Corroded Reinforced Concrete Beams Research Articles

Behavior of artificially corroded RC beams strengthened with CFRP and hybrid CFRP-GFRP laminates

Steel corrosion is a major degradation factor for the reinforced concrete (RC) infrastructure and necessitates a costly repair after short service life. Predicting the strength of corroded and retrofitted structural elements while under service is a challenging task. For this purpose, the impressed current technique is frequently used to achieve the desired degree of corrosion in RC members in the laboratories. This study investigates the effectiveness of this technique on laboratory-scale RC beams and evaluates the behavior of severely corroded beams rehabilitated with carbon fiber-reinforced polymers (CFRP) and the hybrid of CFRP and glass-FRP (GFRP) laminates. Extensive literature is available on the behavior of sound RC members strengthened with FRPs, however, data are scarce on the behavior of corroded-strengthened RC beams. The RC beams were deteriorated by applying an impressed current of 750 µA/cm2 for 15 days. All the beams were tested under four-point bending till failure. The reinforcement mesh was non-uniformly corroded; the flexural bar facing the external cathode experienced a higher degree of corrosion than the opposite bar and the actual applied impressed current reached as high as 2388 µA/cm2. The flexural strength of the degraded beams, with 37 % weight loss on the main rebars, was 41 % less than counter-part sound beams. On the other hand, the CFRP strengthening regained the strength of degraded beams by 45 % compared to the unstrengthened-degraded beams. Whereas the CFRP-GFRP hybrid laminates regained strength up to 60 % compared to the counterpart-degraded beams and 12 % higher than the sound beams. This study demonstrated that a desired degree of corrosion could be achieved on a particular reinforcement portion with the impressed current technique. In addition, CFRP and CFRP-GFRP laminates are effective external strengthening techniques for rehabilitating degraded concrete infrastructure.

Bending behaviour of corroded RC continuous beams with C-FRCM strengthening system

This paper presents a numerical investigation into the bending behaviour of uncorroded and corroded reinforced concrete (RC) continuous beams with a strengthening system. Finite element analysis (FEA) was performed on ten RC beams considering interface performance, including five uncorroded and five corroded beams. The cracks development, bending capacities and load-displacement curves of the simulated RC beams in the loading process were validated against those from tests. Then, a parametric study including 35 RC beam models, considering the effects of carbon-fabric (CF) mesh layer, complete wrapping layer and the degree of corrosion of steel bar on their bending capacities, was conducted. Ductility and strengthening effects of specimens were discussed in the parametric study. It can be found that the carbon-fabric reinforced cementitious matrix (C-FRCM) strengthening system can improve the bending capacities of the corroded RC beams. As the layer of CF mesh increases, the ductility of the specimen decreases. The combined use of the C-FRCM plate and the complete wrapping as the end anchorage enhanced the ultimate loads of RC beams to a greater extent than those strengthened with C-FRCM plate only. The applicability of current design codes for RC beams with C-FRCM strengthening system was examined through comparisons of the bending capacity predictions of RC beams with those obtained from tests and numerical analyses. It was found that European Code (FIB Bulletin 14) provides more accurate predictions than American Specifications (ACI 549.4R-20, AC 434-0616-R1, ACI 440.2R-17) and Chinese Code (CECS 146–2003 (2007)). Therefore, design modifications based on the most accurate design rule of FIB Bulletin 14 were made. By utilizing regression analysis on the numerical results, the formula for bending capacities of the examined RC beams was proposed and showed improved accuracy.

