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Synopsis Tests have been carried out on four concretes to measure their permeability coeficient using both water and nitrogen. In every case the gas permeability was significantly higher than the water permeability, the dlference increasing as the permeability reduced. The theory of gas slippage, first reported in 1875 and subsequently studied in relation to oil sands in 1941, has been identified as a major reason for the recorded differences betweeri the water and gas permeability coefficients for concrete. An equation relating water and gas permeability has been derived for mature, sealed-cured concrete, which takes into account the mean absolute pressure used for gas permeability measurement. This can be used to adjust gas permeability results to give a reasonable approximation of the intrinsic permeability of the concrete.

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The effects of cement type and concrete composition on the resistance to reinforcement corrosion have been investigated using large reinforced concrete blocks exposed to UK coastal splash zone conditions for eight years. The results have been analysed in conjunction with a substantial volume of published data, particularly in relation to the resistance of the concrete to chloride ingress. Concretes containing either pulverized fuel ash or ground granulated blastfurnace slag were found to exhibit markedly better protection of reinforcement than Portland cement concretes of the same grade and a significant benefit was also apparent when comparisons were made at the same water–binder ratio. Variability of both the surface chloride level and the apparent chloride diffusion coefficient was measured over an area of only 0·15m2 on each of six blocks. The scatter was sufficiently high to indicate that several measurements are needed to achieve reliable predictions of future performance. In addition, time-dependent changes in the rate of chloride ingress were observed.

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