Concrete Chloride Research Articles

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.

Effect of Admixed and External Chlorides on the Transport of Chlorides in Concrete

Effect of Admixed and External Chlorides on the Transport of Chlorides in Concrete

Delaying time to corrosion initiation in concrete using brick aggregate as internal curing medium under adverse curing conditions

Absence of proper curing results in weaker and permeable concrete and eventually, reduces the service life of reinforced concrete (RC) structures significantly, particularly in aggressive conditions like marine environment. One of the main causes for reduced service life under marine ambience is chloride induced corrosion resulting from ingress of chloride ion in concrete. The negative impacts caused by the lack of proper curing can be compensated by adapting the internal curing mechanism that ensures better hydration. Brick chip (BC) has the ability to absorb sufficient quantity of water during mixing and desorbs it afterwards and therefore, can be used to produce internally cured concrete. On the other hand, chloride ingress within concrete primarily depends on chloride diffusion coefficient of the concrete. As a result, internally cured concrete with appropriate proportion of BC is expected to linger the time of corrosion initiation in RC structure by producing robust and denser concrete. In this study, the delay in corrosion initiation time and consequent extension of the service life of internally cured concrete with BC under different unfavorable curing conditions was investigated. It was found that corrosion initiation time of internally cured concrete could be increased by several years as compared to conventional concrete depending on adversity of curing conditions and concrete cover. The study shows immense potential of internal curing using BC to enhance service life of concrete under adverse curing conditions and hinder premature repair work of concrete.

Phenomenological model for quantifying concrete chloride diffusion coefficient

Compressive strength and the chloride diffusion coefficient are the common and principal performance measures for designing durable concrete structures. Hence, a comprehensive and consistent phenomenological model is put forward that quantifies a concrete’s effective chloride diffusion coefficient based on the tortuosity factor, aggregate volume fraction, porosity, cement paste chloride diffusion coefficient, compressive strength, cement and cementitious material content and composition. The phenomenological model results are first shown to depict chloride ion diffusion phenomena in porous media. Experimental data reported in the scientific literature are then used to evaluate visually and statistically the accuracy and precision of the phenomenological model. The model results are found statistically equal to experimentally quantified chloride diffusion coefficient values to a 95% confidence level and possess high accuracy and precision for a wide range of concrete mixture proportions, composition and age. The model average percent error is less than the standard test method repeatability and the COV of the reproducibility. The standard error, samples mean, and R2 are found to be 0.41 × 10−12 m2/s, 1.46 × 10−12 m2/s and 0.94, respectively.

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).

Effect of different types of Cement in Concrete Chloride Permeability

Effect of different types of Cement in Concrete Chloride Permeability

Electrochemical impedance spectroscopy analysis of Cl<sup>-</sup> penetration in slag concrete

In order to improve the traditional testing technology of chloride penetration depth of concrete and the influence of different slag content on the penetration depth of chloride ion, we carry out chloride ion penetration experiments of several groups of concrete with different slag content. Meanwhile, a suitable equivalent circuit model is applied to test the electrochemical impedance data of cement based material. The experimental results show that the penetration depth of chloride ion can be reduced by adding slag in concrete. In addition, there is a strong linear relationship between the depth of the chloride ion penetration and the fitting value of the equivalent circuit element. On the basis of the change of electrochemical performance, the penetration depth of chloride ion in concrete can be predicted by the analysis of the content of different slag.

Chloride diffusion model for concrete in marine environment with considering binding effect

This paper presents a new chloride diffusion model for concrete exposed to marine environment, which considers the effects of different types of chloride binding. The present model has following new features. (1) The bound chlorides are divided into two types. One is reversible, which is related to the physical binding, and the other is irreversible, which is related to the chemical binding. (2) The reversible bound chloride remains its charge and continues to provide its driving force to influence the movement of free chloride ions. (3) The governing equation for the mass conservation of chlorides is established on the framework of representative elementary volume of concrete and thus the diffusion coefficient used in the present model is consistent with the effective diffusion coefficient defined in the steady-state diffusion tests of chloride in concrete.