Preliminary results on acoustic emission and vibration-based monitoring of locally corroded reinforced concrete beams

The current tendency to increase the lifetime of reinforced concrete (RC) structures creates concerns about their serviceability and safety. Reinforcement corrosion is the most common deterioration process in RC, which can severely decrease the structural capacity. Corrosion causes a reduction of the rebar’s cross section, cracking and spalling of the concrete cover due to the expansion of the corrosion product and a decrease of the bond strength at the reinforcement-concrete interface. Assessing the structural capacity of corroded existing structures remains an important issue to maintain good safety and to achieve more targeted repairs. On-site quantification of structural reliability requires advanced non-destructive techniques to evaluate the damage and efficient methods for structural health monitoring. This paper presents the initial results of an experimental campaign on corroding RC beams. Beams with a length of 3 m are subjected to local accelerated corrosion while being monitored with the acoustic emission (AE) technique and dynamic vibration testing (DVT). AE investigates the damage progress and underlying causes of the cracks. When cracks are formed, the stress redistribution in the material causes elastic waves, which can be recorded by piezoelectric transducers placed on the surface of the beam. Examination of the waveforms allows for a localization and characterization of the damage source. Additionally, DVT observes the change in modal parameters of the beams, measured by accelerometers. These changes can be related to a loss of stiffness in the structure, resulting in a perception of the decrease in structural capacity. The combination of local (AE) and global (DVT) monitoring techniques improves the damage inspection as both the damage process and the loss of stiffness are observed. The results of AE provides information when the cracks have not yet reached the surface, while DVT is most relevant when severe damage already occurred. After corrosion, a four-point bending test is performed to evaluate the remaining structural capacity.

Fractal characteristics and damage evaluation of corroded beams under four-point bending tests based on acoustic emission techniques

This study investigated the relationship between the acoustic emission (AE) signals parameter sequence fractal characteristics and the damage evolution information of corroded reinforced concrete (RC) beams under four-point bending. Strength deterioration behavior and AE data can be obtained by coupling the four-point bending test and the AE monitoring. The results show that AE ringing counts of corroded and uncorroded beams had prominent fractal characteristics. The fractal dimension values of corroded RC beams all showed a fluctuating rise to a peak and then a sharp drop before the failure. The damage index corresponding to the peak point decreases with the increase of corrosion degree. Fractal dimension peak point could be used as an early warning point for corroded RC beams' failure. Moreover, the AE fractal dimension analysis can effectively reflect the pattern of crack development, which have an important value for evaluating the process of corroded RC beams rupture.

Assessing the shear behavior of steel fiber reinforced concrete beams corroded under chloride attacks

Steel corrosion affects the failure mechanism of deteriorated reinforced concrete (RC) beams. Meanwhile, there is a lack of research on the shear behavior of corroded RC beams, particularly corroded steel fiber reinforced concrete (SFRC) beams. This paper investigates the shear behavior of corroded SFRC beams with a 1.5 shear span-to-depth ratio. All beam specimens included steel fibers with 50 kg/m3. In particular, tensile longitudinal reinforcements were subjected to a corrosion degree of 16.4%, while stirrups were subjected to an approximately 24.1% corrosion degree. These results are compared to those obtained on a non-corroded beam. The obtained results from the four-point loading tests show that the corroded SFRC beams preserve a softening behavior as opposed to the sudden shear failure of RC beams without steel fibers.

Prediction of shear strength of corrosion reinforced concrete beams using Artificial Neural Network

The shear strength of corroded reinforced concrete (CRC) beams is a critical consideration during the design stages of RC structures. In this study, we propose a machine learning technique for estimating the shear strength of CRC beams across a range of service periods. To do this, we gathered 158 CRC beam shear tests and used Artificial Neural Network (ANN) to create a forecast model for the considered output. Twelve input variables indicate the geometrical and material properties, reinforcing parameters, and the degree of corrosion in the beam, whereas the shear strength is the output considered. The database is designed to employ 70 percent of the data point to train the model and 30 percent to assess the performance. The model makes outstanding predictions, according to the results, with an R2 value of 0.989. In addition, five empirical shear strength models in the literature are utilized to test the suggested ANN model, demonstrating that the new model performs much better. With any given service period, the suggested time-dependent prediction model can offer the shear strength of CRC beams.

