The Science
In Donegal a government desktop report published in 2017 identified that high levels of muscovite mica (a non-swelling silicate mineral present in defective concrete blocks) was the cause of cracking and block degradation.
The hypothesis presented was that mica was absorbing water and this could then freeze and thaw again during cold and warm temperatures causing the blocks to crack.
In 2020 homeowners in Donegal began to engage with the government’s defective concrete block scheme, which required geological laboratory tests to be conducted to confirm the homes were made of defective blocks.
The tests followed a protocol developed by the National Standards Authority of Ireland (NSAI) called I.S. 465 which in Donegal required the tests to identify and quantify the presence of muscovite mica and for engineers to assess the risk this had for the property.
As lab reports started to come back to homeowners in 2020, the majority were confirming they had high levels of mica but also other iron sulphide minerals that are widely accepted and understood to be destructive for concrete.
The main one is pyrrhotite, although, pyrite, marcasite and chalcopyrite have also been reported in defective Donegal blocks.
Research into this has identified that pyrrhotite, a highly reactive iron sulfide mineral, is causing internal sulfate attack and is the primary cause of the failure seen in Donegal homes, clearly the science is emerging since the government report in 2017 and in June 2023 the Geological Survey of Ireland funded a€500k research project lead by Ulster University, with partners in Empa Switzerland, Laval University, Canada, University of Connecticut and Concrete Research and Testing LLC, Ohio, USA that is investigating the role of pyrrhotite in the defective blocks issue in Donegal.
This research project will be used to inform the review of the NSAI I.S. 465 which is currently underway. As new science emerges we will post this here, below you can find links to published research, conference talks and other resources on the pyrrhotite and other defective block issues.
How do iron sulphides like pyrrhotite cause damage to concrete?
Pyrrhotite is a mineral known as an iron sulphide. When iron sulphides are exposed to water and oxygen, a series of chemical reactions breaks down the iron sulphides and forms new minerals called sulphates.
These sulphates take up more space than the original iron sulphides. As they grow, the new sulphate minerals push against the surrounding rock, causing it to swell and crack.
According to regulations how much pyrrhotite is allowed in concrete aggregate?
European standard for concrete aggregates (EN 12620) have placed a limit of 1% total sulphur by mass, which is reduced to 0.1% total sulphur if pyrrhotite is identified in the aggregate.
Many defective block houses tested in the Donegal area are showing approx 2-3% pyrrhotite and other deleterious materials.
Research into this has identified that pyrrhotite, a highly reactive iron sulfide mineral, is causing internal sulfate attack and is the primary cause of the failure seen in Donegal homes.
Publications
The “mica crisis” in Donegal, Ireland – a case of internal sulfate attack?
Leemann, A., Lothenbach, B., Münch, B., Campbell, T. & Dunlop, P. (2023),
Cement and Concrete Research Vol 168.
An Examination of Governance Failure by the Irish State: The critical case of the ‘Mica’/Defective Blocks issue.
Doherty, E., Carcary, M., Ramsey, E., Kelly, D., & Dunlop, P. (2022).
In F. Matos, & A. Rosa (Eds.), Proceedings of the 18th European Conference on Management Leadership and Governance, ECMLG 2022 (pp. 154-163). (Proceedings of the European Conference on Management, Leadership and Governance; Vol. 2022-November).
https://pure.ulster.ac.uk/ws/portalfiles/portal/122227240/Doherty_ELG_106_1_.pdf
Pyrrhotite in concrete aggregate. Introduction to mechanism, damage potential and ongoing research
Lindstad, Hallvard; Lindgård, Jan; Pedersen, Bård Magne; Wigum, Børge Johannes; Aasly, Kurt; Ullnæss, Inger Lise; Oberhardt, Nikolas; De Weerdt, Klaartje (2022)
Concrete Damage Due to Oxidation of Pyrrhotite-Bearing Aggregate: A Review.
Duchesne, J.; Rodrigues, A.; Fournier, B. (2021)
RILEM Tech Lett 2021, 6, 82-92.
2017 Government Report
Report of the Expert Panel on Concrete Blocks, Department of Housing, Local Government and Heritage Published on 13 June 2017.
Last updated on 4 December 2020: https://www.gov.ie/en/publication/0218f-report-of-the-expert-panel-on-concrete-blocks/
Seminars, Conference presentations and lectures on the causes of defective concrete
EU webinar ‘The impact on family homes of defective concrete products’ European Parliament, Brussels, March 23rd 2023:
ADEPT Research Group Conference ‘Losing Your Home The Impact of Defective Concrete Blocks in Ireland’ Dr Martina Cleary, Limerick School of Art & Design, 30th May 2023
International Conference ‘The Science and Societal Impacts of Defective Concrete’ Clanree Hotel, Letterkenny, Donegal, 15th November 2022,
Link to conference schedule: https://pure.ulster.ac.uk/ws/portalfiles/portal/107746246/International_conference_schedule.pdf
Link to all talks: https://www.youtube.com/watch?v=lXyP-xbe-20
John T Garret, Chartered Engineer, John Paul Farren of Anytime Coring LTD and Dr Chris Brough of Petrolab “Deleterious Material in Concrete Masonry Units – Sharing the Knowledge”. Presentations by. Engineers Ireland seminar 11th April 2023
Dr Kay Willie, University of Connecticut ‘Crumbling Concrete Foundations Due to Pyrrhotite Bearing Aggregates in CT’ American Concrete Institute, Spring Convention, Orlando, USA, 27-31st March, 2022
Useful websites
University of Connecticut Crumbling Foundation Research Team have produced two videos that provide an introduction to the pyrrhotite problem and includes simple descriptions of the basic chemical processes, and a description of the method they developed for the measurement of the pyrrhotite concentration and what results are provided https://crumblingconcrete.engr.uconn.edu/ourmethod/
Connecticut Department of Energy & Environmental Protection – Pyrrhotite and Crumbling Concrete in Connecticut:
FEMA, Connecticut’s Crumbling Concrete: https://www.fema.gov/case-study/connecticuts-crumbling-concrete