Corrosion Behavior Of Steel Rebar Research Articles

Electrochemical and corrosion behavior of steel rebars in concrete exposed to industrial SO2 and CO2 environment

Investigation into the corrosion mechanism of steel rebars in concrete under the combined influence of SO2 and CO2 is crucial for addressing the corrosion issues in reinforced concrete structures exposed to industrial environments. This study investigated the electrochemical and corrosion behavior of steel rebars in concrete under the combined influence of SO2 and CO2 using electrochemical methods, pH and SO42- concentration tests at the concrete/steel matrix interface, and surface analysis. During the corrosion process, a competitive chemical reaction between SO2 and CO2 occurs. The electrical resistance (Rc) of the concrete cover layer undergoes initial rapid growth, followed by slower increments, and then another period of rapid growth before eventually stabilizing. However, Rc sharply decreases over time, corrosion-induced damage in the concrete cover layer. CO2 diffuses to the vicinity of the rebar before SO2, inducing rebar depassivation. As rust severity increases, significant changes in the rust products are observed, with Fe(III) compounds transforming into Fe(II) compounds, and FeSO4·4H2O and FeSO4·7 H2O are prevalent in the rust products. Furthermore, the formation of ferrous sulfate compounds can lead to local acidification, thereby accelerating the corrosion rate, and hastening the aging and deterioration of the structure, posing a serious threat to the safety of the building structure.

Effect of carbonation on the corrosion behavior of steel rebar embedded in magnesium phosphate cement

Magnesium Potassium Phosphate Cement (MKPC) as a protective binder for steel rebars has been well-established. However, corrosion performance of steel rebars in MKPC subjected to carbonation is still unknown. This investigation aimed at revealing the impact and mechanism of carbonation on corrosion performance of steel rebars in MKPC using electrochemical techniques and surface analyses. The findings indicate that, unlike Portland cement (PC) system, carbonation positively influences corrosion performance of steel rebars when embedded in MKPC, as demonstrated by comparable (M/P = 7) or even higher (M/P = 12) corrosion resistance values. Under carbonation, the ingressive CO2 reacts with Mg-bearing phases in MKPC to form nesquehonite with a higher pH, while the MgO still keep supersaturated. The resultant increase in pH facilitates formation of ferrous oxide and iron phosphate/borate within oxide film developed on steel surface, which enhances protective capability of oxide film and consequently improves the corrosion resistance of the steel rebars.

Steel rebar corrosion and corrosion-induced cracking in reinforced foamed concrete

This study investigated the corrosion behavior of steel rebar in foamed concrete and the effects of water-cement ratio, fly ash, and fiber on reinforced foamed concrete’s corrosion rate and crack width. It was found that the corrosion rate of steel rebar and crack width of foamed concrete increased slowly with time and then developed rapidly, finally growing slowly. The higher the density of foamed concrete, the stronger the corrosion resistance of steel rebar. The best corrosion resistance of steel rebar in foamed concrete is achieved when the water-cement ratio is 0.5, fly ash and fiber are 20% and 0.6%, respectively.

Effect of Nano-SiO2/PVA on Corrosion Behavior of Steel Rebar Embedded in High-Volume Fly Ash Mortar under Accelerated Chloride Attack.

In this paper, the influence of Nano-silica (NS) and Polyvinyl alcohol (PVA) fibers on the corrosion behavior of steel rebar embedded in high-volume fly ash cement mortars under accelerated chloride attack was studied by using an impressed voltage technique. The PVA fibers used were 1.0 vol.%, and two mass fractions of cement (50 and 60 wt.%) were replaced by fly ash. Four NS mass fractions (0, 0.5, 1.0, and 1.5 wt.%) were utilized in this paper. In addition, the mono and hybrid effects of NS and PVA on the mechanical properties and water absorption of mortar were also studied. The results showed that the incorporation of PVA and nano-SiO2 can improve the flexural and compressive strengths of high-volume fly ash mortar. Generally, the flexural and compressive strengths increased with the increase of nano-SiO2 content. Moreover, the incorporation NS can also reduce the capillary water–absorption rate of cement mortar. The impressed voltage corrosion test indicated that the composite incorporation of nano-SiO2 and PVA can significantly delay the deterioration process of steel bars in mortar, effectively reducing the steel rebar’s corrosion level and increasing the exposure time of the surface crack. With hybrid-incorporation 1.0 vol.% PVA and 1.0 wt.% nano-SiO2, the steel rebar had the lowest corrosion degree, which exhibited a mass loss of 49% and increased the broken time by 71% as compared to the control mortar.

