Effect of exposure conditions and concrete quality on pyrrhotite oxidation and internal sulfate attack

Thousands of homes in County Donegal, Ireland, are damaged by cracks formed a few years after construction. The authorities have erroneously attributed the damages to the presence of muscovite mica in the concrete blocks used to build the homes. Only recently, research has shown that pyrrhotite oxidation triggering internal sulfate attack (ISA) is the cause. In this study, the strip foundation, the rising blocks elevating the structure to ground level and the inner and outer leaf of one affected home are investigated. As these four types of structural components differ by concrete quality, exposure condition or both, their effect on pyrrhotite oxidation and ISA is investigated. Sulfur analysis, X-ray diffraction and scanning electron microscopy are used to characterize the concrete.