Evolution of microstructure and transport properties of cement pastes due to carbonation under a CO2 pressure gradient: a modeling approach

Most carbonation models only account for diffusion as the main transport mechanism rather than advection. Nevertheless, in the case of concrete used for underground waste disposal facilities, concrete may be subjected to a high hydrostatic pressure and the surrounding environment may contain a high dissolved CO2 concentration. Therefore, a combination of diffusion and advection should be taken into account. This is also the case in accelerated carbonation where a high CO2 pressure gradient is applied in which advection in the gas phase has a significant contribution to the carbonation process. This study aims at developing a model to predict the evolution of the microstructure and transport properties of cement pastes due to carbonation under accelerated conditions in which a pressure gradient of pure CO2 is applied. The proposed model is based on a macroscopic mass balance for carbon dioxide in gaseous and aqueous phases. Besides the prediction of the changes in transport properties (diffusivity, permeability), the model also enables to predict the changes in microstructure. Data from accelerated tests were used to validate the model. Preliminary verification with experimental results shows a good agreement

Multiscale carbonation reactions: Status of things and two modeling exercises related to cultural heritage

Having in mind as target audience beginner researchers working in the field of cultural heritage, we present succinctly the concept of two-scale modeling of reaction-diffusion problems as it fits to scenarios where the action of the carbonation reaction is relevant. We briefly review well-known contributions concerning multiscale concrete carbonation processes, and finally, we point out two related multiscale modeling exercises. The scope of these notes is twofold: Promoting the language of multiscale modeling, we invite the applied mathematician to pick some of the target problems from the context of cultural heritage. On the other hand, we invite the experimentalist to talk to the applied mathematician whenever the laboratory experiments are unable to answer questions for instance about the long time behavior of materials exposed to the ingress of various chemical species, humidity, and/or temperature (as it is the case of historical monuments and buildings in urban areas) because modeling and simulation approaches might provide at least provisory hints on what could happen further once measurements stop, or when the situation of interest takes place actually outside the laboratory.Comment: 12 pages, 1 figur

A Two-Dimensional Mathematical Model of Carbon Dioxide (CO2) Transport in Concrete Carbonation Proses

A new two-dimensional mathematical model was developed to describe the transport phenomena of carbon dioxide in concrete structures. By treating transport phenomena as a concrete carbonation process, a two-dimensional linear partial differential equation was derived based on the principle of mass balance and convective-dispersive Equation. It was found the analytical solution by the separation of variables method combined with some substitution approaches. The numerical results are presented to illustrate the practical application of this model

Numerical modeling of compositional two-phase reactive transport in porous media with phase change phenomena including an application in nuclear waste disposal

Non-isothermal compositional two-phase flow is considered to be one of the fundamental physical processes in the field of water resources research. The strong non-linearity and discontinuity emerging from phase transition phenomena pose a serious challenge for numerical modeling. Recently, Lauser et al.[1] has proposed a numerical scheme, namely the Nonlinear Complementary Problem (NCP), to handle this strong non-linearity. In this work, the NCP is implemented at both local and global levels of a Finite element algorithm. In the former case, the NCP is integrated into the local thermodynamic equilibrium calculation. While in the latter one, it is formulated as one of the governing equations. The two different formulations have been investigated through several well established benchmarks and analyzed for their efficiency and robustness. In the second part of the thesis, the presented numerical formulations are applied for application and process studies in the context of nuclear waste disposal in Switzerland. Application studies comprehend the coupling between multiphase transport model and complex bio-geo-chemical process to investigate the degradation of concrete material due to two major reactions: carbonation and Aggregate Silica Reaction(ASR). The chemical processes are simplified into a lookup table and cast into the transport model via source and sink term. The efficiency and robustness of the look-up table are further compared with a fully reactive transport model

Effect of supercritical carbonation on the strength and heavy metal retention of cement-solidified fly ash

This paper presents both experimental and multi-physics studies on the carbonation and heavy metal retention properties of cement-solidified fly ashes. Cement-solidified fly ash samples with 40% and 60% fly ash ratios were tested for carbonation depth after being supercritically carbonated. Tests were also carried out for compressive strength and retention capacity of heavy metals of the samples before and after supercritical carbonation. Using CO2 absorption instead of calcium carbonate to measure carbonation degree, a multi-physics model was developed and combined with a leaching model to study the impact of carbonation on Cu and Pb leaching from the cement-solidified fly ash. The results show that supercritical carbonation has both positive and negative impacts on the strength and retention capability of heavy metals of the cement-solidified fly ashes, which suggests that both the carbonation conditions and the amount of fly ash recycled in cementitious materials should be properly controlled to maximize potential positive effect

On the numerical modeling of carbonation phenomenon via multi-reactional kinetics and 3D-randomly distributed spherical grains

In the present contribution, the mathematical modeling and numerical solution of the carbonation phenomenon have been investigated for the porous cement mortars. To achieve this goal, the Papadakis analytical proposal has been fully investigated. The molar concentration variations of the hydrate (CSH and Ca(OH)2 ) and unhydrated products (C2S and C3S) have been analyzed during the carbonation. The numerical simulations have been firstly achieved on the 3D numerical mortar samples including the aggregates using the relevant granulometry, whose applications sustain more realistic outcomes. The solution has been done using the FEM for the non-linear transient system of PDEs. The numerical results have been compared to those done from the experiments using the pH detector and Differential Thermal Analysis (DTA). Some conclusions and outlooks pertaining to the carbonation modeling have been emphasized