The permeability of concrete in a marine environment

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Abstract
Synopsis Permeability is a fundamental property governing the durability of concrete in the marine environment and it has only recently been appreciated that some concretes exhibit a very significant reduction in permeability on immersion in sea-water. To investigate this phenomenon further, a resistivity technique has been developed and used to monitor the changes in permeability of five mortars and one concrete on exposure to sea-water. All mixes studied showed a fall in permeability (increase in resistance) on immersion in sea- water. Indeed 25 mm thick specimens of the two most permeable mortars showed a fall equivalent to over 20 mm of additional thickness after only 10 weeks. This increase is due to the formation of an aragonite-brucite layer on the surface of the mortar plus a more widespread progressive constriction of the cement paste pore system. This effect also has a considerable influence upon the absorption capacity of concrete after a period of drying, which is important in the tidal and splash zones. Synopsis Permeability is a fundamental property governing the durability of concrete in the marine environment and it has only recently been appreciated that some concretes exhibit a very significant reduction in permeability on immersion in sea-water. To investigate this phenomenon further, a resistivity technique has been developed and used to monitor the changes in permeability of five mortars and one concrete on exposure to sea-water. All mixes studied showed a fall in permeability (increase in resistance) on immersion in sea- water. Indeed 25 mm thick specimens of the two most permeable mortars showed a fall equivalent to over 20 mm of additional thickness after only 10 weeks. This increase is due to the formation of an aragonite-brucite layer on the surface of the mortar plus a more widespread progressive constriction of the cement paste pore system. This effect also has a considerable influence upon the absorption capacity of concrete after a period of drying, which is important in the tidal and splash zones.

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