Bond Deterioration Research Articles

An efficient deep learning approach for ultimate bond strength estimations of corroded bar and concrete

Abstract The corrosion behavior of the reinforced concrete structure depends heavily on the interfacial bond behavior between steel and concrete. Over the years, the deterioration of integrated reinforced steel has weakened this bond and potentially led to structural problems. Conventional methods of bond strength evaluation, such as pullout and bond beam tests, is frequently intrusive and tedious. Therefore, there is a growing need for non-intrusive, effective, and reliable forecasting algorithms capable of assessing bond deterioration caused by corrosion. Traditional algorithms for predicting bond strength make it difficult to capture the complex nature of steel-concrete bonds. The present study proposes two different deep learning algorithms, i.e., convolutional neural networks (CNN) and long short-term memory (LSTM), for predicting maximum bond strength in the presence of corrosion. The predictive model is based on a comprehensive dataset comprising 218 datasets from previous studies encompassing diverse input and output variables for predicting the models. The models were trained and tested using the given data to improve early predictions of corrosion-induced bond degradations. The predictive model’s effectiveness was assessed by applying various performance metrics. From this study, the CNN model exhibits higher accuracy and efficiency with mean absolute error, root mean square error, and mean absolute percentage error of 0.25, 0.28, and 95.72, respectively, for predicting ultimate bond strength estimations. The findings of this study provide an accurate and robust prediction model to improve the reliability and safety of the concrete structure by enhancing the residual load-bearing capacity of the concrete structure that has undergone corrosion.

Experimental research of corroded concrete beams with natural cooling after fire considering the bond deterioration

The residual bearing capacity after fire is of great significance for safety assessment and repair of building structures. To accurately evaluate the residual strength of corroded beam after natural cooling, this study investigated the residual bearing capacity of corroded beam considering the bond deterioration after fire exposure. First, the bond behavior and flexural-deformation capacity was conducted by pullout test and bending test after corrosion erosion and fire temperatures damage. The bond deterioration test shows that when the temperature rises above 200℃ and the corrosion level exceeds 4.3%, the bond strength decreases by 16.5%. At the temperature reaches 600℃ or the corrosion degree reaches 13.8%, the bond behavior damage exceeds 50%. The bending test indicates that corrosion and high temperature damage both decrease the bending bearing capacity of the beam, but the influence of high temperature damage on the residual bearing capacity is greater than that of corrosion. The bond property deterioration decreases the strain value of the tensile rebar during the bending process, and decreases the bending capacity of the beam. Finally, a bond-slip constitutive model suitable for corroded beams after fire is proposed, which is applied to the calculation of the ultimate moment of the beam. The modified value of beam bearing capacity considering bond deterioration has better collimation and higher safety margin. The bond-slip constitutive model and the modified calculation method of bending moment of beam are helpful to provide more accurate performance assessment of beam after the coupling effect of corrosion and fire damage.

Stochastic modeling for bond deterioration between rebar and concrete due to reinforcement corrosion

Reinforcement corrosion has a significant impact on the bond behavior between rebars and concrete. Accelerated corrosion tests and pullout tests were conducted on 24 concrete cube specimens with embedded rebars to investigate the non-uniformity of corrosion and establish a deterministic model for the bond strength-slip relationship. Then, the probability distribution of the ultimate bond strength for 132 specimens, the peak slip for 79 specimens, and the stochastic process of the ultimate bond strength changing with the corrosion level for 204 specimens from previously published studies were analyzed. By introducing the probability distribution and stochastic process into this deterministic model, a stochastic model is suggested to evaluate the bond deterioration between the rebar and the concrete owing to the reinforcement corrosion. The results showed that: The non-uniformity of reinforcement corrosion was verified since the remaining diameters obeyed an extreme value I distribution. The ultimate bond strength and peak slip obeyed normal distributions and how the ultimate bond strength changed with the corrosion level was a normal stochastic process. The error percentage between the stochastic model and the test results was less than 5 %, indicating that the bond strength can be well predicted when giving a corrosion level.