Durability of Reinforced Concrete Containing Biochar and Recycled Polymers

In the field of sustainable construction materials, the production of eco-friendly concretes, obtained by the addition of waste products such as biochar and recycled polymer particles, offers interesting alternatives to traditional materials. Biochar is a carbonaceous solid by-product obtained from the thermo-chemical conversion of biomass and its addition into concrete admixtures can offer an eco-friendly carbon sequestration solution, capable to slightly improve concrete properties. Recycled polymer materials can be used to partially replace conventional aggregates with the aim of obtaining lighter concretes that help to face the disposal challenge presented by this non-degradable plastic waste. However, the influence of these waste additions on the corrosion behavior of steel rebars embedded in these “eco-concretes” is still unexplored. Within this context, this work presents some results of an extensive study dealing with the concrete mechanical and physical properties and the rebar corrosion resistance during cyclic exposures to chloride-containing solutions.

Role of mill scale on corrosion behavior of steel rebars in mortar

The role of mill scale on the corrosion behavior of steel rebars in mortar was studied using Hyperbaric-Oxygen Accelerated Corrosion Tests (HOACT) and polarization measurements. Defects of mill scale deteriorated passivity of rebars when mortar and saturated Ca(OH)2 solution contained chloride. Localized corrosion beneath mill scale with defects was responsible for the acceleration of depassivation. SEM observations and Raman spectroscopy measurements revealed that a Fe3O4 layer initially formed under the mill scale and further corrosion resulted in migration of Fe ions through the defects and formation of a rust layer mainly composed of α- and γ-FeOOH on the mill scale.

Corrosion behaviour of steel rebar: effect of simulated concrete pore solution and chloride ions

In this work, we investigate the corrosion behavior of steel rebar (SR) in four simulated concrete pore solutions (CPS): NaOH+KOH (CPS1), Na 2 CO 3 (CPS2), NaOH (CPS3) and Ca(OH) 2 (CPS4) medium. Effect of addition of Cl - anions as pollutant on pitting and uniform corrosion of SR is investigated by using potentiodynamic polarization (PDP) technic. The result obtained show that uniform and pitting corrosion of SR are strongly influenced by the nature of simulated CPS. In unpolluted CPS’s, only uniform corrosion of SR is observed in all cases. SR has excellent corrosion resistance in CPS4 compared to the other simulated CPS. In the polluted CPS’s by Cl - anions, we observe an accelerated uniform corrosion especially in CPS1, CPS3 and CPS4 mediums. The sensitivity to localized corrosion of SR varies from one simulated environment to another. It has the best resistance to pitting corrosion in polluted CPS3 medium. In CPS1 (pH = 13) and CPS2 (pH = 11.6) polluted by 3% NaCl, the tendency to pitting corrosion is the same. The localized attack is more pronounced in polluted CPS4 (pH=12.7). These results demonstrate that there are no limit values of the pH and the content of Cl - ions for the initiation of pitting and / or uniform corrosion. Therefore, it is the chemical composition of the simulated medium which imposes the pH value and the Cl - content for systematic corrosion study of the SR in the simulated CPS.

Feasibility of utilizing 2304 duplex stainless steel rebar in seawater concrete: Passivation and corrosion behavior of steel rebar in simulated concrete environments

AbstractThe feasibility of using 2304 duplex stainless steel rebar in seawater concrete was determined by studying the passivation and corrosion behavior of steel in solutions simulated curing and service stage of concrete, respectively. The results demonstrate that 2304 duplex stainless steel rebar could be used with seawater concrete because of a stable passive film formed on the steel surface during the curing stage of concrete even in the presence of 2 M chloride ions. However, due to the synergistic effect of concrete carbonation, the rebar suffered a corrosive attack by chloride due to the lack of OH− inhibition.

