Concrete Ion Research Articles

Coupling effect of corrosion damage on chloride ions diffusion in cement based materials

The durability of concrete structures in marine environment depends on the migration speed of chloride ions in concrete. If the reinforced steel bars in these structures are attacked by chloride ions and begin to rust, these are considered as failure. In general, the diffusion of chloride ions in concrete is analyzed by solving the diffusion equation based on Fick’s law. In the equation, the diffusion coefficient is assumed to be constant. However, novel studies have shown that corrosion damage could take place in concrete due to the formation of Friedel’s salt during the diffusion process. The evolution of corrosion damage not only causes the diffusion coefficient to be a function of time, but also speeds up the migration of chloride ions. This can decrease the durability of concrete structures. However, few related researches have been reported. Close attention to this study was paid to the coupling effect between corrosion damage and the migration of chloride ions. The variation of porosity of cement based materials due to chemical reaction, physical absorption, continued hydration, and corrosion damage was investigated. Then, a new diffusion equation was derived by considering these factors. By virtue of the numerical method, the spatial-temporal distribution of corrosion damage was evaluated, and its effect on the migration of chloride ions was numerically discussed. These results show that corrosion damage could significantly affect the diffusion of chloride ions.

Transportation Laws for Carbonate and Sulfate Ions in Concrete Based on Compartment Model

Transportation of carbonate and sulfate ions in concrete under the drying‐wetting cycle environment is similar to the ingression and elimination of medicine in human body. Given this similarity, such a process is described dynamically using the classic compartment model in pharmacokinetics. The compartment model was applied to predict the content of carbonate and sulfate ions in different regions of concrete. Factors such as water‐cement ratio, salt category, carbonate‐ion and sulfate‐ion attack depth, and drying‐wetting cycle were synthetically considered in the compartment model. In conjunction with the prediction value of the compartment model, the experiment data uniformly distributed two sides of the model curve, and the difference is within the accepted range, thus verifying the reliability of the model prediction consequence. The compartment model in this article provides references for predicting the drying‐wetting varied cycles and ions attack depth of concrete under carbonate and sulfate ions attack.

Numerical simulation of steel corrosion in chloride contaminated concrete

Corrosion is one of the main reasons for the degradation of reinforced concrete structures, especially of those exposed to a chloride-contaminated environment. To study the effect of chloride ions on the corrosion of steel embedded in concrete, two electrochemical parameters, namely, the anodic Tafel slope and potential, were theoretically analyzed and semi-empirically modified by the concentration of chloride ions in concrete. Subsequently, a numerical model that couples the mass transport and electrochemical corrosion process was established to simulate the transport of chloride ions and the evolution of steel corrosion that occurred simultaneously in the concrete. Based on the proposed numerical model that incorporated the appropriate electrochemical parameters, the corrosion current density and corrosion potential were obtained numerically and they coincided well with the experimental data. Finally, the proposed model was applied to study the chloride ion distribution as well as the corrosion current density around the cross-section and circumference of the steel bar in concrete members with single or multiple steel bars. The results indicate that the proposed numerical modelling method can be used to predict the corrosion-initiation time, as well as the development of the morphology of the corrosion profile of steel bars in concrete structures.

An investigation on the three-dimensional transport of chloride ions in concrete based on X-ray computed tomography technology

In order to demonstrate the three-dimensional chloride ions diffusion in real concrete, the X-ray CT technique was applied to reconstruct the meso- and micro-structure of concrete. An improved threshold method was used to eliminate the noise during X-ray CT images processing. The special distribution of aggregate particles and pores were recognized and analyzed based on the reconstructed meso-structure of real concrete. The reconstructed meso-structure, as well as the interfacial transition zone (ITZ) were introduced into a multi-phase model to numerically characterize the three-dimensional diffusion of chloride ions in real concrete. And the simulation results were verified through electron probe technique. A parameter sensitivity analysis was conducted to furtherly assess the influence of ITZ diffusivity on the chloride ions diffusion in concrete. This investigation indicates that aggregate particles tends to deposit at the bottom of the specimen and the pores are likely to concentrate at the top part. Due to the special distribution of aggregate particles and pores, the chlorides ions diffuse more quickly at the bottom of the specimen. The study proves that the aggregate particles, pores and ITZ are of great importance for the three-dimensional chloride ions diffusion in real concrete.

