Pyrite or Iron Pyrite is a very common mineral that is present in many sedimentary rocks as framboidal crystals. Subject to certain conditions, pyrite is problematic in confined construction, such as under floor filling and bridge embankments. This is due to a chemical reaction that can cause pyritic backfill to swell.
Construction material containing relatively large amounts of pyrite minerals are likely to expand, crack and/or crumble over time. This occurs when framboidal crystalline pyrite, air and moisture, mix causing a chemical reaction to occur that creates expanding crystals within the material.
Areas affected by Pyrite
The confirmed areas that have been affected by pyrite-heave are mostly concentrated in North Leinster, particularly in North County Dublin, Offaly, Meath and Louth.
Why is Pyrite a problem?
The presence of pyrite in aggregate (floor hardcore) can lead to severe deterioration in construction materials as the pyrite oxidises. This results in cracks in floors and walls that will need to be rectified by removing the floor hardcore and replacing it with aggregate that conforms to the new building standards.
It should be noted that the presence of pyrite alone does not directly lead to pyritic heave. Other factors that must be present to lead to a potential problem include the type of pyritec crystals, the presence of oxygen, the availability of moisture and the nature of the rock type. The pyrite reaction may be further accelerated by heat and thiophilic bacteria.