A review of the experience of thaumasite sulfate attack by the UK Highways Agency

Abstract

Abstract The paper summarises and reviews the UK Highways Agency experience of thaumasite sulfate attack. Thaumasite sulfate attack was found in February 1998 in a number of bridge foundations and buried columns on the M5 Motorway in Gloucestershire. The paper will highlight the investigation of these structures, and assess the implications of the results of the extensive testing undertaken at these sites, for other structures. Subsequent to the discovery of thaumasite in Gloucestershire the Highways Agency participated in the Thaumasite Expert Group set up by the Minister for Construction. The report produced by the group influenced the development of the Agencies own guidance. Investigations were undertaken nationally using risk based criteria, to determine whether the occurrence of thaumasite was a local phenomenon, or of more widespread concern. Concurrently guidance was also issued for managing and minimising the risks of thaumasite in new construction, and this culminated in the development of a new specification for buried concrete. There are also implications for ground investigations, and these will be discussed. The paper will also highlight the case study of the A1 Mally Gill Bridge in County Durham, where a markedly different set of circumstances gave rise to thaumasite sulfate attack in a foundation. The Highways Agency has been involved with the development of improved guidance, as a result of the Expert Group Report, to ensure that that there is a consistency of approach across the construction industry. The paper will acknowledge that there are still many unknowns, particularly the mechanism governing the occurrence of thaumasite and the speed of thaumasite production. A particular aspect of concern to the Highways Agency is the ongoing management of structures that are known to be or may be affected by thaumasite. What are the methods for investigation and testing and are there suitable methods for remote detection? Do we need to introduce new inspection regimes? What are the requirements for the repair of thaumasite affected structures? Mention will be made of some of the research in this area, particularly the trial of repaired concrete at Moreton Valence. The paper will summarise the lessons learnt so far from the thaumasite experience, the implications for the future management of structures in potentially higher risk areas, and identify research needs.