Corrosion Behavior Of Rebar Research Articles

Effect of endogenous chloride ion on the corrosion behavior of reinforcement embedded in sea-sand UHPC matrix in different immersion environments

Ultra-high performance concrete (UHPC) is an innovative cement-based composite material characterized by extremely high durability and mechanical properties, which provides a potential possibility of using non-desalted sea-sand as aggregate. However, the long-term steel corrosion behavior in UHPC prepared by simulated sea-sand under different immersion environments remains unclear, which is of great significance for the application of sea-sand UHPC in practical engineering. In this study, the pore structure of sea-sand UHPC matrix was measured using nitrogen adsorption/desorption method. The corrosion behavior of rebar in sea-sand UHPC with different endogenous chloride ion contents soaking in pure water and NaCl solution was characterized by linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP). The experimental results show that the initial UHPC pore structure is refined by incorporation of sea-sand, and is similar to that of ordinary UHPC at the later hydration. Regardless of the endogenous chloride ion content and immersion environment, the corrosion rate evaluated by corrosion current density (icorr) and polarization resistance (Rp) of reinforcement in UHPC is extremely low. The measurement of EIS shows that UHPC group has higher matrix resistance (Rc) and charge transfer resistance (Rct), while lower electric double layer capacitance (CPEdl) of reinforcement, which indicates that the steel in UHPC made of sea-sand is still in a state of passivation. However, the steel bar in comparison specimen OPC soaking in NaCl solution is in the corrosion stage. Furthermore, sea-sand UHPC possesses of excellent ability of anti-pitting corrosion of reinforcement after 180 days of immersion in NaCl solution.

Influence of rubber geometrical characteristics on the corrosion behavior of rebar in rubberized concrete

Reinforced concrete containing rubber is widely used in building engineering, roads and other fields due to good vibration damping and energy dissipation of rubber. Unlike ordinary concrete, the corrosion-induced cracks of rubberized concrete may differ significantly from that of ordinary concrete due to the irregularity of rubber morphology. In this paper, the 3D mesoscale model of rubberized concrete containing rebars is developed, and the corrosion behavior affected by rubber geometrical characteristics is studied by numerical simulation and experiment. Chloride ion and stray current are selected as the main simulation factors, and the corresponding experiment is conducted through applying constant current. On the basis, the influence of different rubber contents, rubber shapes and rubber sizes on corrosion-induced cracks of rubberized concrete is considered. The main conclusions are as follows: (1) The rust is centered on the rebar and develops around in a forked shape. Rubber particles accumulated in concrete can delay the damage development to some extent. (2) The damage range of the longitudinal sections of rebars is close, and the damage degree is the largest in the section near the center of rebars. (3) The complete rust layer shows an oval shape with a large upper part and a small lower part. The maximum rust layer thickness is obtained near the position of 80 mm or 85 mm.

Inhibition Mechanism of Oxalhydrazide on Reinforcing Steel in Pore Solution Contaminated by 3.5%NaCl - Experimental and Theoretical Study

Concrete is one among the most consumed materials on the planet secondary to water. However, the degradation of concrete happens due to the corrosion of reinforcement. Although the pore solution of concrete is alkaline, the corrosion of rebars in concrete is triggered due to aggressive ions like chlorides entering the concrete. The most common method of corrosion inhibition is by utilising corrosion inhibitors which when added to the concrete stays in the pore solution and prevents the corrosion of surface of rebars from aggressive ions. Although there are number of inhibitors, the rise in corrosion deterioration demands the need for new potential inhibitors which are highly effective in different aggressive environments. This study is based on the corrosion of rebars in simulated concrete pore solution in the presence of 3.5% NaCl with oxalhydrazide as the potential inhibiting material. The corrosion behaviour of rebar is obtained by electrochemical studies using EIS and potentiodynamic polarization and theoretically analysed employing molecular mechanics and molecular dynamics simulations. The experimental results revealed that the inhibitor is effective in reducing the corrosion and the values of binding energy of the inhibitors on rebar surface also go well with the experimental results. Oxalhydrazide is found effective in minimizing the attack of chloride ion on rebar in pore solution.

