Depassivation Of Steel Research Articles

Passivation and depassivation of reinforcement steel in alkali-activated materials—A review

This paper reviews the formation and breakdown of passive film on the surface of reinforcement steel in alkali-activated materials (AAMs) considering the characteristics of reaction product and pore solution chemistry. The literature review shows that the pore solution of AAMs has higher concentrations of OH−, Na+, silica and aluminium compared to Portland cement (PC). This relatively high alkalinity contributes to the generation of a passive film, which has positive effects on the corrosion resistance of reinforcement steel embedded in AAMs. The silica-aluminium zeolite layer present on the surface of passive film adsorbs chloride ions and effectively inhibits chloride-induced depassivation. Generally, lower ratios of [Cl−]/[SO42−] and [Cl−]/[S2O32−] potentially inhibit the depassivation of reinforcement steel. The high pH value and the elevated concentrations of HS− of AAMs contribute to the increase of critical chloride content (Ccrit). However, the higher content of reduced sulfide mainly dissolved from slag results in the consumption of dissolved oxygen, which is necessary for the formation of passive film. Generally, the presence of reduced sulfide forms Fe-S complexes on the surface of reinforcement steel in AAMs. Even so, higher corrosion resistance for AAMs is mostly expected with longer depassivation time due to finer microstructure and lower chloride penetration rates compared to PC-based materials. The decrease in pH value in the pore solution of the AAMs is the main factor affecting carbonation-induced depassivation of reinforcement steel, while high concentrations of bicarbonate and carbonate ions inhibit depassivation.

Failure mode of passive film under electric field and chloride environment in concrete

Exploring the failure mode of passive film is the most fundamental issue for corrosion research and prevention of metals. In the actual service of reinforced concrete structures, steel rebars are typically exposed to a complex solution environment, characterized by electric fields, chloride ions, and fluctuating temperatures. Using scanning electron microscope, scanning electrochemical microscope, and a series of electrochemical tests, we present the damage mode of steel passive film in a simulated alkaline environment of concrete; and then establish a deductive diagram to illustrate it. Additionally, we use atomic force microscope, X-ray photoelectron spectroscopy and transmission electron microscope to explore the structural characteristics of passive film on an atomic scale, and confirm that specific ion channels serve as the pathway for chloride invasion. This study can enable a deeper understanding of the micro-mechanisms involved in steel depassivation and the initiation of corrosion electrochemical reaction.

Accelerated chloride-induced corrosion of hot-dipped galvanized reinforcements and its influence on bond strength to concrete

This work studies the behavior of hot-dipped galvanized steel against chloride corrosion and its effect on its bond strength to concrete. Chloride-induced corrosion was accelerated using an electrical field. Two steel diameters were adopted and bond strength was assessed using a standardized pull-out test, followed by measuring different degrees of reinforcement corrosion. Results show that the initial corrosion of hot-dipped galvanized steel, due to the high alkalinity of fresh concrete, does not affect the performance of reinforced concrete and that galvanized steel has superior bond strength to concrete than non-galvanized steel. The relationship between the degree of corrosion of galvanized reinforcement and its bond strength to concrete occurs according to a regular pattern, independently of the diameters of the reinforcements. The pattern shows an initial increase in bond strength, followed by a stabilization region and then a region where the bond strength decreases with the increase in degree of corrosion. Experimental results also show that the corrosion process of galvanized steel may be represented by an adaptation of Tuutti’s model that shows all the phases of the corrosion process: zinc passivation period, initiation period, depassivation of zinc layer, corrosion propagation of zinc, simultaneous depassivation of steel, and corrosion propagation of steel.

Function of Cu-Sb or Al microalloying on the corrosion resistance of 9Cr steel exposed to simulated concrete pore solution

The role of Cu-Sb or Al on the passivation and Cl-induced depassivation of 9Cr steel in simulated concrete pore solution was systematically obtained via electrochemical tests and microstructure characterization. Both microalloying enhanced electrochemical passivation even if the solution pH dropped. Cu and Al participated in the formation of natural passive film, and the properties of passive film were optimized in terms of resistance, composition, and inner film thickness. However, the chloride threshold level (CTL) was not increased with Cu-Sb microalloying and even decreased with Al microalloying, which is understood from the stability of Al-containing products and the hazards of inclusions.

