Electrochemical Rehabilitation Research Articles

Progress and research challenges in concrete durability: ionic transport, electrochemical rehabilitation and service life prediction

Concrete durability degradation problems have received considerable attention in both research field and concrete industry during recent decades. To better understand the underlying mechanisms, various numerical models have been put forward aiming at widely concerned scientific issues involved in the entire life cycle of concrete structures: ionic transport in porous medium, degradations induced by multiple factors, as well as the prediction and rehabilitation method to prolong the service life. This letter aims to summarise the major contributions to these interrelated scientific issues particularly from the modelling perspective. The digital characterization of concrete heterogeneity and its influence on ionic transport behaviour will be firstly reviewed. Subsequently, concrete deterioration mechanisms induced by various factors and their internal coupling relationships are discussed in details. Meanwhile, promising electrochemical repair techniques with multi-fold advantages including chloride removal, corrosion inhibition, ASR mitigation and crack repair are systematically summarized. Finally, existing research gaps and future opportunities in these areas have also been visited, which is hoped to break the ice in this challenging field and promote the sustainable development of the concrete industry.

Repair effect of cracked reinforced concrete based on electrochemical rehabilitation technology

To solve the problem of durability deterioration of cracked concrete structures in coastal environments, this study investigates the effect of repairing loading cracks and corrosive cracks. In particular, the immediate and long-term effects of combining electrochemical repair technology with traditional repair methods were studied. After the repair, the corrosion potential of steel bars, cracking duration, and cracking speed obtained by different repair methods were compared. The results showed that the repair effect of the comprehensive repair technique is significantly better than using a single repair method. Based on the characteristics of the cracks, the sequence of each step in the combined repair technique was designed.

Stiffness degradation for fatigue of reinforced concrete beams after electrochemical rehabilitation

Electrochemical rehabilitation (ER) techniques usually serve as non-destructive methods for addressing the durability hazards of reinforced concrete (RC) structures and for effectively improving their durability. However, the bond damage induced by ER can detrimentally impact the fatigue stiffness of the RC beams. To investigate the effects of ER on the fatigue stiffness of RC beams, this study conducted constant fatigue tests on RC beams after ER, in consideration of three current densities. The crack distribution, mid-span deflection, concrete strain, and stress level of a longitudinal steel bar were used to evaluate degradation in the fatigue performance. The results of numerical analysis and experiment indicated that ER exacerbated the bond damage, thereby decreasing the bending stiffness of the RC beam. As a result, a fatigue damage model for an RC beam after ER was established, based on the residual bending stiffness and current density. This model can help provide a theoretical basis and guidance for assessing the fatigue damage and safety of RC beams after ER.

Control of repair effect and hydrogen embrittlement risk by parameters optimization for BIEM

Bidirectional electromigration rehabilitation (BIEM) is a novel electrochemical rehabilitation method involving the injection of inhibitors into steel bar surface. The BIEM effect and hydrogen embrittlement (HE) risk depend on the electrochemical parameters (current density and duration) and operating condition (stress level and concrete cover thickness) of reinforced concrete structures. Experiments were performed in this study to investigate the relationships between the aforementioned factors. For a small current density group, a linear relationship was established between electric flux and chloride extraction. For a large current density group, the reasonable current density, stress level, and treatment time were obtained. Finally, the querying method of electrochemical parameters combined with treatment time and current density was proposed.

Deterioration of static mechanical properties of RC beams due to bond damage induced by electrochemical rehabilitation

Electrochemical rehabilitation (ER) techniques are very efficient and non-destructive methods to improve the durability of existing concrete structures. However, the induced bond damage between steel bar and concrete will affect the mechanical properties. In order to investigate the effect of ER on the static mechanical properties of concrete structures, three types of tests after electrochemical chloride extraction and bidirectional electromigration were carried out in this study. Based on the desired constitutive models, finite element analysis was then used to verify the effect of bond damage on the static mechanical properties of RC beams. Results showed that the spacing and width of cracks both increased with increasing current density and duration. The yield bearing capacity of beams decreased by 20% when the electrical parameters were 3 A/m2 for 4 weeks and 5 A/m2 for 2 weeks. Careful investigation with experiments, finite element simulations, and theoretical explanation demonstrated that bond damage was the main reason. As a result, a modified flexural stiffness model of concrete beams considering the electrification parameters was established. Combined with data from the relevant literature, the optimal quantity of electric charge for ER balancing chlorine removal efficiency and flexural stiffness was finally determined as 500–1400 Ah/m2.