Prediction of shear strength of corrosion reinforced concrete beams using Artificial Neural Network

The shear strength of corroded reinforced concrete (CRC) beams is a critical consideration during the design stages of RC structures. In this study, we propose a machine learning technique for estimating the shear strength of CRC beams across a range of service periods. To do this, we gathered 158 CRC beam shear tests and used Artificial Neural Network (ANN) to create a forecast model for the considered output. Twelve input variables indicate the geometrical and material properties, reinforcing parameters, and the degree of corrosion in the beam, whereas the shear strength is the output considered. The database is designed to employ 70 percent of the data point to train the model and 30 percent to assess the performance. The model makes outstanding predictions, according to the results, with an R2 value of 0.989. In addition, five empirical shear strength models in the literature are utilized to test the suggested ANN model, demonstrating that the new model performs much better. With any given service period, the suggested time-dependent prediction model can offer the shear strength of CRC beams.

Prediction of shear strength of corrosion reinforced concrete beams using Artificial Neural Network

The shear strength of corroded reinforced concrete (CRC) beams is a critical consideration during the design stages of RC structures. In this study, we propose a machine learning technique for estimating the shear strength of CRC beams across a range of service periods. To do this, we gathered 158 CRC beam shear tests and used Artificial Neural Network (ANN) to create a forecast model for the considered output. Twelve input variables indicate the geometrical and material properties, reinforcing parameters, and the degree of corrosion in the beam, whereas the shear strength is the output considered. The database is designed to employ 70 percent of the data point to train the model and 30 percent to assess the performance. The model makes outstanding predictions, according to the results, with an R2 value of 0.989. In addition, five empirical shear strength models in the literature are utilized to test the suggested ANN model, demonstrating that the new model performs much better. With any given service period, the suggested time-dependent prediction model can offer the shear strength of CRC beams.

Fatigue life of C-FRCM strengthened corroded RC continuous beams under multi-intervention system

A new fatigue life prediction model for reinforced concrete (RC) beams is proposed. The model was applied to carbon-fabric reinforced cementitious matrix (C-FRCM) strengthened corroded RC beams under the impressed current cathodic protection (ICCP) and structural strengthening (SS) multi-intervention system. The stress development of steel bar in the fatigue process was captured by employing the fracture mechanics and finite element (FE) analysis. The concept of equivalent initial flaw size (EIFS) was also introduced to account for the actual initial micro crack size of steel bar. The feasibility of the model was validated through comparisons of the numerical deflection, the strain of steel bar and fatigue life of RC beams against the test results. The validated model was then used to examine the effects of key parameters including load level, corrosion degree of steel bar and polarization degree of C-FRCM. Furthermore, the results of the parametric study were used to fit S-N curve and analyse the reliability. The high accuracy of the model was shown to be suitable for the fatigue life prediction of ICCP-SS system in long-term service. It was also found that the fatigue life of the corroded RC beams was greatly improved through strengthening with C-FRCM.

Effects of galvanostatic and artificial chloride environment methods on the steel corrosion spatial variability and probabilistic flexural capacity of RC beams

The galvanostatic method has been widely used for accelerating the corrosion of reinforcing bars in concrete to complete test studies within a reasonable timeframe. However, which level of current density induces characteristics of steel corrosion spatial variability and the associated structural performance of corroded reinforced concrete (RC) beams that are similar to those observed under natural conditions remains unknown. In this paper, comprehensive experimental research is conducted to compare the characteristics of spatial growth in steel weight loss and crack width and the structural behavior of corroded RC beams by two corrosion-accelerated methods (i.e. galvanostatic method at six current densities and artificial chloride environment method). The effects of these corrosion acceleration methods on Gumbel’s location and scale distribution parameters and the associated yield load capacity of corroded RC beams are investigated using Monte Carlo-based two-dimensional finite element analysis. Finally, a suitable current density is recommended to better simulate the steel corrosion distribution and the associated yield load capacity of RC beams in comparison to those observed under an artificial chloride environment.

