Concrete deterioration in Quebec, Canada
RSK’s materials and structures team was engaged in a major Canadian court case with a value exceeding CAD200 000 000 in late 2019. The work involved Dr Ian Sims and Dr Ian Blanchard acting as expert witnesses in relation to the premature deterioration of concrete used in several hundred houses and almost 100 commercial buildings built across an area of central Quebec.
The cause of deterioration was the coarse aggregate, which contained the iron sulphide mineral pyrrhotite, in the concrete used for the foundations and supporting walls of the buildings. Unfortunately, the issues only became apparent several years after placement, so similarly defective concrete was produced over about five years.
The deterioration of sulphide minerals, in particular iron sulphides, in the presence of water leads to the production of sulfuric acid. This potentially results in both acid attack on cement and any limestone aggregate, and the release of damaging sulphate ions that cause internal sulphate attack. Both of these lead to weakening and cracking. Although this reaction may occur slightly for the common iron sulphide pyrite when it typically produces no more than surface popouts and some superficial staining, the reaction with pyrrhotite is much more rapid and results in extensive and, at times, structurally significant damage. The reaction of pyrrhotite in concrete aggregate had previously been rarely reported in academic literature (about six separate occurrences over the previous century) but was poorly and inconsistently detailed in standards and other industry documents.
RSK’s involvement in the court case included assessing the actions, advice given and professionalism of various third-party laboratories and consultancies, and to what extent they were providing guidance to the quarry’s operators and concrete producers regarding the suitability or otherwise of the aggregate. The quarry was co-owned by two competitor concrete producers. A site visit to the quarry confirmed previously suggested variations in the composition and mineralogy of the coarse aggregate material being used.
For further information, please contact Dr Ian Blanchard, +44 (0)7739 647 476