Search Results (239)

Corrosion protection in reinforced concrete structures exposed to aggressive environments remains a critical challenge in civil and architectural engineering. One promising approach involves the application of corrosion-inhibiting monolayers on the reinforcement, such as those formed using 4-aminobenzoic acid. Two methods have previously been employed to generate these monolayers: one relying on the adhesion of an organic compound and the other utilising an externally modified approach via electrolysis. This study assesses the influence of this treatment on the steel–concrete bond strength and durability, both critical properties for the structural performance of reinforced concrete under service conditions. For this purpose, pull-out tests were performed on specimens subjected to load–unload cycles to analyse bond behaviour and monolayer integrity. The results indicate that these treatments do not adversely affect the bond strength between reinforcement and concrete. Furthermore, the rebars treated with the inhibitor exhibit less corrosion damage than the untreated rebars. This fact is particularly significant in the rebars treated using the natural adhesion method, with the steel section loss being 32–37% lower than in the untreated rebars. These findings support the feasibility of applying this treatment without compromising structural functionality. Full article

A fixed ratio amount, i.e., L-arginine (LA) and trisodium phosphate dodecahydrate (TSP) at 2:0.25, is considered as a hybrid inhibitor. This research aims to extensively investigate the impact of utilizing the hybrid corrosion inhibitor on the corrosion resistance properties in accelerated condition, mechanical characteristics, and predictive estimation of the lifespan of reinforced concrete (RC) structures. Various experiments, such as setting time, slump, air content, porosity, compressive strength, and chloride diffusion coefficient, were conducted to elucidate the influence of the hybrid corrosion inhibitor on the mechanical properties of the concrete matrix. Meanwhile, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) in 10 wt. % NaCl under wet–dry cycles are utilized to assess the corrosion resistance property, corrosion initiation time, and kinetics of the passive film formation on the steel rebar. Alternatively, both deterministic and probabilistic-based predictions of service life by Life 365 software are utilized to demonstrate the efficacy of the hybrid corrosion inhibitor in protecting the steel rebar in RC structures. All the results confirm that the HI-4 mix (LA:TSP = 3.56:0.44) exhibits excellence in preventing the corrosion and extending the service life of RC structures, due to the adsorption of inhibitor molecules and formation of P-Zwitterions-(Cl)-Fe, Zwitterions-(Cl)-Fe, and FePO₄ complexes onto the steel rebar surface. However, HI-3 shows the optimal mechanical and electrochemical properties for RC structures. Full article

The corrosion behaviors in chloride environment of two commercial low-alloy steel bars were studied. Through cyclic wetting tests, accelerated corrosion experiments ranging from 1 to 576 h were conducted on low-alloy bars and original bars. Techniques such as OM, SEM, EDS, AFM, and XRD were employed to characterize the corrosion emergence and expansion behaviors of these bars in a simulated marine wetting and sun exposure environment. The designed low-alloy corrosion-resistant rebar achieved a 500 MPa yield strength. In each corrosion cycle, its corrosion loss and rate were lower than those of same-strength ordinary rebars. Analysis of the rust layer’s macro and micro morphology and alloy element distribution revealed alloy elements had little effect at corrosion initiation. In later corrosion, their enrichment led to a denser rust layer, effectively blocking corrosion expansion and chloride salt infiltration. After 72 h of accelerated corrosion, the corrosion rate growth of both bars slowed. The inner rust layer’s electrochemical potential increased, and local corrosion pits turned into uniform corrosion. The inner rust layer of the rebar formed more stable chromic acid with ionic compounds, reducing corrosion sensitivity. This study offers insights into steel bar corrosion and alloy element roles, guiding the preparation of low-alloy corrosion-resistant steel bars. Full article

The inherent porous structure of concrete enables the penetration of water and Cl⁻ ions through its pores, which eventually leads to rebar corrosion within the concrete. Consequently, the densification and impermeability of concrete protective layers play a critical role in the durability of reinforced concrete structures. This study proposes a composite anti-corrosion treatment for mortar protective layers by integrating nano-ion capillary crystalline with silane hydrophobic processing. Targeting existing mortar samples, a series of experiments were conducted, utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry-thermogravimetry (DSC-TG), X-ray computed tomography (X-CT), contact angle measurements, permeability tests, and electrochemical tests. These experiments systematically evaluated the effects of composite anti-corrosion treatment on the microstructure of hydration products, pore characteristics, surface hydrophobicity, impermeability, and the overall corrosion resistance of mortar-rebar samples in a Cl⁻-contained environment. The results reveal that nano-ion capillary crystalline materials react with free calcium ions in the mortar to produce secondary hydration products, effectively filling micro-pores, densifying the pore structure and inhibiting the invasion of Cl⁻ ions. The combination of capillary crystalline and silane hydrophobic processing synergistically enhances surface hydrophobicity and impermeability, preventing the ingress of corrosive agents, such as Cl⁻ ions, and significantly improving the anti-corrosion performance of mortar in a Cl⁻-contained environment. Full article

