Corrosion Resistance Of Steel Rebars Research Articles

Corrosion behavior of modified cement-based coated steel rebar subjected to different levels of tensile loads

Polymer-modified cement-based coating can provide corrosion protection for steel rebar. However, after the action of the tensile load, the connection between the polymer and the cement matrix was weakened, thus reducing its corrosion resistance. In this study, silica fume, nano-SiO2, and corrosion inhibitor were used to modify EVA (Ethylene Vinyl Acetate Copolymer) and cement-based coatings. Electrochemical experiments were used to evaluate the corrosion behavior of coated steel rebar after the action of different levels of tensile loads, and microscopic characterization and porosity experiments were applied to analyze the changes of microscopic properties of the coatings. The experimental results show that silica fume and nano-SiO2 produce more high-strength C–S–H gels through hydration reaction to improve the tensile properties and compactness of the coating, thus reducing the porosity and chloride ion permeability of the coating after tension. Tetrabasic-modified cement-based coated steel rebar with EVA, silica fume, nano-SiO2, and amino-alcohol corrosion inhibitor displayed the highest coating resistance and the lowest corrosion current density under the action of tensile load. Experimental results proves that nano-SiO2 enhances the tensile properties of the coating. The addition of corrosion inhibitor can further improve the compactness of the coating under tension, hinder the formation of chloride ion transport channel, and adsorb on the surface of steel rebar to improve the corrosion resistance of steel rebar.

Comparative study of corrosion inhibition effect on steel rebars in carbonated concrete-pore-solutions: Tolyltriazole vs. sodium phosphate

Concrete structures exposed to carbonated environments are susceptible to steel reinforcement corrosion, leading to structural deterioration and reduced service life. In this research, the effectiveness of two commonly used corrosion inhibitors, tolyltriazole (TTA) and trisodium phosphate (TSP), in carbonated concrete pore (CCP) solutions was compared to enhance the corrosion resistance of steel rebar. The study involved the preparation of simulated carbonated concrete pore solutions to mimic the environment of concrete structures exposed to carbonation. The concrete-pore solutions were simulated by immersing the specimens in a carbonation chamber. Electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) tests were performed to evaluate the corrosion resistance of the steel rebars. The corrosion potential, polarization resistance, and corrosion current density were measured and compared among the different groups. Additionally, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses were conducted to examine the surface morphology, chemical composition and corrosion products formed on the steel rebars. The CCP solution with equal concentrations of TTA and TSP demonstrated the highest corrosion resistance and corrosion inhibition efficiency. TTA and TSP effectively inhibit pitting corrosion of steel in CCP solution, according to SEM, EDS, and XPS analyses. The findings suggested that there is a competitive interaction between phosphate ions and TTA on the steel surface, leading to an antagonistic impact on corrosion inhibition. It was suggested that the [Fen(TTA)p]m complex would produce a protective coating on the surface of steel, which would act as a synergistic inhibitor.

Mechanical Properties and Corrosion Behavior of Dual-Filler-Epoxy-Coated Steel Rebar under a Corrosive Environment

