Corrosion Of Steel Bars Research Articles

Probability-Based Performance Degradation Model and Constitutive Model for the Buckling Behavior of Corroded Steel Bars

The corrosion of steel bars significantly influences the safety running of concrete bridges. The current bridge design code always ignores the changes in mechanical properties of the materials during their service life which results in an overestimation of the seismic capacity of concrete bridges Therefore, a hysteretic constitutive model that considers the influence of reinforcement corrosion is necessary. This study established a probability-based model for the mechanical property degradation of corroded steel bars using statistical analysis to estimate the mechanical properties under specific corrosion rates. The validity of the proposed degradation model was verified by a series of monotonic tensile tests on corroded steel bars. Moreover, a constitutive model of corroded steel bars based on the Reinforcing Steel Model in OpenSees was obtained. This model considers the influence of corrosion on the slenderness ratio, yield strength, ultimate strength, and elongation. A comparison with the experimental data demonstrated the accuracy of the proposed model. The proposed model is straightforward because its parameters can be predicted using existing research data. The proposed model can provide a basis for the seismic performance evaluation of corroded reinforced concrete (RC) members.

Impact of high volume E.M.D. residue on the corrosion resistance and mechanical properties of construction materials in sulfate environment

This study examines the potential use of Electrolytic Manganese Dioxide (EMD) residue as a replacement of cement (20%wt by cement weight) in construction materials to provide anticorrosion protection on reinforcing steel and improve the strength of cementitious materials under sulfate attack. To assess the corrosion parameters, the constructed building materials were immersed in a 5%wt sulfate salt (Na2SO4), while concrete samples incorporating 20%wt EMD were prepared and subjected to mechanical, porosity and thermal tests. Moreover, SEM images were obtained in order to examine the microstructure of concrete and the extent of damage caused by sulfate ions. The results demonstrate that the inclusion of EMD caused a notable rise in the corrosion of steel bars within cement mortars, as well as a decrease in the mechanical strength of the building materials. Overall, the experimental outcomes of the study suggest that the incorporation of high volume (20%wt) EMD residue leads to the degradation of all measured properties.

Shear behavior of reinforced concrete beams subjected to accelerated non-uniform corrosion

In this paper, a modified accelerated corrosion method based on impressing current was adopted to generate non-uniform corrosion of stirrups in reinforced concrete (RC) beams. The shear performance of corroded RC beams was experimentally investigated, aiming to study the influence of stirrup corrosion induced by two different accelerated corrosion methods on the degradation of shear capacity of RC beams. Different corrosion degree of stirrups, corrosion of longitudinal steel bars, as well as shear span ratio were investigated. Results indicates that, the stirrups subjected to the modified accelerated corrosion method demonstrate a considerably higher circumferential and longitudinal non-uniformity, while the classic accelerated corrosion method induces a rather uniform corrosion. The non-uniformity of corrosion aggravates the propagation of both corrosion-induced and load-induced cracks, leading to the change of shear failure mode. The uniform corrosion induced by the classic accelerated corrosion method underestimates the degradation of shear capacity of RC beam, especially in the cases of corrosion degree no less than 15%. The corrosion of longitudinal steel bars mainly correlates to the decrease in the initial stiffness of RC beam, while little influence on the stiffness is observed with corroded stirrups.

Electrochemical behavior of steel bars in magnesium phosphate cement

The electrochemical characteristics of steel bars in magnesium phosphate cement (MPC) are crucial when applying MPC to reinforced concrete. In this study, the electrochemical behaviors of steel bars in MPC were investigated via electrochemical tests combined with surface analyses. The results indicated that the steel bars in the simulated MPC pore solution could effectively passivate, forming films that mainly consisted of FePO4. In the MPC matrices, the continuous precipitation of phosphates led to the accumulation of passive films, which were responsible for the superior corrosion protection of MPC compared to traditional cement materials. MPC exhibited a self-healing corrosion feature after the depassivation of steel bars, which could be characterized by the dramatic recovery of passive film resistance and charge transfer resistance. Furthermore, the corroded steel bars in MPC with a low magnesia-to-phosphate ratio could re-passivate and stabilize for long periods of time.

