【正文】 rictive measures would be required when dealing with longer service lives for structures and critical/sensitive buried elements, and conversely less severe requirements imposed where structures had short anticipated service lives. Since there were a number of areas where the dearth of research data prevented authoritative remendations for materials, it was agreed that it would be prudent to adopt a _multilayered‘ protection approach, whereby a number of additional protective measures would be instigated, in addition to the material requirements, in appropriate situations. They would represent an important first line of defence and consisted of the adoption of surface protection and drainage requirements, as well as the choice of lower carbonate range aggregates in certain circumstances. Overall the Expert Group Report provided a number of important messages. The number of structures potentially at risk was not thought to be large, and the structural consequences not generally serious. The deterioration would generally provide early warning signs above ground where significant thaumasite sulfate attack was occurring below ground. There was also not thought to be any significant problem for domestic properties. The Report, if followed would minimise the risk of thaumasite sulfate attack, but also pointed out that not all the answers were known and that further research was needed. It also acknowledged that there was a need to update various documents and in particular BS 5328 [3] and BRE Digest 363 [1]. 4. Highways Agency guidance for new construction In parallel with the work of the Thaumasite Expert Group the Highways Agency set down its own advice for new construction, based on the Expert Group requirements. Interim Advice Note 25 [4] was issued, which laid down requirements to be adopted for highway structures, to minimise the risk of thaumasite sulfate attack in new construction. In particular it assumed that in most cases highway structures would be deemed to be high performance level, as befitting the required 120 year service life. The Advice Note also provided some more specific guidance on drainage around structural foundations and the type of protective coatings appropriate for application to buried concrete in highway structures. 5. Highways Agency strategy for existing structures However as well as dealing with new construction, the Highways Agency also needed to address the issues of the occurrence of thaumasite in existing structures and particularly whether it was confined to the existing area of Gloucestershire or more widespread. A decision was taken to embark on a national investigation. The Expert Group had identified a number of primary and secondary factors that must coexist or would influence the occurrence or severity of the attack. Primary factors (a) presence of sulfates and/or sulfides in the ground。 (f) leaking motorway drainage。 (d) physical disposition of the structure (deep foundations and slender concrete elements)。 (b) use of sulfate and sulfide bearing materials for backfilling around the foundations and buried columns (the soil excavated to construct the foundations contained iron pyrites (sulfides) which started to oxidise after exposure to the atmosphere, and added to the reservoir of available sulfates)。 Highways Agency 1. Background In early 1998, in the course of other maintenance and bridge strengthening works, unusual concrete deterioration was found to have occurred in the foundations and buried columns on a couple of bridges on the M5 Motorway in Gloucestershire. Subsequent investigations proved that the observed defects were the result of thaumasite sulfate attack, and the Highways Agency were faced with a number of immediate questions. How serious was the attack? Were there structural implications? How many bridges were affected? Was it a local problem, or national? What were the costs? How do we undertake repairs or other remedial action? Were there any faults in the original design and construction? Were there implications for new construction? What were the implications beyond the Highways Agency interests? Do we need to carry out any research? 09589465/$ see front matter Crown Copyright _ 2021 Published by Elsevier Ltd. All rights reserved. doi:(03)00146X Cement amp。A review of the experience of thaumasite sulfate attack by the UK Highways Agency Neil Loudon Highways Agency, SSR CE SDM Division, Heron House, 4953 Goldington Road, Bedford MK40 3LL, UK 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 M5Motorway in Gloucestershire. The paper will highlight the investigation of these structures, and assess the implications of the resultsof 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 therisks of thaumasite in new construction, and this culminated in the development of a new specification for buried concrete. There arealso 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 sul