The deterioration of steel rebar in reinforced concrete is a major issue that reduces RC structures’ durability and structural integrity. Significant efforts have been devoted to developing high-performance coatings to provide efficient protection of the rebar, and one promising approach is to utilize nanofiller as additives to improve the performance of polymer resins. This study aimed to improve the corrosion resistance of steel rebar by applying an epoxy coating with graphene nanoplatelets (GNPs) and silica nanopowders (NSs) as additives. The corrosion behavior of nanocomposite-coated rebars was characterized via an electrochemical impedance spectroscopy (EIS) test, and salt spray exposure was utilized to evaluate the durability of the coated rebars. Investigation of abrasion resistance and mechanical properties of the coatings was conducted using the falling sand test and tensile coupon test. In addition, the nanocomposites were scanned by micro-CT to explore the effect of binary nanofillers on the intactness of the polymeric matrix. The GNP-NS hybrid filler reduced the void fraction to 0.002%, whereas the void fraction in pure epoxy was 0.07%. Significant reinforcement was found in the mechanical properties; the addition of GNP-NS hybrid filler increased the tensile strength to 37.1 MPa, a 56% increase compared to the pure epoxy. Additionally, the GNP-NS hybrid fillers have led to an improvement of 16% in the Young’s modulus. In terms of corrosion resistance, the Rc value of rebar coated with GNP-NS coating was about three times greater than the ones coated with a single-filler epoxy coating during the initial test, and this value remained undegraded after 200 hr of exposure. In contrast, the group containing hybrid fillers displayed the lowest thickness loss following abrasion testing, with a 74% reduction in thickness loss, showing the coating’s high abrasion resistance. Hence, the results reveal that GNP-NS hybrid fillers have superior wear resistance, mechanical capabilities, anticorrosion properties, and durability. This research provides valuable insights into developing and implementing high-performance polymeric material to protect steel rebars in concrete structures, therefore significantly increasing the sustainability of concrete structures.

Fire endurance and corrosion resistance of nano-modified cement mortars exposed to elevated temperatures

In this study, the influence of high temperature on corrosion resistance of steel rebars and the mechanical strength of nano-modified mortars is investigated. Two (2) different mixtures were prepared and tested in the lab; mortars containing 0.2 wt% multi-walled carbon nanotubes (MWCNTs) and mortars without nanomaterials for comparison reasons. The specimens were heated in a furnace up to 800οC for 1 h. Destructive and non-destructive tests were used to evaluate the fire resistance and durability performance of cementitious materials. In particular, the corrosion protection provided by nanomaterials was investigated using electrochemical and mass loss measurements on reinforcing steel, whilst strength tests of mortars were also carried out to evaluate their mechanical behavior after exposure in elevated temperatures. SEM and XRD techniques were used to analyze the surface and microstructure of the steel bars and mortars. The results showed, that the CNT addition slightly improves the strength and durability of mortars exposed to high temperatures as compared with the plain OPC mortar. At the same time, the corrosion resistance of steel rebars was enhanced using carbon nanotubes in mortars after exposure to high temperatures.

Attempt to Optimize the Corrosion Resistance of HRB400 Steel Rebar with Cr and RE.

The corrosion resistance of the HRB400 steel rebar alloyed with Cr and rare earths (RE) was systematically studied from two aspects, including the properties of the passive film and the protectiveness of the rust layer. The results presented that Cr increased the corrosion resistance of the steel rebar through stabilizing the passive film and was not involved in the formation of corrosion pits, while the pitting corrosion was initiated by the dissolution of (RE)2O2S inclusion, resulting in the local acidification at the bottom of the corrosion pits, which decreased the stability of the passive film. As for the long-term corrosion process, both Cr and RE decreased the corrosion rate of the steel rebar, which was related to the promotion effect on the formation of α-FeOOH in the rust layer from Cr and RE.

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.

Ammonium Phosphate as Inhibitor to Mitigate the Corrosion of Steel Rebar in Chloride Contaminated Concrete Pore Solution.

In the present study, different amounts, i.e., 1–3 v/v% of 1 M ammonium phosphate monobasic, were used as an eco-friendly corrosion inhibitor to mitigate the corrosion of steel rebar exposed to simulated concrete pore (SCP) + 3.5 wt% NaCl solution at a prolonged duration. Potentiodynamic polarization results show that as the amount of inhibitor is increased, the corrosion resistance of steel rebar is increased. The steel rebar exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution exhibited nobler corrosion potential (Ecorr), the lowest corrosion current density (icorr), and 97.62% corrosion inhibition efficiency after 1 h of exposure. The steel rebars exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution revealed higher polarization resistance (Rp) and film resistance (Ro) with exposure periods compared to other samples owing to the formation of passive film. The scanning electron microscopy (SEM) of steel rebar exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution showed homogenous and uniform dendritic passive film which covers all over the surface, whereas, bare, i.e., SCP + 3.5 wt% NaCl solution exposed samples exhibited pitting and irregular morphology. Raman spectroscopy results confirm the formation of goethite (α-FeOOH), maghemite (γ-Fe2O3), and iron phosphate (FePO4) as a passive film onto the steel rebar surface exposed to 3% inhibitor-containing SCP + 3.5 wt% NaCl solution. These phases are responsible for the corrosion mitigation of steel rebar which are very protective, adherent, and sparingly soluble.

