Electrochemical Realkalisation Research Articles

Electrochemical realkalisation of carbonated cementitious matrix: characterization research to influence of time and current density

The depassivation of reinforcement caused by the reduction of concrete alkalinity due to the concrete carbonation process can induce the appearance of steel corrosion. The restoration of alkalinity can be done by chemical realkalinization (CRA) or electrochemical realkalinization (ERA) methods. In this context, the present work aims to evaluate the influence of the application time and the current density used in the electrochemical realkalinization process. For the development of the research, mortar samples were molded with a reinforced bar for electrical connection and remained for 24 months in a carbonation chamber. After this period, the carbonation depth that occurred was verified and then the specimens were submitted to the electrochemical realkalinization process using 3 different current values, 0.5, 1.0 and 1.5A/m2 and remained at different periods (7 , 14 and 21 days) in the recovery process. Additional tests of absorption, compressive strength, carbonation depth measurements, mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TGA) were also carried out on reference, carbonated and realkalinized specimens. Based on the results of the tests, it was observed that the recovery process starts after 7 days with the lowest current density used. A better current density x application time ratio was also observed considering the results of the mercury intrusion porosimetry and thermogravimetric analysis tests in conjunction with the realkalinization process.

Electrochemical Realkalisation of Carbonated Cementitious Matrix: Characterization Research to Influence of Time and Current Density

Electrochemical Realkalisation of Carbonated Cementitious Matrix: Characterization Research to Influence of Time and Current Density

Ethanolamines corrosion inhibition effect on steel rebar in simulated realkalized concrete environments

ABSTRACT This paper reports the corrosion inhibition effect of the realkalization and corrosion inhibitors combination treatment on steel rebars. First, the corrosion was studied in simulated carbonated concrete and simulated realkalized concrete environments and then compared with the corrosion, while realkalization-corrosion inhibitor treatment was applied. The corrosion inhibitors studied are monoethanolamine (MEA), dimethylethanolamine (DEMA) and triethylenetetramine (TETA). Through the electrochemical measurement; the potential of steel rebars in realkalized environment containing MEA and DMEA shifted in positive direction by 84 mV and 66 mV; the current destiny of each group decreased by 3.76 and 2.33 μA/cm2, respectively. Unlike the addition of TETA shifted the potential in negative direction by 281 mV and increased the current density by 27.72 μA/cm2. Comparing steel rebars surfaces, the realkalization-corrosion inhibitors groups showed a better inhibition effect than the two control groups (simulated carbonated concrete and simulated realkalized environments). Among the corrosion inhibitors used, MEA has the best corrosion inhibition effect in the electrochemical realkalized concrete environment, it can form a protective film on the steel rebars through physical and chemical adsorption, which can effectively inhibit the corrosion of steel rebars. The result confirms that, by the combination of MEA and electrochemical realkalization, the corrosion inhibition in carbonated reinforced concrete can improve significantly.

Multi-species reactive transport modeling of electrochemical corrosion control in saturated concrete structures including electrode reactions and thermodynamic equilibrium

The ionic migration in concrete determines the efficiency of electrochemical corrosion control of reinforced concrete structures, such as electrochemical chloride extraction, electrochemical realkalization, and impressed current cathodic protection. In this study, a numerical model of the multi-species reactive transport in saturated concrete structures with electrochemical corrosion control is proposed. The proposed model includes ionic transport, thermodynamic equilibrium and electrode reactions. The electrode reactions at the surface of reinforcing steel are considered using the Tafel equation. The thermodynamic model is adopted to express the physical and chemical reactions between pore solution and hydration products. The diffusivity coefficient of material based on the variation of porosity is updated at the end of each time step of the numerical model. Additionally, a laboratory experiment is conducted to verify the numerical model. The numerical results clearly show that the applied electrochemical corrosion control based on the numerical model is capable of preventing the initiation of corrosion, avoiding the hydrogen embrittlement, arresting the Cl− penetration, and improving the pH value and CH content adjacent to the reinforcing steel.

