PROCEDURES for assessing the risk of Thaumasite concrete attack in pyritic clays can be relaxed, according to a report on the problem published last week.
The report was prepared by Thaumasite Expert Group chairman and former Institution of Structural Engineers president Professor Les Clarke. It presents research results and 20 new cases of the concrete consuming condition discovered in the year since the group's first report.
The review concluded that the pyritic clay condition was the only situation where the conservative procedure for assessing the sulphate class of sulphide bearing ground - as recommended in the group's first report - could be relaxed.
All new cases discovered have occurred in conditions that were anticipated. But Clarke warned the problem was not just confined to the Gloucestershire and Avon area.
Although the new instances have been mostly on highway bridges on the Lower Lias Clay in these areas, another case has been found on burnt colliery spoil a at site in County Durham (NCE 23 March).
Clark suggested that more cases may be identified in burnt colliery spoil, as there is evidence of extensive use of this material in road construction in the former coalfield areas.