Corrosion behavior of steel rebar embedded in hybrid CNTs-OH/polyvinyl alcohol modified concrete under accelerated chloride attack

This study evaluated the mono and hybrid effects of hydroxyl carbon nanotubes (CNTs-OH) and polyvinyl alcohol (PVA) on the corrosion behavior of steel rebars embedded in concrete under accelerated chloride attack by an impressed voltage technique. The contents of CNTs-OH and PVA were fixed at 0.5% and 1% by weight of cement, respectively. Mechanical tests showed that hybrid CNTs-OH/PVA improved the flexural strength and compressive strength by 20% and 9%, respectively. The Mercury Intrusion Porosimetry test showed that adding CNTs-OH/PVA reduced the total porosity and macro-pore content of concrete by 29.9% and 83.2% over the control concrete, respectively. The impressed voltage corrosion test indicated that hybrid CNTs-OH/PVA significantly delayed the deterioration progress of the steel rebar in concrete, as the corrosion level of the steel rebar decreased by 94% and the exposure time increased by 60% before the generation of the surface crack compared to those of the control concrete. The mechanisms for the hybrid effects of CNTs-OH and PVA on enhancing the steel corrosion resistance in concrete include: 1) uniform dispersion of CNTs-OH in PVA colloid; 2) pore-filling effect of both CNTs-OH and PVA; and 3) PVA coated CNTs-OH form electric capacitors to restraint the transport of free ions. The findings in this study reveal the potential of hybrid CNTs-OH/PVA modifiers to improve the corrosion resistance of steel rebars in concrete.

Corrosion behaviour of steel rebar in mortars subjected to magnesium sulfate and sodium chloride mixtures at 5 and 20 °C

Although exposure to sulfate and chloride ions separately is known to result in deterioration of concrete and corrosion of steel rebars, the effects of both ions being simultaneously present are ambiguous, with some studies showing the presence of chloride to be beneficial, while in others attack was accelerated. This paper describes an investigation into the corrosion activity of steel rebars embedded in cement mortars made with CEMI and CEMI blended with 10% limestone filler subjected to combined sulfate (0.6% SO4−2 and 0.152% Mg+2 as Epsom salt) and chloride (0.5 and 2.0% Cl−) at both 5 and 20°C. Evaluation was made by means of linear polarization resistance (LPR) and visual inspection of the mortar specimens and the rebar surfaces. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were also carried out on selective materials collected from steel-mortar interfaces. Mortar specimens stored in composite sulfate and 0.5% chloride solution at 5°C showed deterioration due to thaumasite formation and the associated rebars suffered greater corrosion than for other mixtures. It is concluded that thaumasite formation resulting in the loss of chloride binding in the cement mortars is a crucial factor in accelerating steel corrosion.

Monitoring corrosion of reinforced concrete beams in a chloride containing environment under different loading levels

Corrosion has significant adverse effects on the durability of reinforced concrete (RC) structures, especially those exposed to a marine environment and subjected to mechanical stress, such as bridges, jetties, piers and wharfs. Previous studies have been carried out to investigate the corrosion behaviour of steel rebar in various concrete structures, however, few studies have focused on the corrosion monitoring of RC structures that are subjected to both mechanical stress and environmental effects. This paper presents an exploratory study on the development of corrosion monitoring and detection techniques for RC structures under the combined effects of external loadings and corrosive media. Four RC beams were tested in 3% NaCl solutions under different levels of point loads. Corrosion processes occurring on steel bars under different loads and under alternative wetting - drying cycle conditions were monitored. Electrochemical and microscopic methods were utilised to measure corrosion potentials of steel bars; to monitor galvanic currents flowing between different steel bars in each beam; and to observe corrosion patterns, respectively. The results indicated that steel corrosion in RC beams was affected by local stress. The point load caused the increase of galvanic currents, corrosion rates and corrosion areas. Pitting corrosion was found to be the main form of corrosion on the surface of the steel bars for most of the beams, probably due to the local concentration of chloride ions. In addition, visual observation of the samples confirmed that the localities of corrosion were related to the locations of steel bars in beams. It was also demonstrated that electrochemical devices are useful for the detection of RC beam corrosion.

