Research insights into the cause of Ireland's defective concrete crisis

Description

Abstract

In County Donegal, northwest Ireland, thousands of homes built with defective concrete blocks show an increasing degree of severe structural defects that was first attributed to a high mica content in the aggregates by a government report published in 2017. This hypothesized that excessive levels of mica left the concrete susceptible to freeze-thaw degradation and consequently, the problem is popularly known as the "Mica Crisis". Based on this, the National Standards Authority of Ireland was tasked to develop a new testing protocol called I.S. 465, that in addition to testing for excessive mica levels in Donegal homes, also offers remediation options to families. In 2020 the Irish Government launched a grant scheme to assist homeowners to remediate their homes that is estimated will cost the state between €2.5 to €3 billion. Research lead by Ulster University and Empa, Switzerland in 2022 investigated defective concrete homes in Donegal by microstructural and chemical analysis combined with thermodynamic modelling and identified that mica was not the cause of failure. Apart from mica, the aggregates also contain high levels of iron sulphides, mainly in the form of pyrrhotite, and that the sulfur content of the aggregates considerably exceeds the limit value defined by the European standard for concrete aggregates EN 12620. The results demonstrated that the concrete suffers from internal sulfate attack triggered by pyrrhotite oxidation and that this was the primary failure mechanism of defective concrete in Donegal and not freeze-thaw. This research had implications for I.S.465 and the entire grant scheme and the government asked NSAI to undertake a review of I.S.465, that is due to be completed in March 2025. This presentation provides an overview of the research done by an international consortium led by Ulster University who were funded by the Geological Survey of Ireland and the Department of Housing, Local Government and Heritage to investigate the issue further and to share results directly with the NSAI to inform this review. This has concluded once again that the primary failure mechanism of defective concrete in Donegal is internal sulfate attack.

Period	28 Feb 2025 → 2 Mar 2025
Event title	68th Irish Geological Research Meeting
Event type	Conference
Location	Dublin, IrelandShow on map
Degree of Recognition	National