Micas are a group of sheet silicate minerals e.g. Muscovite and Biotite. Mica is the term used to describe muscovite mica, a silicate mineral that is glass-like and brittle. It exists within Ireland’s North West rock formations.

Studies have shown Mica to be a problem mineral in concrete as it can affect the compressive strength and durability.  

-Mica related: Free mica in blocks could lead to rapid absorption of moisture into the block leading to increased susceptibility to freeze thaw action.  

-Mica related: The absorption of moisture could lead to the leaching of cement.

-Mica related: The presence of free mica in the cement paste could lead to a reduction in compressive strength.

-Mica related: Dissolved CO 2 in water absorbed by the mica could lead to carbonation of the cement.  

*Not exhaustive

Pyrite is an Iron Sulfide.  

Iron Sulfides:  

-Pyrite FeS 2 is a mineral comprised of the elements iron and sulfur.  When pyrite is exposed to moisture and oxygen, chemical reactions can occur and the pyrite will oxidise to form sulfuric acid. The acid may react with other minerals found in the rock.

-Pyrrhotite Fe (1-x) S is another form of iron sulfide which is said to be much more reactive than Pyrite. 

-Marcasite is yet another form of iron sulfide which is said to be more reactive than pyrrhotite.

-Pyrite related (Acid attack): Sulphuric acid generated by pyrite decomposition with carbonated cement paste could lead to Gypsum formation. 

-Pyrite related (Aggregate expansion): With pyrite present in the aggregate, you could have aggregate expansion due to expansive gypsum formation due to a chemical reaction that happens when the block is exposed to moisture and oxygen.  

-Pyrite related: Sulphate attack could be generated by pyrite decomposition and the cement paste in the block. 

  *Not exhaustive

To find out more about sulphide minerals in concrete, please watch the videos from the EU webinar.

It is possible to have mica and iron sulphides in concrete blocks at the same time. Pyrrhotite-related failures could be exacerbated by having more moisture present and the more free mica you have the greater your susceptibility to moisture absorption.

This is the key question as it is through finding out exactly where the failures occurred (that allowed a defective product on the market place) that we can stop this scandal from happening to families again in the future. Outside of the government setting up a public enquiry, it is hoped that courts will help to provide these answers and some measure of restorative justice for affected families.

Clearly, a government-funded research programme is required to develop a fuller understanding of how the defective blocks are failing and the implications of their failure to understand if remedial works are even an option at this stage.