A concrete road pavement at Padiham in Lancashire has been identified as deteriorating because of the alkali-silica reaction. A systematic coring programme of one of the slabs was carried out in order to identify the degree and location of the reaction. This reaction was unlike that seen at other sites examined in that the reaction occurred throughout the whole of the slab, although it was more severe in the areas next to the joints and on the upper surface. The pavement was constructed in two layers using different coarse aggregates, a siltstone and a limestone, which by coincidence were both alkali-silica reactive. This investigation identifies the causes of the reaction in these aggregates and suggests a possible mechanism of reaction. Chloride and alkali content analyses were carried out to see if de-icing salt contributes excess alkali to hardened concrete. (A)

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