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| Hauptseite > Publikationsdatenbank > Pore-scale reactive transport modeling in cementitious materials: Development and application of a high-performance computing code based on the Lattice-Boltzmann method |
| Hauptseite > Publikationsdatenbank > Pore-scale reactive transport modeling in cementitious materials: Development and application of a high-performance computing code based on the Lattice-Boltzmann method |
| Book/Dissertation / PhD Thesis | FZJ-2025-02170 |
2025
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-812-4
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Please use a persistent id in citations: urn:nbn:de:0001-2511170823113.117943807682 doi:10.34734/FZJ-2025-02170
Abstract: The presence of cementitious materials in the modern world is ubiquitous, since concrete is one of the most important construction materials in civil engineering. Cementitious materials are also commonly used in nuclear waste management, e.g. for solidification of radioactive wastes, or as construction and backfill material in deep geological repositories for radioactive wastes. In this context, cementitious materials provide barrier functions to reduce the migration of radionuclides in the repository near field. However, despite the vast application of cementitious materials in this context, the long-term evolution of several material properties is not yet fully understood, in particular the changes in fluid and solute transport properties induced by long-term alteration due to interaction of cementitious materials with groundwaters, taking into account the time scales relevant for nuclear waste disposal. Since alterations of the microstructure have significant effect on macroscopic transport properties of the materials, this work focuses on the improvement of the quantitative description of the alteration of cementitious materials at the pore-scale. Pore-scale reactive transport models are appealing techniques to analyze the alteration of phase assemblage, microstructure, and transport properties in cementitious materials, to get deeper insights into their long-term macroscopic evolution. In this work, a Lattice-Boltzmann based approach was used to simulate degradation and alteration of cementitious materials due to interaction with groundwater. A modular reactive transport toolbox deployable in high-performance computing (HPC) environments was developed by coupling a Lattice-Boltzmann transport code (Palabos) to a geochemical solver (PhreeqC), which can account for fluid-mineral interactions controlled by thermodynamics and reaction kinetics, in the sequential non-iterative approach (SNIA) fashion. After extensive optimization and validation, the code named iPP (interface-Palabos-PhreeqC) was applied to simulate in particular the alteration/leaching of a bespoke low-pH cementitious material destined for application in a nuclear waste repository, amongst other test cases. Input data for the simulations such as the microstructures of the non-degraded materials were derived from synthetically generated microstructures and by developing a segmentation algorithm, subsequently applied to μ-XCT image data of hardened cement pastes. In the application case, a granite groundwater was used as leaching solution, leading to decalcification of calcium-silicate-hydrates (CSH) in the simulations in agreement with results from experiments and observations from underground research laboratories. Due to saturation of the granitic water with respect to calcite, the simulation results revealed calcite precipitation on the surface of the cementitious material, which resulted in a partial clogging of the system. For an improved description of the precipitation of solids, different model assumptions were implemented in the reactive transport code (e.g. assuming local equilibrium or taking into account classical nucleation theory and/or porosity-controlled solubility effects) and tested. The results of the leaching simulations were analyzed, for example, with respect to the resulting phase assemblages, porosity profiles and mass balances. Furthermore, the effect of the alteration processes on the effective diffusivity of the degraded cementitious material was analyzed. Pore-scale reactive transport models such as iPP provide the means to enhance the understanding of the impact of long-term alteration processes (e.g. leaching by groundwater, carbonation, reactions at clay/cement interfaces, etc.) on the transport properties of cementitious barrier materials in nuclear waste repositories (e.g. with respect to solute transport/radionuclide migration, or gas transport, etc.) and can thus be employed as process models in support of the safety case. Moreover, an enhanced understanding of the evolution of transport properties on the pore-scale might facilitate the selection of optimized cementitious materials for specific purposes in repository design.
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