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@PHDTHESIS{Rohmen:1041222,
      author       = {Rohmen, Stephan},
      title        = {{P}ore-scale reactive transport modeling in cementitious
                      materials: {D}evelopment and application of a
                      high-performance computing code based on the
                      {L}attice-{B}oltzmann method},
      volume       = {659},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2025-02170},
      isbn         = {978-3-95806-812-4},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {X, 295},
      year         = {2025},
      note         = {Dissertation, RWTH Aachen University, 2024},
      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.},
      cin          = {IEK-6},
      cid          = {I:(DE-Juel1)IEK-6-20101013},
      pnm          = {1411 - Nuclear Waste Disposal (POF4-141) / Cebama -
                      Cement-based materials, properties, evolution, barrier
                      functions (662147)},
      pid          = {G:(DE-HGF)POF4-1411 / G:(EU-Grant)662147},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2511170823113.117943807682},
      doi          = {10.34734/FZJ-2025-02170},
      url          = {https://juser.fz-juelich.de/record/1041222},
}