【正文】 (g) relatively cold conditions. These factors are illustrated in Fig. 1. When the deterioration was first observed, a decision was taken to close the local road carried by the bridge, on safety grounds, until such time as the extent and nature of the problem could be determined. Subsequently the defects were found to be surface effects, with a sound central core of concrete remaining. Assessment of the structure showed that the road could be safely reopened whilst the investigations continued. Based on the information available at the time, and the need to undertake the planned strengthening work on the columns against vehicular impact, it was decided that the columns should be removed. This decision was reached after considerable deliberation, and assessment of costed options, but was influenced by the lack of available information on how to repair structural elements affected by thaumasite. There was also uncertainty as to whether the concrete deterioration had _stabilised‘ or was continuing. In the event the most effective strategy was the plete removal of the bridge columns. A system of temporary propping was introduced to allow the columns to be cut up and removed, and a new foundation and supports cast on top of the existing foundation. Alongside the continuing site investigation work, records of the structure were inspected, and also available geotechnical information. It was evident that the design of 30 years ago had been undertaken in accordance with the standards and specifications of the time, based on the contemporary soil survey. This had duly taken account of the prevailing soil conditions in regard to the occurrence of sulfates. However at that time there was no requirement to consider sulfides, and so in parison to the rules developed in 1999 in response to the discovery of thaumasite, may have underestimated the influence of sulfates by 2–3 classes (based on BRE Di 1052 N. Loudon / Cement amp。 (d) physical disposition of the structure (deep foundations and slender concrete elements)。 (c) presence of carbonate generally in coarse and/or fine concrete aggregates。 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。 (c) changes to ground chemistry and water regime resulting from construction。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