Effective and Apparent Diffusion Coefficients of Chloride Ions and Chloride Binding Kinetics Parameters in Mortars: Non-Stationary Diffusion–Reaction Model and the Inverse Problem

A non-equilibrium diffusion–reaction model is proposed to describe chloride transport and binding in cementitious materials. A numerical solution for this non-linear transport with reaction problem is obtained using the finite element method. The effective chloride diffusion coefficients and parameters of the chloride binding are determined using the inverse method based on a diffusion–reaction model and experimentally measured chloride concentrations. The investigations are performed for two significantly different cements: ordinary Portland and blast furnace cements. The results are compared with the classical diffusion model and appropriate apparent diffusion coefficients. The role of chloride binding, with respect to the different binding isotherms applied, in the overall transport of chlorides is discussed, along with the applicability of the two models. The proposed work allows the determination of important parameters that influence the longevity of concrete structures. The developed methodology can be extended to include more ions, electrostatic interactions, and activity coefficients for even more accurate estimation of the longevity.

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Effect of Carbonation and Sulphate on Chloride Ingress in Cement Pastes and Concretes with Supplementary Cementitious Materials

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.711.241 ◽

2016 ◽

Vol 711 ◽

pp. 241-248 ◽

Cited By ~ 1

Author(s):

Mickael Saillio ◽

Véronique Baroghel-Bouny ◽

Sylvain Pradelle

Keyword(s):

Diffusion Coefficients ◽

Cementitious Materials ◽

Chloride Ions ◽

Supplementary Cementitious Materials ◽

Chloride Diffusion ◽

Chloride Ingress ◽

Chloride Binding ◽

Cement Pastes ◽

Binding Isotherms ◽

In Situ Conditions

The main cause of premature deterioration of reinforced concrete structures is the corrosion of steel bars, induced by chloride ions (for example in marine environment) and/or by carbonation (atmospheric CO2). At the same time, environmental-induced degradations of concrete can also affect the structure, such as sulphate attack. This can lead to the formation of ettringite, inducing expansion inside the materials and finally degradation. Carbonation, chloride and sulphate ingress are usually studied separately in the literature. This is not representative of in-situ conditions since they can occur at the same time and can have an influence on each other. In this paper, chloride ingress are studied for concretes and cement pastes partially carbonated or/and in presence of sulphate in chloride contact solution. The mixtures contain OPC alone or with supplementary cementitious materials (SCM). SCMs are here pozzolanic materials (Fly Ash or Metakaolin) or alkali-activated materials such as ground granulated blast furnace slag (GGBS). The materials, partially carbonated (2 months in chamber at 1.5 % of CO2) or not, are put in contact with chloride solutions in presence of sulphate. This study focuses on the apparent chloride diffusion coefficients, as well as chloride binding isotherms which are obtained by the profile method. In addition, some aspects of the microstructure and of the pore structure are investigated, by using Mercury Intrusion Porosimetry and 27Al NMR, in order to better understand the results obtained relatively to the apparent chloride diffusion coefficients and to the chloride binding. Chloride ingress increases when sulphates are present in the contact solution for all cement materials tested (partially carbonated or not). In addition, chloride ingress is faster when the material is partially carbonated before contact with chloride solution. It appears that both carbonation or presence of sulphate decrease chloride binding, thus explaining the results. The results show an evolution of the properties as a function of the cement replacement ratio by SCMs.

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Effect of W/B to the Time Dependent Chloride Diffusion in Concrete with GGBS

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.174-177.144 ◽

2012 ◽

Vol 174-177 ◽

pp. 144-147

Author(s):

Lu Guang Song ◽

Wei Sun ◽

Jian Ming Gao

Keyword(s):

Diffusion Coefficients ◽

Chloride Concentration ◽

Time Dependent ◽

Chloride Diffusion ◽

Concentration Increase ◽

Apparent Diffusion Coefficients ◽

Apparent Diffusion ◽

Influence Of Water ◽

Binder Ratio ◽

Water To Binder Ratio

This paper studied the influence of water to binder ratio to time dependent diffusion coefficients in concrete exposed to marine environments. And a refined diffusion model which considered the time dependent apparent diffusion coefficients and time dependent surface chloride concentration was established. It was found that both apparent diffusion coefficients and surface chloride concentration are time dependent and both are significantly influenced by water to binder ratio. Apparent diffusion decrease with time while surface chloride concentration increase with time. but water to binder ratio has similar influence to the constant of time dependent diffusion coefficients and the parameter of time dependent surface chloride concentration.

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Influence on GGBS to Time Dependent Chloride Diffusion Coefficient of HPC

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.5703 ◽

2011 ◽

Vol 243-249 ◽

pp. 5703-5710 ◽

Cited By ~ 1

Author(s):

Lu Guang Song ◽

Wei Sun ◽

Jian Ming Gao ◽

Yun Sheng Zhang

Keyword(s):

Diffusion Coefficient ◽

Diffusion Coefficients ◽

Great Influence ◽

Chloride Diffusion ◽

Chloride Diffusion Coefficient ◽

Time Dependency ◽

Apparent Diffusion Coefficients ◽

Granulated Blast Furnace Slag ◽

Apparent Diffusion ◽

Furnace Slag

This paper investigates the influences of dosage of ground granulated blast furnace slag (GGBS) (0%, 20%, 40%, 60% and 80%) to chloride diffusion coefficient. And the time dependency of apparent diffusion coefficient as the submerging time from 60 days to 360days has also been studied. The result shows that the addition of GGBS into concrete has great influence on the chloride diffusion. The diffusion coefficients of the mixes containing GGBS decrease rapidly with time than that of the mix PC Control. But there were little differences of the values of apparent diffusion coefficients among the mixes SL20, SL40 and SL60. The addition of GGBS in concrete has great influence on the time dependency of concrete. And the concrete which has 40%-60% replacement of GGBS has greater ability to resist the diffusion of chloride than other replacement.

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