Acoustic Emission Monitoring of Bond Deterioration in GFRP-Reinforced Concrete Members: An Entropy-Based Approach

The primary objective of acoustic emission (AE) monitoring is to accurately detect imminent critical damage, preventing premature failure by analysing the dynamic evolution of AE parameters. This study introduces AE entropy, a distinctive parameter derived from Shannon's entropy, employed to monitor the bond degradation between glass fibre-reinforced polymer (GFRP) rebars and the concrete interface in GFRP-reinforced concrete elements. Characteristic AE parameters have been synchronously collected during flexural bond tests, and information entropy and weighted information entropy, composed of typical AE characteristic parameters based on Shannon’s information entropy theory in the time domain, have been defined. Findings indicate that, with increasing bond stress, the specimens exhibit a trend characterized by "decreasing, stabilizing, and then increasing" in both AE characteristic parameters and weighted information entropy. The information entropy value shows fluctuations during any damage associated with GFRP-concrete bond deterioration. At peak bond stress values, information entropy values experience a rapid surge, indicating significant deterioration. The evolution process of debonding between GFRP rebar and concrete, switching between a chaotic state that develops randomly and an organized state that produces in order, follows specific laws (disordered–ordered–disordered), corresponding well to AE characteristic parameters weighted information entropy. Moreover, entropy values, both individual and weighted, when correlated with bond stress and slip variations in the test specimens, distinctly outline and predict various stress transfer mechanisms between the GFRP bar and concrete. In summary, this research underscores the utility of AE entropy as a valuable tool for damage monitoring in GFRP-reinforced structures. Its ability to capture microstructural deformations positions AE entropy as a promising candidate for improving critical damage identification and preventing premature failure

Comprehensive assessment and monitoring of bond deterioration in GFRP-reinforced concrete beams using guided wave and acoustic emission techniques

The debonding between glass fiber-reinforced polymer (GFRP) rebars and concrete significantly reduces the bond strength and jeopardizes the safety and durability of GFRP-reinforced concrete (GFRP-RC) structures. As a result, it is imperative to monitor the structural integrity of infrastructures being built using these composite materials in structural elements during their service lives. Previous studies have primarily focused on artificially induced debonding scenarios for guided wave (GW)-based monitoring, which has resulted in an inability to capture debonding events that arise naturally due to external loads. Furthermore, flexural bond test investigations simulating real loading scenarios in GFRP-RC structures have not been linked with acoustic emission (AE) and GW monitoring. The present study addresses these research gaps by comprehensively examining the flexural bond integrity in GFRP-RC structural elements subjected to realistic loading conditions using a hybrid approach combining GW and AE as active and passive structural health monitoring techniques, respectively. A series of bond tests, conforming to RILEM specifications, have been performed to investigate various parameters (including rebar surface characteristics, embedment length, and confinement conditions) that affect the flexural bond degradation response of GFRP-RC members. Damage indices based on GW and AE signal parameters have been developed to evaluate the characteristics of confined and unconfined specimens distinctly. It has been observed from the test results that the L (0,3) GW mode is more sensitive to debonding than other modes and that a threshold of 25% has been established for the GW damage index to denote significant bond damage. Furthermore, AE damage indices have provided valuable insights into concrete damage, including splitting and damage at the rebar-concrete interface. Thus, a thorough understanding of bond deterioration in GFRP-RC structures has been developed by combining GW and AE health monitoring techniques, with implications for enhancing structural safety and durability.