Compressive behavior of corroded reinforced concrete columns strengthened with BFRP reinforced ECC in marine environment

Corrosion of reinforced concrete (RC) columns due to chloride ions in marine environments is a significant problem. Reinforcement technologies, such as the engineered cementitious composite (ECC)-fiber reinforced polymer (FRP) reinforcement technology, have proven to be effective measures to improve the compressive capacity of RC columns. However, the confinement mechanism and design formula for this reinforcement technology remain unclear. In this study, the compressive behavior of corroded reinforced concrete column strengthened with basalt fiber reinforced polymer (BFRP) reinforced ECC was investigated by numerical analysis, including the load-displacement curves, the confinement mechanism, the stresses distributions and the effect of key parameters. Additionally, a theoretical model was developed to predict the peak load of the strengthened column. The results showed that the corrosion of the longitudinal steel bar and the stirrup were respectively significantly weakened the compressive capacity and the deformation capacity of the strengthened column; The stress in the BFRP grid reached 10% of its ultimate stress under point B, and increasing the number of BFRP grid layer was found to be beneficial in delaying the load degradation in the softening stage; The theoretical model established in this study could accurately predict the peak load of the strengthened column.

Research on Hybrid FRP–Steel-Reinforced Concrete Slabs under Blast Load

The service environment of civil air defense engineering structures is relatively harsh, and the corrosion of steel bars is the main reason for reducing the durability of concrete structures in civil air defense engineering. A hybrid FRP–steel-reinforced concrete (hybrid-RC) structure has excellent durability. Therefore, it is a good choice to apply hybrid-RC to civil air defense engineering structures. In order to study the blast resistance of hybrid-RC structures, close blast and contact blast experiments were carried out on hybrid-RC slabs, steel-reinforced concrete (SRC) slabs and GFRP-reinforced concrete (GRC) slabs. For the close blast experiment, the steel reinforcement in the SRC slab first entered the plasticity stage, whereas the GFRP reinforcement in the hybrid-RC slab was in the elastic stage under the close blast. Therefore, the capacity to dissipate energy through the vibration in the hybrid-RC slab was better than that of the SRC slab. The residual deformation in the hybrid-RC slab after the close blast experiment was smaller than that of the SRC slab. The Blast Recovery Index (BRI) was introduced to evaluate the recovery capacity of the concrete slab after the close blast, and damage assessment criteria for the hybrid-RC slabs were proposed according to the maximum support rotation θm and BRI. There was little difference in the size of the local damage in the hybrid-RC slab and the SRC slab under the contact blast. However, since the GFRP reinforcement was still in the elastic stage and the steel reinforcement was plastic after the contact blast, the ratio of the residual bearing capacity to the original bearing capacity in the hybrid-RC concrete slab would be larger than that of the SRC slab. The prediction formula for the top face diameter D and blasting depth L of the hybrid-RC slab was obtained through dimensionless analysis. This research can provide a reference for the anti-blast design of hybrid-RC slabs.

A Discussion on Utilization of Zinc Anode Applied in Cross-section Repair of RC Member Damaged by Chloride Attack - Time-Lag Application of Different Zinc Anodes -

This paper discusses the effectiveness of zinc anode cathodic protection applied to RC beam specimens severely damaged by chloride attack. Based on the experiment, that is, the zinc anode cathodic protection is applied to the 41-year-old RC beam specimens exposed to natural marine environments, suitable application method of zinc anode is discussed. In the experiment, repair was performed in three stages. In the first stage, polymer-modified mortar was cast to replace existing concrete in the middle tensile part with zinc anodes embedded in the repair mortar. After protective current became stable value, the anodes were disconnected from steel bars for a year defined as the second stage. During the one year of second stage, the steel bar in the repair area remained be passive state, without any sign of corrosion. As for the third stage, additional zinc anodes were installed in the existing concrete part in order to protect the steel in old chloride contaminated concrete. From one-year observation after the application of zinc anodes in old concrete part, it is confirmed that “time lag application” could stop the corrosion of steel bar in both parts.

