Modelling ion diffusion mechanisms in porous media

The main objective of this investigation is to describe the interaction between cement hydrates and electrolyte solution to understand multi-ionic transport in cementitious materials. A surface complexation model in PHREEQC including an electrostatic term is used to simulate the ionic adsorption on the calcium silicate hydrate (C-S-H) surface. The equilibrium constants for the adsorption of ions on C-S-H surfaces are obtained by fitting experimental data to the model. The adsorption of both divalent and mono-valent cations, and also anions significantly changes the surface charges of hydrated paste. Chloride is being held in a chemical binding as Friedel's salt and bound mainly by the adsorptive action of C-S-H. An integrated modelling approach employing a phaseequilibrium model, a surface complexation model, and a multi-component diffusion model has been developed in PHREEQC to simulate the multi-ionic transport through hydrated cement paste. It was found that the physical adsorption of ions on C-S-H, the size of pores, and the surface site density of C-S-H govern the rate of penetration of ionic species. Finally, the proposed model has been validated against chloride profiles measured in this study as well as with data available in the literature for hydrated cement paste.

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“…There are a number of models for simulation of the ionic transport into cementitious materials [4][5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

“…Over the years, Nernst-Planck/Poisson equations have been successfully applied to evaluate the electrical coupling between ions in dilute solution as well as in concentrated solutions where the chemical activity effects are significant [4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Ion-cement hydrate interactions govern multi-ionic transport model for cementitious materials

Elakneswaran

Iwasa

Nawa

et al. 2010

Cement and Concrete Research

107

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“…where, C is the chloride concentration at time t, and r t is the adsorption rate at time t. Most advanced modelsdsuch as the electrochemical chloride removal (ECR) [44] and NernstePlanck/ Poisson model [33]dinclude electro-neutrality in the presence of ionic charges, however here it is reasonable to use the Fickian diffusion model to simulate the chloride transport in cement paste influenced by CLDH. Ionic interactions have a minor effect on the chloride diffusion process without externally applied voltage, with the adsorption process being a dominant condition in the ionic transport.…”

Section: Chloride Transport Model In Cement Paste With the Inclusion mentioning

confidence: 99%

Chloride adsorption by calcined layered double hydroxides in hardened Portland cement paste

Yoon

Moon

Bae

et al. 2014

Materials Chemistry and Physics

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h i g h l i g h t sWe examine the adsorption equilibrium and kinetics of CLDH in the hydrated cement. CLDH capacity to bind chloride ions in the hydrated cement paste is determined. We model chloride adsorption by CLDH through the cement matrix. CLDH reforms the layered structure with ion adsorption in the cement matrix. s t r a c tThis study investigated the feasibility of using calcined layered double hydroxides (CLDHs) to prevent chloride-induced deterioration in reinforced concrete. CLDHs not only adsorbed chloride ions in aqueous solution with a memory effect but also had a much higher binding capacity than the original layered double hydroxides (LDHs) in the cement matrix. We investigated this adsorption in hardened cement paste in batch cultures to determine adsorption isotherms. The measured and theoretical binding capacities (153 mg g À1 and 257 mg g À1 , respectively) of the CLDHs were comparable to the theoretical capacity of Friedel's salt (2 mol mol À1 or 121 mg g À1 ), which belongs to the LDH family among cementitious phases. We simulated chloride adsorption by CLDHs through the cement matrix using the Fickian model and compared the simulation result to the X-ray fluorescence (XRF) chlorine map. Based on our results, it is proposed that the adsorption process is governed by the chloride transport through the cement matrix; this process differs from that in an aqueous solution. X-ray diffraction (XRD) analysis showed that the CLDH rebuilds the layered structure in a cementitious environment, thereby demonstrating the feasibility of applying CLDHs to the cement and concrete industries.Crown

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“…Implementations of models in higher spatial dimensions for the time-dependent NPP problems are scarce. Samson et al [27] published an interesting work on modeling electrodiffusion mechanisms in porous media in 1D and 2D geometries. Finite-difference methods used for initial value problems involving the NPP equations cover a wide spectrum of algorithms between entirely explicit and entirely implicit techniques.…”

Section: Numerical Solutions Of the Full Set Of The Time-dependent Nementioning

confidence: 99%

Numerical simulations of the full set of the time-dependent Nernst-Planck and Poisson equations modeling electrodiffusion on a simple ion channel.

Valent¹

2012

JCIS

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The concept of electrodiffusion based on the Nernst-Planck equations for ionic fluxes coupled with the Poisson equation expressing relation between gradient of the electric field and the charge density is widely used in many areas of natural sciences and engineering. In contrast to the steady-state solutions of the Nernst-Planck-Poisson (abbreviated as NPP or PNP) equations, little is known about the time-dependent behavior of electrodiffusion systems. We present numerical solutions of an NPP system modeling dynamics in the interior of a membrane channel containing an electrolyte after a potential jump at one side of the membrane (voltage-clamp). The NPP equations were solved using the VLUGR2 solver based on an adaptive-grid finite-difference method with an implicit timestepping. The used approach allows for solving the full set of the NPP equations without approximations such as the electroneutrality or constant-field assumptions. Calculations reveal interesting nonlinear time evolution of the ionic concentrations and potential.

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Modelling ion diffusion mechanisms in porous media

Cited by 39 publications

References 0 publications

Ion-cement hydrate interactions govern multi-ionic transport model for cementitious materials

Ion-cement hydrate interactions govern multi-ionic transport model for cementitious materials

Chloride adsorption by calcined layered double hydroxides in hardened Portland cement paste

Numerical simulations of the full set of the time-dependent Nernst-Planck and Poisson equations modeling electrodiffusion on a simple ion channel.

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