【正文】 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) low temperatures. Secondary factors (a) type and quantity of cement used。 Concrete Composites 25 (2021) 1051–1058 1055 the only other positive result from the national investigation occurred in County Durham on the Mally Gill Bridge on the A1 in County Durham. Initial desk study assessment had indicated that this bridge and others in the area were at relatively low risk from thaumasite sulfate attack, as there appeared to be no known source of sulfates in the ground. However site investigations in advance of other planned works revealed concrete deterioration on the foundation. This was observed in flanking concrete acting as protection to a concrete hinge detail at the bottom of a deck support column, and was clearly a critical area for the structure. Fortunately the hinge itself and the adjacent concrete appeared to be unaffected. After further investigation and testing by our Maintenance Agents, and also by BRE ,the concrete deterioration was confirmed as thaumasite sulfate attack, although the extent and severity was less than that observed at the TredingtonAshchurch Bridge. Tests confirmed carbonates in the concrete aggregates, however the source of the sulfate was not so readily apparent. Further work determined that the sulfates originated from a red burnt colliery shale, an industrial waste product, which had been widely used in the 1960s and 1970s. In this instance it had been utilized as an economic road subbase material, and some was also present in the backfill around the bridge foundations. This produced a significant _reservoir‘ of sulfates, and lead to the accumulation of critical levels in the backfill to the bridge foundation. Once again this fitted the pattern identified in the Expert Group Report,which had specifically identified burnt colliery shale as a potential source of sulfates. Concrete repairs were subsequently undertaken as part of the planned maintenance a result of this discovery it was also necessary to review the findings of the desk study and investigate other structures in proximity to known areas where burnt colliery shale has been used. Further cases have now e to light in this area. 7. Gloucestershire/Avon area Special investigations were made in the area where thaumasite was initially discovered. The aim was to anticipate the severity of deterioration, in advance of other planned work, so that decisions on the required remedial work could be taken. Further cases were expected, and indeed came to light. About thirty structures are known to be affected, though others are expected in the future. None have deterioration as severe as Tredington Ashchurch. 8. Updating of Bre Digest 363 [1], BS 5328 [3] One year on from the original publication of the Expert Group Report, a review was carried out by Professor Les Clarke for the DETR. This confirmed that the originally issued guidance was still fundamentally sound, although it was apparent that a number of documents required urgent updating to achieve consistency. There were also a number of issues that had emerged requiring clarification, as a result of the issued guidance. In particular the requirements in the Report in relation to precast concrete products, the Additional Protective Measures, especially the _design drainage‘ remendation, and Structural Performance Levels needed further explanation and interpretation. A small mittee was set up, under the auspices of BRE, to update BRE Digest 363 [1], which up to the publication of the Expert Group Report, represented the authoritative guidance on sulfate attack. There was a need to ensure that all the issued guidance remained patible and so this mittee retained strong links with the BSI mittee updating BS 5328 [3] for concrete, to ensure that there was good coordination and consistency was achieved. The opportunity was taken to update the guidance for concrete requirements based on the experience with the Expert Group Report, and the latest available research information. The replacement Digest was drafted to include Design Guides to assist designers and concrete suppliers. It also included a revised classification of soil conditions based on their aggressive nature (ACEC Class) (for definition refer to [6]). The work has been pleted and is now published as BRE Special Digest 1 [6]. As a result the Highways Agency needed to update its own technical advice and specification to align with this latest industry documentation, and this is now in hand. 9. M5 Moreton Valence site trial The Expert Group Report made a great deal of use of the available research on thaumasite. This had been conducted largely by BRE, but also by other academic researchers and by various groups in the construction industry. However as has already been indicated, there were many areas where further work was identified. One particular aspect concerned the suitability of repair techniques, where the Expert Group does not make definitive remendations, although guidance is provided. In particular information is needed on the amount of defective concrete to be removed, the suitability of concrete removal techniques and materials for repair.