Chloride Diffusion In Concrete Research Articles

Propiedades de durabilidad en concreto y análisis microestructural en pastas de cemento con adición de mucílago de nopal como aditivo natural

The present study evaluated the addition of a 3% nopal cactus mucilage solution to cement pastes, in its effects on setting times, flow, hydration, and microstructure, as well as on capillary water absorption and chloride diffusion in concrete. Hydration was characterized through XRD and microstructure was characterized with SEM. The mucilage solution/cement and water/cement ratios tested were 0.30, 0.45, and 0.60. The results in cement pastes indicate that the addition of mucilage increases setting times, reduces flow, slows cement hydration, and inhibits the formation of calcium hydroxide crystals in comparison with the control. Capillary absorption was significantly reduced in concrete containing mucilage, and chloride diffusion coefficients dropped up to 20% in the mixture with a mucilage/cement ratio = 0.30. The mixture with a mucilage/cement ratio = 0.45 displayed marginal reduction, and the mixture with mucilage/cement ratio = 0.60 exhibited a diffusion coefficient that was greater than the control for the specimens without moist curing.

Analysis of chloride diffusivity in concrete containing red mud

Red mud is a solid waste produced in the alumina production process and, due to its high pH, is classified as hazardous. Its incorporation in concrete mixtures, acting as due to the particles fineness, might be an interesting reuse alternative. The focus of this paper is to study the chloride diffusivity of concrete mixtures containing red-mud. The concentration of chlorides was monitored by measuring the conductivity of the anolyte, which was distilled water initially. In addition, the estimation of the chloride ions diffusion coefficients in steady and non-steady conditions, Ds and Dns, was obtained from the ''time-lag'' and ''equivalent time'' between diffusion and migration experiments. Due to superfine particle-size distribution and the filler effect, the red mud addition seems to assure lower chloride diffusivity.

A numerical method for the chloride diffusivity in concrete with aggregate shape effect

Owing to its importance in the durability assessment and design of reinforced concrete structures exposed to chloride-ladden environments, it is essential to determine the chloride diffusivity in concrete. This paper presents a numerical method for predicting the chloride diffusivity in concrete with aggregate shape effect. To reduce the number of elements, an equivalent aggregate model is constituted by modeling the aggregate as inclusion and the interfacial transition zone (ITZ) as matrix and the chloride diffusivity in equivalent aggregate is derived analytically. Based on the simulated mesostructure of concrete, the lattice model is applied to the analysis of chloride diffusion in concrete. In this analysis, the physical properties of each phase constituent are taken into account in the formation of element matrix of bar elements. After the validity of the developed numerical method is verified with two independent sets of experimental results, the effect of aggregate shape on the chloride diffusivity in concrete is evaluated in a quantitative manner. It is found that, when the aspect ratio of elliptical aggregate particles increases from 1 to 3, the chloride diffusivity in concrete decreases by 6.48%, 8.94%, and 10.67% for a given chloride diffusivity ratio of ITZ to cement paste at 2, 6, and 10, respectively. The paper concludes that the numerical method developed in the paper can predict the chloride diffusivity in concrete with an average relative error smaller than 7% for the two selected verification examples.

Effect of Aggregate Shape on the Chloride Diffusivity of Concrete

The effect of aggregate shape on the chloride diffusivity of concrete is studied. To represent the heterogeneity of concrete, a three-phase composite ellipse model is constructed and the relative dimensions are determined by calculating the area fraction of interfacial transition zone in a numerical manner. The height of each bar in the lattice mesh is derived analytically. The lattice method is then used to estimate the chloride diffusivity of concrete. After the validity of the numerical method is verified with experimental results, the effect of aggregate shape on the chloride diffusivity of concrete is evaluated in a quantitative manner.

Effect of Aggregate Shape on the Chloride Diffusivity of Concrete

The effect of aggregate shape on the chloride diffusivity of concrete is studied. To represent the heterogeneity of concrete, a three-phase composite ellipse model is constructed and the relative dimensions are determined by calculating the area fraction of interfacial transition zone in a numerical manner. The height of each bar in the lattice mesh is derived analytically. The lattice method is then used to estimate the chloride diffusivity of concrete. After the validity of the numerical method is verified with experimental results, the effect of aggregate shape on the chloride diffusivity of concrete is evaluated in a quantitative manner.

Perturbation Stochastic Finite Element Method for Chloride Diffusion with Time-Dependent in Concrete

The random analysis of the process of chloride diffusion in concrete is a basis of the reliability assessment for durability of concrete structures. In this paper, the diffusion coefficient with time-dependent is introduced to Fick's second law, and perturbation stochastic finite element method (SFEM) with time-dependent(TD) is proposed. The stochastic finite element equation with TD is solved by the perturbation method with a group of recursive equations, by which the mean value and standard deviation of chloride concentration in concrete can be determined. An example is given to demonstrate the accuracy and efficiency of the presented method and shows that the analysis of chloride diffusion with time-dependent for concrete structures is closer to engineering practice.

