Modelling the transport of chloride and other ions in cement-based materials

In this work, the transport equations of ionic species in concrete are studied. First, the equations at the porescale are considered, which are then averaged over a representative elementary volume. The so obtained transport equations at the macroscopic scale are thoroughly examined and each term is interpreted. Furthermore, it is shown that the tortuosity-connectivity does not slow the average speed of the ionic species down. The transport equations in the representative elementary volume are then compared with the equations obtained in an equivalent pore. Lastly, comparing Darcy’s law and the Hagen–Poiseuille equation in a cylindrical equivalent pore, the tortuosity-connectivity parameter is obtained for four different concretes. The proposed model provides very good results when compared with the experimentally obtained chloride profiles for two additional concretes.

show abstract

“…Substituting Equation (27) and Equations ( 33)-(36) into Equation ( 25), the transport equations at the macroscopic scale are obtained:…”

Section: The Transport Equations At the Macroscopic Scalementioning

confidence: 99%

“…The second term corrects the mass flux by accounting for the complex geometry of the porous medium as shown below for the diffusion flux. For the sake of simplicity, the fluxes related to migration and chemical activity are neglected [5,27]. 4.6.1.…”

Section: The Surface Integralsmentioning

confidence: 99%

On the Tortuosity-Connectivity of Cement-Based Porous Materials

et al. 2021

Self Cite

View full text Add to dashboard Cite

show abstract

“…In spite of this huge number of papers, some uncertainties remain [21]. Numerous papers are only confirming previous findings, by using other variables as concrete mix proportions, types of binders which cause slight changes in the testing conditions, or making general reviews that are interesting, but do not propose solutions [22][23][24] to the still pending open questions on the long term prediction of the chloride ingress in concrete. Neither has found accurate enough practical engineering solutions that could be applied in the daily design of structural concrete.…”

Section: Introductionmentioning

confidence: 99%

Finite Boundary Conditions Due to the Bar Presence in the Model of Chloride Penetration

Tavares

Andrade

2022

Materials

View full text Add to dashboard Cite

The chloride penetration is usually modelled through the application of a solution of Fick’s second law of diffusion, based on the assumption of semi-infinite boundary conditions. However, the presence of the bars, on whose surface the chlorides accumulate, makes this assumption incorrect. As the time progresses, the chlorides in the steel/concrete interface increase in concentration more than the chlorides overpassing the bar position without obstacles. This circumstance, although previously studied, has not been introduced in common practice, in spite of it supposes early reaching of the chloride threshold. The study in this paper shows a deterministic analysis of the chloride diffusion process by the finite element method (FEM) which numerically solves Fick’s second law, taking into account the accumulation of the chlorides on the bar surface. Several examples are calculated and factors between the finite/semi-infinite solutions are given. These factors depend on the cover depth and the diffusion coefficient, and with less importance, on the diameter of the bar, which make it unfeasible to propose a general trend.

show abstract

“…[ 12 , 19 , 20 , 21 , 22 , 23 ]; however, the components of NaCl diffusion source solution are not similar to those in the actual environment, such as marine engineering and underground engineering environment. With the deepening of research, some researchers [ 24 , 25 , 26 ] have paid attention to the influence of the cationic type on the diffusion behavior of chloride. Kondo [ 27 ] and Ushiyama et al [ 28 ] studied the diffusion behavior of chloride in hardened cement paste under different chloride by diffusion cell and found that the relationship of the chloride diffusion coefficient is D Cl (MgCl 2 ) > D Cl (CaCl 2 ) > D Cl (LiCl) > D Cl (KCl) > D Cl (NaCl).…”

Section: Introductionmentioning

confidence: 99%

Influence of Hydrostatic Pressure and Cationic Type on the Diffusion Behavior of Chloride in Concrete

Liu

Jiang

2021

Materials

View full text Add to dashboard Cite

The durability of the concrete in underground and marine engineering is affected by the underground and ocean environment. Chloride diffusion coefficient under hydrostatic pressure is a key parameter of concrete durability design under corresponding conditions. Therefore, this paper studies the diffusion behavior of chloride in different diffusion source solutions by experiment and simulation. Based on the experimental results, this paper proposes a new chloride diffusion model under the coupling effect of diffusion and convection. The interaction of ions and compounds in the diffusion source solutions, concrete pore fluid, and concrete material are considered in the new chloride diffusion model. The experimental results show that chloride diffusion rate is significantly affected by hydrostatic pressure, which increases with the increase of hydrostatic pressure. The chloride diffusion coefficient shows a certain difference in difference diffusion source solutions. The chloride diffusion coefficient in divalent cationic diffusion source solutions is the largest, the chloride diffusion coefficient in the divalent and monovalent cationic compound ones is in the middle, and the chloride diffusion coefficient in the monovalent cationic ones is the smallest. There is a linear relationship between the chloride diffusion coefficient and the hydrostatic pressure whether in single or combined cationic diffusion source solutions.

show abstract

Modelling the transport of chloride and other ions in cement-based materials

Cited by 32 publications

References 33 publications

On the Tortuosity-Connectivity of Cement-Based Porous Materials

On the Tortuosity-Connectivity of Cement-Based Porous Materials

Finite Boundary Conditions Due to the Bar Presence in the Model of Chloride Penetration

Influence of Hydrostatic Pressure and Cationic Type on the Diffusion Behavior of Chloride in Concrete

Contact Info

Product

Resources

About