【文章內容簡介】 any 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 the matrix of the concrete or (b) _TF‘ for thaumasite formation where thaumasite is present in preexisting voids in the concrete, but there is no deterioration evident (a latent stage in development of TSA). The Report also contained practical information on the requirements and methods for identification and testing of concrete and soils in existing structures, to determine if thaumasite is present. Particularly important was the strong message to clients and designers of new structures to undertake a thorough soil survey as part of the design process. This has always been undertaken on road building projects and major civil engineering contracts, but less so on smaller works, and in the domestic property market. Chapter 9 of the Report provided detailed specification requirements for new construction to minimise the risk of thaumasite sulfate attack, based on the approach already adopted in BRE Digest 363 [1], namely by classifying the sulfate conditions in the soil adjacent to the designed concrete, and by setting a series of restrictions and options for the concrete mixes for each classification. However this approach was extended to adopt a ―package‖ of measures to deal with all ground classifications. It sought to leave as many options open to designers, and particularly to the contracting and concrete supply industries, and all such options were deemed to be equally effective. There was also a desire to keep all guidance and remendations as simple as possible, and user friendly. The Report remendations consisted of detailed materials requirements for concrete mixes and this was allied to a risk based strategy based on different structural performance levels, depending on the required service life and usage of the structure. There was an overarching assumption that the soil/ground water classification had been correctly assessed, and the remendations in chapter 6 of the Report had been followed, and so consequently the concrete requirements were appropriate to the existing and anticipated future ground conditions. The remended concrete options followed on from this correct sulfate classification of the soils, with due allowance for any sulfides present. Other related guidance involved consideration of the construction operations and the need, where appropriate, to provide additional drainage around structures, to avoid creating sumps, and where possible not to use reworked sulfate/sulfide bearing backfills. The concrete materials requirements embodied various controls on cement content, and free water/cement ratios, but adopted a new classification of aggregates by defining different carbonate ranges depending on the amount of carbonate present in the fine and coarse aggregate fractions. In terms of the structural performance level the philosophy adopted was one based on banding of structures into high, normal and low performance, representing a range from long service life structures to low performance for short service life structures, and structures with massive buried concrete foundations or those with slender or critical buried elements. This recognized that thaumasite attack in reality was assumed to be a relatively slow process, and may be insignificant for structures with only a short design life. More restrictive measures would be required when dealing with longer service lives for structures and critical/sensitive buried elements, and conversely less sever