【正文】 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 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. Crown Copyright _ 2021 Published by Elsevier Ltd. All rights reserved. Keywords: Thaumasite。 (d) type, depth and geometry of buried concrete. Instructions were issued to all the Maintenance Agents in England to mence an investigation. This was divided into two parts, initially based on a risk based desk study, and followed up where necessary with site investigation work. The aim of the desk study was to determine the coexistent presence of the primary factors, and particularly whether carbonate bearing aggregates had been used in buried concrete, and whether structural backfill or adjacent ground included sulfate/sulfides. The assessment was also related to structural significance and work needs, such as planned maintenance work. Of particular interest were structures such as those exhibiting signs of distress above ground, such as settlement or other ground movements or unexplained cracking. This desk study required the critical examination of structures records and soil survey information. In some cases there was insufficient information available, and limited confirmatory material testing was required. As part of the desktop assessment, structures were prioritised on the basis of risk. Follow up investigations were then conducted on a limited number of the higher priority structures in each area (if necessary), and with judgement made on the ease of access to buried concrete, so as to minimise the amount of temporary works and traffic management required. The aim of the investigation was to determine whether there were any visible signs of thaumasite attack present. If there was, then detailed sampling of the backfill/soils, and concrete coring was undertaken, backed up by laboratory testing. It was important to confirm for the highest priority structures that record information was correct. If all the critical factors were present, both positive and negative results were important. The absence of thaumasite, where carbonate in the aggregates and sulfates/sulfides in the soils was present, was just as important as if thaumasite was found. Significant results of the investigation were passed back to BRE to assist with their future research. The results of this investigation were very much as expected, and confirmed the findings of the Expert Group Report, and particularly the perceived areas of greatest risk. Apart from the Gloucestershire/Avon area where further cases emerged, the only significant positive result was from County Durham, and is reported later in this paper. However the investigation was invaluable, as it also confirmed that no thaumasite was present in the lower risk areas. Some words of caution about areas of risk are required, in particular about the presence of carbonates in aggregates. Aggregates can and often were transported substantial distances from their quarry source to their eventual place of use and assumptions cannot be made just on the basis of quarry locations. Although the Expert Group remendations for concrete and related measures were very detailed, they were not in the form that had been used by the Highways Agency for its published Specification for Highway Works and the related Notes for Guidance in relation to concrete. Consequently, and with the assistance of BRE, a specification for concrete was drawn up to be integrated with the existing requirements for structural concrete, and was included in the republished Specification in June 2021 [5]. 6. A1 Mally Gill Bridge County Durham Other than in the Gloucestershire/Avon area, where further cases of thaumasite were expected and emerged, N. Loudon / Cement amp。 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 bridg