Failure mode-based calculation method for bending bearing capacities of normal cross-sections of corroded reinforced concrete beams

This paper proposed a failure mode-based calculation method for bending bearing capacities of corroded reinforced concrete (RC) beams with corroded tensile steel bars and/or corroded compressive steel bars. Three balanced failures and corresponding three balanced corrosion ratios of tensile steel bars were identified. Based on three balanced corrosion ratios, four failure modes were identified and corresponding calculation methods for bending bearing capacities under different failure modes were proposed for corroded RC beams. Subsequently, the proposed calculation method, as well as modified conventional methods, was compared with tested ultimate bending moments of 421 corroded and 96 non-corroded control RC beams. Moreover, several examples were designed and calculated by the proposed method and modified conventional methods to illustrate the differences among different calculation methods. The comparisons and analyses showed that the bending bearing capacities predicted by the proposed method had good match with the test results in the full range of corrosion ratios of tensile steel bars, but the modified conventional methods theoretically remained valid only in partial ranges of corrosion ratios. The proposed failure mode-based calculation method will contribute to both accurate performance assessment of existing RC structures and efficient reliability analysis of new planned RC structures.

Developing a three-dimensional finite element analysis approach to simulate corrosion-induced concrete cracking in reinforced concrete beams

Corrosion-induced concrete cracking is a significant stage of structural deterioration in reinforced concrete (RC). Numerous numerical studies were conducted to address this problem, but relatively few considered the effects of stirrups and non-uniform corrosion in three dimensions. In this study, a three-dimensional finite element analysis (FEA) approach was developed to simulate corroded RC beams, considering non-uniform steel corrosion and a detailed arrangement of stirrups. The cracking patterns obtained from the simulation results agreed well with experimental observations. Subsequently, using the proposed FEA approach, the effects of the non-uniform corrosion and stirrup constraints on the cracking pattern were investigated. The simulation results indicated that an RC structure under non-uniform corrosion showed more severe cracking and reached the serviceability limit state earlier. The stirrups limited the propagation of the corrosion-induced cracks, but the constraint weakened with increasing distance from the location of the stirrups.

Experimental study of corroded RC beams: dissipation and equivalent viscous damping ratio identification

Corrosion of steel reinforcement is one of the most common durability issues for reinforced concrete (RC) structures, especially when located in marine areas. The study of the mechanical consequences of this pathology is of great importance to assess their performance. Experimental campaigns have been carried out on corroded structures. So far, assessing quasi-static behavior or predicting the dynamic response of structures have been based exclusively on quasi-static loadings. In particular, the dissipated energy and the damping capacity, which are important features to study when assessing the seismic performance of corroded RC members, are evaluated based on quasi-static loadings. The objective of this study is to characterize these two significant engineering demand parameters (EDP) using both quasi-static and dynamic tests. To reach this goal, an experimental campaign is conducted on large-scale RC beams. The corroded and non-corroded RC beams are subjected to a four-point bending loading and to dynamic loading keeping the same loadings and boundary conditions. The dynamic loading is applied on the specimen by means of the AZALEE shaking table. In this paper, a brief description of the experimental campaign is made. Then, results showing the influence of the corrosion rate on the dissipation capacity of RC structures are exposed. Especially, the consistency between quasi-static and dynamic results is assessed and discussed.

Effectiveness of carbon textile reinforced concrete in shear strengthening short-span corroded reinforced concrete beams

This paper will present the shear behavior of the corroded stirrups reinforced concrete (RC) beams strengthened with textile reinforced concrete (TRC). The shear resistance contributions from the corroded RC beams and carbon TRC at various volume ratios were carefully examined. Eighteen beams were tested, including twelve subjected by an electrochemically accelerated aging technique for 60 and 90 days to obtain the theoretical mass loss in their stirrups of 10% and 20%, respectively. The stirrups were locally corroded in the shear span. After the corrosion accelerating treatment, corrosion cracks on concrete surfaces were marked, and their widths were measured to observe their distributions. A three-point bending test was applied to obtain the shear performances of the corroded beams subjected to the monotonic and repeated loading. Eight corroded RC beams were strengthened using 2 and 3 U-wrap layers of bidirectional carbon textile. The shear behavior will be discussed, including the ultimate capacity, failure mode, load-deflection, load–strain relationship, and crack distributions. Compared to the controlled specimens, the averaged shear strength of corroded specimens decreased by 16.08% and 25.34%, corresponding to the degree of corrosion ranging from 12.3% to 23.6%. The experimental results also demonstrate that the shear capacities of the corroded RC beams strengthened with carbon TRC had been improved 60.6% compared to the severely corroded controlled specimens.