Experimental Study on the Protection of an Asphalt Coating to Reinforcement in Magnesium Oxychloride Cement Concrete

To mitigate the corrosion of steel bar in magnesium oxychloride cement concrete (MOCC), an asphalt coating is used for protection. According to the service environment in the Salt Lake area of western Qinghai, China, a solution immersion test on MOCC was performed. The test results showed that, after soaking for 2160 days, the corrosion current density icorr was 7.88 µA/cm2, and RC was 113.51 Ω for group A and icorr is 0.08 µA/cm2 and RC is 842.57 Ω for group B. The time parameters for groups A and B fell in the high-frequency range of 103–105 Hz and low-frequency range of 10−2 to 10−1 Hz. The relative dynamic moduli of the elasticity evaluation parameters ω1 and ω2 were 0.942 and 0.959 and 0.946 and 0.962 for groups A and B, respectively, at 2160 days, exhibiting a downward trend on the whole. Fourier transform infrared spectroscopy and microscopic testing revealed that the corrosion of the chloride solution on asphalt was mainly the corrosion of chloride in the interior of the asphalt and that the invaded salt provided a channel for the water solution to invade into the interior.

Time-dependent nonuniform numerical model of corrosion process and consequent corrosion-induced concrete cracking under chloride attack

Corrosion of steel bars and consequent concrete cracking are complicated processes and they mutually affect one another. In this study, a 3D time-dependent numerical model was developed to simulate localised corrosion in both circumferential and longitudinal directions, incorporating effects of nonuniform corrosion-induced cracks. Time-dependent evolution of corroded area in the circumferential direction around the steel bar was calculated as a function of chloride concentration, while two configurations of corroded length along the steel bar axis were simulated: (1) the entire length of steel bar was corroded at the same time and (2) the corroded length progressively developed from the middle of the bar towards its two ends. Microcell and macrocell mechanisms were applied to determine the total corrosion rate. Consequently, a finite element model was developed to simulate nonuniform corrosion-induced concrete cracking. It was found that once a vertical crack propagated through the concrete cover, not only did the corroded area spread faster, microcell and macrocell current densities also substantially increased, and the shape of corroded depth became more rounded.

Dissolution characteristics of chloride ion in alkali residue and its effect on the properties of light-weighted soil

Environmental pollution and steel-bar corrosion are worsening owing to the high content of chloride ions (Cl-) in alkali residue (AR), and its application is limited. In this study, a washing program is proposed to remove Cl- and manufacture AR-based light-weighted soil (A-LS). Several tests were conducted to analyze the influence of the number of washing cycles on AR and the performance of A-SL. The results show that Cl- can be effectively removed by the washing program. After washing, the particle size of the AR decreases, and the water absorption is enhanced. The pore structure of A-LS changes, and its compressive strength decreases with washing. According to the requirements of the specification for Cl-, the AR must be washed twice. Finally, when A-LS is mixed with ordinary Portland cement (OPC), ground granulated blast slag (GGBS), and AR washed two times in the ratio of 30:40:30 (wt%), the compressive strength is 1.03 MPa based on the water–solid ratio of 0.9 and wet density of 600 kg/m3 at 28 d; this meets the application requirements of most filling projects. The findings of this study can help reduce the usage of OPC and avoid environmental pollution, portraying great social and economic benefits..

Nonlinear numerical simulation of bond performance between recycled concrete and corroded steel bars

Abstract In this article, the bond performance between recycled concrete and corroded steel bars is analyzed by the nonlinear numerical simulation. The result shows that the maximum bond strength between recycled concrete and steel bar decreases with the increase in steel bar corrosion rate; when the recycled concrete strength is large, the simulated maximum bond strength is in good agreement with the experimental maximum bond strength; when the recycled concrete strength is small, the simulated maximum bond strength is in relatively poor agreement with the experimental maximum bond strength, but there is still an error within the allowable range; the slip between recycled concrete and steel bar increases with the increase in steel bar corrosion rate; when the steel bar corrosion rate exceeded 5%, the bond strength decreases more rapidly; the maximum bond strength increases with the increase in specimen sizes under the same steel bar corrosion rate; the maximum bond strength decreases with the increase in steel bar diameter under the same steel bar corrosion rate.