Quality control of the concrete and corrosion damage of cables of prestressing reinforcement of KA beams, bridge in Chomutov

The aim of this paper is to assess the condition of the diagnosed bridge structure, at which previous bridge inspections identified corrosion damage of cables of prestressing reinforcement of KA beams, to assess the extent of corrosion damage of prestressing reinforcement, the condition of chloride ions in concrete of the bearing structure, and to draw up a detailed corrosion assessment of the prestressing reinforcement, then to propose a possible method of the bridge renovation with partial use of new materials (UHPC).

An effective transport model of sulfate attack in concrete

Abstract This paper presents both an experimental and theoretical investigation of the consumed and accumulated rates of sulfate ions in concrete. The authors analyze the effects of sulfate solution concentration and the water-cement ratio on the sulfate ions distribution. Based on the diffusion theory, a sulfate transport model for concrete was established considering the effect of surface sulfate concentration. On this basis, an effective transport model of sulfate attack is presented, which relies on effective diffusivity. This model can be applied to predict the sulfate ions distribution; moreover, its predicted values are in good agreement with the experimental ones.

Simulating chloride penetration in fly ash concrete by a fractal derivative model

In the real engineering field, the chloride ions behave abnormal diffusion phenomena in concrete caused by different compositions of the concrete which lead to the complex physical and chemical properties. This paper utilizes a fractal derivative model and a fractional derivative model to describe the diffusion phenomena. Furthermore, according to actual experimental data in the field, the fractional and fractal model can simulate the diffusion behavior of chloride ions in concrete. In comparison to the fractional derivative model, the fractal derivative model gives a simpler mathematical expression and lower calculation costs. In addition, the linear regression analysis method is used to establish an effective relationship between the internal composition of concrete and the parameters of fractal model such as fractal order, ?, and diffusion coefficient, D. As a result, the fractal model with the parameters estimated by previous relationship can predict the diffusion behavior of chloride ions.

Analysis of the Properties of Expansive Concrete With Portland and Blast Furnace Cement

AbstractThe properties of expansive concretes made of two types of cement: Portland cement CEM I and blast furnace slag cement CEM III were tested. The expansion of the concrete was caused by using an expansive admixture containing aluminium powder added in an amount of 0.5; 1 and 1.5% of cement mass. It was found that the compressive strength of concrete with CEM I decreased after using an expansive admixture in the amount of more than 0.5% of the cement mass. The compressive strength of concrete with CEM III decrease after addition of admixture in the entire range of dosages used. On the basis of electrochemical measurements, it was found no influence of an expansive admixture on corrosion of reinforcing steel. The use of an expansive admixture causes a slight increase in the effective diffusion coefficient of chloride ions in concrete.

Effect of interfacial transition zone on the transport of sulfate ions in concrete

Long-term external sulfate attack can result in significant concrete degradation. The purpose of this study is to develop an experimentally validated reactive transport model to investigate the transport behaviour of sulfate ions in concrete containing interfacial transition zone (ITZ). The model takes into account the spatially dependent pore size in ITZ and the change of diffusion coefficient of sulfate ions due to the formation of ettringite and gypsum in concrete pores resulting from the chemical reaction between sulfate ions and concrete components. The developed model was firstly validated by performing a series of experiments involving concrete specimens and sodium sulfate solution. Then, a series of parametric studies were carried out to identify the critical parameters that govern the transport of sulfate ions in concrete. The backscattered electron microscopy (BSE) results show that the porosity of concrete within ITZ is relatively higher than that in bulk paste with a six-fold higher porosity in inner ITZ (5 µm from aggregate surface) than that in outer ITZ (50 µm from aggregate surface). The model predictions suggested that the concentration of sulfate ions initially increases rapidly in concrete during the first 20 days and then the rate of increase gradually decreases due to the reduction in the diffusion coefficient of ions as a result of the ettringite and gypsum formation in concrete pores. In addition, it demonstrates that self-induced electric field has little influence in the transport of sulfate ions.

A multiphase numerical simulation of chloride ions diffusion in concrete using electron microprobe analysis for characterizing properties of ITZ

In order to demonstrate the chlorides ions diffusion in concrete, a multi-phase numerical model was established at mesoscale. The thickness of interfacial transition zone (ITZ) surrounding aggregate was measured based on an element analysis using electron probe technique. And the diffusivities of ITZ and mortar matrix were deduced through a one-dimensional transmission test. By introducing the experiment parameters into the two-dimensional numerical model, the chloride ions diffusion in concrete was simulated and verified through the electron probe technique accordingly. A sensitivity analysis on the parameters was conducted to furtherly assess the influence ITZ on the chloride ions diffusion in concrete. This study indicates that the size of coarse aggregate has no influence on the thickness of ITZ which follows a normal distribution. The properties of ITZ, including its the thickness and diffusivity, have significant affections on the diffusion of chlorides ions in concrete. And for the concrete employed in this research, the diffusivity affects the diffusion more severely than thickness of ITZ.

