Quantifying water permeability and pore size through capillary absorption

In Belgium the construction of a repository for low and intermediate short living radioactive waste is in preparation. The safety is, among other aspects, based on engineered barriers of cementitious materials preventing release of radionuclides to the atmosphere or to the surrounding soil. Relatively low water infiltration through these concrete constructions for a significant time period is important aspect to assure a safe disposal of these wastes. In this context it can be interesting to test multiple candidate concretes for water permeability. However testing for water permeability is a difficult task because of the relative high hydraulic pressures needed to percolate water through high quality dense concrete. In the present paper we are presenting results of the water permeability flows obtained at different pressures. These clearly indicate the measurement is greatly affected by the pressure applied. Therefore another type of measurement which does not involve a pressure head was developed. Indeed capillary absorption was used to deduce pore size distribution and water permeability. Not only is this method very easy to bring into practice, the conditions are also close to the real environmental conditions of these concrete structures due to the absence of a pressure head. A good fit can be made with mercury intrusion porosity. This is illustrated in the paper for two different concretes