Corrosion of rebars in recycled glass concrete under tropical marine environment

AbstractThis study demonstrates the potential use of recycled powder glass as cement replacement to prepare durable concrete and avoid infrastructure corrosion in tropical marine environments using limestone as fine and coarse aggregates. Samples for corrosion measurements were prepared with #3 (∼9.5 mm) bars and without reinforcement for carbonation, chloride penetration, and mechanical strength tests. Powder glass was used as partial cement replacement by 0 %, 5 %, 10 %, and 15 % (weight percent). Over two years, the corrosion behavior of rebars was recorded through corrosion potential measurements and linear polarization resistance. In addition, carbonation depth and chloride penetration were analyzed from samples that were not reinforced. Results showed that replacing cement with glass does not change the mechanical strength at 28 days, but after 90 days of curing showed an increment as a function of time and recycled glass powder amount. The chloride penetration and the carbonation front are reduced substantially. Consequently, a moderate corrosion level was observed when the corrosion onset was established. Excellent corrosion protection was identified for a 0.70 water to cement ratio and 5 % cement replacement.

Corrosion Behavior of Reinforcing Steel with Mill Scale in Concrete

Corrosion of reinforcing steel rebar is a main cause for losing the long-term reliability of concrete structures. When the rebar is corroded, the rust induces cracks and detachment of the cover concrete. On the rebars, the mill scale which is a thick oxide film is formed when the rebar is hot rolled. The role of mill scale on corrosion behavior of rebars in concrete has not been clarified, yet. In this study, the corrosion behavior of rebars with mill scale in concrete was studied using a new accelerated corrosion test we developed. Commercial rebars with 19 mm diameter, which have mill scale of several tens of micrometers in thickness, were used in this study. The corrosion behavior of rebars with and without mill scale in mortar was investigated. To remove the mill scale on the rebar surface, electrolytic polishing was carried out. The rebars with or without mill scale were embedded in mortar with 5.5 mm cover thickness and the sample was cured for 28 days. In order to prompt breakdown of passive film on the rebars, 2.06 M NaCl solution was mixed to the mortar. Using these samples, Hyperbaric-oxygen accelerated corrosion test (HOACT) was carried out [1]. In the HOACT, pressurized oxygen gas is supplied to the sample, and the oxygen reduction reaction on the steel surface is enhanced, which leads to the corrosion acceleration of the steel. In this study, the mortar-covered rebar samples were located in a high pressure gas chamber, and pressurized oxygen gas of 0.6 MPa was supplied. The periods of HOACT were 14, 28 and 56 days. After finishing the HOACT, the samples were embedded in resin, and then the cross section of the sample was observed using an optical microscope. The rust composition was analyzed using Raman spectroscopy measurement. The corrosion of the rebar with mill scale was more significant than that without mill scale. In the case of the sample with mill scale after 14-day HOACT, a rust layer was formed between the steel surface and mill scale, whereas no obvious corrosion was observed on the rebar without mill scale. To investigate the effect of the mill scale on the corrosion resistance of the rebar, anodic polarization measurements of the rebars with and without mill scale were carried out in a saturated Ca(OH)2 solution with Cl-. The pitting potential of the rebar with mill scale was more noble than that of the sample without mill scale. However, when the mill scale was scratched the pitting potential was significantly shifted to the less noble direction and it was below that of the rebar without mill scale. These results show that the mill scale improves the corrosion resistance of the rebar in mortar, whereas the corrosion resistance of the rebar becomes even worth than that of the rebar without mill scale when the mill scale contains defects. After 56-day HOACT of the sample with mill scale, two rust layers were observed above and beneath the mill scale. Raman spectroscopy revealed that the rust layer above the mill scale was mainly composed of a- and g-FeOOH, and the layer just beneath the mill scale was mainly composed of Fe3O4. The rust formed on the sample with mill scale during 14-day HOACT was monolayer just above the steel surface and it was composed only of Fe3O4. It is speculated that the Fe3O4 layer grows under the mill scale at the early stage of corrosion of a rebar. [1] K. Doi, S. Hiromoto, H. Katayama and E. Akiyama, Journal of the Electrochemical Society, 165(9), C582-C589 (2018).

Effect of Ultrasonic Parameters on Electrochemical Chloride Removal and Rebar Repassivation of Reinforced Concrete.

