Electrochemical Chloride Extraction Research Articles

Modeling electrochemical chloride extraction in surface carbonated concrete

This paper investigated the Electrochemical Chloride Extraction (ECE) process in concrete with carbonated surface layers. First, the ECE model for surface carbonated concrete was proposed based on pore size distribution function. Subsequently, to validate the model, concrete cube specimens exposed to natural coastal environments were modified and designed for ECE tests. Based on the validated ECE model, parametric studies were conducted. Parametric studies show that increasing the thickness of the surface carbonation layer up to 20 mm leads to a 57% increase in extraction duration, whereas the thickness of the partially carbonated zone has a relatively minor impact on the ECE process. The parametric study shows that the surface carbonated zone will pose hindrances to the extraction of chloride ions. Due to the simultaneous presence of concrete carbonation and chloride ion ingress in the actual marine atmospheric environment, considering the actual carbonation depth is of significant importance for predicting chloride ion migration during Electrochemical Chloride Extraction.

Applicability of electrochemical chloride extraction to concrete made with different binders

The present study concerns the application of electrochemical chloride extraction to concrete designed with partial replacements from different binders, namely ground granulated blast furnace (GGBS), pulverized fly ash (PFA) and Silica Fume (SF), aiming to attend the need of corrosion repair for structures made in the more recent years. Concrete specimens were used to assess characteristics such as compressive strength and resistance to chloride penetration on different binders. Meanwhile, mortar samples were used for ECE treatment and chloride profiling. Additionally, microscopic examination was performed to quantitatively confirm the formation of C–S–H gel in the cement matrix, which is subsequently indicative of which type of chloride binding is more expected. ECE was applied to the specimens at a current density of 2A/m2 for 4 weeks. In fact, the chloride binding mechanisms were found to have important implications on the different performance perceived for all binders. For a change in the chloride profile, the removal of bound chlorides at the depth of the steel was more significant in GGBS, due to a possible release of adsorbed chlorides from the silicate hydrates, at bigger intensities for that material. However, even though GGBS had greater rates of bound chloride removal it had still the same percentage as OPC for total efficiency due to the fact that in OPC the removal of free chlorides is then more expressive.

Probabilistic assessment of silane impregnation and electrochemical chloride removal treatment on protection effect against steel corrosion in marine concrete structures

This paper concerns the protective performance of maintenance strategies, i.e. silane impregnation (SI) and electrochemical chloride extraction (ECE), against chloride-induced corrosion for concrete elements in marine environment. The effectiveness of SI treatment is researched through long-term exposure tests, and the efficiency of ECE treatment is considered using a quantitative expression. The failure probability evolution is calculated through reliability theory and Monte-Carlo simulations. The maintenance planning is established, and relevant maintenance costs are determined. The obtained results show that (1) the effective protection life of initially applied silane is longer than 12 years, but the protective performance of reapplied silane is not as pronounced as the silane initially applied; (2) the chloride ions at steel surface are efficiently removed after ECE which is more conducive to sustain the steel rebars free from corrosion; (3) ECE treatment attains the optimal cost and is recommended for long life-span concrete elements in marine environment.

Effect of ECE in removing chlorides at free and bound ones in concrete contaminated with chlorides in cast and with penetrated chlorides

The present study concerned the effect of electrochemical chloride extraction (ECE) to chloride-contaminated concrete on chloride removal with incremental depths after the ECE at 1000 mA/m2 for 2, 4 and 8 weeks. The steel reinforcement was taken as an anode, while the titanium mesh as cathode. The chloride was extracted by diluting concrete dust sample in acid solution and still water for total and free chlorides, respectively. As a result, most free chlorides were removed from concrete at the increased current density, while bound chlorides were quite removed, presumably due to a reduction of the alkalinity of concrete.

Modelling of Chloride Transport in the Standard Migration Test including Electrode Processes.

The modelling of chloride transport in concrete under an electrical field requires taking into account the electrode processes. These processes are very rarely introduced into the literature, despite their impact on chloride migration and the electroneutrality of the pore solution of the material. This paper aims to propose a multi-ion model for chloride migration that takes into consideration the electrode processes. The model is applied to simulate the standard chloride migration test. The generation of OH- in the cathode and H+ in the anode allows for the monitoring of the electroneutrality. The model considers all of the ions in the pore solution. Ion fluxes are calculated using the Nernst-Planck equation. The Langmuir model is used to simulate the chloride isotherms. The thermodynamic equilibrium in the material is considered, which reflects the ion-solid interactions during the migration. Measurements of water porosity and the chemical composition of the pore solution are essential to provide input data and the initial and boundary conditions. The numerical results of the ion profiles in the material studied confirm the electroneutrality at any point within the material, in contrast with models that do not take the electrode processes into account. The proposed model allows for the more accurate simulation of the chloride migration test and electrochemical chloride extraction in reinforced concrete structures subjected to NaCl as part of maintenance and repair strategies.

