Engineering implications of the oxidation of pyrite: An overview, with particular reference to Ireland

Abstract

This overview provides a background to the processes by which the oxidation of iron sulphides can lead to distress in structures, with particular reference to the problems which have occurred in Dublin in the 2000s. It discusses the formation of pyrite and pyrrhotite and the chemical reactions involved in their oxidation, the effects of the oxidation process and how its by-products can lead to both heave and/or the degradation of concrete. Examples are provided from Canada, the UK and Ireland. Attention is drawn to the significance of the different forms of iron sulphide and the nature of the various host lithologies. The factors which affect the rate/extent of oxidation are considered. Having reviewed the relevant guides and Standards, attention is drawn to some difficulties in assessing the potential for sulphate-related damage to structures and the limitations of the documentation currently available. Some common misunderstandings in interpreting the results of both physical and chemical tests on pyritiferous material are discussed. Acceptability criteria and the assessment of marginal material are considered.