Determination of diffusivities of dissolved gases in saturated cement-based materials

Diffusion is an important property for characterizing concrete durability because it governs the penetration of aggressive substances responsible for degradation. However, data on the diffusion of substances (other than Cl−) in concrete are very scarce due to time and resource consuming measurements. This work describes a method to determine the diffusion coefficients of dissolved gases in saturated cement-based materials in order to study the effects of degradation on the transport properties The method is based on a through-diffusion methodology and allows simultaneous determination of diffusivities of two dissolved gases diffusingin opposite directions A cement plug is mounted between two water reservoirs pressurized by two different gases at equal pressure (~1 MPa) to avoid advection. The changes in the dissolved gas concentration (at the opposite sides) are measured indirectly via gaseous phases which are in equilibrium with aqueous phases according to Henry's law. Additionally, a simple 1-D diffusive transport model (based on 1st and 2nd Fick's laws) is developed to interpret the experimental data. The concentrations at outlet and inlet are used as inputs for the model, and the diffusivity is obtained by a fitting procedure.