Gold-sputtered LPG fiber sensor pulse electroplated with iron-carbon for monitoring passivation and depassivation of carbon steel in concrete pore solutions

Monitoring the passivation and depassivation of reinforcement steel is of significant importance, particularly for certain reinforced concrete structures that define the time of steel rebar depassivation as the end of the durability service life. In this study, a gold-sputtered long-period grating (LPG) optical fiber sensor coated with pulse-electroplated iron-carbon is characterized for continuous monitoring of the surface state of carbon steel from passivation to depassivation in concrete pore solutions. Electrochemical corrosion and optical tests are performed simultaneously using an electrochemical workstation and an optical instrument. A protective passivation film with a thickness of approximately 4.05 nm was formed on the iron-carbon coating after 5 days of immersion in the simulated concrete pore solution, and its thickness is nonlinearly correlated with the wavelength shift of the LPG optical fiber sensor during the passivation process. The resonant wavelength changes in the opposite direction after depassivation, which can be used for the detection of the depassivation time. After depassivation, the wavelength shift and mass loss of the iron-carbon coating can be divided into three phases, and a linear relationship exists in each phase. The gold-sputtered fiber sensor coated with pulse-electroplated iron-carbon investigated in this study, demonstrates better performance than silver-deposited LPG fiber sensors.

3D mesoscale investigation of non-uniform steel corrosion in reinforced concrete under chloride environments

Chloride-induced corrosion of steel in reinforced concrete (RC) exhibits complicated mechanisms such as chloride diffusion, oxygen diffusion, electrochemical polarization, dissolution and deposition of steel. This work investigates the 3D non-uniform corrosion behavior of steel in RC by integrating all the possible mechanisms and mesoscale heterogeneities, for the first time. The anodic Tafel slope is used to describe the depassivation of steel induced by chloride, while the dynamic process of oxygen supply and consumption is considered as well as the inhibition of the cathodic reaction caused by oxygen concentration. The coupling of mass transfer and electrochemical corrosion in RC is developed and validated. Mesoscale RC models with realistic aggregate, mortar, steel and interface are generated through a physically-based approach similar to casting procedures. The simulation results show that the 3D mesoscale RC model can simultaneously capture the non-uniform corrosion patterns of steel along the circumferential and longitudinal directions, offering significant application value in accurately predicting steel corrosion morphology. The random distribution of aggregates affects the local non-uniform corrosion of steel, but has little influence on the overall cumulative corrosion level. The local non-uniform corrosion of steel gradually weakens with the increase in chloride erosion time. The non-uniform corrosion of side steel is enhanced with the increase of the steel diameter and the decrease of the protective layer thickness. Bi-directional erosion mainly enhances the uniform corrosion of corner steel.

Durability Assessment of the Laureano Gómez Bridge: a Key Element for New Colombian Infrastructure

AbstractThe durability of reinforced concrete bridges is crucial for ensuring their long‐term functionality and safety. Among the various deterioration mechanisms, carbonation and chlorides are the most significant and widespread problems affecting these structures. This paper aims to assess the durability condition of the historical Colombian Bridge “Laureano Gómez”, which has been in service for over 40 years. The condition assessment involved measurements of the concrete cover, carbonation depths, concrete resistivity, compressive strength, crack survey, and visual inspection of the steel surface. Estimating the remaining service life showed that the stay elements are the most prone to steel depassivation due to carbonation, primarily due to low concrete cover and exposure conditions. The insights from this study could provide valuable information for the durability prognosis of the new bridge built next to it.

Robust numerical solution for assessing corrosion of reinforced concrete structures under external power supply

Impressing current is a popular technique to adjust corrosion behaviors of structures, both in academic investigation and engineering practice. Focusing on the specific problem, this paper presents a robust solution strategy for analyzing corrosion of reinforced concrete structures, under both voltage-controlled and current-controlled power supply. Following fundamental electrochemistry, a nonlinear numerical model incorporating field and global variables is developed, where the ways of considering power supplies with different controlling modes are presented. To tackle the essential global variable to problems under current-controlled power supply, a pseudo discretization method is newly developed to facilitate the highly nonlinear finite element analysis. Given moisture-induced nonuniform concrete resistivity, the moisture field in concrete is also modelled and solved together with the corrosion propagation through a staggered solution scheme. The proposed approach is carefully validated against a variety of reported experiments. Moreover, by directly controlling steel passivation state, the influence of steel depassivation extent on the cathodic protection performance for aging reinforced concrete structures under different saturation degree is numerically investigated for the first time. It is discovered that the protection effectiveness is closely related to the steel depassivation state. It is also revealed that the influence of concrete saturation degree on protection performance in a current-controlled system is generally more complex than that of a voltage-controlled system.