Effect of Imperial Smelting Process Slag Addition in Self Compacting Concrete Concrete on the Efficiency of Electrochemical Chloride Extraction.

This paper presents the analysis of how ISP slag addition affects the effectiveness of chloride extraction from self-compacting concrete. Corrosion processes were initiated by chloride ions added to concrete by the method accelerated with an electric field. Corrosion of reinforcement was monitored using the method of linear polarization resistance (LPR). Polarization measurements of steel reinforcement and chloride profiles were analysed to evaluate the effectiveness of electrochemical extraction. Microstructural analysis was conducted on a specimen of concrete after migration and extraction of chlorides. The presence of chloride ions and the application of an electric field during migration were tested with respect to the changed microstructure of concrete evaluated on the basis of image analysis using a scanning electron microscope (SEM). The research contributes to a better understanding of the corrosion processes caused by the presence of chloride ions in concretes in which ISP slag was used as a substitute for sand in various amounts. Thanks to the treatments of concrete with already corroding reinforcement bars, it can be concluded that the moderate replacement of sand with ISP slag limited to 25% allows for the effective inhibition of corrosion processes taking place in these concretes. However, it is not possible to completely withdraw already started corrosion processes in steel. The observations of the microstructure of concrete in which sand was completely replaced with ISP slag indicate that after prolonged use of the chloride extraction process, we can expect a change in the microstructure and the formation of ettringite, which may cause the concrete structure to burst. The obtained information will contribute to the development of modelling methods for chloride ion extraction from a wide range of currently used concretes.

Reinforced Concrete Structure Composition Analysis after Electrochemical Chloride Extraction

Reinforced Concrete Structure Composition Analysis after Electrochemical Chloride Extraction

Modeling electrochemical chloride extraction process in cement-based materials considering coupled multi-ion transports and thermodynamic equilibriums

This paper proposes an electrochemical chloride extraction (ECE) model for cement-based materials that considers coupled multi-ion transport, adsorption and dissolution. Then ECE tests were designed and conducted to validate the proposed ECE model. Based on the proposed ECE model, parametric studies were conducted. Parametric studies show that the chloride binding capacity of cement pastes depends heavily on the contents of aluminate ferrite monosulfate (AFm) and alumina ferrite tri-sulfate (AFt). Moreover, the content compositions of free, absorbed and chemically-bound chloride ions vary with the types of chloride salts, i.e., the cations in the chloride salts. Moreover, temperatures within the range between 5 °C and 40 °C pose negligible influences on the ECE process. Current densities and durations are the most influential factors affecting the ECE process, which are thus the main parameters to be determined for the design of ECE. In addition, the chloride ion content distributions are bell curves during the ECE process and peaks exist within the concrete cover. Therefore, it is recommended to adopt three chloride ion contents as controlling indexes for the ECE process, i.e., 1) the chloride ion content at the surface of steel bars, 2) the average chloride ion content within the concrete cover and 3) the peak chloride ion content within the concrete cover.

Novel application of electrochemical chloride extraction fixing polymer-modified conductive repair mortar as anode

Electrochemical chloride extraction (ECE) technique provides an effective technique to remove the chloride ions from concrete and realize reinforcements performance recovery. In this study, a novel type of polymer-modified conductive repair mortar (PCRM) was developed as the anode of ECE system, while the impacts of electrochemical parameters, anode types and reinforcements layout on the chlorides extraction efficiency were investigated, in addition, an innovative method is also proposed to further enhance the ECE efficiency. The results highlight that PCRM can be successfully fabricated with proper initial/final setting time, which presents the similar extraction efficiency compared with PC-based repair mortar and stainless-steel mesh anode. Furthermore, reinforcement cages provide target concrete with lower extraction efficiency inside the cage, and the efficiency can be remarkably increased by pulse current. Most importantly, the chloride extraction efficiency of PCRM anode is increased from 45.1% to 59.6% (electrochemical parameters), 53.7% (reinforcements layout), 60.2% (pulse current), respectively.

