【正文】 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。 (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。 (c) changes to ground chemistry and water regime resulting from construction。 (b) presence of mobile groundwater。 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。 (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)。 (c) presence of carbonate generally in coarse and/or fine concrete aggregates。 (b) quality of concrete mix and paction。 (d) physical disposition of the structure (deep foundations and slender concrete elements)。 Structures。 (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