Accelerated test device and method for critical chloride concentration initiating steel depassivation in cement-based materials

Abstract In order to overcome the disadvantages of traditional test devices and methods, new accelerated test device and efficient test method for critical chloride concentration (Ccrit) initiating steel depassivation in cement-based materials were developed. Based on the theory of electromigration, a new accelerated test device for Ccrit was invented first by combining with the chloride electromigration system and electrochemical test system. Then the influences of applied voltage and continuous power-on time on electrochemical parameters including open-circuit potential, polarization resistance, and corrosion current density during the steel depassivation process were investigated. Moreover, an efficient test method for Ccrit was proposed based on the quantitative criterion in terms of corrosion current density. Analysis results show that Ccrit can be measured quickly and accurately based on the accelerated test device and method by selecting appropriate applied voltage (e.g., 3–6 V) and continuous power-on time (e.g., 48–72 h).

Corrosion mechanism of reinforcement in LC3 cement pastes under coupled carbonation and chloride attack

Limestone Calcined Clay Cement (LC3) has good chloride (Cl−) binding capacity and is reported as a qualified binder for concrete manufacture with desalinated sea sand. In this study, corrosion mechanism of reinforcement in LC3 under coupled Cl− and carbonation attack was studied. Electrochemical measurement, optical microscopy and X-ray photoelectron spectroscopy were applied to assess safety of embedded reinforcement; OH− and Cl− profiles in LC3 paste were monitored to evaluate progress of carbonation degree. Results showed that LC3 pastes were carbonated with a pronounced speed, which was due to the decrease in calcium hydroxide content during its hydration stage. Due to decomposition of Friedel's salt and release of Cl−, obvious increase and redistribution of free Cl− were detected and progressed with carbonation duration. Depassivation of mild steel were observed at early stage of carbonation when CO2 had not reached its location, thus it was resulted from carbonation-induced Cl− increase rather than alkalinity decrease under the applied exposure. In summary, LC3 performed a good protection on embedded reinforcement under impact of the premixed Cl−, but this protection diminished quickly at a carbonation scenario.

Influence of tensile stress on chloride-induced depassivation of carbon steel in simulated concrete pore solution

To study the influence of tensile stress on the depassivation behaviour of carbon steel, the critical chloride threshold CCl,crit, chemical composition, surface morphology, thickness, and shedding rate of carbon steel passive films were investigated using electrochemical tests and XPS and SEM analyses. The results showed that CCl,crit decreased gradually, and the shedding rate of the passive film increased remarkably with the applied tensile stress. Slight change of Fe0 content can be found under less tensile stress. As the tensile stress increased to 200 MPa, the content of Fe0 increased significant by about 57%. A correlation model between CCl,crit and the characteristic evolution of the passive film is proposed to describe the depassivation process of carbon steel under tensile stress. The decrease in CCl,crit could be attributed to the degradation of the passive films. Additionally, a relationship between CCl,crit and tensile stress is proposed, and a method for determining the depassivation of carbon steel under stress based on electrochemical parameters is established.

Corrosion of 1.4016 Ferritic Steel by Urea at High Temperature

The corrosion behavior of a ferritic unstabilized stainless steel 1.4016 during decomposition of aqueous urea solution at high temperature has been investigated. Corrosion was obtained from 100 h of cyclic heating (from room temperature up to 600 °C) and injection of aqueous urea solution on the steel plate in a laboratory-scale test bench. The evaluation procedure covered the metallographic analysis of corroded steel samples by high-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (TEM). Uniform corrosion underneath deposits was found as one of the drivers for degradation of the steel. Damage happened by high-temperature depassivation of stainless steel due to the excess of the aggressive medium. Besides uniform corrosion, a nitridation layer underneath surface oxides together with chromium carbonitride particles precipitated through the whole depth of the sample was identified resulting in intergranular attack.

Influence of organic corrosion inhibitors on steel corrosion in concrete under the coupled action of freeze–thaw cycles and chloride attack

Organic corrosion inhibitors (OCIs) are commonly used to enhance reinforced concrete durability in the marine environment. In this contribution, the effects of OCIs on steel corrosion in concrete exposed to coupled deterioration of freeze–thaw cycles and chloride attack have been evaluated. Concrete samples with mild steels were mixed with three commonly used OCIs (alcoholamines-, carboxylic acids-, and esters-based), and exposed to freeze–thaw cyclic test in a 3% NaCl solution. The corrosion-resistance mechanisms of OCIs on steel corrosion were revealed using the open circuit potential test (OPC) and electrochemical impedance spectroscopy measurement (EIS). The steel–concrete interface micromorphology was observed by the optical microscope and the scanning electron microscope (SEM). The results showed that salt-frost resistance of concrete incorporated with alcoholamines-, carboxylic acids-, and esters-based OCIs was improved by about 50%, 350% and 200%, respectively. However, internal damage caused by freeze–thaw cycles was aggravated after adding easter-based OCIs due to the reduction in pore diameter caused by hydrophobic calcium salt lining. Alcoholamines- and carboxylic acids-based OCIs could significantly delay the steel de-passivation. Alcoholamines could increase the passive film resistance and carboxylic acids could replace the chloride attached to the steel surface.

