ABSTRACT
In Figures 3 and 4 it can be seen that air permeability is less for the low water/cement samples, as expected. What was not expected is that it would be more on the mature samples. It is thought that this is explained by a drying out process in the samples as they sat for the two months in the dry laboratory. It is known from previous gas permeability tests with CO2 that a gas does not easily displace water in the pores of concrete at the low pressures used so, if a surface layer is drier to a greater depth, the intruding gas will be able to disperse to a greater depth with less resistance. Silane alone does not improve the air permeability of concrete very much. This is clearly seen and understood since silane does not block pores to molecules of the size found in air. However, the two materials containing acrylic do show an improvement in air permeability. They seal the surface much better to small molecules. This is of importance if the protection required is from carbon dioxide and carbonation.