Predicting the flexural capacity of corroded reinforced concrete beams using artificial intelligence models

Predicting the residual flexural capacity of corroded reinforced concrete (RC) structures is to help civil engineers decide to repair or strengthen the structures. This study presents the application of six single algorithm-based models of artificial intelligence, such as artificial neural network (ANN), support vector machine (SVM), classification and regression trees (CART), linear regression (LR), general linear model (GENLIN), and automatic Chi-squared interaction detection (CHAID) to predict the residual flexural capacity of corroded RC structures. The predicting results are compared to the surveyed data including 120 corroded RC beams from the projects built before 1975 to rank the efficiency of single models. Some combined models are applied to investigate the improvement in predicting the flexural capacity of corroded RC structures compared to the single models. The result shows that LR and GENLIN models give almost the same results and the best efficiency. The combined models can not improve the efficiency compared to the two best single models

Effect of pre-existing longitudinal and transverse corrosion cracks on the flexural behaviour of corroded RC beams

Assessing the residual capacity of corroded reinforced concrete (RC) beams depends on quantifying the corrosion cracks and rebar cross-section loss, and understanding their influence on the structural behaviour. Relations between corrosion crack widths and cross-section loss have been developed in the literature, and experimental studies have shown a decrease in the flexural capacity of corroded RC beams. However, their results were only related to longitudinal cracks and rebar cross-section loss. In real structures, corrosion of stirrups causes transverse cracks. In this paper, their influence on rebar pitting and failure of corroded beams is investigated through an experimental test programme in which RC beams are corroded and then tested in bending. Firstly, the effect of transverse cracks on the relation between crack widths and cross-section loss is studied. Secondly, the role of each type of corrosion damage on the flexural failure of the beams is investigated. It is found that transverse cracks lead to localized cross-section loss causing non-linearity in the relation between the longitudinal crack widths and the cross-section loss. Additionally, it is found that longitudinal corrosion cracks decrease the number of flexural cracks, while transverse cracks form weak spots to initiate the beam failure. Furthermore, it is observed that beams fail at the location of either the transverse cracks or the minimum rebar cross-section or both. Moreover, transverse corrosion cracks may lead to misaligned minimum cross-sections on the tensile rebars, which cause a skewed critical cross-section during bending failure. Finally, the study concludes that pre-existing longitudinal corrosion cracks deteriorate the tension-stiffening effect, while transverse cracks cause local pits in the tensile rebars and affect the failure mechanism of the beams.

Experimental study and numerical model of the seismic behavior of reinforced concrete beams in an artificial corrosion environment

The corrosion of reinforcement materials induced by chloride attacks is the primary reason for the deterioration of the seismic performance of reinforced concrete (RC) structures. In this paper, 12 RC beams with different corrosion levels, shear span to depth ratios and stirrup ratios were subjected to accelerated corrosion tests in an artificial climate as well as quasistatic cyclic loading tests, and the corrosion form, failure process, bearing capacity, deformation capacity, energy dissipation capacity, stiffness and strength degradation of corroded RC beams were investigated. The results showed that the artificial climate corrosion method could simulate the uneven corrosion form of steel bars in a natural environment; the corrosion of steel bars would intensify the shear failure characteristics of specimens; the degradation rates of the bearing capacity and deformation capacity of corroded RC beams with different shear span to depth ratios and stirrup ratios are significantly different; and the degradation degree of bearing capacity of specimens with a high shear span to depth ratio is 3.58 times higher than that of specimens with a low shear span to depth ratio. Subsequently, a numerical modeling method for corroded RC beams based on SFI-MVLEM was proposed, empirical formulas for the stiffness coefficient of the corroded dowel were determined based on experimental data, and the bond-slip deformation was simulated by the infinitesimal algorithm and zero-length fiber section element. The proposed model was accepted to numerically simulate 12 corroded RC beams in this paper, and the average values of the bearing capacity error and energy consumption error of the simulation results were 10.07% and 13.09%, respectively, indicating that the proposed model had good accuracy and could be adopted to predict the residual seismic performance of corroded RC beams.