Comprehensive analysis of bond stress transfer mechanisms in glass fiber-reinforced polymer-reinforced concrete beams using acoustic emission monitoring

The present study investigates the critical bond characteristics between glass fiber-reinforced polymer (GFRP) bars, which is essential for the application bars as corrosion-resistant components in structural concrete. The interfacial bond deterioration and stress transfer mechanisms have been investigated in the present study by employing acoustic emission (AE) monitoring in hinged-type GFRP-reinforced concrete (GFRP-RC) beam specimens. The bond strength of the test specimens, governed by chemical adhesion, mechanical interlocking, and frictional resistance, has been intricately examined. Various AE signal parameters as well as historic and severity indices derived from the AE signal parameters have been meticulously evaluated and correlated with bond stress and rebar slip variations. The present study has also introduced an innovative approach of using the sentry function for the assessment of bond deterioration and associated mechanisms. The results of the present study demonstrate the reliability of AE parameters in monitoring debonding and bond strength variation, the effectiveness of the sentry function in evaluating damage progression, and the utility of historic and severity indices in capturing micro-mechanism transformations. The accurate localization of debonding and the qualitative distribution of bond stress have also been demonstrated by through correlations between cumulative AE parameters and rebar slip, Additionally, the present study also highlights the significance of peak frequency variations in AE signals, serving as a crucial tool for quantifying the mechanical interlocking and interfacial friction. The results contribute significantly to precise assessments and development of effective strategies for mitigating bond deterioration in GFRP-RC elements.

3D nonlinear finite element simulation of RC beams corroding under service loads

ABSTRACT In the present study, a 3D nonlinear finite element (FE) model has been developed to simulate reinforcement corrosion in RC beams under sustained load. The corrosion effects were modelled as bond deterioration at the rebar-concrete interface, damage in cover concrete and mechanical degradation of corroded rebars. A simplified temperature field-based methodology was proposed in the commercial program ABAQUS to simulate the evolution of corrosion degradation while a sustained load is maintained in the beam. The FE model was validated using available experimental results in terms of cracking behaviour and load-deflection response and found to be in good agreement. Parametric investigations were carried out to analyse the performance of beams under simultaneous corrosion and sustained loads. The findings demonstrated that pitting corrosion under simultaneous loading conditions can significantly compromise a beam’s structural integrity. Specifically, a scenario with 20% mass loss and 60% sustained load resulted in a 33.3% increase in concrete strain and a significant increase of 738% in the tensile steel strain leading to yielding. Furthermore, the influence of load and corrosion sequence on the behaviour of the beam was assessed by comparing its response when corroded under sustained load with a beam corroded and subsequently loaded.

A hybrid method for bond-slip behavior of reinforcement rebar in steel-polypropylene hybrid fiber reinforced concrete structures in marine environments

Fiber-reinforced concrete is an advanced class of construction materials that display higher mechanical and durability performance, but limited information is available on the bond behavior of reinforcement rebar in steel-polypropylene hybrid fiber reinforced concrete (SPHFRC) in marine environments, which produce crack states commonly seen in reinforced concrete structural components. In this study, a hybrid method for predicting the bond response behavior of SPHFRC under monotonic and cyclic loading was developed. The proposed method combining mechanical-driven model and generative adversarial networks (e.g., GAN) method. Experimental databases were constructed. Two empirical models were developed. The GAN method enhanced its prediction accuracy through adversarial training support by database and hyper-parametric analytics. Finally, to verify the accuracy and effectiveness of the developed model, a total of 65 SPHFRC specimens under cyclic loading were conducted. The comparison shows that this model can reproduce the corrosion-induced bond deterioration of SPHFRC. The model can also capture the cyclic bond degradation of SPHFRC and other types of ultra-high-performance concrete with an acceptable range.

Bond Deterioration of GFRP Concrete Enhanced with Steel Fibers Subjected to External Sulfate Attack

Concrete structures are exposed to sulfate and chloride attacks when are used in different environments such as seawater, deicing salts or industrial waste. Sulfate corrosion is considered one of the most important factors that responses for deterioration of construction materials performance. When sulfate attacks concrete, sulfate ions interact with cement materials to form chemical compounds inside the concrete. These compounds result volume increase and create internal stresses causing cracks, spalling and reduction in concrete strength. In this paper, the effect of external sulfate attack on properties of concrete samples enhanced with and without steel fibers (SF) and on bond damage between glass fibers reinforced polymer GFRP bar and concrete were investigated. Samples were completely immersed in 10% magnesium sulfate solution for two different exposure periods (60 & 120 days) to compare with control samples. Compressive and tensile strengths, density and pulse velocity were experimentally investigated. Push-out test was also carried out to study the damage in bond between concrete and GFRP rod. The results of concrete samples immersed in magnesium sulfate solution for 60 days showed an increase in compressive strength, tensile strength and density, while the results decreased for samples immersed for 120 days.