Perturbation Stochastic Finite Element Method for Chloride Diffusion with Time-Dependent in Concrete

The random analysis of the process of chloride diffusion in concrete is a basis of the reliability assessment for durability of concrete structures. In this paper, the diffusion coefficient with time-dependent is introduced to Fick's second law, and perturbation stochastic finite element method (SFEM) with time-dependent(TD) is proposed. The stochastic finite element equation with TD is solved by the perturbation method with a group of recursive equations, by which the mean value and standard deviation of chloride concentration in concrete can be determined. An example is given to demonstrate the accuracy and efficiency of the presented method and shows that the analysis of chloride diffusion with time-dependent for concrete structures is closer to engineering practice.

Difference Solution to Chloride Diffusion in Concrete

Fick’s second law and its analytical solution were usually used for analysis of chloride diffusion in concrete. But discretization of the continuous variables is more appropriate in modeling and discrete model is more suitable for engineering applications. In this paper, Difference Equation equivalent to partial differential equation was established with the difference method, and three-dimensional differential equation of Fick's second law was resolved. Based on this study，the convergence conditions of difference Equations for one-dimensional, 2D and 3D diffusion was given.

Evaluation of Fiber and Blast Furnace Slag Concrete Chloride Penetration through Computer Simulation

Durability of concrete is an important issue, and one of the most critical aspects affecting durability is chloride diffusivity. Factors such as water.cement ratio, degree of hydration, volume of the aggregates and their particle size distribution have a significant effect on chloride diffusivity in concrete. The use of polypropylene fibers(particularly very fine and well dispersed micro fibers) or mineral additives has been shown to cause a reduction in concrete's permeability. The main objective of this study is to evaluate the manner in which the inclusion of fiber(in terms of volume and size) and blast furnace slag(BFS) (in terms of volume replacement of cement) influence the chloride diffusivity in concrete by applying 3D computer modeling for the composite structure and performing a simulation of the chloride penetration. The modeled parameters, i.e. chloride diffusivity in concrete, are compared to the experimental data obtained in a parallel chloride migration test experiment with the same concrete mixtures. A good agreement of the same order is found between multi.scale microstructure model, and through this chloride diffusivity in concrete was predicted with results similar to those experimentally measured.

A multi-phase model for predicting the effective diffusion coefficient of chlorides in concrete

In this paper, a mesoscopic structure model is proposed and is used to investigate the chloride diffusion behaviour in concrete. The concrete is treated as a heterogeneous material composed of cement paste and aggregate two phases. The chloride diffusion is assumed to take place only in the cement paste phase. By modelling concretes with different aggregate volume fractions the effect of aggregate content on chloride diffusion in concrete is examined. The results show that the effective diffusion coefficients obtained from the two- and three-dimensional models are different. The two-dimensional series and parallel models provide upper and lower bounds of the effective diffusion coefficient, respectively, whereas the three-dimensional model provides the accurate effective diffusion coefficient. The three-dimensional simulation also demonstrates that the Maxwell model is able to predict accurate effective diffusion coefficient of chlorides in concrete.

ITZ volume fraction in concrete with spheroidal aggregate particles and application: Part II. Prediction of the chloride diffusivity of concrete

Owing to its importance in the durability assessment of reinforced concrete structures located in a marine or de-icing salt environment, it is essential to determine the chloride diffusivity of concrete. The intention of the present paper is to present an analytical solution for the chloride diffusivity of concrete with aggregate shape effect. A three-phase composite spheroid model for the concrete matrix is proposed to represent the heterogeneous nature of concrete and to take into account the aggregate shape effect. By reducing the three-phase composite spheroid to two two-phase composite spheroids, an analytical solution for the chloride diffusivity of concrete is derived. After the validity of the derived analytical solution is verified with two sets of experimental results, the effects of main factors that affect the chloride diffusivity of concrete are evaluated in a quantitative manner. It is found that the chloride diffusivity of concrete increases with the increase of the thickness and chloride diffusivity of the interfacial transition zone (ITZ), but decreases with the increase of the aspect ratio of spheroidal particles and the maximum aggregate diameter. It is also found that the aggregate gradation has a significant influence on the chloride diffusivity of concrete. The paper concludes that the analytical solution derived here can predict the chloride diffusivity of concrete with reasonable accuracy.

