【正文】 (d) low temperatures. Secondary factors (a) type and quantity of cement used。 (c) groundwater movements。 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。 Concrete Composites 25 (2021) 1051–1058 gest 363 [1]). Clearly this was very significant, but no fault could be attached to the design or construction process of 30 years ago. Whilst work was taking place at Tredington Ashchurch Bridge, a further maintenance contract at Grove Lane Bridge further south on the M5 Motorway, revealed similar signs of thaumasite deterioration in buried concrete, although evidently not as severe or as widespread. In this case after initial investigation, conventional concrete repairs were conducted, after removal of the contaminated concrete. 3. DETR Expert Group When the concrete deterioration was first discovered in the motorway bridges, it was immediately apparent that the thaumasite attack was very serious, and there were potential implications for all new construction as well as existing buildings and civil engineering structures. The Highways Agency briefed the Department of the Environment Transport and the Regions (DETR) and Government Ministers. It also transpired that BRE, through Dr. Norah Crammond and other colleagues, had been investigating thaumasite related concrete deterioration for nearly 10 years, though the results of this research had not been published, and the current edition of BRE Digest 363 [1], made only passing reference. A decision was taken at Ministerial level to set up a National Expert Group under the chairmanship of Professor Les Clarke of University of Birmingham, with a remit to investigate thaumasite and report back within six months. This was a very tight constraint, but it was decided that it was essential to provide authoritative guidance at the earliest opportunity to allay public and industry concerns. The Expert Group was derived from a wide cross section of industry and the author was also seconded to represent the Highways Agency. After considerable discussion and deliberation a report entitled ―The Thaumasite Form of Sulfate Attack: Risks, Diagnosis, Remedial Works and Guidance on New Construction― [2] was produced and published in January 1999. As such, it was a significant achievement to publish a very detailed report in such a short timescale, and represented a collaborative and very constructive approach by all the participants, although it was apparent that there were differing views on many aspects, and especially the detailed and plex chemistry involved in thaumasite. It was also apparent that many of the construction industry representatives, had understandable concerns about the mercial implications for their own sector of the market. The report dealt with the nature and risk of thaumasite and sulfate attack, inspection and testing requirements, structural assessment, remedial works, and a specification for new works, and it is particularly with this last section I was involved. However the report as a whole provided authoritative guidance and remendations for both new works, and for clients and property owners managing structures and buildings. The report itself set out _guidance‘ in areas where only limited research and case studies had been undertaken,but _remendations‘ where more reliable and well documented information was available. It was acknowledged that not all the answers were known. In particular there was much debate surrounding the mechanisms for occurrence of thaumasite, and the timescales over which it occurred, and in this area further research was essential. Consequently some caution had to be exercised in the detailed the report acknowledged that there had been relatively limited occurrence of thaumasite in practice, although laboratory work indicated that conditions for thaumasite could be recreated relatively easily. One aspect of major importance, particularly as regards new construction, was the need to strike the correct balance between technical issues and mercial interests. To do this the Report had to deal authoritatively with the technical concerns without unnecessarily placing restrictions on the use of the constituent materials to produce concrete. At the time it was published the Report acknowledged that the information was of an interim nature and would need to be updated as more evidence concerning thaumasite bee available. It also sought to _minimise‘ the risk of future occurrence,rather than the introduction of draconian measures to pletely eliminate the risks. Key facets to the Report were the identification of a number of primary and secondary factors governing the occurrence of sulfate (these are referred to later in the paper) and the classification of thaumasite in affected structures: (a) _TSA‘ for thaumasite sulfate attack where there is significant damage to t