Chloride concentration and resistivity were measured in the top surface of eight 50 year old concrete bridge decks selected from a short length of the A82 trunk road. Chloride concentrations were determined by acid extraction on powdered concrete samples obtained by percussion drilling. Resistivity values were determined by the Wenner four-probe method used in situ on the decks. The chloride data are presented as normalised frequency distributions. The shapes of these distributions are used to predict whether the spatial variations of contamination of the decks are systematic or random. The data are used to predict the risk of corrosion, and alternative methods of ranking the decks in order of increasing corrosion risk are discussed.

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