Evaluation of critical crack width for reinforcement corrosion in RC member based on numerical simulation of transport of chloride ions in concrete

Chloride-induced reinforcement corrosion in reinforced concrete structures exposed to marine environment is one of the most important factors affecting the durability of structures. To minimize the effect of cracks on the deterioration of RC structures, current design codes often limit the crack width. However, recent investigations indicated that condition of steel-concrete interface is a more essential criterion related to reinforcement corrosion. The purpose of this study is to clarify the effect of various conditions including cover thickness, water-cement ratio, environment action and interfacial void on limitation of crack width. The validity of crack width limitation in design codes is discussed based on analytical results.

The content of chlorides in blast-furnace slag cement as a factor affecting the diffusion of chloride ions in concrete

Blast-furnace slag cement (CEM III) has a wide range of acceptable Cl- content according to EN 197-1: 2012. This makes possible to use alternative fuels for the production of cement, which can increase the chlorides content in the clinker. However, it raises several new research problems, among them the problem of increase of the risk of Cl- penetration intensity due to the higher concentration of chlorides in cement, presented in this paper. Studies have shown that after a short hardening time (28 days) the rate of diffusion of chloride ions increases slightly with the increase in the content of chlorides in the cement CEM III, but after full stabilization of concrete properties (1 year), the content of chlorides in cement CEM III practically does not affect the diffusion rate of chloride ions in concrete.

Investigation on the transport properties of chlorides in concrete (I) Identification of ITZ

Concrete is a multiphase composite material, in which the mortar, aggregate and interfacial transition zone (ITZ) have important influence on the chloride ions transport. In this research, the thickness ITZ was measured and the concentration distribution of chloride ions in concrete was obtained through electron microprobe analysis. The experiment results that the thickness of ITZ follows a normal distribution and the size of aggregate shows no clear influence on the thickness of ITZ.

Predictive Models of Chloride Penetration in concrete: An Overview

Abstract: This article presents a brief review of the models aimed to predict the penetration of chloride ions in concrete. The work highlights the two well-known approaches i.e. Fick's laws and Nernst-Planck equation. Difference of opinion about the two approaches as well as within each approach is also elaborated. Diverse accelerated methods for determining the chloride diffusivity in concrete are also described. Different numerical schemes and analytical solutions as adapted in the models are also mentioned. Effort is made to present the models in a chronological way and therefore the presented list is not exhaustive.

Mechanical and Durability Evaluation of Concrete with Sulfate Solution Corrosion

Concrete material has been a choice for the construction structures, even in the cold regions and saline zone. However, these environmental factors have critical damaging effect on the concrete characters. Consequently, this damage will decrease the servicing time of the concrete construction within this environment. In order to evaluate the durability of concrete, the behavior of concrete specimens under the sulfate solution corrosion attacks was studied in this presented work. Two groups of the specimens were immersed into the sulfate solutions with a concentration of 10% and 20%, respectively. The strength development of the specimens under different immersing time was studied. Based on Fick’s law, a steady diffusion equation for sulfate ions in concrete was presented, and the depth of penetration of the attacking sulfate ions was also determined. Based on the depth of penetration and the definition of damage, a damage model for concrete material is developed and a new equation (strength-time) describing the chemical corrosion concrete material is proposed. Results show that the suggested analytical methods can quantify the damage process of concrete under sulfate attack, and the power laws damage developing formula can be used to describe the damage development of the concrete construction subjected to chemical corrosion.

Corrosion risk of steel fibre in concrete

In the present study, the corrosion risk of steel fibre in concrete was assessed by measuring the corrosion rate of steel fibre in chloride-contaminated mortar. Simultaneously, the rate of chloride transport in steel fibre mortar was determined by chloride profiles. Then, the interface of the steel fibre was examined by the scanning electron microscopy to ensure the porosity in the vicinity. As a result, it was found that the corrosion resistance of steel fibre against chloride was slightly higher than for reinforcing steel rebar in concrete, presumably due to the presence of mille scale on the surface; the chloride threshold level ranged 0.8–1.0% by weight of cement. However, transport of chloride ions in concrete containing steel fibre was accelerated by increased porosities in the vicinity of steel fibre, implying that external aggressive ions may easily penetrate the concrete then to chemically degrade concrete properties. In fact, the diffusion coefficient of chloride in mortar containing steel fibre ranged 4.79–9.61×10−12m2/s, as being 2–3 times higher for steel fibre-free mortar.

