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The permeability of concrete to liquids, ions and gases is of direct relevance to both durable concrete and to leak-resistant concrete for containment. Analytical models used to predict the age at which corrosion of the reinforcement will be initiated require a detailed knowledge of the transport mechanisms involved and the permeability of the concrete. Some specifications for projects in extreme environments (e.g. the Middle East) or requiring very long lives (e.g. railway tunnels) have specified permeability criteria, based on some form of analytical durability model, to be verified by testing the supplied concrete or precast concrete elements. A simple permeability test could form part of the quality assurance (QA) scheme for any precast concrete element, to check on the variability of standard units.
However, there does not appear to be any agreement on the test methods that should be adopted. Concrete Society Technical Report, Permeability testing of site concrete (2008) reviews how permeability can be measured and what typical results are achieved. The Report explains the meaning of porosity, permeability, diffusion and the various coefficients and units that are used. There are many different ways in which results can be presented, and some information is given on how values can be converted into the different units since, without these conversions, it is often difficult to compare one set of results with another.
To establish values for the permeability of site concrete, measurements can be made either in situ on site, or in the laboratory on samples removed from site. Many of the tests described in the Report do not measure permeability directly, but produce a permeability index which is related closely to the method of measurement. In general the test method used should be selected as appropriate for the permeation mechanism relevant to the performance requirements of the concrete being studied. The Report includes a number of case histories where permeability results are available from site cast concrete.
A Table is included in TR 31 which attempts to indicate the range of values given by the various test methods for concrete having high, medium and low permeability.
See also separate entries Hardened concrete testing/Figg test and Hardened concrete testing/Clam test.
Acknowledgement: The Concrete Society
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