Long-term effects of electrochemical realkalization on carbonated concrete

The long-term effects of electrochemical realkalization on carbonated reinforced concrete with a W/C ratio of 0.65 were studied. Fourteen out of 16 carbonated specimens had been subjected to realkalization seven years ago, and the alkalinity of the concrete, the electrochemical characters (corrosion current density and potential) of the specimens and the corrosion conditions of the steel bars were examined. Results of different specimens and also at different time (4, 10, 13 months and 7 years after realkalization) were compared. According to the phenolphthalein and pH meter test, the alkalinity of the concrete had disappeared after seven years. Based on the potentiodynamic polarization test, various corrosion conditions had developed on the steel bars, which was verified by visual observation. All bars were in the depassivated state, and their corrosion current densities increased significantly after seven years. Cracks developed in some of the specimens, and the diverse compactness of concrete and excessive current of realkalization were considered to be possible causes. The effects of the realkalization treatment vanished after seven years.

Efficiency of electrochemical realkalisation treatment on reinforced blended concrete using FTIR and TGA

The present study evaluates the efficiency of the application of electrochemical realkalisation (ER) as a prevent technique for partially carbonated blended reinforced concrete using two pozzolanic additions, metakaolin (MK) and silica fume (SF), replacing 10% cement. In this study, the concrete was exposed to controlled climate conditions (1% CO2, 65% RH, 25 °C) until 65% carbonation was reached (without initial pre-corrosion). Subsequently, ER was applied for a period of 7, 15 and 21 days for the concrete specimens without additions (OPC, reference material); in the case of blended concretes, a single period of 15 days was carried out. In all cases, sodium carbonate (Na2CO3) as an electrolyte and a current density of 1 A/m2 were used. The influence of the additions on the efficiency of ER was studied by the pH evaluation method, using an alcoholic solution of phenolphthalein at 1% as an indicator, and the test was performed before and after the ER process. As a complementary test, FTIR and TGA were used. Linear polarization resistance (LPR) and half-cell potential (Ecorr) were used to monitor the progress of the corrosive process. The results verified that this method increased the pH of the cement matrix; however, ER was more effective for OPC concretes compared to blended concretes. After the ER treatment, the corrosion levels tended to decrease over time; however, the values did not reach the initial pre-corrosion state before the application of ER.

Influence of Mineral Admixtures on the Electrochemical Realkalization of Carbonated Concrete

AbstractThis paper presents the results of research on the electrochemical realkalization (ER) of carbonated concrete with fly ash and slag. The results show that the realkalization depth in concre...

Study of a repair technique in carbonated blended mortars: Electrochemical re-alkalization

<p>The present article studies the influence of two pozzolanic additions, metakaolin (MK) and silica fume (SF), and the water/binder ratio (w/b) on the electrochemical re-alkalization (ER) of reinforced mortars as a technique to prevent reinforcement corrosion in carbonated concrete. Mixtures with a 10% (by weight) addition as a replacement for cement at w/b ratios of 0.45 and 0.65 were prepared. Test specimens were exposed to carbonation in a chamber under controlled conditions (1% CO2, 65%RH, and 25°C), until reaching two levels of carbonation (50% and 100%). ER was applied for a period of 15 days using sodium carbonate as the electrolyte and a current density of 1 A/m2. From the evaluated additions, MK is highlighted, which generated a resistance increase of 53.51% relative to that of the reference mixture and contributes to improvements of durability properties. Regarding the ER technique, the specimens with greater w/b ratios and partial carbonation were more effective.</p>

Resistance to carbonation of concrete after re-alkalization by absorption of sodium carbonate solution

The paper presents experimental research on the durability of a non-conventional technique for the repair of reinforced concrete damaged by carbonation-induced corrosion of steel reinforcement. The technique is called electrochemical re-alkalization and is often considered as an option for the repair of buildings, structures, and other artefacts made of reinforced concrete, for which conservation requirements are becoming increasingly important, in spite of their relatively young age. Absorption of a sodium carbonate solution is one of the processes that lead to concrete re-alkalization. The aim of the work is to investigate the contribution of this process to preventing future carbonation of re-alkalized concrete. Concrete specimens with six different compositions were initially carbonated, then re-alkalized through absorption of a sodium carbonate solution, and then exposed again to carbonation (re-carbonation). The results showed that the pH of concrete after re-carbonation was only slightly lower compared to that of re-alkalized concrete, highlighting a contribution of the treatment in preventing future pH reduction.

