Determining the carbon dioxide permeability of paint films

An in-house set-up was developed for determining the permeability of, paint films towards carbon dioxide. The system implemented the so-called Wicke-Kallenback method, described in EN 1062-6. This method consists of a two-chamber permeation cell divided by a supported paint film. A carbon dioxide/nitrogen mixture stream (15% CO₂/85% N₂) is fed to the retentate chamber and a nitrogen carrier stream is fed to the permeate chamber. Carbon dioxide permeates from the retentate to the permeate chamber. The carbon dioxide flow rate is obtained from the permeate concentration and flow rate. From the carbon dioxide flow rate it is possible to calculate the paint film permeability towards this gas. The coating system is applied on a Kraft paper support sheet; the Kraft paper by itself shows negligible permeation, resistance. Coatings to be considered as “surface protection systems for concrete” must comply with EN 1504-2. This standard requires that the paint film permeability have an equivalent air thickness of S_D≥50 m. The unit developed was able to quickly determine permeabilities as low as an equivalent air thickness of S_D=1500 m.