Corrosion resistance evaluation of rebars with various primers and coatings in concrete modified with different additives

Corrosion of steel rebars in concrete can reduce the durability of concrete structures in coastal environments. The corrosion rate of these concrete structures can be reduced by using suitable concrete additives and coating on rebars. This paper investigates the corrosion resistance of steel rebars by the addition of pozzolanic materials including fly ash, silica fume, polypropylene fibers, and industrial 2-dimethylaminoethanol (FerroGard 901) inhibitors to the concrete mixture. Three different types of rebars including mild steel rebar st37, and two stainless steel reinforcements, AISI 304 and AISI 316, were used. Various types of primer and coating including alkyd based primer, hot-dip galvanized coatings, alkyd top coating, zinc-rich epoxy primer, polyamide epoxy primer, polyamide epoxy top coating, polyurethane coatings, double layer of epoxy primer and alkyd top coating, and double layer of alkyd primer and alkyd top coating were applied on steel rebars to investigate the effect of coating type on the corrosion resistance of steel rebars in concrete. Polarization tests, electrochemical impedance spectroscopy, compressive strength and color adhesion tests were conducted. The best reinforced concrete mix design for corrosion resistance was the one including the rebar with zinc-rich epoxy primer and 25% fly ash, 10% silica fume, and 3% FerroGard 901 inhibitors by cementitious material weight. Polyurethane was the best coating due to the highest strength and the lowest corrosion rate. Alkyd primer was the weakest coating, although it was the most economical coating system.

Effects of corrosion inhibitor and functional components on the electrochemical and mechanical properties of concrete subject to chloride environment

This study aims to solve the long-term durability issues regarding chloride-induced corrosion of concrete structures. The electrochemical methods were used to investigate the anticorrosion performance of migrating corrosion inhibitor (MCI-0), and the axial compression and electric flux of high performance concrete with different mix formulations incorporating inhibitor, nano-components and functional components were performed. The results showed that the corrosion resistance of steel rebar greatly was improved with the addition of inhibitor. Meanwhile, the corrosion inhibitor revealed a satisfactory electrochemical performance, and the polarization potential of reinforced bar maintained stable when ≥2% of the inhibitor was added to the concrete. While the dosage of nano-components (i.e., nano-SiO2) reached 2%, the strength and electric flux of concrete can meet the performance requirements. And the mechanical and electrochemical properties of reinforced concrete were effectively improved when the electric flux was less than 1000 Coulombs with 15% of compound functional components included. However, the electric flux dropped significantly while mineral admixtures and corrosion inhibitor were incorporated simultaneously, and they present a synergistic effect on the durability of concrete. In view of the field marine environment exposure test in splash zone, the addition of 20% nano-modified cementitious material can improve the strength of concrete and the resistance to chloride ions penetration within samples, indicating the corrosion inhibitor and functional components are promising and applicable in marine engineering.