Residual Mechanical Properties of Corroded Steel Bars after High-Temperature Exposure

Accidental fires in aged concrete structures can lead to combined damage from corrosion and fire. In this study, we aimed to explore the effects of corrosion and high temperature on the residual mechanical properties of hot-rolled plain and ribbed bars. The results indicated that the corroded steel bars still exhibited ductile failure after high-temperature exposure. Moreover, the combined action of high temperature and corrosion has little effect on the elastic modulus. The residual bearing capacity of the hot-rolled steel bar became smaller under the condition of temperatures above 600°C. When the temperatures experienced by the plain and ribbed steel bars were less than 600°C and 500°C, respectively, the high temperature accelerated the decrease in the nominal yield and ultimate strength. However, the yield and ultimate strengths based on the minimum cross-sectional area remained unchanged with an increase in the cross-sectional loss ratio. Similar to that at room temperature, the ultimate strain of steel bars subjected to high-temperature exposure decreased exponentially with an increase in the cross-sectional loss ratio. The new findings of this study can provide a theoretical basis for the safety assessment of aged reinforced concrete structures after exposure to fire.

Bond performance between corroded steel bars and concrete in cathodic protection system with CFRP as anode

Bond performance between corroded steel bars and concrete in cathodic protection system with CFRP as anode

Prediction of residual bond strengths between corroded steel bars and concrete after exposure to high temperatures

Reinforced concrete structures used in aggressive environments (e.g., coastal and ocean regions) may suffer from steel corrosion. On the other hand, structures with corroded steel bars are likely to experience fire hazards during their service life. Therefore, the combined effect of high-temperature exposure and steel corrosion may lead to a significant reduction in the post-fire bond strength between the corroded steel bars and surrounding concrete, which will further affect the residual load-capacity assessment of fire-damaged RC members. This paper presents an analytical model for predicting the residual bond strengths between the corroded steel bars and surrounding concrete after exposure to high temperatures. In the analytical model, the concrete cover around the steel bar is considered as a thick-walled cylinder whose inner surface is subjected to uniform pressure due to the combined action of the pull-out load and the volume expansion of the corrosion products. Three stages of the concrete cover (i.e., uncracked, partially cracked and fully cracked stages) are considered one by one in the analytical model to determine the internal pressure. During the analysis, the tensile softening behavior of the cracked concrete and the material property degradations of concrete after high-temperature exposure are properly considered. The accuracy and reliability of the proposed analytical model are verified by comparing the analytical predictions with the corresponding pull-out test results collected from the literature. A detailed parametric analysis is then performed to gain insight into the effects of various factors on the post-fire residual bond strengths of corroded steel bars.

Effect of Corrosion on the Bond Behavior of Steel-Reinforced, Alkali-Activated Slag Concrete

Alkali-activated slag concrete (ASC) is regarded as one of the most promising sustainable construction materials for replacing ordinary Portland cement concrete (OPC) due to its comparable strength and outstanding durability in challenging environments. In this study, the corrosion of steel bars embedded in ASC and OPC was studied by means of an electrically accelerated corrosion test of steel bars in concrete. Meanwhile, the bond performance of the corroded steel bars embedded in ASC was tested and compared with corresponding OPC groups. The results showed that ASC and OPC behaved differently in terms of bond deterioration. The high chemical resistance of ASC decreased the corrosion of steel bars and, thus, increased the residue bond strength and the bond stiffness.

Investigation of corrosion inhibitor used in cement

Steel bar corrosion inhibitor can be incorporated into concrete (or mortar) with a small amount, or coated on the cement surface to protect the steel materials. It can prevent or delay the corrosion of metal bars by directly acting on the steel bars in concrete (or mortar), but it does not affect the structure and properties of concrete. In this paper, the single component corrosion inhibitor was screened and evaluated at room temperature by salt water immersion test and static coupon weight loss method. The results show that hydrazine hydrate and KNO3 can effectively prevent the corrosion of reinforcement after being placed in simulated corrosion solution for 7 days. When the concentration of hydrazine hydrate and KNO3 is greater than 0.5%, the corrosion inhibition rate of KNO3 is 95.44% (100mg·L−1).

