Rebar Corrosion Research Articles

A robust carbonation depth model in recycled aggregate concrete (RAC) using neural network

Carbonation depth involves complex physical process and interactions of multiple variables and is thus extremely complicated to predict in concrete structures. It is imperative to quantify this depth due to its vital role in the corrosion of rebars in recycled aggregate concrete (RAC). This paper developed a novel carbonation depth prediction model from a large database of 445 experimental results using artificial neural network (ANN). The relative importance and effect of the independent parameters in the carbonation depth are identified using Garson index and parametric analysis, respectively. Among all the architectures considered, the N 8-10-1 having 10 nodes in the hidden layer provided the best prediction in good agreement with experimental results. The model demonstrated superior performance relative to existing carbonation depth equations in the literature. Despite the presence of fuzziness in the data, the effect of each variable in the development of carbonation is explored in great detail. The model proposed here can provide a robust prediction of carbonation depth that can be used as a basis for assessing the structural health of recycled aggregate concrete structures.

Automatic spacing inspection of rebar spacers on reinforcement skeletons using vision-based deep learning and computational geometry

Improper spacing of rebar spacers (RSs) in reinforced concrete structures can lead to corrosion and damage of rebars, ultimately decreasing the strength and durability of the structure. The current method for RSs spacing inspection entails a manual inspection that utilizes a measuring tape, which is both labor-intensive and time-consuming. This paper presents a novel method for automatically inspecting RSs spacing using a vision-based deep learning and computational geometry. The proposed method consists of three modules including the RSs location and classification module, the keypoints detection module and RSs spacing inspection module. The RSs location and classification module employ object detection of faster-region convolutional neural network (Faster-RCNN)-based deep learning to accurately locate and classify RSs. The keypoints detection module uses human pose estimation of cascaded pyramid network (CPN)-based deep learning to detect the three keypoints necessary for accurate RSs spacing calculations. In RSs spacing inspection module, the computational geometry is applied to derive an accurate expression for calculating RSs spacing in the transverse and longitudinal directions, based on the RSs keypoints coordinates and camera parameters. The RSs spacing is subsequently evaluated to check its compliance. In the experiment, the algorithms of the three modules were integrated into a robot that can automatically move and take pictures to accomplish the task of automatically inspecting RSs spacing in a large reinforced concrete component plant. The experimental results indicate that this method yields an average RSs spacing measurement error of 1.35 cm. Finally, the robustness of the proposed method was validated by changing the conditions of image acquisition processes.

Hybrid machine learning-based model for predicting chloride ion concentration in coral aggregate concrete and its ethically aligned graphical user interface design

The chloride ion concentration distribution in coral aggregate concrete (CAC-CC) holds significant importance for evaluating CAC performance, assessing rebar corrosion, and understanding chloride ion diffusion. Thus, this study employs hybrid machine learning algorithms to establish predictive models for CAC-CC under three environmental conditions (salt spray zone, tidal zone, and underwater zone) and evaluates the accuracy and generalization ability of these models. The results demonstrate that the genetic algorithm-optimized support vector regression (GA-SVR) model provides predictions closer to the actual values, exhibiting smoother error fluctuations. The GA-SVR model also exhibits smaller mean and standard deviation in the residual distribution. Furthermore, the GA-SVR model excels in five performance evaluation metrics, with R2, MAE, MAPE, MSE, and RMSE values of 0.986, 1.25e-2, 3.24e-2, 0.276e-3, and 1.66e-2, respectively. Hence, the GA-SVR model emerges as the optimal choice for CAC-CC prediction. Additionally, this work utilizes Shapley Additive Explanations (SHAP) to assess the contribution of eight features. The analysis reveals that the water-binder ratio and the pre-wetted water to total water ratio are the two most critical features. Moreover, an increase in the pre-wetted water to total water ratio and a decrease in the water-cement ratio hinder chloride ion diffusion. Mechanistic analysis of the feature contribution to CAC-CC is further explored in this study. Based on the GA-SVR model, a graphical user interface for CAC-CC has been developed, enabling visualization of CAC-CC predictions. This research introduces a novel approach to optimize CAC performance and predict chloride ion concentration, laying the foundation for CAC application in reef construction.

