Measurements of combined diffusive and advective radon transport in aerated concrete have ken made and compared with model calculations. The experimental set-up consists of a leaktight vessel conlaining a hollow aerated-concrete cylinder that divides the vessel into an inner (inside the cylinder) and outer (outside the cylinder) cornpartmenl [I]. The measurements were conducted with a radon source in the inner compartment, for a range of ventilation rates in the inner and outer compartment and for various flows through the concrete. Pressure, temperature and relative humidity in the set-up were kept constant. It was found that a combined diffusion-advective flow (Fick-Darcy) model does not describe the data. A much better fit is obtained by assuming an advective-velocity-dependent diffusivity in the model calculations. The dependence of the diffusivity on the flow velocity may result from mechanical andlor hydrodynamic dispersion. Alternatively, a model assuming two parallel porous media with distinct volume and permeability also describes the data quite well. The results of this parallel-media model indicate a preferential airflow. About 90% of the airflow is transported through 7% of the material.
Pal, van der, M., Spoel, van der, W. H., Meijer, de, R. J., Hendriks, N. A., & Graaf, van der, E. R. (2005). Measurements and modelling of combined diffusive and advective radon transport in porous building materials. Radioactivity in the Environment, 7, 371-380. https://doi.org/10.1016/S1569-4860(04)07042-1, https://doi.org/10.1890/070160