Multi-scale prediction of the effective chloride diffusion coefficient of concrete

The N-layered spherical inclusion theory is applied to develop a multi-scale model to predict the effective diffusion coefficient of chloride ion in concrete. The model treats concrete as four-phase composite materials consisting of matrix phase, aggregate phase, ITZ (interfacial transition zone) and their homogenization phase. With hardened cement pastes characterized by three parameters such as the porosity, tortuosity and constrictivity, the effect of the cement paste microstructures and ITZ on the chloride diffusivity in concrete is taken into account and the porosity distribution function and effective chloride diffusion coefficients of the ITZ are given in the model based on the cement particle distribution characteristics of the ITZ in concrete. To validate the proposed model, the diffusion coefficient of chloride ion by the steady-state migration test is measured on a series of mortar and concrete specimens and good agreement between the model and experiment is obtained. In addition, the model predicts that the chloride diffusivity of concrete composite materials depends on the chloride diffusion coefficient of the matrix and ITZ, volume fraction of the aggregate and ITZ, with the volume fraction of the ITZ influenced by aggregate size distribution, the volume fraction of aggregate and thickness of the ITZ.

Diffusion of Multi-Ionic Species in Recycled Aggregate Concrete

In recent years, recycled aggregate concrete has been used in reinforced concrete structures. Concrete structures exposed to chloride environment often encountera premature deterioration due to corrosion of steel reinforcement. In order to avoid unplanned maintenances or repairs, it is necessary to develop a reliable prediction model for the chloride diffusion in concrete. The basic formulation of the transport theory will be presented first and then its application to Recycled Aggregate Concrete (RAC) will follow. Chloride diffusion in RAC is different from the diffusion in regular concrete, because the material parameters of RAC such as chloride diffusion coefficient are different from those of regular concrete. In this paper, a multi-scale and multi-phase model will be developed to characterize theinternal structure of the recycled aggregate with a layer of residual cement paste on the surface of natural aggregate and another layer of surface treatment material on the surface of the residual cement paste. The multi-scale and multi-phase model will also be used to characterize the chloride diffusion coefficient of RAC. The numerical analysis of the diffusion equations is performed by using finite element method.

Corrosion of Epoxy-Coated Rebar in Marine Bridges—Part 2: Corrosion in Cracked Concrete

Abstract The extent of corrosion of epoxy-coated rebar (ECR) in marine bridges was found to be generally correlated with concrete chloride diffusivity, DApp, with significant corrosion observed for bridges with DApp values reaching up to ∼10−7 cm2/s but not for sound concrete locations in bridges with DApp approaching the order of 10−9 cm2/s. However, significant ECR corrosion was observed in several preexisting cracked concrete locations of a low DApp bridge after only ∼15 years of service. Well-manifested, enhanced chloride and moisture penetration took place through the preexisting cracks of this bridge. The corrosion products in that case were solid and grew underneath the epoxy coating and had a composition consistent with that of chloride-substituted Akaganeite (β-FeO[OH]). Laboratory experiments showed that oxygen presence was not necessary for the formation of similar corrosion products, suggesting that corrosion damage could develop even with thin, moisture-filled cracks that would restrict oxyge...

Determination of the concrete chloride diffusion coefficient based on an electrochemical test and an optimization model

The chloride diffusion coefficient is an indication of the capacity of any type of concrete to resist chloride penetration and is used to predict the service life of reinforced concrete structures. Its determination has been subject of intense study in the last 50 years and today there is no complete agreement in the methodologies used. In addition, its experimental determination is time and recourse consuming. As alternative, this article presents a new methodology to find the fundamental properties of concrete including the diffusion coefficients. From the measurement of the electrical properties of concrete during a migration test and using and integrated physical–neural network model the chloride related properties can be found. Results of experiments of normal diffusion were compared with the results of the new methodology and gave encouraging results.

Assessing the influence of ITZ on the steady-state chloride diffusivity of concrete using a numerical model

In this study, the influence of the aggregate-cement paste interfacial transition zone (ITZ) on the steady-state chloride diffusivity of mortars and concretes was examined using a semi-empirical, three-phase composite sphere model. Mortars and concretes were modelled as three-phase composites consisting of the aggregate, bulk cement paste and an inhomogeneous ITZ. The latter was divided into a series of homogenous concentric shell elements of equal thickness. The initial porosity and cement gradients at the ITZ were first estimated from the overall water/cement ratio ( w 0/ c). The evolution of the porosity, solid hydration products and remnants of unreacted cement were then calculated from the hydration degree and local water/cement ratio ( w/ c) using Powers' empirical model. Based on the Laplacian equation, an element transfer matrix was derived analytically to predict the steady-state chloride diffusivity. The model was calibrated using the available experimental data and then applied to perform a sensitivity analysis to evaluate the effects of aggregate content, water/cement ratio, curing period, ITZ width, maximum aggregate size and aggregate gradation on diffusivity. Some of these variables are impractical to quantify by laboratory experimentation. Implications of the findings with regard to the role of ITZ on mass transport properties are discussed.