“I don’t watch that anymore”: an analysis of online comments by German soccer fans on their relationship to their favored clubs

IntroductionSoccer fans are important stakeholders of their favored clubs; yet, although there is manifold literature on this subject, there are still open questions concerning supporters’ relationship and loyalty to those clubs, such as potential fan exits, where supporters turn away from their preferred team. Existing literature describes diverging evidence as to whether an exit is possible and whether fans’ loyalty prevents that response. Against this background, it is important to examine how the relationship between fans and soccer clubs presents itself from the fans’ perspective. This study focuses on German soccer fans because an increasing number of media reports note problems for the fans in this regard, reporting eroded loyalty, increasing alienation, or turning away.MethodsBy means of a qualitative and explorative approach (thematic analysis), this study analyzes online fan comments associated with the mentioned reports. A purposive sample of 17 media reports with 10,902 associated comments written/published between 2020 and 2023 was included in this study.ResultsThe thematic analysis show that fans reflect their relationship to favored clubs in three ways: negative changes in the emotional relationship, negative behavioral changes in the relationship, and no or positive changes in the relationship. A wide continuum of negative emotional and behavioral changes is identified, ranging from a deterioration of the inner bond with the favored club to different levels of ceasing soccer-related consumption. As explanations for the (potential) dynamics and changes in the relationship, fans reflect a broad and diverse field of developments in the context of German soccer. The differentiated developments are systemized within four categories: commercialization, governance, attractiveness, and the COVID-19 pandemic.DiscussionThe results are discussed and contextualized referring to the Exit-Voice-Loyalty-Framework and thematically relevant literature. Particularly far-reaching is the finding that there are indeed fans in the field of soccer who are capable of permanently abandoning (exiting) formerly supported clubs. The article concludes with theoretical and managerial implications emerging from the results, as well as limitations and areas of interest for further research.

Experimental study with DIC technique on the bond failure of structural concrete under repeated reversed loading with different amplitude

The bond between deformed steel rebar and concrete plays a critical role against seismic action, thus it is important to capture the dynamic bond loss and establish the bond-slip model with cyclic loading. To explain the macroscale performance such as bond-slip relationship and establish the bond strength model, it is meaningful to capture the mesoscale and local behaviors between ribs and concrete. In this paper, pull-out specimens with rebar embedded in concrete and small windows excavated in the cover concrete are adopted with DIC technique to monitor the strain variation and crack development along the interfaces under static and reversed loading of different amplitude. From the test, it is found that DIC is an effective approach to obtain the localized characteristics including the normal and shear deformations. Through parametric study, the effects of concrete cover depth and the existence of stirrups on bond deterioration in terms of both global and local behaviors are studied. Interestingly, the global slip and local crack-width show synchronically increase under the pulling-out action, which demonstrates that the macroscale behaviors could be clarified from mesoscale measurement with the aid of DIC technique.