Quantification of concrete chloride diffusion coefficient – A critical review

Most concrete deterioration mechanisms are driven by the transport properties, in particular the chloride diffusion coefficient. As such, experimental and analytical tools have been developed to quantify the chloride diffusion coefficient. This study employs the experimental data reported in the literature to critically assess the accuracy and precision of the proposed analytical models for quantifying the concrete chloride diffusion coefficient. The models assessed range in scope from statistical models to hybrid models with the former employing statistical tools to fit the response function and the latter combining material science, physical science and mathematical tools to characterize the property. The test data include two standard test methods, i.e. bulk diffusion and migration test, and consider the following mixture design variables: water to cement ratio, cement type and content, supplementary cementing material, aggregate volume fraction, and air content. The results revealed that hybrid models are more accurate and precise in comparison to the statistical model. The “best” model is found to account for the capillary porosity, pore structure parameters, solid phase diffusivity, cement paste diffusivity, aggregate volume fraction, and interfacial transition zone properties yielding a ±95% confidence predictability of 0.86 and 0.97 of the quantified diffusion coefficients. Cement paste thickness which controls the ratios of the various diffusion coefficients is found missing in all the models.

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.

Corrosion at low moisture content in both carbonated and chloride polluted concrete – Villa E-1027, a case study

Corrosion in reinforced concrete is generally attributed to either carbonation or chloride presence in the vicinity of the bars. But in the field of cultural heritage, especially for the most ancient monuments, it is not rare to encounter both carbonated and chloride polluted concrete, inducing heavy corrosion, as was the case in the Villa E-1027 in Roquebrune-Cap-Martin, on the French Mediterranean seashore. The villa was designed by Eileen Gray and Jean Badovici between 1926 and 1929. Due to aggressive environmental conditions and a period of dereliction, the concrete of the villa was quite heavily decayed and a deep restoration was led between 2000 and 2006. But after a little more than 10 years, and despite active maintenance, the villa is again facing corrosion induced decay. Prior to the definition of a new restoration protocol, to better evaluate the corrosion activity, in 2017 a permanent monitoring of moisture and temperature both in the air and in the concrete was installed. In the meantime, a series of instant electrochemical measurements was performed from 2017 to 2018. A first analysis of the results of the monitoring and the non-destructive tests clearly evidences that probably due to the conjunction of the carbonation of the concrete and external active chloride pollution, corrosion can happen at quite low moisture content.

Instant performance verification after electrochemical chloride extraction by enhanced corrosion testing

Electrochemical chloride extraction (ECE) is meant to re-establish the corrosion protection of concrete for the embedded reinforcement by removing chloride non-destructively and by enhancing the alkalinity of the rebar surrounding concrete. Both effects depend on various parameters, such as concrete cover, rebar spacing, chloride profile (especially if chloride ingress is deeper than the outside rebar layer) and concrete permeability. Often these parameters require long or multi-stage treatments, which basically can achieve any desired target level of chloride profile and impressed charge, but become a costly solution after a while. The acceptance criteria mentioned in CEN TS 14038-2 clause 8.6 refer to the achieved chloride content and to the amount of impressed charge, which are the conventional, easy measurable, but not direct parameters for evaluating the corrosion activity. A third parameter – the re-measurement of potentials for assessing (intended) low potential gradients and more positive average potentials – requires some weeks to months of depolarization and evaporation of water, before such a measurement can be applied successfully. A promising approach for an instant performance testing after an ECE treatment has been made on several occasions with follow-up measurements of electrolyte resistance, polarization resistance and corrosion current. Convincing changes towards significantly lower corrosion activity could be obtained (and compared to known classified values) – regardless of sometimes high residual chloride and very wet concrete. These data could be verified when re-assessed after some weeks, so enhanced corrosion measurements seem to be a useful tool for either establishing that the designed treatment time has been sufficient or to check on possible earlier termination of the treatment during a running ECE.

Quantitative determination of chlorides by molecular laser-induced breakdown spectroscopy

The presented work reports on an improved analysis of chlorides in cement and concrete using molecular LIBS. The quantitative determination of the atomic chlorine emission requires sophisticated setups under helium atmosphere and specialized spectrometers. Molecular LIBS can be performed with standard spectrometers and without additional buffer gas. In a LIBS plasma of chloride contaminated cement or concrete atomic chlorine and calcium form calcium-mono-chloride (CaCl) radicals which will be used for the quantification of chlorides. By calculating the intensity ratio of chlorine dependent and independent molecular band emission the standard deviation of the intensity ratio compared to the absolute species emission can be reduced by a factor of 5. Air purging further reduces the total standard deviation by two-thirds compared to measurements in ambient air without purging. A linear calibration with a limit of detection and limit of quantification complying with the threshold of a critical chloride contamination in concrete is determined. Spatially and temporally resolved measurements of different fixed concentrations of chloride are shown to proof the homogeneity of reference samples. In order to determine the diffusion process of the chloride contamination measurements on a drilling core are presented. As supplemental method for micro analysis, spatially resolved energy dispersive X-ray (EDX) measurements are performed. EDX can help to reveal the atomic distribution in a hydrated sample on a scale much smaller than the spot size of the laser. Thereby, relevant reaction partners for the molecular formation could be identified.

