【正文】 (c) changes to ground chemistry and water regime resulting from construction。 (b) presence of mobile groundwater。 (e) construction regime, particularly the excavation of a large hole through undisturbed ground which was subsequently backfilled with the excavated materials and created a _sump‘ around the buried columns。 Concrete Composites 25 (2021) 1051–1058 This paper covers the responses to some of these questions, and summarises the current situation, and identifies other issues for the future. 2. TredingtonAshchurch Bridge Thaumasite sulfate attack was first observed in early 1998 on a Highways Agency structure in the substructure of the TredingtonAshchurch Bridge, an overbridge carrying a local road over the M5 Motorway situated between Junctions 9 and 10 in Gloucestershire. At about the same time similar, but less severe defects, were also found in Grove Lane Bridge foundations, also on the M5, but further south, between Junctions 12 and 13. TredingtonAshchurch is a four span overbridge with a reinforced concrete deck. Supporting columns are sited in the central reserve and verges, and extend through placed fill for about 5 m to reinforced concrete spread footings. The bridge was built about 30 years ago, to the applicable contemporary Ministry of Transport standards and specifications. Regular structural inspections and testing of the concrete elements above ground have not indicated any observable signs of distress to the bridge in the intervening period. Planned strengthening work to the columns of the bridge necessitated excavation of some of the backfill surrounding the concrete supports, and in the course of this work site staff observed some unusual deterioration in the exposed concrete. This indicated that some of the concrete surfaces had turned to a _mushy‘ consistency, and of _warty‘ appearance with evidence of expansion of the residual material. This was unexpected to the say the least, and potentially extremely serious. Diagnosis was first made by our Maintenance Agents, Gloucestershire County Council/Halcrow and later confirmed by the Building Research Establishment (BRE) as thaumasite sulfate attack, after initial concrete samples had been analysed. Further excavation of the backfill ensued to pletely expose the buried columns and the top surface of the foundations, entailing extensive temporary works to provide the necessary support. A large programme of investigation was initiated, including extensive concrete sampling, and soil and groundwater testing, backed up by a thorough laboratory testing regime, and analytical work to correlate soil conditions with concrete defects. The objective was to determine the precise causes of the deterioration, and to see if parameters could be found that would assist future identification of affected structures and their investigation. Other papers at the conference will deal with the TredingtonAshchurch case study in much more detail, however suffice to say that it transpired that a number of critical factors in bination had occurred (listed below), which were significant in terms of the deterioration that occurred, and particularly in relation to the severity of the thaumasite sulfate attack: (a) use of limestone aggregates in the concrete。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 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