Chloride ion control of under-constructing concrete structure based on ECE with different electric field intensities

Electrochemical chloride extraction (ECE) technology can effectively reduce the harmful chloride ions in concrete and decline the durability failure risk of concrete structures. In this study, early-age sea-sand concrete was treated by ECE with strong electric field and conventional electric field, respectively. The chloride ion content analysis and microscopic observation were adopted to evaluate the durability improvement effect with ECE treatment. The results showed that at the early ages of 3, 5, and 7 d, the chloride ions were drastically reduced upon the application of a strong electric field for 40, 80, and 120 min or the conventional electric field for 15 d. Treating time of ECE with strong electric field is 0.19 %–0.56 % of that of ECE with conventional electric field. Under a strong electric field, the distribution of residual chloride ions in specimens was more uniform. Application of an electric field during the curing period caused the directional migration of ions and subsequently changed the pore structure and microhardness of the specimen. However, these changes were recovered with the continuous hydration of concrete during the curing period. Finally, based on engineering cases, the field implementation schemes of the strong electric field and conventional electric fields were analyzed. The energy consumption of ECE with strong electric field is 17.8 %–53.3 % of that of ECE with conventional electric field. The results of this study provide the technical means for the timely treatment of excessive chloride ion concentration in sea-sand concrete structures.

Chloride Removal from Polluted Reinforced Self-Compacting Concrete Using Electrochemical Chloride Extraction

Chloride Removal from Polluted Reinforced Self-Compacting Concrete Using Electrochemical Chloride Extraction

Evaluating the Impact of Concrete Design on the Effectiveness of the Electrochemical Chloride Extraction Process.

This paper presents a simple comparative method for evaluating the impact of concrete design on the effectiveness of repair with the electrochemical chloride extraction (ECE) process of reinforced concrete structures. This comparison covered two concretes with different types of used cement. Penetration of chloride ions to induce corrosion processes was accelerated with the electric field. However, the corrosion process itself occurred naturally. When the corrosion process was found to pose a risk to the reinforcement, the profile of chloride ion concentration was determined at the depth of concrete cover. Corrosion current intensity during migration and extraction processes of chloride ions was measured with the LPR method. Then, this serious condition for the structure was repaired with electrochemical chloride extraction. Rates of chloride extraction were determined from the derived concentration profiles. It should be noted that the critical concentration Ccrit = 0.4% at the rebar surface was reached after 21 days of the migration process. Moreover, after the same time of extraction, the concentration was reduced by 95% at the rebar surface, which could suggest that extraction rate was slower than chloride ion migration to concrete within the electric field. Using the migration coefficient for predicting the extraction time, as well as ignoring the variability of the extraction coefficient and the initial concentration over time, may result in too short or unnecessarily long extraction times.

A State-of-the-Art Review of Electrochemical Chloride Extraction for Concrete Structures

Electrochemical chloride extraction is a promising technique for the rehabilitation of concrete structures under chloride induced corrosion. This study consists of an extensive literature review of this treatment including application cases. It is found that the rate of chlorides removed is affected by the total charge passed, whereas increasing charge in a range between 1500 to 2000 Ah/m2 increases the amount of chlorides removed and this can be more effective by increasing current density instead of duration of treatment. Bound chlorides are extracted during treatment and, water works better than Ca(OH)2 as an electrolyte, possibly due to modifications on the concrete pore structure. Moreover, ECE is not efficient in repassivate structures but is efficient in its purpose of removing chlorides if treatment setup is well planned, which justifies the need for better international standards on the topic.

The application of electrochemical chloride extraction to reinforced concrete – A review

• This paper presents a state of the art of electrochemical chloride extraction. • ECE is an interesting treatment for RC structures suffering from chloride induced corrosion. • Efficiency of ECE is studied based on chloride extraction, steel corrosion mitigation and pH. • ECE potential side effects are described. • Long-term efficiency of ECE needs to be validated. In a context of ageing reinforced concrete structures, electrochemical chloride extraction (ECE) is an interesting treatment for structures damaged by chloride-induced corrosion. This paper summarises the state of the art by presenting the concept of ECE, assessing available measurement techniques and discussing influencing factors. The determination of ECE efficacy requires the consideration of different results, and particularly those pertaining to chloride extraction, corrosion mitigation and evolution of pH. This literature review also highlights the potential side effects and risks to the concrete structure. Further work is needed to ascertain the long-term performance of ECE.