Long-term corrosion of silicon carbide/enamel composite coatings on steel rebars: A microstructure-dependent corrosion behavior

Steel rebar's corrosion greatly affects the durability of reinforced concrete (RC) structures. Recently, enamel coatings have been developed for steel rebar's corrosion protection. Given that the anticorrosion performance of enamel coatings is strongly related to their microstructure, in this study, pure enamel coating (PE) and three silicon carbide/enamel composite coatings with 2.5, 5, and 7.5 wt.% silicon carbide addition (S2.5, S5, and S7.5) were prepared on low-carbon steel rebars, representing four different microstructure states, which are severely cracked with porosity of 6%, partially cracked with porosity of 17%, slightly cracked with porosity of 20%, and uncracked with porosity of 26%. The long-term corrosion behavior of different coated rebars was investigated by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, neutral salt-spray test, and morphological observation to understand the effect of silicon carbide content and coating microstructure on the corrosion behavior. Long-term electrochemical studies (210 days) showed that the Rpor and Rct of S7.5 remained 12 times and 5 times that of PE, respectively, indicating an improved corrosion protection with silicon carbide addition. Combined corrosion studies and microstructure results revealed that the corrosion behavior of enamel coated rebars was closely related to the coating microstructure, especially the pores and microcracks. Furthermore, the competitive mechanism of electrolyte penetration degeneration and “self-healing” like enhancement was proposed to interpret the corrosion evolution modes of different coated rebars. The findings of this work give a deep understanding of the corrosion behavior of silicon carbide/enamel composite coatings and provide a solution for long-life RC structures.

Green ionic liquids with high corrosion inhibition of steel rebars in cement pore solution

Abstract For the prevention of steel rebar corrosion in cement pore solutions, new ionic liquids with an imidazole base were tested using the polarization and mass loss methods. The structure of the cations of imidazole base ionic fluids with various derivatives makes them good mixed-type inhibitors by adsorbing them on steel bars to suppress both anodic and cathode processes. The best performance efficiencies recorded by mass loss and polarization methods at 100 ppm were 97.4 and 96.1 %, respectively. These results will motivate numerous researchers to continue their arduous research to identify new ionic liquids’ anti-corrosion properties in the field of concrete additives.

Challenges in corrosion surveys on reinforced concrete structures – practical experiences from more than 20 years

AbstractCorrosion related measurements on reinforced concrete structures are often easy to apply, and many guidelines indicate that a straight and formal handling of the received data is possible. But practical experience advises to be careful, since similar data readings can be caused by very different, even contradicting situations and hence require an individual, distinguished assessment. For example, negative potential values may be caused either by true, chloride induced corrosion or just by extremely wet concrete – without any possibility of active rebar corrosion. For avoiding wrong interpretations and improper repair strategies, the recommended approach is to obtain various, different parameters, including a sound visual and acoustical inspection, and to compare them thoroughly on a common, plausible pattern. The paper gives some examples where usual survey approaches basing on potential mapping and chloride sampling only would have resulted in either not recognizing the extent of corrosion problems properly or in concluding on severe problems that in fact do not exist.

Protection and Time-Varying Characteristic of Rebar Corrosion in Magnesium Oxychloride Cement Recycled Concrete under the Simulated Salt Lake Environment

Protection and Time-Varying Characteristic of Rebar Corrosion in Magnesium Oxychloride Cement Recycled Concrete under the Simulated Salt Lake Environment

Application of Interval Analysis to Assess Concrete Cover Degradation in Accelerated Corrosion Tests.