Hydrogen embrittlement risk control of prestressed tendons during electrochemical rehabilitation based on bidirectional electro-migration

Abstract Bidirectional electro-migration rehabilitation (BIEM) is type of electrochemical rehabilitation that allows for simultaneous chloride ion removal and inhibitor injection into the steel bar surface. The inhibitor migrates across the surface of the steel bar, altering its pH and forming a thin layer of isolation that reduces hydrogen evolution. In this paper, sensitivity of hydrogen embrittlement was studied using constant strain rate tensile analysis, fracture energy ratio, and fracture morphology. When compared with electrochemical chloride extraction (ECE), BIEM treatment enhanced the critical current density and reduced the stripes number in radical zone. The fracture energy ratio remained at a high level, even with a current density and BIEM treatment time that were no more than 3 A/m2 and 14 d respectively. The results indicated that the sensitivity of prestressed tendons to hydrogen embrittlement after BIEM was markedly lower than that after ECE. Collectively, these results indicate that BIEM treatment can mitigate the application limitations of the current electrochemical rehabilitation technology used on prestressed concrete structures.

Multi-phase modelling of electrochemical rehabilitation for ASR and chloride affected concrete composites

Reinforced concrete structures experience severe durability degradation when subjected to alkali–silica reaction (ASR) and chloride attack. A special electrochemical rehabilitation treatment, containing lithium compound anolyte, has been developed to drive lithium ions into concrete composites and remove chlorides simultaneously, for mitigating both the ASR-induced cracks and the chloride-induced reinforcing steel-bar/fiber corrosion. In this study, the efficiency of the impregnation of lithium ions and the removal of chloride ions through a specific electrochemical treatment is numerically evaluated, which results into the distribution profiles of all typical ionic species. A heterogeneous numerical model, which treats concrete as a three-phase composite, is presented to examine the response of inner structures, especially the interaction between active aggregates and lithium ions that are supposed to mitigate ASR. The ionic interaction between different species, binding and the electrochemical reaction at electrodes are also considered. Through a detailed modelling of multi-phase and multi-species, a systemic parametric analysis based on a series of significant factors during electrochemical treatment (e.g., current density, treatment time, temperature, cathode position and concentration of lithium solution) reveals some important tendencies of ionic electromigration in concrete structures, which are supposed to guide the field applications.

Effect of electrochemical chloride extraction treatment on the corrosion of steel rebar in chloride contaminated mortar

Purpose This work aims to demonstrate the use of electrochemical chloride extraction (ECE) to remove chloride ions away from the steel rebar in chloride-contaminated mortar and to mitigate the corrosion of the embedded steel. Design/methodology/approach To simulate salt contamination in concrete, sodium chloride was added at 0.5 per cent by weight of cement in the fresh mortar featuring a water-to-cement ratio of 0.45. The ECE treatments were varied at two electrical current densities (1 and 5 A/m2), using two electrolytes (0.1M NaOH and 0.1M Na3BO3 solutions) and for two periods (2 and 4 weeks). The average free chloride concentration in cement mortars before and after ECE treatment was quantified using a customized chloride sensor, whereas the spatial distribution of relevant elements was obtained using energy-dispersive X-ray spectroscopy. The effect of ECE treatment on the electric resistivity of mortar and the corrosion resistance of steel rebar was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements, respectively. Findings The experimental results reveal that the ECE treatment was effective in removing chlorides and in improving electric resistivity and compressive strength of the mortar, when using the sodium borate solution as the electrolyte. In this case, a 4-week ECE treatment at 1 A/m2 decreased the free chloride content in the mortar by 70 per cent, significantly increased the Ca/Si ratio in the mortar near rebar, led to a more refined and less permeable microstructure of the mortar and significantly improved its compressive strength. The ECE treatment was able to halt the chloride-induced corrosion of steel rebar by passivation. A 4-week ECE treatment at 1 A/m2 using sodium hydroxide and sodium borate solutions decreased the corrosion rate of rebar by 36 and 34 per cent, respectively. Originality/value This electrochemical rehabilitation of steel-reinforced concrete under chloride-contaminated condition is very effective in prolonging its service life.

A new electrochemical rehabilitation method for reinforced concrete employing the DFRCC anode system

In this study, a new electrochemical rehabilitation method is proposed and experimental investigation on the viability of this method is carried out. This rehabilitation method employs an anode system that bonds to concrete surface with the aid of ductile fiber reinforced cementitious composites which works to improve both durability and mechanical performance. From results of chemical analysis of concrete and half-cell potentials of steel bars, protective and repair effects against steel corrosion were achieved by the proposed method. In addition, results of flexural bending test of treated specimens showed that bending strength and flexural ductility of the specimens was improved by bonding of the anode system and strengthening effect was not reduced by the electrochemical treatment.