The service of reinforced concrete structures (RCSs) in harsh coastal environments is often threatened by chloride corrosion. The penetration of chloride ions through concrete pores into the steel/concrete interface will cause the depassivation and corrosion of steel rebars, which will lead to the deterioration and failure of RCSs durability. It is important to repair and protect the corrosion damage of existing concrete structures and ensure their high durability, and the high performance of repairing and protecting materials is crucial. In this paper, a novel cement-based protective coating material with low porosity, high impermeability and chloride-corrosion resistance was designed and prepared by introducing polypropylene fiber and high-performance cement into commercial cement-based protective materials through the double modification strategy of fiber-toughening and substrate-enhancing, in order to provide a reliable corrosion protection solution for the high durability and long life of RCSs under chloride erosion environment. Based on this, the microstructure and pore structure of the double-modified coating material was systematically analyzed by SEM, XRD, X-CT and other characterization methods. The impermeability and chloride corrosion resistance of this material were scientifically evaluated, and the protection mechanism was systematically discussed. The results show that the impermeability of the double-modified coating material is about 2.8 times higher than that of the untreated mortar. At the same time, the corrosion current density was significantly reduced to 8.60 × 10⁻⁷ A·cm⁻², which was about 86% lower than that of the untreated sample (6.11 × 10⁻⁶ A·cm⁻²). The new cement-based coating material optimized by double-modification effectively inhibits the formation and propagation of microcracks in the protective coating through the bridging effect of fibers. At the same time, the regulation of cement hydration products and the densification of pore structure are realized by adjusting the composition of cement matrix. Based on the above two aspects of microstructure improvement, the chloride-corrosion protection performance of the novel cement-based protective coating material has been greatly improved. Full article

Reinforced concrete structures deteriorate over time when exposed to environmental effects throughout their service life, resulting in a loss of structural performance and ultimately a reduction in service life. One of the most critical deterioration mechanisms in this process is the corrosion of the reinforcement steel. The initiation and propagation of corrosion adversely affect the load-bearing capacity, bond strength, and overall structural behavior of reinforced concrete elements, thereby threatening the structural safety. Therefore, understanding the corrosion process and accurately predicting the service life of reinforced concrete structures is critical to ensuring their long-term durability. This study comprehensively examines the effects of chloride-induced rebar corrosion on the service life of reinforced concrete structures. Various mathematical models used to predict corrosion initiation and propagation times are analyzed in detail. These models provide a scientific basis for understanding the effects of environmental conditions and structural properties on the corrosion process and estimating how these effects affect the service life. In particular, the study investigates the effect of parameters such as concrete cover thickness, rebar diameter, crack presence, corrosion rate, and environmental conditions on the corrosion process, all of which also affect structural performance. Cracks in reinforced concrete elements shorten the corrosion initiation period depending on their thickness. Considering that the presence of cracks also changes the structural behavior, it is recommended to use the Kwon model, which takes the presence of cracks into account, in the service life calculations. The presence of cracks is ineffective in the corrosion propagation period, and it is recommended to use the Morinaga model for this period. For reinforced concrete elements exposed to aggressive environments, increasing the thickness of the concrete cover and the diameter of the reinforcement has been shown to increase the service life. Columns with larger diameter reinforcement showed a longer service life than beams with smaller diameter reinforcement. Therefore, evaluating each element separately in service life calculations will ensure that a safer approach is taken. In conclusion, this study serves as a valuable resource for developing design strategies to improve the long-term durability of reinforced concrete structures and to minimize the adverse effects of corrosion on structural performance. It provides design and field engineers with guidance to make more accurate service life assessments and implement effective decisions to improve structural performance. Full article

The aim of this paper was to investigate the corrosion behaviour of zinc in simulated concrete solutions using resistometric sensors and to describe the kinetics of zinc corrosion. The sensors provide corrosion data information in real time; thus, it is a useful technique for observing zinc corrosion behaviour in concrete environments. The replacement of carbon steel rebar by galvanized steel in concrete is a discussable topic with contradictory results in the literature presented in the introduction. In our case, zinc resistometric sensors were used, and they showed results in good agreement with other techniques, such as corrosion potential monitoring and EIS measurements. According to our results, zinc is able to passivate in a simulated concrete solution and even in a simulated carbonated solution. The corrosion rate was reduced by almost 40 times, during the active to passive transition. The zinc remains passive even in simulated concrete solutions contaminated with low levels of chloride ions up to 0.9 wt.%. Full article