This paper presents the application of interval algebra in affine formulation to assess damage propagation in test reinforced concrete elements subjected to accelerated corrosion of rebar, taking into account the uncertainty of parameters. Corrosion interactions were captured by introducing the interval tensor of the velocity of volumetric strain. Analysis of the model for limit values of velocities of volumetric strains (inf(ε¯˙V) and sup(ε¯˙V)) using the finite element method for locally and gradient-formulated concrete models with degradation, elastic, and elastic-plastic was conducted using ANSYS and ATENA software. Computer calculations were performed assuming a parameter uncertainty of 0, 10, and 20%. The results of the calculations were compared with the results of detailed tests of elements subjected to accelerated corrosion of reinforcement using an electrolyzer with full monitoring of the electrical parameters of the system. The obtained results of the calculations were verified using the Monte Carlo method, treating the model parameters as random variables with a uniform distribution.

Unraveling the anti-corrosion mechanisms of a novel hydrazone derivative on steel in contaminated concrete pore solutions: An integrated study

IntroductionCorrosion-induced deterioration of infrastructure is a growing global concern. The development and application of corrosion inhibitors are one of the most effective approaches to protect steel rebar from corrosion. Hence, this study focuses on a novel hydrazone derivative, (E)-N′-(4-(dimethylamino)benzylidene)-2-(5-methoxy-2-methyl-1H-indol-3-yl)aceto-hydrazide (HIND), and its potential application to mitigate corrosion in steel rebar exposed to chloride-contaminated concrete pore solutions (ClSCPS). ObjectivesThe research aims to evaluate the anti-corrosion capabilities of HIND on steel rebar within a simulated corrosive environment, focusing on the mechanisms of its inhibitory effect. MethodsThe corrosion of steel rebar exposed to the ClSCPS was studied through weight loss and electrochemical methods. The surface morphology of steel rebar surface was characterized by FE-SEM-EDS, AFM; oxidation states of the steel rebar and crystal structures were examined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) methods. Further, experimental findings were complemented by theoretical studies using self-consistent-charge density-functional tight-binding (SCC-DFTB) simulations. The performance of HIND was monitored at an optimal concentration over a period of 30 days. ResultsThe results indicated a significant reduction in steel rebar corrosion upon introducing HIND. The inhibitor molecules adhered to the steel surface, preventing further deterioration and achieving an inhibition efficiency of 88.4% at 0.5 mmol/L concentration. The surface morphology analysis confirmed the positive effect of HIND on the rebar surface, showing a decrease in the surface roughness of the steel rebar from 183.5 in uninhibited to 50 nm in inhibited solutions. Furthermore, SCC-DFTB simulations revealed the presence of coordination between iron atoms and HIND active sites. ConclusionThe findings demonstrate the potential of HIND as an effective anti-corrosion agent in chloride-contaminated environments. Its primary adsorption mechanism involves charge transfer from the inhibitor molecules to iron atoms. Therefore, applying HIND could be an effective strategy to address corrosion-related challenges in reinforced infrastructure.

Classification of concrete corrosion states by GPR with machine learning

The evaluation of rebar corrosion in reinforced concrete by using ground penetrating radar (GPR) and machine learning (ML) is a complex process. In this paper, a multi-variate method is presented. It uses full-volume data obtained from the amplitude domain in a regular GPR x-y scanning exercise, and the shape of the rebar’s reflection to categorise different corrosion phases. This method allows multi-dimensional analysis with quantifiable GPR attributes. GPR data were extracted from the field and laboratory and then labelled according to the ground truths and reference specimens. A classic ML algorithm, logistic regression, was applied. The cross-validation accuracy (sensitivity and specificity) of individual corrosion phases was high (>99%), and the false alarm rate was low (<1%). This work shows that GPR as an evaluation tool can assess unseen data like doing blind tests. Nonetheless, continuous expansion of the training database is suggested to increase its diversity in the future.

