Corrosion Of Bars Research Articles

Development of a method for obtaining Nyquist plots identical to those of the three-electrode AC impedance method in concrete-embedded rebar without requiring electrical continuity

Corrosion of steel bars is one cause of deterioration in reinforced concrete structures. The state of corrosion of rebar in concrete structures can be measured using the AC impedance method. The typical three-electrode AC impedance method requires electrical continuity between the rebar and the measurement device, which may be inconvenient because the structure requires to be partly damaged by processes such as drilling. The present study proposes a method to obtain the same impedance spectra as the three-electrode method by modifying the electrode configuration of the four-electrode method. The procedures for such a measurement are as follows: first, place the counter electrode and the measurement reference electrode at the measurement point; place another counter electrode at a sufficient distance from the measurement point; place another reference electrode at a sufficient distance from both the measurement point and the applied counter electrode; and connect WE_I to the applied counter electrode, WE_V to the reference electrode, CE to the applied counter electrode, and RE to the applied counter electrode, and measure the impedance. In this paper, the physical experiments and the numerical experiments demonstrate the validity of the above method. Under the conditions of this physical experiment (concrete W/C = 54.2%, cover 50 mm), the distance between the measurement point and the application counter electrode was required to be about 1.3 m. The distance between the measurement point and the reference matching electrode was also required to be about 1.3 m.Graphical abstract

New fluorescent pH indicators for characterizing cement carbonation

Fluorescent indicators of a wider labeling pH range of 7.0–12.5 were prepared to characterize the pH evolution of the accelerated/natural carbonation of cement and the corrosion of steel bar. Compared with conventional indicators (phenolphthalein, pH range of 8.2–8.5), these indicators indicate multiple pH-induced switches of different fluorescence emissions for the fluorescence resonance energy transfer between donor–acceptor. The results showed that the newly-developed indicators are sensitive and applicable for labeling both natural and accelerated carbonation of cement. Investigations by Fourier Transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis demonstrated the reliability of these indicators, that is, in the “uncarbonated area” shown by phenolphthalein, carbonization actually occurs as exhibited by fluorescent indicators. Furthermore, electrochemical impedance spectroscopy, as well as dynamic potential polarization studies showed that rusting/corrosion of reinforcing steel started when the pH dropped to 11.5 in the simulation study. This work promoted the contribution of fluorescent indicators in cement carbonation characterization, with a wide pH response.

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.

A review on FRP bars and supplementary cementitious materials for the next generation of sustainable and durable construction materials

As the problem of environmental deterioration becomes increasingly prominent, demand for reinforced concrete with favorable sustainability, durability and mechanical properties is growing. Fiber reinforced polymer (FRP) bar is more durable than traditional steel rebar. Supplementary cementitious materials (SCMs) are used as substitutions for cement, to reduce carbon emissions. A well-organized review on previous studies on FRP and SCMs is therefore necessary for developing the next generation of sustainable and durable construction materials. Therefore, this study aims to systematically compare the sustainability, durability and mechanical performances of FRP bars and SCM blended concrete. The sustainability of both materials are evaluated by their carbon emissions. The durability performance of FRP bars mainly includes resistance against alkali, chloride and freeze–thaw cycles. The durability performance of concrete includes resistance against alkali, chloride, sulfate attack, freeze–thaw cycles and carbonation. The effects of various SCMs on concrete are quantitatively analyzed. Analyses indicate that the alkaline corrosion of FRP bars may be mitigated by carbonating concrete. The combination of BFRP bars and carbonated SCM concrete potentially represents the next generation of sustainable and durable construction materials.

Experimental Study on the Mechanical Properties and Cracking Characteristics of Bacterial Concrete

Concrete has been used as a construction material for a long period. When the concrete members are exposed to extreme conditions cracks develop. When a crack opens harmful contaminants may enter the concrete matrix. Water may enter through this crack and result in the corrosion of reinforcement bars. Corrosion of the reinforcement bar also results in the formation of cracks. Compressive strength, flexural strength, split tensile strength and permeability are adversely affected by the formation of cracks. Once damaged these structures need to be repaired. Self-healing concrete is an environmentally friendly and cost-effective method for repairing small cracks. An efficient microbial agent for preparing self-healing concrete is the bacillus species. The sample preparation is done by using Bacillus subtilis. The concentration of bacillus opted for the sample preparation is cells per millilitre. The mechanical properties of bacterial concrete are experimentally evaluated and compared with that of conventional concrete. The tension in concrete is usually overlooked while evaluating the strength of reinforced concrete sections because it makes such a small contribution to member strength. Yet it makes a significant contribution to members’ performance under service loads. In this work, tension stiffening of bacterial concrete is experimentally evaluated on concrete prismatic members made of M20 grade concrete reinforced with 8mm and 12mm diameter bars. The direct tension specimen has a cross-sectional dimension of 60 X 60mm and a length of 600mm. The total length of the steel-reinforced specimens, including the bars, is 900 mm. The tension-stiffening properties of bacterial concrete are compared with that of conventional concrete.