Bond Deterioration between Corroded Reinforcing Bars with Variable Diameters and Concrete at Elevated Temperatures

Bond Deterioration between Corroded Reinforcing Bars with Variable Diameters and Concrete at Elevated Temperatures

Modelling of long-term performance of RC beams under coupling steel corrosion and bond deterioration

The steel-to-concrete bond deterioration due to corrosion in the reinforced concrete (RC) structures still needs more investigation because the existing models were established based on pull-out tests, which do not represent the real RC beams owing to the flexural cracks. This paper presents a new approach that discusses the bond deterioration of corroded steel bars embedded in RC beams. The study presents simulations for an experimental database of existing corroded RC beams from previous papers using a nonlinear finite element model. The simulated specimens were divided into two categories: accelerated and long-term (after 14,23, and 28 years) corroded beams to identify the key corrosion parameters in these two conditions. The results indicated that the behavior of the RC beams, which corroded via the accelerated method, failed by concrete crushing after steel yielding, and it could be simulated considering the reduction of both steel area and bond strength only. On the other hand, the spalling pressure is a key parameter to simulate the long-term corroded RC beams because it controls the ultimate deflection, and the failure is governed by concrete cover spalling due to concrete deterioration. As an innovative result, a novel bond-slip model was proposed to predict bond deterioration due to corrosion in the RC beams, and it showed excellent accuracy compared to the existing models.

Assessment of repaired reinforced concrete dapped-end beams exhibiting bond deterioration under static and cyclic loading

An experimental investigation has been conducted to scrutinize the behavior of reinforced concrete dapped end beams repaired with different configuration of CFRP sheet under static and cyclic loading due to induced cracks from previous examination. The static load was adopted to determine the amplitude of cyclic loading at an increment of 15% until failure. It was demonstrated that retrofitting increased load capacity and ductility significantly; approximately 28% increase in capacity and 1.5 times higher ductility over the un-retrofitted beam under static loading, and approximately 80% higher capacity with three times increase in ductility and a change in crack orientation under cyclic loading. Nonetheless, the reentrant corner's significant concrete spalling is a major concern. It is thus essential to focus on the dapped section for monitoring and maintenance of this beam.

Investigation of reinforced concrete members with bond deterioration under tensile load

Bond deterioration in reinforced concrete (RC) structures is frequently caused by aging, environmental factors, overloading, or poor design. This deterioration may cause the structure to lose its aesthetic, and eventually collapse. The behavior of structures that exhibit bond deterioration is poorly understood and inadequately maintained. The response of RC structures exhibiting bond loss under tension load is presented in this paper. In order to comprehend the impact of bond loss in RC composite, the RC system was first built for a pullout. It was then expanded to the nib corner of RC dapped end beams. Additionally, the system was analytically examined using 3-dimensional FEmodel. The bond loss created a weak zone with internal cracks parallel to the bar’s axis. The nib section separated from the full depth of the dapped end, while the hanger reinforcement resisted the diagonal tension cracks. The dapped section must therefore be given more consideration during monitoring and maintenance.

A two-phased modelling approach for corrosion-induced concrete cracking and bond deterioration in reinforced concrete

Bond deterioration is one of the major consequences of reinforcement corrosion in reinforced concrete (RC) structures. In this paper, a two-phased numerical modelling approach is presented that aims to determine the constitutive behaviour (bond–slip) at the reinforcement-concrete interface at a certain corrosion level. The novelty of the approach is that it consists of a crack model and a bond model, and that the flow of corrosion products into the pores and corrosion-induced cracks as well as the effect of the bonded length and concrete cover are taken into account in the 2D crack model. The resulting expansion of corrosion products from the crack model is used as input in the 3D bond model. The combination of both models leads to a procedure that balances computational time and modelling detail. The model is validated on a substantial amount of experimental pull-out test results. A good agreement is obtained between the experimental data and the models for different corrosion levels in terms of crack width, crack pattern, corrosion-induced bond loss, and failure mode.

Bond behavior of glass fiber reinforced polymer bars with varying confinement levels under cyclic loading

Local bond behavior of glass fiber reinforced polymer (GFRP) bars under cyclic loading is systematically analyzed by beam-end tests. Meanwhile, the corresponding bond tests under monotonic loading were carried out for comparative analysis. In addition, the influence of concrete strength and lateral confinement from the concrete cover and stirrups on the bond behavior was considered in the tests. The results revealed that the specimen under cyclic loading exhibits narrower cracks but more seriously damaged bond interface than that under monotonic loading. It indicates that interface crushing exerts a decisive role in inducing the bond deterioration under cyclic loading, and the bond deterioration of specimens under cyclic loading was more severe. The increase of concrete strength and lateral confinement magnified the effects of cyclic loading on bond deterioration. Furthermore, a bond stress-slip model for GFRP bars under cyclic loading was put forward to better predict the bond behavior of GFRP bars with different confinements.

