Relationship between radon and oxygen diffusion coefficients in OPC concretes

Exposure to radon in indoor settings is presently the second cause of lung cancer. One of the solutions proposed to prevent its penetration and accumulation in buildings is to install radon barriers such as concrete flooring with suitable characteristics, a low radon diffusion coefficient in particular. That raises the need to determine the radon diffusion coefficient in ordinary Portland cement (OPC) concrete, the type normally deployed in such applications.The diffusion coefficient for radon gas in concrete is difficult to establish experimentally for a number of reasons. The first and foremost is the need for a standardised source of radon, which is normally costly. Another is trial duration, which lasts several days given the need to ventilate the diffusion cell once the radon concentration in the receiver container reaches the steady state. Hence the pursuit of alternative, less complex methods for finding the radon diffusion coefficient, based on more readily determined parameters. The oxygen diffusion coefficient, for instance, can be found experimentally at lower cost and complexity for it obviously calls for no source of radon. Rather, oxygen is drawn from the laboratory air itself and the test takes much less time for it involves no need to ventilate the cell.This article describes a preliminary study conducted to establish the relationship between the oxygen and radon diffusion coefficients in OPC concrete. It focuses on the equations to calculate the radon coefficient from empirical measurements of the value for oxygen, which can be measured more readily or even derived from other parameters such as air permeability or electrical resistivity. Inasmuch as gas diffusion in concrete is closely related to material porosity (in turn primarily dependent on concrete batching, curing and moisture content), the results for several types of concrete with different porosities are discussed.