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.

Shear Strength Prediction of Concrete Beams Reinforced with FRP Bars and Stirrups Using Gene Expression Programming

Existing reinforced concrete (RC) structures in humid regions suffer from deterioration due to the corrosion of ordinary reinforcement bars damaging the whole system. The deterioration of the transverse reinforcement leads to shear failure, which is one of the most dangerous failure modes. Therefore, researchers suggested using fiber-reinforced polymer (FRP) bars as a replacement for reinforcement bars in humid regions to integrate sustainability and improve their serviceability and durability. A simple model that can accurately estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is lacking. This research proposed a simplified Gene expression programming (GEP) based model to estimate the shear strength of FRP concrete beams. Seven parameters that principally dominate the shear behavior of FRP beams were utilized to create the GEP model. The parameters are the beam width, beam depth, concrete compressive strength, FRP tensile longitudinal reinforcement ratio, area of stirrups, spacing between the stirrups, and the ultimate FRP strength of stirrups. A comparison was made between the GEP and ACI-440 models; the R2 values of the total database were 92% and 54% for the GEP and ACI models, respectively. The R2 of the GEP model is considerably higher than that measured for the ACI model, and the errors of the GEP model are low, which affirms that the GEP is superior to the ACI model in estimating the shear strength of FRP beams. The trends of the GEP and ACI-440 models and the empirical results are similar, confirming the GEP model’s consistency. Using the GEP model to estimate the shear strength of concrete beams designed with FRP longitudinal bars and stirrups is recommended.

Experimental Investigation on Seismic Performance of Non-Uniformly Corroded RC Moment-Resisting Frames

To investigate the effect of non-uniform corrosion on the seismic performance of reinforced concrete (RC) frame structures, seven RC frame specimens, including one uncorroded and six corroded frames, were tested under quasi-static loading. The damage modes, force-displacement hysteresis curves and skeleton curves, stiffness degradation, ductility and the energy dissipation capacity of specimens were studied. The influences of the corrosion degree, non-uniform corrosion characteristic value, and axial compression ratio on the seismic performance of the specimens were analyzed. The test results show that non-uniform corrosion of longitudinal bars has a significant effect on the development of seismic damage in RC frames. In comparison with non-corroded RC frames, the loading carrying capacity of corroded frames with non-uniform corrosion characteristics values of 0.18, 0.59, and 0.72 decreased by 8.5%, 14.8%, and 22.3%, the displacement ductility ratios decreased by 6.7%, 8.7%, and 10.0%, and the total cumulative energy dissipation at ultimate displacement values decreased by 24%, 41%, and 54%. For corroded frames with low axial compressive ratios, the loading carrying capacity and energy dissipation capacity rose with the increase in the axial compression ratio.

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).

マンションの老朽化認定の評価方法に関する検討 その2：判定式および判定基準

For proffer the authorization standard of the act on facilitation reconstruction of deteriorated condominium buildings, studied on evaluation methods and criteria about buildings having the risk of falling cover concrete caused by rebar corrosion. Based on the concept of the binomial test, the number of the deteriorated reinforced concrete elements which highly probable to be the reinforcing bar corrosion higher, is determined by using the data from a survey of the actual buildings. And then, each number of survey points, the criteria for certification was set.

Deterioration of mechanical properties at the anchor-mortar interface considering the effect of two-phase corrosion

Factors in the environment may cause corrosion of the anchor rod and mortar, thus degrading the mechanical properties of the anchor rod-mortar interface and eventually leading to failure of the anchor structure. In this paper, a method is designed to accelerate the migration of corrosive ions (Cl-，SO42-) from solution to penetrate the mortar, resulting in the corrosion of both the mortar and the bolt. Taking corrosion of the steel bar as the control, the deterioration law for the interfacial anchor-mortar bond during two-phase corrosion was studied. The mechanical properties deteriorating mechanism of the anchor-mortar interface was revealed based on changes in the composition and amount of corrosion products and the damage extent of anchor rods and mortars. The test results showed that, in acidic environments, the rib height of the bolt decreased due to corrosion, which led to a decrease in the mechanical bite force of the interface. The needle and rod-shaped ettringite generated by the mortar during corrosion can destroy the internal structure of mortar, promote more corrosive solution to participate in the chemical reaction, and reduce the radial binding force on the steel bar. In an alkaline environment, corrosion of the rebar is slow. The plate ettringite formed by the mortar during corrosion provides a filling effect and delays the corrosion reaction of the rebar. Corrosion of the reinforcement and mortar results in deterioration of the interface bond strength between the bolt and mortar. Based on the test results, the current model of bond slip was modified to include deterioration of the anchor and mortar material properties and weakening of the restraining effect of the mortar. A model for the anchor-mortar bond-slip relationship was proposed and included corrosion of both materials. The results of this research will provide guidance for future studies of the failure mechanisms of anchorage structures and evaluations of the durability of anchored slopes.

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.