Cs Retention and Diffusion in C-S-H at Different Ca/Si Ratios

26 June 2018, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Cement and concrete have been widely used as a barrier to isolate many types of contaminants, including radioactive waste, in repository sites. Nevertheless, the intrusion of groundwater in those nuclear repositories may release those contaminants by leaching mechanisms. Because of this, the retention and diffusion processes in cement matrix require to be analyzed in depth. The adsorption in cement and C‐S-H gel, its main hydration product, is influenced by factors as the pH, the composition or the alkali and alkaline earth content. In this work, molecular dynamics simulations were employed to study the role of Ca/Si ratio of the C‐S‐H in the capacity to retain Cs and diffusivity of these ions in gel pores. For that purpose, we built four different C‐S‐H models with Ca/Si ratios from 1.1 to 2.0. The results indicate better cationic retention at low Ca/Si ratios due to the interaction of the cations with the bridging silicate tetrahedrons. However, the average diffusion coefficients of the cations decrease at higher Ca/Si ratios because the high ionic constraint in the nanopore that induces a longrange ordering of the water molecules.


C-S-H gel
Molecular Dynamics


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