Concrete damage due to pyrrhotite in the Trois-Rivières area (Québec, Canada): risk of future damage to undamaged concrete

Over 1700 buildings in the Trois-Rivières area (Québec, Canada), with the concrete manufactured with aggregates containing pyrrhotite have been inspected by the defense experts involved in a first trial. Nearly 500 of them, undamaged at the time of a first inspection, were reinspected about every 2 years. Only 23% of these (113/497) showed signs of concrete swelling due to internal sulfate attack with time, but only 8 did so more than 8 years after construction. Among the 384 still undamaged buildings, 99 were over 10 years old despite aggregate pyrrhotite contents of 0.25 to 1.00 vol%. The risk of future damage to undamaged concrete is based on three factors relating to: (1) aggregate pyrrhotite content, (2) type of concrete component and exposure conditions, climatic or other, and (3) age of concrete. Since 2017, the protocol has been applied to many buildings, and proved to be both reliable and conservative.