Electrochemical chloride removal (ECR) from reinforced concrete can be considered as an environment-friendly technique since it can reduce the environmental issues arising from demolition and reconstruction. In this study, we used ultrasonic waves to promote the ECR efficiency without increasing the current density so as to shorten the overall power-on time, lowering the power consumption and electricity-induced material damage. Rebar-embedded cement mortar specimens were prepared and a set of ultrasonic-assisted ECR test devices was designed. For obtaining the optimal parameters, different ultrasonic frequencies and powers were adopted to conduct the ECR test. After that, the discharged and residual chloride ion amounts were detected to characterize the ECR efficiency. The corrosion behavior of rebar was characterized by electrochemical method. It was found that ultrasonic waves can not only promote the discharge of chloride ions, but also promote the passivation process of steel bar. For this investigation, the ultrasonic waves with a frequency of 40 Hz and a power of 60 W had the best auxiliary effect and could reduce the work time by 64%. It is considered that the ultrasound-assisted method has potential to promote the application possibilities of the ECR technique.

Effect of Crack on Durability of RC Material under the Chloride Aggressive Environment

Exposed to aggressive environments, the rebar in reinforced concrete (RC) bridges will be corroded gradually. Durability of RC material mostly depends on the rebar corrosion behavior. In this research, influences of crack on rebar corrosion were investigated. Firstly, RC specimens with different crack number, width and spacing were prepared and the rebar corrosion was conducted through an accelerated chloride penetration method. Then, corrosion current densities of rebar were calculated from electrochemical test methods including liner polarization (LP), Tafel potentiodynamic polarization (TPP) and electrochemical impedance spectroscopy (EIS) measurements. Finally, the discussion was presented about a more reasonable electrochemical testing method for rebar corrosion in RC material. Besides, the significant influence factor among crack width, number and spacing was evaluated based on both One-way analysis of variance (One-way ANOVA) and Turkey’s honest significant difference (Turkey’s HSD) test. The results revealed that a more reasonable way to obtain corrosion current densities of rebar is combining EIS measurement with TPP measurement. Crack number shows the most significant effect on corrosion behavior of rebar, while crack spacing possesses the least one.

Corrosion behaviour of rebars 1.4003 in cracks of RC structures containing chlorides

The durability of chloride exposed reinforced concrete components is decisively determined by the corrosion behaviour of the reinforcement in the crack containing chlorides. In this case, high corrosion rates may occur using conventional rebar steel, which can lead to a significant cross-sectional loss of the rebar in a short period of time. One possible way to minimise the risk of corrosion in cracks containing chlorides is to use stainless rebars. Here, mostly expensive stainless steels of the material numbers 1.4571, 1.4401 etc. are used. An efficient alternative is the use of Chromium reinforcing steels (e.g. X2CrNi12) 1.4003. Corrosion tests on cracked reinforced concrete beams with chloride exposure and different chloride concentrations have been carried out in the laboratory of the University of Applied Sciences in Munich. The results of these investigations show a significant increase of the critical corrosion inducing chloride content of the rebars within the cracks. These results will be discussed in regard of the durability of reinforced concrete structures with Chromium reinforcing steels and cracked RC-structures in parking decks and floor slabs.

Effect of chromium micro-alloying on the corrosion behavior of a low-carbon steel rebar in simulated concrete pore solutions

A new low-cost corrosion-resistant rebar (HRB400R) was designed and fabricated by chromium micro-alloying. The effects of Cr on the passivation and corrosion behavior of this rebar in the simulated concrete pore solutions were studied systematically, and its improved corrosion resistance was revealed. In the Cl--free saturated Ca(OH)2 solution, the HRB400R rebar presented nearly the same passive film and similar passivation ability compared to the common carbon steel rebar. In the long-term immersion corrosion test in the Cl--contained Ca(OH)2 solution, the HRB400R rebar presented improved corrosion resistance and obvious longer passivation-maintaining period. Micro-alloying of Cr element in the rebar matrix enhanced its corrosion resistance against Cl--attack and retarded the corrosion initiation in the matrix. In the alkaline NaCl salt spraying test, the HRB400R rebar also presented obviously lower mass-loss rate. The enrichment of Cr element in the rust layer improved its retardant effect to the penetration of aggressive medium, and decreased the corrosion propagation rate of the rebar.