Effects of lightweight sand and steel fiber contents on the corrosion performance of steel rebar embedded in UHPC

Ultra-high-performance concrete (UHPC) is able to provide better protection for embedded steel rebar from corrosion due to its superior impermeability characteristics. Lightweight sand (LWS) and steel fibers are utilized in mixing UHPC to promote internal curing and improve flexural strength, respectively. But the effects of different contents of LWS and steel fibers on the corrosion performance of steel rebar and resistance of UHPC matrix are rarely investigated. In this study, steel bar reinforced UHPC specimens with different LWS and steel fiber contents were prepared for electrochemical tests, involving open circuit potential (OCP), Tafel polarization, linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS). The experiment results indicated OCPs values based on ASTM C876 could not be applied to decide the corrosion state of steel rebar since lower content of oxygen in UHPC reduced the cathodic reaction, which led to lower OCP values. Chloride ions did not penetrate into UHPC matrix and steel rebar were in passive state in the whole test period of 147 days (d). Corrosion resistance of steel rebar, and resistance of UHPC matrix and passive film displayed an increasing trend with time. Generally, the resistance decreased when the LWS and steel fiber contents were increased. This is because LWS increased the permeability of UHPC and steel fibers led to shortcut of current. For better electrical resistance and compressive strength of UHPC, it is recommended to limit the LWS replacement ratio to 25%. It is also concluded that, steel fiber with the volume content up to 3% will not lead to corrosion of steel rebar and can be safely used in UHPC.

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.

Application of statistical analysis to evaluate the corrosion resistance of steel rebars embedded in concrete with marble and granite waste dust

In recent years, the production of waste materials has increased due to the growth of industrial activities around the world. Therefore, recycling and reusing these waste materials for different applications would make a tremendous contribution to waste elimination and sustainable building construction. The objective of this paper is to investigate the effect of marble and granite waste dust (MGWD) as a result of marble and granite stone processing on concrete properties. To achieve this purpose, a total of 15 mixes were prepared with up to 30% of MGWD cement replacement. After 28-day immersion of specimens in lime-saturated water, they were placed in a NaCl solution with 3.5% by weight for 90 days. Then, splitting tensile and compressive strength, scanning electron microscopy (SEM), open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) tests were performed alongside a statistical analysis. The mechanical results indicate that utilizing MGWD as cement replacement at a maximum amount of 20% does not notably influence the mechanical properties of concrete. The OCP assessment revealed that using 10% of granite and 10% of marble waste dust instead of cement enhances the corrosion resistance of steel rebars embedded in concrete, and also increases the potential compared to the other tested concrete mixes.

Improving corrosion resistance of steel rebars in concrete with marble and granite waste dust as partial cement replacement

In this research, the effect of marble and granite waste dust (MGWD) as partial cement replacement (up to 20%) on the mechanical and corrosion behaviour of concrete specimens was investigated. Water cured specimens were kept in a 3.5% by weight of NaCl solution for 92 days. Uniaxial compression and water absorption tests, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and Scanning Electron Microscopy (SEM) analysis were conducted. The compressive strength test results showed insignificant negative effect from using MGWD. OCP and EIS measurements revealed that specimens with 20% cement replacement have higher potentials and corrosion resistance than all the others.

Impedance Measurements to Monitor Concrete Degradation and Rebar Corrosion

The degradation of steel-reinforced concrete is serious problem in infrastructures. It is well known that the rebar corrosion in concrete is strongly influenced by the conditions of cover concrete. Figure 1 shows schemes of interface between steel rebar and concrete. Thin water layer is formed at this interface due to water absorption in the concrete which covers the steel rebar. And this water layer is called “transition zone” in the field of civil engineering. The pH of water at transition zone is high when the concrete is good health status, and the passive film is formed on steel rebar. The breakdown of passive film occurs by neutralization and chloride concentration in the water layer with the degradation of concrete. Corrosion resistance of steel rebar is influenced by the water quality in the transition zone. Thus, we can conclude that rebar corrosion in concrete is electrochemical process at metal/water interface. Electrochemical measurements are useful to investigate the corrosion mechanisms. There are some literatures regarding the electrochemical tests, which are mainly measurements of corrosion potential [1] and polarization curves, to evaluate the stability of passive film formed on rebar in concrete. Dawson et al. [2] applied an electrochemical impedance spectroscopy (EIS) to the investigation of rebar corrosion in concrete because the charge transfer resistance at rebar/concrete interface can be determined from the impedance spectrum. The authors developed an electrode as a sensor probe to monitor concrete degradation and rebar corrosion. A couple of electrodes, which were made of same material as rebar, can be embedded in concrete structure and complex impedance can be measured continuously on the basis of two-electrode method. In this presentation, the authors report the results of three impedance measurements as follows. (1) Impedance between two electrodes in aqueous solution that simulates the water quality of transition zone (laboratory test). (2) Impedance between two electrodes embedded in the concrete which was fabricated in the laboratory. (3) Field test at bridge pier of the highway in coastal marine environment.

