Permeability and absorption tests

Since corrosion of steel in concrete is usually caused by the ingress of various agents (Cl , CO2, H2O, O2) through the concrete cover, many attempts have been made to calculate and measure the permeability and absorbtion characteristics the concrete. Measurements are most accurately done on a conditioned core in the laboratory, since the environment (i.e. degree of saturation) will strongly influence field measurements. However, field measurements are made with vacuum devices and water absorption kits to give a rating of the permeability. 

In the laboratory, diffusion, permeability permittivity and absorption can all be measured under controlled conditions. When conducting such an investigation it is important to differentiate between permeability which is measured under steady state conditions driven by a constant pressure difference, and initial surface absorption driven by rapid capillary absorption (Concrete Society, 1997a, p. 54). 

Most laboratory tests are concerned with modelling the flow of chloride into concrete. Unfortunately even the most accurate measurements in the laboratory can rarely be equated to field conditions where wetting and 

Field devices are most effective when used to check improvements in water absorption after a treatment such as the application of a penetrating sealer such as silane. The ISAT test (BS 1881-208, 1996) is particularly useful for checking the effectiveness of coatings. 

Concrete Society Technical Report 50 is a Guide to surface treatments for protection and enhancement of concrete (Concrete Society, 1997a). This gives the following criteria for the ISAT test  

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