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.

Influence of cracks on chloride diffusivity in concrete: A five-phase mesoscale model approach

This paper presents a mesoscale numerical approach to investigate the chloride diffusivity in cracked concrete. Concrete is treated as a five-phase material, including cement paste, aggregate, interfacial transition zone (ITZ), crack, and damaged zone (DZ), for its heterogeneity. In the mesoscale model, the randomly distributed aggregates were treated as impermeable, whereas all other phases are assumed permeable but with different diffusion coefficients. It is assumed that the crack is located in the middle of the DZ, and there is a liner relationship of the chloride diffusion coefficients between the DZ and the crack. The developed mesoscale model is validated by comparing the simulation results with the experimental data. Finally, the influence of the DZ, such as the chloride diffusion coefficient, the width and length of the DZ, the width and length of the crack, on the penetration of chlorides in cracked concrete is examined and discussed.

The effect of w/c ratio and aggregate volume fraction on chloride penetration in non-saturated concrete

The diffusion of moisture and chloride in non-saturated concrete is considered as two coupled transport processes. Two coupling terms are added in the governing equations based on Fick’s first law to represent the interaction between the moisture and chloride during the transport processes. The first coupling term is for the effect of moisture movement on chloride transfer, and the other is for the effect of chloride transfer on moisture movement. In this paper, an experimental study was conducted to investigate the effect of the variation of the water-cement ratio and the aggregate volume fraction on the coupling parameter associated with the first coupling term (DCl-H). To this end, a chloride ponding test was designed and performed on two sets of fully and partially saturated concrete samples made with different water-cement ratios and aggregate volume fractions. The coupling parameter was determined based on the obtained test data. The results indicate that the coupling parameter DCl-H is strongly dependent on the concentration of chloride ions, water to cement ratio, and volume fraction of aggregate. A material model for the coupling parameter was developed using the experimental results.

EVALUATION OF CHLORIDE ABSORPTION IN PRE-CONDITIONED CONCRETE CUBES

The chloride contamination will occur from an application of de-icing salts. It was confirmed that, the application of de-icing salts caused a significant reduction in structural and serviceability reliabilities. The chemicals used in the snow and ice control operations (de-icers) may cause corrosion damage to the transportation infrastructure such as reinforced/pre-stressed concrete structures/steel bridges. There are many ways to manage the corrosive effects of de-icers, such as selection of high-quality concrete, adequate concrete cover and alternative reinforcement, control of an ingress and accumulation of deleterious species, injection of beneficial species into concrete, and use of non-corrosive de-icer alternatives and optimal application rates. In fact, snow and ice on streets and highway are a major threat to human life and limb. Traffic accidents and fatalities climb as snow and ice reduce traction on roadways. Lengthened emergency response times create additional risks for persons in urgent need of medical care, particularly in cases of heart attacks, burns, childbirth and poisoning. Thus the de-icing salts are necessary to provide safe winter driving conditions and save lives by preventing the freezing of a layer of ice on concrete infrastructure. However, the safety and sense of comfort provided by these salts is not without a price, as these salts can greatly contribute to the degradation and decay of reinforced concrete transportation systems. An importance of chloride concentration as a durability-based material property has received greater attention only after the revelation that chloride-induced corrosion is the major problem for concrete durability. Therefore, there is a need to quantify the chloride concentration in concrete which is of paramount importance. The present research work was made an attempt to interpret the concrete chloride absorption in ordered to characterize the different concrete mixtures design for in case of pre-conditioned concrete cubes such as dry/fully/partially saturated condition which was salt ponded with chloride solution for about 160 days. Thus the objectives of this present research are such as: First, this research will examine an influence of conditioning such as dry/fully/partially saturated condition on the results of chloride absorption performed on concrete cubes with different mixtures proportion in which slump, and w/c ratio value was varied with constant compressive strength as in the First case and compressive strength, and w/c ratio value varied with constant slump as in the Second case. Seventy-two concrete cubes (100 mm3) with Grades of concrete ranges from 25 to 40 N/mm2 were prepared and evaluate the chloride absorption under different exposure condition. It’s concluded from the results that, in dry/saturated conditioned concrete cubes, the chloride absorption value was increased in all designed mixtures type. Similarly, average chloride absorption was decreased in solvent/water based impregnation DCC/PSC/FSC cubes as when compared to control DCC/PSC/FSC cubes for constant higher compressive strength and varied slump value as well as varied compressive strength and constant slump value. Whereas average chloride absorption was increased in solvent/ water based impregnation DCC/PSC/FSC cubes for lesser compressive strength and constant slump value as when compared to constant higher compressive strength and varied slump value and the chloride absorption was goes on decreases with an increased compressive strength and constant slump value.