Study of EMISE Ionic Liquids Inhibitor on the Corrosion Behavior of Steel Rebar by Statistical Methods in Alkaline Chloride Solution

The pit corrosion behavior of steel rebar in alkaline chloride solutions without and with EMISE ionic liquids inhibitor were investigated by means of electrochemical noise (EN). The experimental results of electrochemical noise measurement revealed that the pit corrosion was inhibited and corrosion pitting process was retarded significantly. The mechanism of the inhibition effect of the inhibitor was analyzed based upon the combined stochastic theory and shot noise theory using the Weibull distribution and Gumbel distribution function.

Corrosion behaviour of steel rebars in reinforced concrete containing thermoplastic wastes as aggregates

In the frame of an extended research program dealing with the utilization of thermoplastic wastes in concrete, the effect of the above polymers on the reinforcement corrosion of concretes containing them as aggregates has been studied. Two types of thermoplastic waste were used, high density polyethylene and polypropylene. Measurements were carried out in order to investigate whether the corrosion behaviour of the rebars has changed due to the replacement of the conventional aggregates by the polymers, up to 240days of immersion of specimens in 3.5wt% NaCl solution. Results showed that the replacement of conventional aggregates by the two polymers studied does not worsen rebars’ corrosion behaviour.

Corrosion behaviour of steel rebars embedded in a concrete designed for the construction of an intermediate-level radioactive waste disposal facility

The National Atomic Energy Commission of the Argentine Republic is developing a nuclear waste disposal management programme that contemplates the design and construction of a facility for the final disposal of intermediate-level radioactive wastes. The repository is based on the use of multiple, independent and redundant barriers. The major components are made in reinforced concrete so, the durability of these structures is an important aspect for the facility integrity. This work presents an investigation performed on an instrumented reinforced concrete prototype specifically designed for this purpose, to study the behaviour of an intermediate level radioactive waste disposal facility from the rebar corrosion point of view. The information obtained will be used for the final design of the facility in order to guarantee a service life more or equal than the foreseen durability for this type of facilities.

Influence of a biopolymer admixture on corrosion behaviour of steel rebars in concrete

AbstractAmong the multitude of concrete structure pathologies, corrosion of rebars is one of the most important problems of concrete durability. In the context of sustainable development, it appears of primary importance to develop new means to protect the rebars against corrosion. This study aims to develop a new eco‐friendly and corrosion‐inhibiting admixture based on EPS 180 exopolysaccharides, biopolymers used in coatings already studied for the corrosion inhibition on steel in seawater. C15 rebars embedded in CEMI and CEMV cement paste containing EPS 180 were immersed in natural seawater and their electrochemical behaviour was studied using open circuit potential measurements and electrochemical impedance spectroscopy. These tests highlight the decrease of the cathodic reaction kinetics due to the EPS 180 action at the rebars surface, and the absence of effect on the passive layer. Capillary imbibition tests carried out on cement paste and mortars showed that although limiting the imbibition kinetics for cement pastes, the EPS 180 did not influence the water imbibition of mortars. Tests comparing capillary imbibition of soaked cement pastes and mortars with EPS 180 solution and the same samples containing the EPS 180 admixture highlight that the corrosion inhibition induced by EPS 180 admixture is more due to the modification of the cement – rebars interface than to the clogging of the cement porous network.

Corrosion behavior of steel rebar in coal gangue-based mortars

Corrosion of steel rebar is the most important durability problem of reinforced concrete. The aim of this research was to investigate the corrosion behavior of steel rebar in simulated pore solutions and gangue-blended cement mortar. The simulated pore solutions were based on the pore solution composition of gangue-blended cement. The pH and Cl− concentration of simulated pore solutions had significant effects on corrosion potential. However, an increase in pH reduced the influence of Cl− concentration on corrosion potential. The corrosion behavior of steel rebar in gangue-blended cement is different from that in simulated solutions. The gangue cementitious mortar surrounding steel rebar provides stable passivity environments for steel, leading to a decrease in ion diffusion coefficients. Alternating current impedance (ACI) analysis results indicated that the indicator Rc for concrete resistivity is higher for gangue mortar than for ordinary Portland cement (OPC), which improves its corrosion potential. The results from energy dispersive X-ray analysis (EDX) showed more aluminates and silicates at the rebar interface for gangue-blended cement. These aluminates improve the chloride binding capacity of hydrates in mortar, and increase the corrosion protection of steel rebar.