建立再碱化技术修复火害后钢筋混凝土之pH值控制模式

由火害后钢筋混凝土内部钢筋腐蚀主要是因为钝化膜被破坏，而钝化膜破坏的主要原因是钢筋周围的碱性环境的消失。因此利用再碱化技术控制火害后钢筋混凝土周围的OH−的浓度。本研究主要建立以再碱化后钢筋周围溶液的pH值为目标的控制模型。根据试验建立了以控制混凝土保护层内的pH值为目标的再碱化控制模型为 ，j为电路流密度(A/m2)，T为通电时间(s)，d为中性化深度(mm)，fcu为火灾后混凝土实际强度(MPa)，k为孔隙率的参数。本研究估计火害普通强度的混凝土孔隙率参数k值为6.3 × 10−4，而火害高强度的 值2.5 × 10−5，该模式可应用于以再碱化技术修复火害后钢筋混凝土的pH的估计。 The passive film in internal reinforcement corrosion was destroyed by the fire-damaged of rein-forced concrete. However, the destruction of the passive film is caused by the disappearance of the alkaline environment around reinforced corrosion. This study was to establish the modeling pH value for electrochemical realkalisation to repair of fired-damaged reinforced concrete. The pH value of fire-damaged reinforced concrete is determined by the equation , in which j is the circuit current density (A/ m2), T is power-on time (s), d is neutral depth (mm), fcu is actual strength of concrete after fire-damaged (MPa), k is the parameter of porosity. The parameter of k of porosity for the or-dinary strength fire-damaged is 6.3 × 10−4, while the high-intensity fire-damaged is 2.5 × 10−5. This equation can be used to estimate the pH value for fire-damaged reinforced concrete to repair by electrochemical realkalisation.

Electrochemical realkalisation and combined corrosion inhibition of deeply carbonated historic reinforced concrete

The electrode reaction and the change in composition and morphology of the rust layer on rebar surfaces after electrochemical realkalisation treatment are investigated by electrochemical measurement and scanning electron microscopy. The results show that the rust layer is gradually reduced following the sequence Fe3+→Fe2+→Fe0 through mechanisms postulated to involve proton exchange and dissolution–deposition. The realkalisation process can restore the alkalinity of the pore solution in carbonated concrete adjacent to cathodically polarised rebar and also reduce rust layers on rebar in severely carbonated concrete structures. However, though the alkalinity of pore solution is restored and the corrosion potential of the rebar in deeply carbonated concrete becomes more noble after cathodic polarisation, the rebar cannot repassivate while polarised. Thus, to assist in repassivation, additional inhibitor injection is proposed. The results demonstrate that the adjunction of inhibitor can limit the corrosion of the rebar. Therefore, the combination of inhibitor plus electrochemical treatment is likely to prolong the durability of deeply carbonated reinforced concrete structures.

Electrochemical realkalisation of carbonated concretes – Influence of material characteristics and thickness of concrete reinforcement cover

This work studies the influence of concrete characteristics, such as cement type and water to cement ratio, and concrete cover thickness on the electrochemical realkalisation of carbonated concretes. Results show the treatment efficiency for recovering concrete alkalinity. More time and total electrical charge passed are demanded in proportion as water to cement ratio decrease, concrete cover thickness increase and when concrete has lower alkalinity reserve. The tendency of reinforcement reaching passive condition is observed by corrosion potential measurements. For this variable, concretes that demand more charge and time for realkalisation reach the passive condition in a shorter time. Corrosion current density shows a decrease tendency over time and, although not reaching the level that represents passive condition in most of the cases, it was not far from this reference.

Study on the Effects of Electrochemical Realkalization Method with Alcamines Inhibitors as Electrolyte

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Cement Based Anode in the Electrochemical Realkalisation of Carbonated Concrete

Cement Based Anode in the Electrochemical Realkalisation of Carbonated Concrete

Electrochemical Realkalization as a Conservation Technique for Reinforced Concrete

Electrochemical realkalization (ER) is a repair technique aimed at restraining corrosion of steel in carbonated concrete. ER is based on the application of a current to restore concrete alkalinity—the favorable environment for the protection of steel from corrosion. The treatment lasts from few days to weeks; then, when the entire concrete cover is realkalized, the external anode that supplied the current is removed, leaving the surface unchanged. Moreover, ER does not require the replacement of carbonated concrete if it is not damaged, so it can be advantageous compared with the traditional repair, which usually requires the removal of large amounts of mechanically sound (although carbonated) concrete. Although ER treatment was introduced in the 1980s, debate continues on some aspects connected with its application. This study presents the preliminary results of a long-term experimental research aimed at investigating this technique. The results obtained allowed determining ER effects in terms both of realkalization of the initially carbonated material and of protection of reinforcement from corrosion.