Simple approach to calculate chloride diffusivity of concrete considering carbonation

Chloride diffusivity of concrete is a crucial material parameter for service life determination and durability designing of marine concrete. Many research works on this issue have been conducted, varying from empirical solutions obtained experimentally to image analysis, based on multi-scale modeling. One of the simple approaches is to express the chloride diffusivity of concrete by a multi-factor function, however, the influences of various factors on the chloride diffusivity are ambiguous. Furthermore, the majority of these research works have not dealt with the carbonation process of concrete, although this process affects the chloride diffusivity of concrete significantly. The purpose of this study is to establish a simple approach to calculate the chloride diffusivity of (non)carbonated concrete. The chloride diffusivity of concrete should be defined, based on engineering and scientific knowledge of cement and concrete materials. In this paper, a lot of parameters affecting the chloride diffusivity, such as the diffusivity in pore solution, tortuosity, micro-structural properties of hardened cement paste, volumetric portion of aggregate, are taken into consideration in the calculation of the chloride diffusivity of noncarbonated concrete. For carbonated concrete, reduced porosity due to carbonation is calculated and used for calculating the chloride diffusivity. The results are compared with experimental data and previous research works.

Simple Approach for Computing Chloride Diffusivity of (Non)Carbonated Concrete

The purpose of this study is to establish a simple approach to compute the chloride diffusivity of (non)carbonated concrete. The chloride diffusivity of concrete should is defined, based on engineering and scientific knowledge of cement and concrete materials. In this paper, parameters affecting the chloride diffusivity, such as the diffusivity in pore solution, tortuosity, micro-structural properties of hardened cement paste, volumetric portion of aggregate, are taken into consideration in the calculation of the chloride diffusivity of noncarbonated concrete. For carbonated concrete, reduced porosity due to carbonation is calculated and used for calculating the chloride diffusivity. The results are compared with experimental data and previous research works.

Three-Phase Composite Sphere Model for the Prediction of Chloride Diffusivity of Concrete

In predicting the chloride diffusivity of concrete as a three-phase material, the morphological characteristics of the three phases, the physical properties of each phase constituent material, and the interactions of the three phases in the concrete matrix should all be taken into account. The present paper attempts to develop an analytical method to achieve this. A three-phase composite sphere model for the concrete matrix is proposed to represent the heterogeneous nature of concrete and a closed form solution for the chloride diffusivity of concrete is derived. After verifying the derived closed form solution with experimental results, the effects of key factors that affect the chloride diffusivity of concrete, namely the chloride diffusivity and thickness of the interfacial transition zone (ITZ), the maximum aggregate diameter, and the aggregate gradation are examined in a quantitative manner. It is found in the paper that the most important factor influencing the chloride diffusivity of concrete is the chloride diffusivity of ITZ. When the aggregate volume fraction is equal to 0.8, the relative chloride diffusivity of concrete to cement paste for a given relative chloride diffusivity of ITZ to cement paste at 10 is almost four times that for a given relative chloride diffusivity of ITZ to cement paste at 2. The second most important factor is the thickness of ITZ. When the aggregate volume fraction is equal to 0.8, the relative chloride diffusivity of concrete to cement paste for a given ITZ thickness at 0.05 mm increases by 76% as compared to that for a given ITZ thickness at 0.02 mm. The least important factors are the maximum aggregate diameter and aggregate gradation. The extent to which they influence the chloride diffusivity of concrete is in the range of 10 — 55%. The paper concludes that the closed form solution derived here can predict the chloride diffusivity of concrete with reasonable accuracy.

A Numerical Method for Predicting the Chloride Diffusivity of Concrete with Interfacial Cracks

Due to its importance to the durability assessment of reinforced concrete structures located in a marine or de-icing salt environment, it is essential to determine the chloride diffusivity of concrete. This paper presents a numerical method for predicting the chloride diffusivity of concrete with interfacial cracks. By modeling concrete as a three-phase composite material composed of aggregate, interfacial transition zone and cement paste, a composite circle model with an interfacial crack located on the aggregate surface is constructed. The finite element method is used to solve the composite circle under a given boundary condition and the chloride diffusivity of concrete is then determined numerically. After verifying the numerical method with experimental results obtained from the literature, the effect of interfacial cracks on the chloride diffusivity of concrete is evaluated in a quantitative manner. It is found that the chloride diffusivity of concrete increases with the increase of the subtended angle of interfacial cracks. The paper concludes that the numerical method presented in this paper can predict the chloride diffusivity of concrete with reasonable accuracy.