Since 2019, geologists at Petrolab have tested concrete block samples from over 1800 properties in County Donegal and observed deterioration patterns based on the aggregate types used within those concrete blocks. Across these properties more than 25 aggregate types have been used within concrete block, with seven distinct types considered high risk when assessed against relevant standards.
With respect to those considered high risk, elevated free mica and elevated reactive sulphides (predominantly pyrrhotite) contents appear to play a critical role, particularly in phyllite aggregates commonly found in defective blockwork. The particular concentration of both of these mineral groups is considered the main cause of the rapid degradation often observed with this aggregate type.
Other high-risk aggregates have lower amounts of one or both of these mineral groups, but they are still present in concentrations that are cause for concern and associated in some instances with damaged property.