Concrete Damage Attributable to the Oxidation of Pyrrhotite

In late 1982 or early 1983, a quarry in northeast Connecticut began extracting rock for aggregate that contains pyrrhotite, a reactive iron sulfide mineral known to oxidize in the presence of air and water. When the pyrrhotite oxidizes, the expansive reaction byproducts may crack the concrete, allowing moisture and air to more easily penetrate the concrete, leading to further damage. Depending upon rock geology and characteristics of the concrete mix, the problem manifests itself over varying periods of time—ranging from a few years to more than 20. As a result, an affected foundation may exhibit damage that ranges from barely discernible to very serious. Presently, there is no known solution to the problem save removal and replacement of the foundation. Thus, the visible attributes of the damage resemble those of alkali silica reaction (ASR), and it typically requires a petrographic analysis to definitively discern between ASR and damage from pyrrhotite.