Analysis of corrosion rate, inhibition efficiency, and economic cost of XD3 reinforced concrete related to inhibitor and plasticiser types

The main problem in concrete structure is rebar corrosion, which is caused by the penetration and diffusion of chloride ions into reinforced concrete structures; therefore, it is essential to give the most attention to preventing or limiting the impact of this condition. So, in order to find a practical solution to the problem of corrosion of rebar, the current article focuses on demonstrating the beneficial effects of green and calcium nitrate inhibitors on chloride-induced corrosion. Thus, this paper presented an analytical procedure based on corrosion rates and the economic cost to evaluate the efficacy of such an inhibitor. Ten samples with various concrete mixtures were divided into two groups according to the type of plasticiser and inhibitor have been immersed in an aqueous solution of 3.5 wt% sodium chloride at room temperature for 18 months. The optimal results in which the corrosion rate was significantly reduced were for the two groups of concrete mixtures, first group was (C2), which contains 3 wt% orange peels extract inhibitor mixed with 2.4 wt% Oxydtron as water-resisting admixture, and the second group was (E2) included 3 wt% calcium nitrate inhibitor with 2.4 wt% Oxydtron as water-resisting admixture. These two groups samples have been showed more excellent corrosion resistance against the saline solution after the completed immersion period. The inhibition efficiency analysis showed that there is a direct relationship between the inhibitor concentration and the efficiency of corrosion inhibition. However, the inhibition efficiency in the case of samples containing calcium nitrate inhibitor was higher than their counterparts containing green inhibitor extract. Finally, the economic cost analysis showed that the cost of the green inhibitor extract-containing samples was lower than that of the calcium nitrate inhibitor-containing samples.

Reliability based service life prediction of bridges in Indian coastal region

AbstractChloride‐induced corrosion in concrete bridges is a common problem in coastal regions. This study assesses the reliability‐based service life of a reinforced concrete (RC) T‐girder bridge subjected to pitting rebar corrosion. The impact of spatial variability of rebar pitting corrosion has been considered to accurately predict the service life. Service life models have been applied to both strength and serviceability parameters for coastal bridges in India. The results indicate that rebar corrosion influences the shear resistance deterioration of the bridge girder more rapidly than the flexure resistance deterioration, which significantly impacts the bridge's reliability and service life. Further, it has also been observed that due to chloride‐induced corrosion, the serviceability parameters are impacted more than the strength parameter leading to an early requirement of repair for the serviceability conditions.

Contribution of vertical ground motion on seismic response of multi-span simply-supported T-girder RC bridges in the presence of corrosion-fatigue degradation

Highway bridges, located in heavy traffic and corrosive environments, are prone to corrosion-fatigue degradation, due to which material properties of steel and concrete in bridge girders get altered and effective area of rebars reduces resulting in reduced flexural stiffness of girders. Consequently, exposed bridges become weaker to resist earthquake loads, particularly for the ones having three significant translational components. It is, therefore, important to evaluate life-long performance of bridges that suffer from corrosion-fatigue degradation and are subjected to seismic events having substantial vertical ground motions (VGMs). Such a threatening scenario for seismic safety of bridges has not been explored yet. The current study demonstrates the confronting role of corrosion-fatigue degradation and VGM on bridge seismic response through a representative multi-span RC bridge in Gujarat, India, and required information on corrosion, traffic, and seismic activities is acquired from appropriate sources. The degradation mechanism is modeled as a coupled phenomenon of pitting corrosion of rebar and traffic-induced fatigue stresses that give rise to fatigue cracks at deep pit locations of rebars in girders. Developed numerical model of the bridge composes of all essential features to accurately capture the gradual degradation along life-span and fluctuations in response of key vulnerable bridge components under horizontal and vertical excitations. Results suggest that ignoring the impact of this degradation mechanism and VGM can lead to higher seismic vulnerability of bridges and endanger their safety under future earthquakes.

Effect of slag on strength, microstructure and rebar corrosion of chloride-rich geopolymer concrete