The corrosion of steel reinforcements substantially degrades the longevity of reinforced concrete structures, particularly in marine settings. This investigation introduces a comprehensive model that simulates the processes involved in moisture and chloride ion transport, rebar corrosion, and the consequent cracking of concrete. The model reveals that the transport dynamics of chloride ions are primarily dictated by their penetration rates through the solution. The sensitivity of the steel to corrosion is a function of the concentrations of water and chloride ions, whereas the rate of corrosion predominantly depends on the availability of oxygen at the corrosive site. Oxygen diffusion is the rate-limiting step in the entire process of the electrochemical reactions of the rebar. And the peak corrosion rates are observed at the interface between the solution and the gas phase. The model calculates the stress and strain in the concrete resulting from volumetric expansion due to oxidization of the steel bars. By accurately reproducing the progression of corrosion-related damage, this model provides crucial insights for predicting the service life of offshore concrete structures and enhancing durability against aggressive environmental conditions. Full article

Composite reinforcements are attracting attention in the reinforced concrete (RC) field for their high corrosion resistance, low thermal conductivity, and low electromagnetic interference behavior. However, compared to metallic reinforcements, composites are less ductile and may lead to brittle failure. Three-point flexural tests provide information on the mechanical behavior of metal- and composite-reinforced concrete beams with distinct crack patterns. The structural conditions and failure mechanisms can be defined based on stress change and crack propagation. This study employs finite element analysis (FEA) to simulate the mechanical responses of composite- and metal-reinforced concrete beans under three-point flexural tests and predict the crack propagation in the beams. Machine learning-based algorithms are trained using FEA data to assess the spatial–temporal conditions of the RC beams. The findings indicate that composite rebars provide better reinforcement than metallic rebars in terms of stress fields (30.27% less stress in composite rebars) and crack propagation (fewer cracks in composite RC beams), with the initiation of shear cracks and maximum von Mises stress in rebars being correlated. The findings highlight the effectiveness of the Random Forest Regression (RFR) algorithm ($R^2=0.96$) in assessing RC beam conditions under flexural loads, offering insights for efficient industry applications. Full article

The absence of carbon fiber-reinforced rebar performance standards in Korea has limited its reliability. This study investigates the durability performance of carbon fiber-reinforced polymer rebar as an alternative to traditional steel reinforcement in concrete structures. Concrete beams reinforced with carbon fiber-reinforced polymer rebar were exposed to chloride environments for durations of 35 and 70 days and then subjected to bending tests to evaluate their durability. The results demonstrate that the strong bond between the carbon fiber-reinforced polymer and concrete effectively prevented brittle fracture, even under exposure to harsh chloride. A scanning electron microscope analysis of the specimens exposed to chloride showed no deterioration of the carbon fiber-reinforced polymer rebar, highlighting its exceptional resistance to corrosion. Furthermore, durability tests were conducted in a carbonation chamber for 8 and 12 weeks, with no signs of degradation in the carbon fiber-reinforced polymer rebar. These findings suggest that carbon fiber-reinforced polymer rebar offers excellent resistance to both chloride-induced corrosion and carbonation, making it a promising solution to enhance the longevity and durability of reinforced concrete structures exposed to aggressive environmental conditions. Full article

Corrosion in reinforced concrete (RC) structures has led to the increased adoption of non-corrosive materials, such as carbon fiber-reinforced polymers (CFRPs), as replacements for traditional steel rebar. However, ensuring the long-term reliability of CFRP grids under sustained stress is critical for achieving safe and effective designs. This study investigates the long-term tensile creep rupture behavior of CFRP grids to establish a design threshold for their tensile strength under sustained loading conditions in demanding structural applications. A comprehensive laboratory experiment was conducted over 10,000 h, during which CFRP grid specimens were subjected to constant stress levels ranging from 92% to 98% of their ultimate tensile strength. The results confirm the excellent creep rupture resistance of CFRP grids. Specimens subjected to a sustained stress ratio of 92% of their ultimate tensile strength remained intact throughout the testing period, with minimal creep strain ranging from approximately 1% to 4% of the initial strain. The mean extrapolated creep rupture factors were found to be 92.1% and 91.7% of their ultimate tensile strength for service lives of 50 and 114 years, respectively. Based on the results of this study, a tensile stress limit of 48% of the ultimate tensile strength is recommended for CFRP grids to ensure long-term creep rupture resistance over a 100-year service life. Full article