Influence of cation type on diffusion behavior of chloride ions in concrete

In the previous paper, a model considering multi-phase reactions and ionic interactions was created to describe the diffusion behavior of chloride ions in concrete immersed in NaCl and CaCl2 solutions. In this paper, more experimental tests and numerical simulations are conducted to improve the model and to study the influence of cation type on chloride diffusion behavior in concrete. In the experimental part, the total and the water-soluble chloride concentrations are determined after 180days of immersion in the NaCl, KCl, MgCl2 and CaCl2 solutions. The test results show that the chloride binding capacities associated with the four cation types decrease in the order Ca2+>Mg2+>Na+≈K+ while the apparent diffusion coefficients of them decrease in the order K+≈Na+>Ca2+>Mg2+. In the numerical part, the equations of magnesian ions are newly considered so that the improved model can be applicable for more cation types. Based on the improved model, the chloride binding capacity of concrete in natural diffusion process is a complicated function concerning with many factors, among which the cation type and the contact duration are significantly important.

Chloride ion transport mechanism in concrete due to wetting and drying cycles

AbstractThe transport mechanism of chloride ions in concrete during wetting and drying cycles of varying duration is evaluated in this paper. The experimental test results were used to validate a numerical simulation model in order to assess the influence of diffusion coefficient, surface chloride ion concentration and ratio of dry‐wet cycle durations on the transport mechanism of chloride ions in concrete. Experimental and numerical analysis results indicate that the maximum transmission depth of chloride ions in concrete depends on the diffusion coefficient and the dry‐wet cycle regime but has little relationship with the surface concentration of chloride. The chloride ion transmission in the surface zone accelerates only if the dry‐wet ratio is > 1. As the dry‐wet ratio increases, so the chloride ion transmission accelerates. It tends to become stable when the dry‐wet ratio reaches 5:1. The dry‐wet cycles accelerate the transport process of chloride ions within a certain distance from the surface; beyond this distance, chloride ions in the complete immersion specimen migrate more rapidly than those under dry‐wet cycles. The peak concentration of chloride ions within the convection zone has a relationship with the diffusion coefficient, the surface chloride ion concentration and the dry‐wet regime. The smaller the diffusion coefficient, the higher the surface chloride concentration; the greater the dry‐wet ratio, the higher the peak of convection can be.

Meso-scale modeling of chloride diffusion in concrete with consideration of effects of time and temperature

A meso-scale truss network model was developed to predict chloride diffusion in concrete. The model regards concrete as a three-phase composite of mortar matrix, come aggregates, and the interfacial transition zone (ITZ) between the mortar matrix and the aggregates. The diffusion coefficient of chloride in the mortar and the ITZ can be analytically determined with only the water-to-cement ratio and volume fraction of fine aggregates. Fick's second law of diffusion was used as the governing equation for chloride diffusion in a homogenous medium (e.g., mortar); it was discretized and applied to the truss network model. The solution procedure of the truss network model based on the diffusion law and the meso-scale composite structure of concrete is outlined. Additionally, the dependence of the diffusion coefficient of chloride in the mortar and the ITZ on exposure duration and temperature is taken into account to illustrate their effect on chloride diffusion coefficient. The numerical results show that the exposure duration and environmental temperature play important roles in the diffusion rate of chloride ions in concrete. It is also concluded that the meso-scale truss network model can be applied to chloride transport analysis of damaged (or cracked) concrete.

Properties of ordinary concretes incorporating crushed queen scallop shells

The large quantities of seashells produced in the North-West of France and the depletion of quarries motivates the research of new sources of aggregates. This article examines the influence of incorporating crushed queen scallop shells on ordinary concretes in order to assess the feasibility of reusing marine by products in the form of aggregates. For this purpose four different concrete mixes were produced, one of them used as reference with natural aggregates and the others prepared with 20, 40 and 60 % of crushed queen scallop shells replacing the natural aggregates. Concretes were characterized at fresh state by its workability, the air content and the density, and at hardened state by the mechanical and durability properties. The incorporation of crushed queen scallops causes an increase of the entrapped air of concrete, a reduction of the mechanical properties and an increase of the concrete porosity facilitating the transport of fluids and chloride ions in concrete.