Concrete damage due to pyrrhotite in the Trois-Rivières area (Québec, Canada) – Influence of type of concrete element and exposure conditions

The concrete components of two commercial buildings corresponding to extreme cases in terms of aggregate pyrrhotite content and soil conditions, were investigated. Unlike the above-ground concrete of foundation walls exposed to climatic conditions, the concrete of such walls and footings buried on both sides, at least more than 30 cm in depth, is undamaged, has a high water saturation degree, and contains pyrrhotite that is not at all or almost non-oxidized. The water saturation degree of this concrete is too high for the pyrrhotite it contains be sufficiently oxidized. For damage to occur, the original concrete must first dry sufficiently for the pyrrhotite be oxidized, and then, external moisture supplies are needed for expansive sulfates be formed. The on-ground, structural and steel-deck slabs analyzed, whatever their covering (bare, vinyl or ceramic), were undamaged, except locally where they were frequently exposed to water.