The corrosion of the steel reinforcing bar (rebar) reduces the strength capacity of concrete structures. Corrosion detection at the early stage of steel rebar implementation is important for the maintenance of concrete structures. Using the eddy current testing method, we developed a portable system to evaluate the corrosion of steel rebars. An AC current was sent to the excitation coil to produce an AC magnetic field and an eddy current was induced in the steel rebar. A detection coil was used to detect the signal produced by the eddy current. A lock-in amplifier was used to obtain the same phase signal and a 90-degree phase difference signal and an X-Y graph was plotted. From the slope of the X-Y graph, the corrosion of the steel rebar or steel wire can be evaluated. We examined the effects of excitation frequency, coil type, and coil size on the experimental results to optimize the system. The signal-to-noise ratio and the detection depth were improved with a specially designed probe. Full article

The use of carbon fiber reinforced polymer (CFRP) strands as prestressed reinforcement in prestressed concrete (PC) structures offers an effective solution to the corrosion issues associated with prestressed steel strands. In this study, the flexural behavior of PC beams reinforced with prestressed CFRP strands and non-prestressed steel rebars was investigated using finite element modeling (FEM) and artificial neural network (ANN) methods. First, three-dimensional nonlinear FE models were developed. The FE results indicated that the predicted failure mode, load-deflection curve, and ultimate load agreed well with the previous test results. Variations in prestress level, concrete strength, and steel reinforcement ratio shifted the failure mode from concrete crushing to CFRP strand fracture. While the ultimate load generally increased with a higher prestressed level, an excessively high prestress level reduced the ultimate load due to premature fracture of CFRP strands. An increase in concrete strength and steel reinforcement ratio also contributed to a rise in the ultimate load. Subsequently, the verified FE models were utilized to create a database for training the back propagation ANN (BP-ANN) model. The ultimate moments of the experimental specimens were predicted using the trained model. The results showed the correlation coefficients for both the training and test datasets were approximately 0.99, and the maximum error between the predicted and test ultimate moments was around 8%, demonstrating that the BP-ANN method is an effective tool for accurately predicting the ultimate capacity of this type of PC beam. Full article

The corrosion of steel rebar embedded in concrete under marine conditions is a major global concern. Therefore, it needs a proper corrosion mitigation method. Various types of corrosion inhibitors are used to mitigate the corrosion of steel rebar in chloride-contaminated concrete; however, selecting the appropriate inhibitor and determining its optimal concentration remains a concern. Therefore, in the present study, three types of inhibitors—calcium nitrite (CN: Ca(NO₂)₂), N,N′-dimethyl ethanol amine (DMEA: (CH₃)₂NCH₂CH₂OH), and L-arginine (LA: C₆H₁₄N₄O₂) in three different concentrations, i.e., 0.3, 0.6 and 1.2 M—were compared with a control (without inhibitor, i.e., blank) sample to determine the optimum concentration of the inhibitor for corrosion resistance performance evaluation of reinforcement bars immersed in 0.3 M NaCl-contaminated concrete pore (NCCP) solution for various durations. The corrosion resistance properties were assessed using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) with immersion duration, and potentiodynamic polarization (PDP) after 168 h of exposure. The results showed that the CN inhibitor performed exceptionally well (corrosion inhibition efficiency greater than 97%) in terms of corrosion resistance. However, due to its hazardous nature and its ban in the U.S. and European Union, CN cannot be used in construction. In comparison, while DMEA showed some effectiveness, LA performed better and is also eco-friendly. The corrosion resistance efficiency of samples containing 0.6 M LA remains above 97% even after 168 h of immersion in the NCCP solution. This efficiency is consistent throughout the entire immersion period, from 1 h to 168 h. Therefore, it is recommended that LA be used as a corrosion inhibitor for steel reinforcement bars instead of CN, particularly in chloride-contaminated concrete, as it is both effective and safer than CN. Full article

Due to the complexity of the marine corrosive environment, the rebar corrosion in reinforced concrete (RC) bridge piers is usually longitudinal non-uniform. However, the study on the mechanical behavior of longitudinal non-uniformly corroded RC structural members is very limited. To systematically study the deformation performance of the longitudinal non-uniformly corroded RC columns, the finite element models of 106 RC columns with different parameters were established using the commercial software ABAQUS 2016. The effects of the height of the bottom section (represented in the text by the variable “position”), the length, and the rebar corrosion ratio of the corroded segment on the deformation performance of the longitudinal non-uniformly corroded RC columns were analyzed. It is found that the change in the position of the corroded segment on the column may change the most unfavorable section of the column and the failure mode. The length of the corroded segment significantly affects the yield deformation. The ultimate plastic deformation increases with the increase of position or length of the corroded segment. With the increase of rebar corrosion ratio of the corroded segment, the ultimate plastic deformation decreases. Full article