Pyrrhotite in concrete aggregate. Introduction to mechanism, damage potential and ongoing research

Abstract

Pyrrhotite is an iron sulfide which when present in concrete aggregate may lead to expansive reactions, cracks and finally disintegration of the concrete. This potential risk when using aggregates containing sulfides in concrete production has been known for several decades, and international concrete standards take this into account. Though, recent examples of deterioration of concrete structures in Canada and USA, and the rejection of tunnel masses for application as concrete aggregates for the construction of the Follo line tunnel in Norway, have raised questions regarding the test methods and regulations for sulfides and pyrrhotite in concrete aggregates. A Norwegian R&D project led by NTNU is currently looking into the characterization and quantification of sulfide minerals in aggregates (WP1) and working with the development of test methods for documentation of the damage potential in concrete (WP2). There is a close collaboration between the Norwegian research team and researchers from the university of Laval in Canada which have been working with pyrrhotite in concrete for over a decade. This paper introduces the basic chemistry of the reactions of pyrrhotite in concrete, presents examples of deterioration caused by pyrrhotite and lists the relevant regulations currently in place in Norway and North America. Eventually, the challenges and research questions raised will be discussed and how we are planning to tackle these will be presented.