Measurements of combined diffusive and advective radon transport in aerated concrete have been made and compared with model calculations. The experimental set-up consists of a leak-tight vessel containing a hollow aerated-concrete cylinder that divides the vessel into an inner (inside the cylinder) and outer (outside the cylinder) compartment. 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 and/or 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.
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