Atomic scale insight into the mechanisms of chloride induced steel corrosion in concrete

Chloride (Cl) induced steel corrosion is a major cause of durability issues of reinforced concrete (RC) structures and causes a large economic loss every year. Understanding the mechanisms of Cl induced steel corrosion in concrete is of great importance to develop anti-corrosion methods and further lowers down the repair and strengthening frequency and cost. Hence, the nature of steel depassivation and corrosion induced by Cl at atomic scale was revealed through the density functional theory (DFT) calculations to better understand the Cl induced corrosion mechanism. The results indicated that Cl species weakened the bonding of oxygen (O) with outer iron (Fe) atoms while enhanced the hybridization of O with inner Fe atoms, thus induced the breakdown of passive films. Besides, Cl facilitated the charge loss of outer Fe atoms and improved the interactions of water molecular (H2O) with these Fe atoms. When co-adsorption with O atom, hydroxyl (OH) generated by dissociative adsorption of H2O enhanced the charge loss of outer Fe atoms. Then OH strongly bonded with the neighboring Fe atoms to form the initial corrosion products, iron hydroxides (Fe-OH). The above DFT calculations are consistent with the experimental results about the steel depassivation and corrosion processes in concrete and hopefully these results can guide the anti-corrosion design of RC structures.

Effect of limestone powder addition on corrosion initiation time of reinforced concrete

This work aimed to evaluate the effects of limestone powder (LP) replacement fraction (8–24 wt%) on chloride diffusion and chloride threshold (Cth) for corrosion initiation. Depassivation of steel was diagnosed by monitoring the self-corrosion potential and corrosion current density using open circuit potential and AC impedance tests, respectively. Corrosion initiation time (Tini) was estimated based on the measured Cth coupled with a dual time-varying diffusion model. The results indicate that the chloride diffusion coefficient decreases with 8 wt% LP addition, though further increase in LP content reverses the trend. With increasing exposure duration, both the surface chloride concentration and diffusion coefficient vary remarkably at first and eventually tend to be stable. As the cover depth decreases from 55 mm to 45 mm, Tini is found to decrease by 30.0%–42.9%. Incorporation of LP appreciably decreases Cth regardless of its replacement fraction, consequently leading to a decreased Tini, despite a low chloride diffusivity can be obtained with appropriate LP addition.

Chloride-induced depassivation and corrosion of mild steel in magnesium potassium phosphate cement

This study investigated the chloride-induced depassivation and corrosion of mild steel in the magnesium potassium phosphate cement (MKPC) pore solutions at different magnesia-to-phosphate (M/P) ratios via several electrochemical methods and surface characterisations. Results showed that although the pH of MKPC is much lower than that of PC, the corrosion resistance of mild steel is significantly higher, with critical chloride values in MKPC being several orders higher than that in PC. Chloride-induced corrosion resistance increases with increasing M/P ratios. Whilst both pH and HPO42-/PO43- ions influence the formation of corrosion products, the pH plays a dominant role in the corrosion resistance.

Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation

Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation

Corrosion prediction models for steel bars in chloride-contaminated concrete: a review

Concern has been expressed in the recent decades about the corrosion prediction of concrete structures in a chloride environment. This paper summarises the corrosion prediction models developed for chloride-contaminated concrete, including both the empirical and electrochemical corrosion models. The definition methods of the steel de-passivation process for electrochemical models, such as anode–cathode ratio (Aa/Ac), critical chloride concentration (CCl,crit), modification of anodic Tafel slope (βa) or passive film resistance (Rf), are considered essential and discussed in detail. Furthermore, electrochemical parameters regarding the definition and selection in electrochemical models and experimental measurements are discussed. This study confirms that Aa/Acand CCl,crithave been generally used in recent years, and that the modifications of βaand Rfrelated to free chloride concentration are technically feasible. In addition, the discreteness of electrochemical parameters in electrochemical models and experimental measurements are observed, and time-dependent characteristics of electrochemical parameters are scarcely presented in the existing literature.

Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation

Role of CaS Inclusions in Pitting Initiation of Carbon Steel: Triggering Steel Depassivation

Depassivation and repassivation of stainless steels by stepwise pH change

AbstractImmersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5‐day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium‐rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.