Corrosion Resistance of Steel Rebar in Simulated Concrete Pore Solution in Presence of Trisodium Phosphate and Zn2+

The inhibitive performance of Trisodium Phosphate (TSP) in controlling corrosion of rebar steel immersed in simulated concrete pore solution prepared in well water in the absence and presence of Zn2+ has been evaluated by the weight loss method. The formulation consisting of 250 ppm of TSP and 50 ppm of Zn2+ offers 95 % inhibition efficiency to rebar steel. Potentiodynamic polarization and electrochemical impedance studies confirmed that a TSP -Zn2+ system function as an anodic inhibitor and the formulation controls the anodic reaction predominantly. Surface analysis by CV, SEM and AFM confirmed the formation of protective layer on the rebar steel surface.

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.

Chloride-induced corrosion behavior of reinforcing steel in spent fluid cracking catalyst modified mortars

Concrete properties can be improved by various additives. Nowadays there is a strong interest concerning the use of spent fluid catalytic cracking catalyst (SFCC) as an admixture to improve mechanical properties of concrete. This work aims at studying the corrosion resistance of steel rebars in SFCC modified mortar specimens. Results of physicochemical characterization indicate the acceleration of cement hydration due to pozzolanic activity of SFCC. Electrochemical measurements show that the addition of the SFCC enhances corrosion resistance by delaying its corrosion onset and decreasing the corrosion rate. These benefits can be attributed to the reduction of the mortar permeability.

Corrosion resistance and mechanism of steel rebar coated with three types of enamel

Corrosion resistances of steel rebar with different enamel coatings, and with fusion bonded epoxy coatings were investigated in 3.5wt.% NaCl solution by Electrochemical Impedance Spectroscopy (EIS). The sensitivity to damage of the coatings was characterized and it was found that the pure and double enamel coatings can protect the steel rebar better than the mixed enamel coating due to their denser microstructures with isolated pores. Damaged enamel coating was locally corroded, whereas corrosion at a defect often undercut the epoxy coating. The intact epoxy coating offered better corrosion protection than the enamel coatings.

Cement-matrix structural nanocomposites

This paper reviews cement-matrix structural nanocomposites, including those with particulate and fibrous reinforcements. Silica fume is valuable for improving numerous mechanical properties, in addition to enhancing the freeze-thaw durability, the vibration damping capacity, the abrasion resistance, the bond strength with steel rebars, the chemical attack resistance and the corrosion resistance of steel rebars. Furthermore, silica fume decreases the alkali-silica reactivity, the drying shrinkage, permeability, creep rate and thermal expansion. On the other hand, carbon nanofiber is not attractive, as it fails to compete with conventional discontinuous carbon fiber as a reinforcement.

Improving both bond strength and corrosion resistance of steel rebar in concrete by water immersion or sand blasting of rebar

Water immersion (2 days) and sand blasting were similarly effective for treating steel rebars for the purpose of improvement steel-concrete bond strength and corrosion resistance of steel in concrete. The increase in bond strength is due to surface roughening in the case of sand blasting and the presence of a surface layer in the case of water immersion. The increase in corrosion resistance is due to the surface uniformity rendered by either treatment.