BREAKING: Council engineer calls for update of IS465 to include sulphide minerals

Administering the current Defective Concrete Blocks Scheme is proving “extremely difficult” members of Donegal County Council's Mica Redress Committee (MRC) have been told.

According to a presentation made this afternoon at the ongoing online meeting of the committee, the difficulties have arisen from the operational reality of trying to administer the scheme, from a technical and administrative perspective, in accordance with the requirements of IS465.

IS465 is the standard developed by the National Standards Authority of Ireland (NSAI) Concrete Block Committee for the assessment, testing and categorisation of damaged buildings incorporating concrete blocks containing certain deleterious materials.

However, under IS465, while a private homeowner can test for sulphide minerals, the current Defective Concrete Blocks Scheme does not cover all deleterious materials. There is a public perception, when the Mica Redress Scheme was designed, it was designed for remedial works only.

A Council engineer involved in the Defective Concrete Blocks Scheme has called for an update of IS465 to include sulphide minerals

The MRC presentation said: “Donegal County Council acknowledges the developing expertise that has and is evolving out of the implementation of the Defective Concrete Blocks Scheme, however it is difficult to process many current applications on hand having regard to the issues outlined.”

Outlining the challenges in administering the current scheme, Donegal County Council said: “Recent availability of substantial additional test data incorporating detailed petrographic examinations, SEM examinations for free mica content, cement content, sulphate content and compressive strength, obtained from samples in Donegal has further enhanced the expertise and knowledge in the area.

“In Donegal, the presence of deleterious materials pyrite and pyrrhotite is a highly reactive and unstable form of iron sulphide. It is susceptible to oxidisation resulting in expansion. Pyrrhotite alteration requires the presence of both moisture and oxygen.

“Chemical analysis for total sulphur varied from small percentages to 0.7%. ISEN 12620 (aggregates for concrete) and SR16 require total sulphur content to be less than 0.1%. The potential risk of concrete block deterioration posed by the presence of pyrite and pyrrhotite exists however there is uncertainty regarding whether or not the pyrrhotite will alter and research is required.

“If the inner leaf is exposed to moisture, the potential for pyrrhotite alteration exists.

“Combined effect of: mica, pyrite, pyrrhotite, wetting / drying and leaching of cement in mica rich blocks requires consideration in addition to freeze / thaw.

“Review of IS 465: 2018 plus A1:2020.

“Outcome of Geological Survey Ireland current research to improve understanding of the effects of excessive amounts of pyrite and / or muscovite mica in concrete blocks and reduce the level of unknown risks which may be present in structures affected by these deleterious materials.

“Effect of full cavity insulation on moisture movement.

“The potential degradation due to wetting / drying of mica-rich external and internal rising walls require further consideration and research.”

“The Council has sought guidance and further advice from the Department of Housing, Local Government and Heritage, to assist us with the implementation of the current scheme, and particularly to enable us to make the appropriate decisions in Stage 1 applications and 'change of circumstance' applications," concluded the Donegal County Council presentation.