Polymer-modified sulphoaluminate cement-based mortar anode and its optimal arrangement for electrochemical chloride extraction

Electrochemical chloride extraction (ECE) is becoming a common method for repairing reinforced concrete structures exposed to marine environments, and the development of more efficient and durable anode materials is important. Therefore, this study designed a polymer-modified sulphoaluminate cement-based mortar (PSCM) as an anode for ECE, which can effectively remove chloride ions and repair damaged concrete. The results show that the PSCM, prepared using sulphoaluminate cement as the main cementitious material with 2% ethylene–vinyl acetate (EVA) and 0.6% carbon fibre as additives, possessed strong bond performance, high conductivity, and good repair function. In addition, the chloride removal efficiency was improved to 58.9%, when the PSCM was used as an ECE anode. The grid-like PSCM anode arrangement and stainless steel mesh/PSCM double-anode arrangement could overcome the shortcoming of chloride ion enrichment between the concrete and PSCM anode, and the chloride removal efficiency could reach 64.3%.

A Numerical Study on the Electrochemical Treatment of Chloride-Contaminated Reinforced Concrete

Electrochemical treatment, specified as electrochemical chloride extraction (ECE), is one of the common techniques developed for the rehabilitation of chloride-contaminated reinforced concrete. In practice, ECE is time-consuming; for instance, the treatment duration could last several weeks or even longer. In order to reduce the laboratory work, this paper presents some results about a numerical study of the ECE. It is to solve a series of physical equations governing multiple ionic transport making use of a finite difference method. The effects of some critical factors are discussed in detail, such as the treatment duration, the current density and the cover thickness. In addition, for the sake of validation, the numerical results are also compared with those obtained from an experimental test.

Effects of Electrochemical Chloride Extraction on the Properties of Chloride-Contaminated Reinforced Concrete by Using Magnesium Phosphate Cement Bonding Carbon Fiber Reinforced Plastics as Anode

Effects of Electrochemical Chloride Extraction on the Properties of Chloride-Contaminated Reinforced Concrete by Using Magnesium Phosphate Cement Bonding Carbon Fiber Reinforced Plastics as Anode

Durability control of sea-sand concrete components utilizing strong electric field during early curing period

Electrochemical chloride extraction (ECE) technology can effectively reduce the harmful chloride ion content of concrete structures and thus decrease their durability failure risk. This paper applied the ECE technology to sea-sand concrete with an excessive chloride ion content through a strong electric field. Further, testing the chloride ion content, meso- and micro-mechanical properties, and mechanical performance of the concrete columns verified their durability performance after the action of the strong electric field. The results show that, for the early-age concrete with a curing period of 3, 5, and 7 days, the strong electric field with an electrifying time of 40, 80, and 120 min can significantly enhance the ECE efficiency, and the chloride ion content of the concrete can fulfill the specification requirements. During the curing period, compared with the unelectrified concrete components, the strain and displacement of the electrified columns increase under the same load when the components are loaded immediately after the action of the strong electric field. However, after applying the electric field, if the member is standardly cured for 28 days, its ultimate bearing capacity increases, and its mechanical properties improve. The bearing capacity of ECEC-3, ECEC-5 and ECEC-7 after curing 28 days are 315.2kN, 320.1kN and 340.9kN which are closed to 326.2kN of ECEC-28. Regarding the adverse effect of the electric field on the performance of the columns, a technical scheme was designed to avoid their hydrogen embrittlement and plastic reduction.

Comparison of Electrochemical Chloride Extraction Models for Reinforced Concrete Structures Based on Multiple Potential Theories

For chloride-contaminated RC structures, steel corrosion is one of the most common reasons causing the deterioration of reinforced concrete (RC) structures. Electrochemical chloride extraction (ECE), which migrates the chloride ions out of the RC structure, is preferred as it is a nondestructive repairing method. In this context, electrokinetic models are often used to investigate ECE processes. Currently, electrokinetic models based on different potential theories, such as the constant potential, electroneutrality, and Gauss’ law, may be used to solve the potential distribution. Although many ECE numerical simulations have been conducted, there has been no systematic comparison of models based on different potential theories. Therefore, in this study, a comprehensive comparative study has been conducted on these models in terms of the potential distribution, current density, quantity of electric charge, and ion concentration. Two commonly used ECE methods, namely, steady voltage and steady current, were numerically simulated and analyzed. The numerical results with actual ECE data were also compared. Although the electrokinetic model based on electroneutrality might overestimate the residual chloride concentration and underestimate current density and hydroxyl concentration, critical analysis suggests that electroneutrality is more appropriate than the constant potential and Gauss’ law for electrokinetic modeling.

Polymer-Modified Sulphoaluminate Cement-Based Mortar Anode and its Optimized Arrangement Applied to Electrochemical Chloride Extraction

Polymer-Modified Sulphoaluminate Cement-Based Mortar Anode and its Optimized Arrangement Applied to Electrochemical Chloride Extraction