A multi-stage mesoscopic numerical approach to simulate the flexural behavior of concrete beams with corroded rebars

Corrosion is the main factor affecting the service performance of reinforced concrete (RC) structures, especially in offshore or coastal areas. In this paper, taking RC beam as the research object, a three-dimensional meso-scale numerical model involving rebar corrosion was established. The corrosion effects on the mechanical behavior of RC beam was explored through a multi-stage analysis method (namely, corrosion induced expansion stage and structural deterioration stage). The non-uniform radial displacement was applied to concrete around the steel to simulate the expansion of rebar corrosion. The cracking process and the damage pattern of concrete caused by corrosion can be obtained. Then, taking this state as the initial condition, the mechanical analysis of corroded RC beam was carried out. The agreement between the numerical and the test results validates the rationality and correctness of the multi-stage analysis model. According to the simulation results, the concrete damage due to corrosion is mainly concentrated in the diagonal of reinforcement and the middle of adjacent reinforcement. The rust expansion pressure increases gradually when the corrosion level increased. For severely corroded beams, the concrete strain no longer conforms to the plane section assumption. In addition, corrosion reduces the bearing capacity and ductility of the beams. The coupling effects of corrosion of tensile and compression bars on the performance of the beam are more serious than that of only corrosion of tensile bars. Based on the data regression, a relationship to evaluate the bearing capacity of beams was established. It indicates that the flexural bearing capacity decreases by about 1.4%, 1.7% annually in the conditions of tensile reinforcement corroded only and both tensile and compressive reinforcement corroded.

Effect of Stirrup Corrosion and Fire on Shear Behavior of Reinforced Concrete Beams

This article presents an investigation on corrosion damage effects on the shear bearing capacity of reinforced concrete (RC) beams after a fire. Accelerated corrosion tests were conducted using four RC beams designed with corrosion crack widths ranging from 0.1 mm to 0.3 mm to simulate an aggressive corrosion-prone environment. One control beam (B1) did not undergo accelerated corrosion. The fire test was conducted separately on each beam for two hours to explore how the different widths of corrosive cracks affect heat propagation at elevated fire-induced temperatures. A residual capacity test determined the effects of corrosion on the beams’ residual shear strength after a fire. The experimental results showed that corrosion cracks accelerate the heat propagation in concrete during a fire; moreover, the post-fire residual shear strength for corroded RC beams slightly decreased with an increasing degree of corrosion on the stirrups. The authors also developed a corresponding simplified calculating method to determine residual shear strength, which showed shear design provisions that could improve some existing codes.

Probabilistic estimation of flexural loading capacity of existing RC structures based on observational corrosion-induced crack width distribution using machine learning

Corrosion-induced crack width can provide effective information on the deterioration level of in situ corroded reinforced concrete (RC) structures. However, the uncertainty associated with the relationship between corrosion-induced crack width and steel corrosion in RC structures is quite large. In this study, a probabilistic framework for estimating the structural capacity of corroded RC structures using the observational corrosion-induced crack width distribution and machine learning is proposed. Based on the experimental results of corroded RC beams, random field theory, and finite element (FE) analysis, artificial samples composed of corrosion-induced crack width and steel weight loss distributions over the RC beams are generated. Two machine learning-based models are then developed using these samples to estimate the steel weight loss distribution from the observational corrosion-induced crack distribution. Finally, a Monte Carlo-based FE analysis with the estimated steel weight loss distribution as the input data is conducted to obtain the probability density function (PDF) of the structural capacity of corroded RC beams. For illustrative purposes, the effect of observational corrosion-induced crack width distribution on the PDF of flexural capacity of an existing RC beam is investigated using the proposed framework. The results show that the proposed framework using a machine learning-based model is a reliable and computationally efficient approach for estimating the structural capacity of corroded RC members and demonstrates the potential for assessing the deterioration condition of existing RC structures based on the corrosion-induced crack width distribution.