Electrochemical rehabilitation methods for reinforced concrete structures: advantages and pitfalls

There are still many unresolved issues concerning the efficiency of electrochemical realkalisation and electrochemical chloride removal as electrochemical rehabilitation methods for corroding reinforced concrete structures. The present paper seeks to answer a number of questions which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic communities, despite the vast amount of work that has been devoted to research on corrosion in concrete embedded steel, such as whether corrosion can be stopped once it has started, whether corroded reinforced concrete structures can be repassivated, and whether it is sufficient to remove the sources of corrosion in order to stop rusting. A discussion is conducted on the relationship between the prerusting grade of rebars and the possibility of their repassivation; on whether electrochemical rehabilitation methods treatments are efficient, and if so, when and on whether a simple potential measurement can determine the passive or active state of a rebar. For this purpose an analysis is made, using electrochemical, gravimetric and metallographic techniques, of the response of clean and previously corroded steel electrodes in a Ca(OH)2 saturated solution with and without a sodium nitrite corrosion inhibitor and in cement mortar. The effectiveness of electrochemical realkalisation and electrochemical chloride removal for repassivating prerusted steel in concrete is found to depend heavily on the prerusting grade.

Reflexiones sobre los métodos electroquímicos de rehabilitación de las estructuras corroídas de hormigón armado

Electrochemical realkalinisation and electrochemical chloride removal have shown their capacity to eliminate, in just a few weeks, the causes of corrosion of reinforced concrete structures (RCS), and for this reason are currently receiving very special attention. This communication seeks to answer some fundamental questions that continue to arouse great controversy, which are summarized in the question: removing the causes of corrosion in RCS suffice to stop rusting? To this end an analysis is made of the responses of clean and precorroded electrodes in a solution that simulates the aqueous phase of the concrete pore network. According to the results obtained, the efficiency of electrochemical rehabilitation methods depends heavily on the degree of precorrosion of the rebars.

Several questions about electrochemical rehabilitation methods for reinforced concrete structures

Electrochemical realkalisation (ERA) and electrochemical chloride removal (ECR) have shown their capacity to eliminate, in just a few weeks, the causes of corrosion in reinforced concrete structures (RCS), and for this reason are currently receiving very special attention. Nevertheless, the present state of the art has not progressed enough to dissipate doubts about the efficiency of ERA and ECR as electrochemical rehabilitation methods (ERM) for corroding RCS. A series of highly important questions persist, and continue to be cause of controversy among specialists in the construction sector, which can be summed up in one all-encompassing question, namely: • Is removing the sources of corrosion in RCS sufficient to stop rusting? To obtain a response to this capital question, electrochemical corrosion analysis techniques are used to study the responses of clean and precorroded steel electrodes embedded in small mortar specimens without chloride additions and large mortar slabs with and without chloride contamination. According to the results obtained, ERM are efficient in delaying the start of corrosion if used preventively. However, if applied too late they do not assure the repassivation of rebars with high precorrosion levels and consequently are not useful.

Consideraciones sobre la repasivación de las estructuras corroídas de hormigón

An analysis is made of the responses of clean and precorroed steel electrodes in Ca(OH) 2 saturated solutions and in cement mortar, using gravimetric, metallographic and electrochemical techniques, essentially polarisation resistance measurements. The paper aims to answer some important questions about the corrosion of reinforced concrete structures (RCS) which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic circles, such as the following: What corrosion rates are dangerous in RCS? What concrete resistivities guarantee sufficient durability of RCS? Is it possible to detain corrosion once it has begun? Can corroded RCS be repassivated? Are electrochemical RCS rehabilitation methods efficient, and if so, when? The results obtained indicate that electrochemical chloride removal and realkalisation cannot repassivate heavily corroded steel surfaces, however they can be effective methods to prevent corrosion provided they are used before the transition from the passive state to the active one occurs. If applied to late, are useless for this purpose.

Cosmic-ray radiographic image of large structural materials: 39478 Minato, S.; Fukaya, M. Transactions of the American Nuclear Society, Vol. 56, Supplement No. 3, p. 63 (Conference on Industrial and Radioisotope Measurement Applications, Pinehurst, North Carolina, 7–9 Sep. 1988)

Electrochemical realkalisation (ERA) and electrochemical chloride removal (ECR) have shown their capacity to eliminate, in just a few weeks, the causes of corrosion in reinforced concrete structures (RCS), and for this reason are currently receiving very special attention. Nevertheless, the present state of the art has not progressed enough to dissipate doubts about the efficiency of ERA and ECR as electrochemical rehabilitation methods (ERM) for corroding RCS. A series of highly important questions persist, and continue to be cause of controversy among specialists in the construction sector, which can be summed up in one all-encompassing question, namely:•Is removing the sources of corrosion in RCS sufficient to stop rusting?To obtain a response to this capital question, electrochemical corrosion analysis techniques are used to study the responses of clean and precorroded steel electrodes embedded in small mortar specimens without chloride additions and large mortar slabs with and without chloride contamination. According to the results obtained, ERM are efficient in delaying the start of corrosion if used preventively. However, if applied too late they do not assure the repassivation of rebars with high precorrosion levels and consequently are not useful.