EVALUATION OF CHLORIDE ABSORPTION IN PRE-CONDITIONED CONCRETE CUBES

The chloride contamination will occur from an application of de-icing salts. It was confirmed that, the application of de-icing salts caused a significant reduction in structural and serviceability reliabilities. The chemicals used in the snow and ice control operations (de-icers) may cause corrosion damage to the transportation infrastructure such as reinforced/pre-stressed concrete structures/steel bridges. There are many ways to manage the corrosive effects of de-icers, such as selection of high-quality concrete, adequate concrete cover and alternative reinforcement, control of an ingress and accumulation of deleterious species, injection of beneficial species into concrete, and use of non-corrosive de-icer alternatives and optimal application rates. In fact, snow and ice on streets and highway are a major threat to human life and limb. Traffic accidents and fatalities climb as snow and ice reduce traction on roadways. Lengthened emergency response times create additional risks for persons in urgent need of medical care, particularly in cases of heart attacks, burns, childbirth and poisoning. Thus the de-icing salts are necessary to provide safe winter driving conditions and save lives by preventing the freezing of a layer of ice on concrete infrastructure. However, the safety and sense of comfort provided by these salts is not without a price, as these salts can greatly contribute to the degradation and decay of reinforced concrete transportation systems. An importance of chloride concentration as a durability-based material property has received greater attention only after the revelation that chloride-induced corrosion is the major problem for concrete durability. Therefore, there is a need to quantify the chloride concentration in concrete which is of paramount importance. The present research work was made an attempt to interpret the concrete chloride absorption in ordered to characterize the different concrete mixtures design for in case of pre-conditioned concrete cubes such as dry/fully/partially saturated condition which was salt ponded with chloride solution for about 160 days. Thus the objectives of this present research are such as: First, this research will examine an influence of conditioning such as dry/fully/partially saturated condition on the results of chloride absorption performed on concrete cubes with different mixtures proportion in which slump, and w/c ratio value was varied with constant compressive strength as in the First case and compressive strength, and w/c ratio value varied with constant slump as in the Second case. Seventy-two concrete cubes (100 mm3) with Grades of concrete ranges from 25 to 40 N/mm2 were prepared and evaluate the chloride absorption under different exposure condition. It’s concluded from the results that, in dry/saturated conditioned concrete cubes, the chloride absorption value was increased in all designed mixtures type. Similarly, average chloride absorption was decreased in solvent/water based impregnation DCC/PSC/FSC cubes as when compared to control DCC/PSC/FSC cubes for constant higher compressive strength and varied slump value as well as varied compressive strength and constant slump value. Whereas average chloride absorption was increased in solvent/ water based impregnation DCC/PSC/FSC cubes for lesser compressive strength and constant slump value as when compared to constant higher compressive strength and varied slump value and the chloride absorption was goes on decreases with an increased compressive strength and constant slump value.

Durability of cement concrete under chemical erosion

This paper launches the study on how the sulfate particle and chloride ions interact to impact the concrete durability. It is analyzed that there is a diffusion law of two particles in concrete, whether the concrete presents corrosion resistance and permeability as contacts with them. The findings reveal that the content of chloride ions decreases with the deepening of the concrete profile. The presence of sulfate ions does not break up the diffusion trend of chloride ions in concrete, but in the case when Cl- and SO42- act together, the content of chloride ions at a constant profile depth is less than that under the action of a single Cl-. When sulfate ions permeate the cement, they will react with hydrate product of cement to generate new chemical substances that fill the inner pores of the cement, thereby suppressing the diffusion of chloride ions. The higher the concrete water-binder ratio, the lower the compression strength; the more inner pores, the weaker its resistance to chemical attack. When mineral admixtures are added to the concrete, the sulfate ions can react with the hydrate products of the cement and mineral admixtures to generate new crystals that largely fill the original pores in the concrete and make it more compact. In this way, the concrete corrosion resistance is built up. Concrete gets most vulnerable to sulfate attack at an ambient temperature of 21-24°C, and relieved at 30- 35°C. Lower relative humidity, high temperature environment are the decisive factors that accelerate the concrete erosion.