Sorption of radionuclides onto C-S-H and C-A-S-H at various degradation stages

Cementitious materials are ubiquitous in the current designs of both surface and geological disposals of radioactive waste. Calcium-silicate-hydrate (C-S-H) and calcium-aluminate-silicate-hydrate (C-A-S-H) are the most important hydration products of cement and also the main sorbing phases with respect to radionuclides. On the time scales of a nuclear waste repository, the cement phases will degrade and their physico-chemical properties will change. Understanding the radionuclide retention mechanisms and linking it to the physico-chemical properties of both C-S-H and C-A-S-H along degradation is therefore essential to assess and predict the role of cementitious materials in retarding the migration of radionuclides. The main objectives of this PhD are to test different synthesis routes for C-A-S-H phases, to identify the sorption mechanisms of relevant radionuclides onto C-S-H/C-A-S-H along the degradation path (e.g. leaching and carbonation) and to develop a conceptual model for radionuclide sorption onto C-S-H and C-A-S-H phases.