Influence of Organic Inhibitors on the Corrosion Behavior of Steel Rebar insideMortar Specimens Immersed in Saturated NaCl Solution

The long. term effects of four kinds of amine. alcohol based inhibitors on the corrosion behavior of steel rebar inside mortar specimens immersed in saturated NaCl solution were studied by electrochemical impendence spectroscopy (EIS), half cell corrosion potential (E(corr)), and macrocell corrosion current density (I(corr)) measurements. We found that the E(corr) and the impedance modulus were higher than those in the control specimen after inhibitor addition. Additionally, I(corr) decreased over the initial 100 d of immersion revealing that the steel rebar electrodes are kept in passive state and the inhibitors showed good inhibition effects. With an increase in the immersion time, E(corr) and the impedance modulus for all the inhibited mortar specimens decreased while I(corr) increased. After immersion for 125 d there were no obvious differences between E(corr) and I(corr) for the inhibited systems by comparison to those in the blank sample, except for the specimen containing CI-4. This suggests that the surface of the electrode changes from passive state to active state. The best inhibition was obtained in the presence of the CI-4 inhibitor. We briefly discuss the inhibition mechanism based on the competitive adsorption of the inhibitor molecules with Cl(-) on the steel rebar surface.

Corrosion Behavior of Steel re-bars in Mortar, Containing Waste Products

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Current research in Egypt on optimisation of combined mechanical strength and corrosion behaviour of steel rebar

The effect of accelerated water cooling on the mechanical and corrosion properties of steel rebars produced from steel with composition of 0·17–0·286%C, 0·62–0·72%Mn, 0·15–0·20%Si has been assessed. The bars were rolled from continuously cast steel billets to 12, 16, 20 and 25 mm diameter. Immediately after the last rolling stand the steel bars entered the quenching box. Cooling conditions were varied by changing the number of cooling nozzles and the water flowrate. Initial bar temperature and equalised temperature were calculated using a mathematical model and recorded by pyrometers at the entry of the quenching box and the entry of the cooling bed. Corrosion resistance was determined potentiodynamically and by immersion tests in NaCl and Ca(OH)2 solution. Equalising temperature decreased with increasing cooling time and water flowrate. Yield strength and ultimate tensile strength (UTS) increased and elongation decreased with decreasing equalising temperature, indicating that different steel grades can be obtained from billet of the same composition using accelerated cooling. Though no direct relationship was observed between mechanical properties and corrosion resistance, the results indicate that cooling conditions and process parameters for thermomechanical treatment should be selected on the basis of corrosion requirements as well as to produce the desired mechanical properties.

Electrochemical Impedance Spectroscopy as a Tool for Studying Steel Corrosion Inhibition in Simulated Concrete Environments—Red Mud Used as Rebar Corrosion Inhibitor

Abstract Red mud is the main by-product of the Bayer process for alumina extraction from bauxite. Rich in iron, aluminum and silicon oxides, it is believed to have corrosion protection properties. Some are studied in the present paper. The corrosion behavior of steel rebars in chlorine containing solutions and mortars is studied and compared with the same systems containing red mud in suspension (case of solutions) or added as powder to the mix (case of mortars). The results in solution show that red mud is able to maintain steel passivity for more than 90 days in highly chlorinated alkaline solutions while in NaOH and Ca(OH)2 solutions having the same pH pit formation is observable at 25 and 55 days, respectively. Additions of red mud to mortar as powder representing 2 % by weight of cement are able to block chloride depassivation. EIS data allow understanding the protecting mechanism and comparing the behavior in mortar and in solution.