The effects of slag substitution (0, 30 and 60%) and chloride concentration (1.5 and 3.5% sodium chloride) on microstructural changes during strength development between 28 and 360 days, rebar corrosion up to 600 days and chloride binding capacity (CBC) in chloride-rich geopolymer concrete (GC) were investigated. The microstructural changes of the GC were evaluated through field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy analyses. The strength enhancement was higher for the GC mixes based on fly ash (FA) (F-GC mixes) than for the GC mixes based on FA and slag (F/S-GC mixes). The presence of chloride in the GC mixes caused a strength reduction at all ages, but the F/S-GC mixes with the higher slag content mostly showed a smaller strength reduction than the other mixes. Furthermore, the F/S-GC mixes made with the higher slag content exhibited less negative corrosion potential and lower corrosion current density than the other mixes, indicating better resistance against rebar corrosion. The CBC was mostly higher for the GC mixes with a higher slag content. A greater amount of calcium-bearing gels and a higher atomic calcium/silicon ratio in the F/S-GC mixes were responsible for reducing the influence of chloride on strength reduction and rebar corrosion, when compared with the F-GC mixes. Shifting of the Si–O–Si(Al) bond to a lower wavenumber indicated the formation of more binding gel, and thereby a denser microstructure, in the F/S-GC mixes.

In-situ monitoring of pH and Cl− concentration and rebar corrosion at the rebar/mortar interface

This study performed in-situ monitoring of pH and [Cl−] in pore water near the rebar/mortar interface using embedded electrochemical sensors (i.e., IrOx and Ag/AgCl electrodes). Membrane potential (Emembrane), which is the potential difference across the mortar/bulk electrolyte interface, was found to bring significant errors in determining pH and [Cl−]. These errors could be eliminated by measuring the potential of the sensors against the home-made-embedded reference electrode. In a long-term immersion experiment, the corrosion of steel rebar was recorded using electrochemical impedance spectroscopy. Results showed that over the 75 days of immersion experiment, [Cl−] in pore water near the rebar/mortar interface increased from 0.005 mol∙L−1 (at day 2) to 1.37 mol∙L−1, while pH decreased from 13.4 to 11.5. With the evolution of [Cl−] and pH, the corrosion of steel surface was accelerated due to passive film breakdown. The “passive to active” transition occurred when [Cl−] was ≥0.25 mol∙L−1 and pH was ≤12.1.

Residual load-bearing capacity of corroded reinforced concrete columns with an annular cross-section

Reinforced concrete (RC) columns with an annular cross-section are commonly utilized as supporting structural members in ocean engineering structures, and their structural performance deterioration is mainly caused by the corrosion of rebar in aggressive marine environment. This paper proposes an effective method to investigate the effects of rebar corrosion on the structural performance of the annular RC columns under various loading conditions. Firstly, the material degradation and residual structural strength models are proposed based on the analysis of the corrosion-induced deterioration of RC structures. Then, the general method for determining the load-bearing capacity is developed using the equivalent steel ring assumption. To improve computational efficiency and practical applicability, an effective method for assessing the residual load-bearing capacity is proposed by simplifying the calculations of rebar load-bearing capacity coefficients using the regression fitting approach. Finally, the effectiveness of the proposed simplified method is demonstrated with the relevant experimental data available. The results show the capacity deterioration rate is strongly related to the corrosion level and loading condition with the most severe degradation typically at the corrosion level of 5–10%, and the smaller and larger eccentric columns drop the capacities by about 28% and 41% at 10% corrosion level, respectively.

The Effects of a Multifunctional Rust Inhibitor on the Rust Resistance Mechanism of Carbon Steel and the Properties of Concrete

To address rebar corrosion in existing concrete structures, a multifunctional compound rust inhibitor was developed. This study investigates the impact of this inhibitor on carbon steel rust resistance, as well as the mechanical properties and durability of concrete. The results demonstrate a significant reduction in weight loss of carbon steel when using a multifunctional rust inhibitor, with a rust inhibition efficiency of 82.6%. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to observe and analyze the surface elements of carbon steel, both with and without the presence of a rust inhibitor. The findings indicate that the use of a rust inhibitor leads to a smoother and more stable surface film. The results of the experiments on compressive strength, chloride ion electromobility, and the rapid carbonation test of concrete with varying rust inhibitor contents indicate that increasing the amount of rust inhibitor can improve the compressive performance of concrete and can regulate the mobility of chloride ions. Specifically, when the rust inhibitor content reaches 4%, it has a notable positive impact on the performance of concrete, and further increases in content lead to smoother results.

