Cs retention and diffusion in C-S-H at different Ca/Si ratio

Cement and concrete are commonly used in the construction of repository sites for radioactive wastes. The correct isolation of those contaminants requires good adsorption and low diffusion rates. Both parameters are highly affected by many factors, such as pH, temperature or composition. The large variability of experimental conditions and formulations makes it extraordinarily difficult to tackle the influence of each of them independently in experimental samples. To this effect, molecular dynamics simulations have been employed in this study to investigate the role of the composition in the capacity to retain Cs and diffusivity of these ions in calcium silicate hydrate (C-S-H) gel pores. The results indicate that the adsorption of Cs ions is worsened at high Ca/Si ratios due to a lower interaction of the cations with the C-S-H surface, while hydrophilicity of the C-S-H nanopore rises, resulting in higher long-range ordering and lower diffusion coefficients of Cs ions.

Automated summary

Cement and concrete are commonly used in the construction of repository sites for radioactive wastes, requiring good adsorption and low diffusion rates for proper isolation. Molecular dynamics simulations were used to study the influence of composition on Cs retention capacities and diffusivity in C-S-H gel pores, showing that higher Ca/Si ratios worsen Cs ion adsorption but increase hydrophilicity, leading to higher ordering and lower diffusion coefficients.