A comparative study on corrosion behavior of rebar in concrete with fatty acid additive as phase change material

The aim of this study is to evaluate thermal and corrosion behavior of concrete with fatty acid (FA) mixture as phase change material (PCM) used for energy saving in buildings. We compared direct use of fatty acid mixture (capric acid and myristic acid) and its microencapsulated form in concrete. The work is based on thermal analyses (DSC, TGA, thermal buffering and thermal regulation effect), and also corrosive behavior of PCM on reinforcement steel (rebar) by using electrochemical impedance spectroscopy. Temperature development of fresh concrete in the first 40h shows that PCM additives do not affect the hydration reaction, but peak temperature was lowered due to the absorption of heat by PCM. This also indicates retarding effect of PCM in concrete. Additionally, exposed metal surfaces and concrete samples in contact with rebar were examined with SEM for determination of corrosion products. Concrete samples showed enhanced thermal behavior and buffering effect to temperature fluctuations. Compressive strength was decreased by up to 38% with the addition of PCM into concrete. The polarization resistance determined from EIS results does not change significantly addition of PCM in concrete. Thus, PCM has no corrosive effect on metal surfaces in concrete.

Corrosion Behavior of Cr Micro-alloyed Corrosion-resistant Rebar in Neutral Cl−-containing Environment

A new low-cost corrosion-resistant rebar (HRB400R) was designed and fabricated by Cr micro-alloying. The HRB400R rebar had uniform distribution of Cr element in ferrite grains. The corrosion behavior of the rebar in the neutral Cl−-containing environment was studied systematically, and the improved corrosion resistance of the HRB400R rebar was revealed. According to the corrosion-morphology observation and electrochemical monitoring during the constant immersion corrosion in the 3.5 mass% NaCl solution, the HRB400R rebar presented alleviated corrosion damage, nobler Ecorr, lower Icorr, and larger Rt values, and these phenomena were more remarkable in the initial corrosion period. The elevated electrode potential of the rebar, caused by the solid-solution of Cr micro-alloying in the ferrite grains, was the key to the corrosion-resistance improvement. The HRB400R rebar also presented much lower mass-loss rate in the salt spray corrosion test. Besides the elevated corrosion resistance of the matrix, the doping and enrichment of Cr element in the rust layer was another factor for the higher corrosion resistance, which retarded the penetration of aggressive medium through the rust layer.

Corrosion Behavior of Steel Reinforcement in Simulated Concrete Pore Solutions with Various pH and Chloride Contents

Corrosion of rebar in reinforced concrete is a major problem affecting the integrity and loading capacity of the structures. Usually concrete pore solution provides high alkaline environment to protect steel from corrosion. However, the ingress of chloride ions or carbon dioxide would reduce the alkalinity and destroy the stable oxide film which could accelerate the corrosion process of rebar. This study was aimed to evaluate the combined effect of pH and chloride contents on corrosion behavior of rebar using simulated concrete pore solutions. Weight-loss measurement were performed to obtain the corrosion rate. Meanwhile, explore the effect of carbonation and chloride contents to Half-cell potential value on mortar and concrete. Test results show that both pH and chloride content are significant factors influencing the corrosion behavior of rebar. Higher corrosion rate was found in the rebar immersed in the solutions with smaller pH and higher chloride content.

The Corrosion Behavior of Rebar in Stressed Mortars

The corrosion behavior of stainless steel and carbon steel in the mortars suffered stress is studied by electrochemical tests. The results show that the corrosion of rebar is accelerated as the magnitude of stress increasing. Under the same stress magnitude, compressive stress more seriously degraded the corrosion resistance of rebar than tensile stress in mortar in an aggressive environment.

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 rebars in fly ash mortar exposed to carbon dioxide and chlorides

Addition of fly ash has beneficial effects on some mechanical properties of concrete, as well as on the corrosion process induced by the chloride ion. The aim of this study was to investigate the effect of fly ash addition on the corrosion process occurring in reinforced concrete exposed simultaneously to carbon dioxide and chloride. The corrosion process of steel rebars embedded in mortar with 15% and 30% of fly ash was tested under carbon dioxide and sodium chloride contamination. Monitoring of open circuit potential and electrochemical impedance spectroscopy (EIS) were used to follow the corrosion process. Results have shown that under accelerated carbonation fly ash mortar shows higher corrosion rates. The chloride content in mortar exposed to accelerated carbonation increases with the amount of fly ash. However, under natural carbonation it decreases with the addition of fly ash.