Two beams forming part of the roof over the swimming pool at the school collapsed. The investigation showed that the cause of the failure was loss of strength due to conversion of high alumina cement concrete followed by sulphate attack leading to disruption of the concrete. The degree of conversion and loss of strength was greater than expected for the quality of concrete specified, and it was inferred that this may have been due to a combination of the following factors: (1) the freewater/cement ratio may have exceeded the maximum of 0.4 aimed at in production; (2) the temperature during the first day after casting may have been excessive; and (3) the aggregate used, which contained the minerals feldspar and mica, had an accelerating effect on the rate of conversion and loss of strength. Details are given of the results of the tests carried out during the investigation. (Author)