Microcell and macrocell corrosion of steel bars in reinforced concrete slabs under different corrosive environments and cathode/anode configurations

This paper presents an experimental study and electrochemical mechanisms of microcell and macrocell corrosion kinetics of steel bars in reinforced concrete slabs subjected to three different corrosive environments and three configurations of uncorroded/corroded steel bars. Effects of combined chloride contamination and carbonation were investigated and compared to individual causes either from chloride contamination or carbonation. Under each corrosive environment, two cathode/anode area ratios, as well as steel bars-contact and -noncontact conditions, were tested. As a result, the combined chloride contamination and carbonation induced larger microcell and macrocell corrosion rates than those attacked by solely chloride or solely carbonation. Although a larger cathode/anode ratio increased macrocell current density, it actually decreased microcell rate compared to a smaller ratio. In addition, when corroded steel bars were in contact, microcell and macrocell current densities became larger than those in noncontact samples for all three corrosive environments. Based on the test results, electrochemical mechanisms of both microcell and macrocell corrosion were proposed using thermodynamic theory, anodic and cathodic polarisation kinetics to draw precious insights into the corrosion behaviour under different corrosive environments and cathode/anode ratios.

Corrosion behavior and mechanism analysis of triethanolamine and imidazoline in the simulated pore solution of concrete

In this paper, to solve the previous instability of nitrate rust inhibitors, and their environmental hazards, the rust inhibition performance of green and environmentally friendly triethanolamine and water-soluble imidazoline rust inhibitor was studied under simulated pore solution conditions. The corrosion of steel bars was evaluated by electrochemical and dry-wet cycle tests of carbon steel sheets, and characterization was done by scanning electron microscopy (SEM). Triethanolamine and water-soluble imidazoline rust inhibitors could effectively inhibit the rapid development of carbon steel rust in the composite salt environment. When the dosage ratio was 4:6, the electrochemical impedance of the carbon steel sheet increased, the potential increased, the corrosion current density decreased, the mass loss rate decreased, the surface texture of the carbon steel was clear, and the thickness of the rust product was almost zero. The adsorption mold formed by the organic rust inhibitor made the harmful ions impenetrable, and the rust inhibition effect was optimal.

Development of Fe-C film coated polymer optical fiber sensor for steel bar corrosion monitoring

Corrosion detection is one of the most important studies in structural health monitoring systems (SHM) for reinforced concrete structures such as bridges. Due to the high initial investment and technical limitations of conventional technology, SHM systems are mostly deployed in the existing mega-scaled bridge infrastructures. This work demonstrates a novel nondestructive method using Fe-C film-coated polymer optical fiber sensor for steel bar corrosion monitoring. The sensing performance of the proposed sensors was investigated in the simulated corrosion test. The results showed that the sensors with different thicknesses of Fe-C film shared similar output curve characteristics but different sensitivities to the same corrosion state. The sensors embedded in the mortar specimens with the reinforced structure were then evaluated under the accelerated corrosion condition. The results indicated that the output signals of sensors were in agreement with that of the earlier experiment, and the thinner Fe-C film showed higher sensitivity to corrosion.

Investigation of Corroded Bond-Slip Effects for Corroded RC Columns

Steel bar corrosion is one of the most common causes of structural performance degradation for reinforced concrete (RC) columns subjected to extreme loads such as earthquakes. Due to the different characteristics of corrosion effects, a comprehensive and efficient finite element (FE) modeling approach is necessary for the performance assessment of corroded RC columns. To this end, this study provides an effective FE modeling approach using a recently developed geometrically nonlinear fiber-based frame element that considers bond-slip, allowing for explicit representation of corrosion-affected bonding. This aspect necessitates the use of an explicit material model for corroded bond-slip and its associated corroded properties. Since the existing models of corroded bonding properties in the literature were developed based on the highly scattered and limited experimental data, this study develops a new probabilistic model for corroded bonding properties based on more experimental data compiled from the literature and quantifies the prevailing uncertainties. To facilitate its use for modeling corroded RC structures, a cyclic corroded bond-slip model in an open-source FE software framework is implemented. In this paper, the FE modeling approach is first used to model two corroded RC columns tested in the literature, with comparison to the conventional modeling approach (i.e., assuming perfect bonding). The influence of corroded bonding on the static and dynamic behaviors of RC columns is further explored deterministically. Furthermore, the impact of uncertainty in corroded bonding properties on the static and dynamic behavior simulations of RC columns is examined. This work is concluded that (1) the FE modeling approach provided for corroded RC columns proves to be effective in capturing corrosion effects; and (2) corroded bonding plays an important role in simulating the behavior of corroded RC columns, and thus cannot be neglected. This is particularly true considering its associated uncertainty and its impact on the performance assessment of RC columns under severe corrosion conditions.