CORROSION RATE OF REINFORCED CONCRETE WITH COMBINED DETERIORATION BY CHLORIDE ATTACK AND ASR

Chloride ions destroy the passive film of steel bars in concrete and induce corrosion. Moreover, the alkali-silica reaction (ASR) produces map cracks in concrete through the formation and expansion of a hygroscopic gel around aggregates. Some existing structures simultaneously experience these two types of deteriorations. In this study, the corrosion rate of steel embedded in mortar with this combined deterioration was evaluated. That is, the presence or absence of reactive aggregates and chloride ions was set as experimental parameters, and specimens with single or combined deterioration of chloride attack and ASR were produced. Cracks and rebar corrosion rates were measured and the influences of chloride ions and ASR on rebar corrosion were discussed based on the polarization curves and resistivity. As conclusions, compared with chloride attack alone, concrete with combined deterioration had more oxygen supply through ASR cracks and a faster corrosion rate. Furthermore, the presence of chloride ions facilitated the formation of electric circuits. In contrast, ASR cracks hindered the formation of an electric circuit. Therefore, the mortar resistivity was the lowest in the case of chloride attack alone, the highest in the case of ASR alone, and intermediate in the case of combined deterioration.

Thermodynamic Effect of High-Rise Reinforced Concrete Typology on Asian Cities: Effect of Socioeconomic Obsolescence Factors on Thermodynamic Complexity

The construction of reinforced concrete (RC) apartments played a crucial role in accommodating the substantial increase in urban populations during the post-war period in Asian cities. However, the RC process in these regions exhibits limitations in terms of the building’s life cycle duration. These limitations arise due to two main factors: the inherent hybrid nature of RC and the insufficient measures for addressing inner rebar corrosion, as well as the lack of adequate control over the management of the “structural class” amid rapid economic expansion. This study examines the impact of rapid urbanization and economic growth on the construction industry, with a specific focus on the utilization of concrete buildings. Drawing on Odum’s urban energetics theory, macroeconomic data are analyzed to investigate the patterns and implications of widespread concrete construction during the late 20th century, particularly in Asian countries. The findings are then compared with earlier periods of economic expansion in other countries, aiming to provide a comprehensive understanding of the interplay between urbanization, economic growth, and the use of concrete structures. The application of Odum’s theory enhances the analytical process, offering valuable insights into the dynamics of the macro urban energy system. In this assessment, four countries are selected based on the stage of their urban economic expansion. The selection is determined using the recent changes observed in three key factors: (1) urban concentration, (2) GDP growth rate, and (3) gross fixed capital formation (GFCF) on housing volume. The assessment identifies the point in time when production, represented by the GDP growth rate, surpasses consumption, represented by GFCF on housing volume. Through this assessment, it becomes possible to make macro-scaled predictions about the urban energy system, even with limited archival data available.

Performance of Soy Methyl Ester-Polystyrene as a Concrete Protectant: A State-of-the-Art Review

Freeze–thaw cycles, application of deicing salts, and rebar corrosion are becoming main sources of concrete deterioration in bridge decks and pavements. During the past few decades, concrete surface treatments have begun to receive wide acceptance because of their effectiveness in sealing the concrete. Surface treatments achieve this by limiting fluid ingress, thereby reducing damage associated with freeze–thaw cycles, deicing salt application, and rebar corrosion. Soy methyl ester-polystyrene blends (SME-PS) have been shown to be an innovative, promising method of topical sealing. SME-PS, which is a derivative of soybean oil and expanded polystyrene, has been continuously studied since 2008. In this context, a comprehensive literature review compared the performance of SME-PS with that of traditional concrete sealers, including organic, inorganic, hybrid, and biotic sealers. These sealers were reviewed for performance in reducing water absorption and chloride penetration and improving freeze–thaw durability of concrete. The reviewed papers indicate that SME-PS possesses superior performance as a concrete protectant for reducing water absorption, chloride penetration, and freeze–thaw damage. To further enhance the feasibility of SME-PS, future studies may include investigating the physical and chemical protecting mechanisms of SME-PS, understanding the factors that affect the penetration behavior of SME-PS in concrete, and evaluating the short and long-term effectiveness of SME-PS in concrete.