Diffusion and adsorption studies on hardened cement paste and the effect of carbonation on diffusion rates

The diffusion and sorption behaviour in disc shaped samples of hardened cement paste (HCP) has been studied for the radionuclides Cl-36, I-125 and Cs-134 using the through-diffusion technique. The experiments were performed both in controlled atmosphere glove boxes ( P CO 2 ≈ 10 −5.5 bar ) and under atmospheric conditions for periods of up to several months. The samples had a high water to cement ratio (W/C) of 1.3 and a hydraulic conductivity of ≈2.10 −10 m s −1. All tests carried out under atmospheric conditions showed a considerable decrease in diffusion rates with time due to carbonation, whereas no such effect was observed in the experiments performed in the controlled atmosphere glove boxes. Effective diffusion coefficients, D e, and sorption values were calculated for each radionuclide. It was possible to model the diffusion-sorption results by linear isotherms.