Electrochemical Realkalisation of Carbonated Concrete: an Alternative Approach to Prevention of Reinforcing Steel Corrosion

Electrochemical Realkalisation of Carbonated Concrete: an Alternative Approach to Prevention of Reinforcing Steel Corrosion

Efficiency investigations of electrochemical realkalisation treatment applied to carbonated reinforced concrete — Part 1: Sacrificial anode process

The aim of this study was to assess the efficiency of a realkalisation treatment using sacrificial anodes applied to reinforced concrete degraded by carbonation. Analytical determinations (acid/base indicators, quantitative pH, alkaline profiles, SEM and micro-Raman) together with electrochemical characterizations (rest potential, impedance, linear polarisation resistance and corrosion current densities) were performed on artificially carbonated slabs, before and after treatment (mainly 15 days, 11 weeks, 6 and 12 months). The treatment efficiency was demonstrated by an increase of pH and by an alkaline ion penetration in the concrete cover. Rest potential and corrosion current densities indicated a slight decrease of the rebar corrosion activity. Complementary Raman spectroscopy showed a change in the oxide species and SEM observations indicated that the cement matrix remained almost unchanged.

Study on the Effects of Realkalization Rehabilitation Method Auxiliary Alcamines Inhibitors in Simulative Experiment

In this paper, the feasibility of inhibitor auxiliary re-alkalization was investigated. The effect of realkalization auxiliary inhibitor repair technique was studied by simulative experiment. It studied the changes of electrochemical parameters of the natural carbonated reinforced concrete during the electrochemical realkalization in 1mol/L Na2CO3 solution and the mixed solution of 1mol/L Na2CO3 and 1 mol/L DMEA , as well as the impedance spectroscopy and polarization curves in the process of relaxation. The results showed that: there appears to be no effect of DMEA on the corrosion potential and the impedance of the steel in the process of realkalization. That was, the performance was the same as that in the sodium carbonate solution except corrosion current of rebar with DMEA which showed much lower. But of the samples which the DMEA existed in the electrolyte was significantly shorter at the same relaxation time after realkalization. At the same relaxation time the corrosion potential was more positive and the corrosion current density was smaller. It improved significantly the effect of realkalization.

Electrochemical repair techniques in carbonated concrete. Part I: electrochemical realkalisation

Corrosion induced by concrete carbonation can be controlled through the application of electrochemical techniques such as cathodic protection (CP) or electrochemical realkalisation (ER). These methods are generally considered effective in the repair of structures; however, few data are available on the effects of different parameters such as the concrete composition or the exposure conditions. For the temporary technique of ER, moreover, scarce information exists on the durability of the treatment. An experimental research was carried out, aimed at investigating some aspects connected with the application of these techniques in reinforced carbonated concrete. Six different types of concrete mixes were considered. The tests were performed both in a wet and a dry environment. The effect of the pre-corrosion of the reinforcement in concrete was also considered. This article presents results obtained with the technique of ER and discusses the role of the different factors considered. The technique of CP will be discussed in Part II.

Electrochemical repair techniques in carbonated concrete. Part II: cathodic protection

The role of several factors such as concrete composition, exposure condition and pre-corrosion of steel reinforcement in concrete on the effectiveness of the electrochemical realkalisation (ER) technique was discussed in Part I of this article (Bertolini and Redaelli in J Appl Electrochem, doi:10.1007/s10800-011-0301-4, 2011). Here the same factors will be considered in the case of cathodic protection (CP). CP differs from ER since it is a permanent technique with much lower applied current density. It was originally introduced to protect steel from corrosion in chloride-contaminated concrete; however, it can be advantageous even in carbonated concrete, in particular compared to conventional repair. CP tests were carried out on reinforced specimens made with six different types of concrete, subjected to accelerated carbonation. CP was applied with a current density of 10 mA m−2 of steel preceded by a start-up current density of 100 mA m−2 for 3 weeks. Reference specimens in the same conditions were also considered.