Cementitious materials act as a diffusion barrier, immobilizing liquid and solidradioactive waste and preventing their release into the biosphere. The retention capability of hydratedcement paste and its main hydration product, C-S-H gel, has been extensively explored experimentallyfor many alkali and alkaline earth cations. Nevertheless, the retention mechanisms of these cations atthe molecular scale are still unclear. In this paper, we have employed molecular dynamics simulationsto study the capacity of C-S-H to retain Cs, Ca and Na, analyzing the number of high-affinity sites onthe surface, the type of sorption for each cation and the diffusivity of these ions. We have also exploredthe impact of aluminum incorporation in C-S-H at a constant concentration of the ions in the gel pore.We found strong competition for surface sorption sites, with notable differences in the retention of thecations under study and a remarkable enhance of the adsorption in C-A-S-H with respect to C-S-H.
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Duque-Redondo et al. (2018) studied this question.