar 2023
Publication statusPublished online - 15 Mar 2023
EventThe Science and Societal Impacts of Defective Concrete - Atlantic Technical University, Donegal & Ulster University, Magee Campus, Letterkenny & Derry, Ireland
Duration: 15 Nov 202217 Nov 2022


  • concrete
  • pyrrhotite
  • internal sulfate attack
  • microstructure
  • cracking


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