Steel–concrete bond deterioration in reinforced concrete tension members due to primary cracks

Primary cracks in reinforced concrete tension members lead to the deterioration of the steel–concrete bond. This study aims to investigate this bond deterioration by establishing a novel relationship between the bond force and slips near the cracks. The descending part of this relationship represents the bond deterioration, with its parameters determined by the structural responses. An iterative algorithm is proposed based on this relationship to analyze the bond behaviors of tension members. The effectiveness of the proposed method is validated using reinforced concrete tension members from experiments in the literature. The results demonstrate a gradual decrease in bond forces from local maximum to zero near the cracks, indicating the presence of the descending part of the bond–slip relationship. The length, slope, and characteristic points of the descending part vary with crack spacing and slips at the cracks, leading to nonlinearity in steel strains. In comparison to existing methods assuming constant length or slope, the proposed method accurately predicts these variable parameters, and provide precise estimations of bond force.

Experimental and analytical assessment of fatigue damage in reinforced concrete tension members

In this paper, the effects of bond deterioration due to fatigue loading on the structural response of reinforced concrete tension members are studied. A comprehensive experimental campaign on reinforced concrete ties and pull-out specimens was carried out under monotonic and repeated loading. The use of distributed fibre optical sensing to assess the local strains allowed the bond deterioration mechanism under repeated loading to be observed. Previously applied load cycles caused a reduction in tension stiffening for load levels below the maximum cyclic load but did not significantly influence the deformation behaviour of the member near the ultimate load. The bond stresses at the maximum cyclic load decreased fairly linearly with the logarithm of load cycles, with the most pronounced reduction in bond stresses near the cracks. At the minimum cyclic load, the bond stress distribution along the tie changed and bond stresses reversal occurred close to the cracks. This caused negative tension stiffening in some cases, i.e., the mean strains exceeded those occurring in a bare reinforcing bar at the same load. The mean steel stresses and the steel stress amplitudes between the cracks increased with the number of load cycles due to the gradual reduction of the concrete contribution and bond degradation. Bond degradation occurred linearly on a semi-logarithmic scale, as expected for the generated bond stresses, which were below the fatigue bond strength. The test results highlight that accounting for shrinkage-induced strains is essential for a realistic evaluation of tension stiffening and residual deformations in particular.Based on the experimental observations and previously developed models for monotonic and cyclic loading, two approaches were used to predict the response of reinforced concrete tension members under repeated loading: the Local Fatigue Damage Model (LFDM), based on the local bond stress-slip relationship, and the adapted Tension Chord Model (TCM) which assumes constant bond stresses and mean strains. The results of both approaches agree well with the test results at the maximum load but yielded less satisfactory predictions at the minimum loading level where only the LFDM was able to be applied successfully. Further research is required to validate the negative bond stresses occurring upon slip reversal in the LFDM and the reduction factor proposed in the adapted TCM.

Effect of chloride-induced corrosion on bond performance of various steel fibers in cracked SFRC

This study investigates the chloride-induced corrosion behavior of various steel fibers and associated effects on their interfacial bond performance in cracked steel fiber reinforced concrete (SFRC). Three types of deformed fibers, including hooked-end (H), crimped (C), and milled-cut (M) fibers, were embedded in high strength matrix and then exposed to wet-dry cycles of chlorides under cracking conditions. The scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) technique were employed to gain insights into the surface morphologies and corrosion products at the micro-scale. The bond behaviors of corroded fibers were further evaluated through pull-out tests, where the influences of fiber type, corrosion duration, crack width, and embedded length were discussed. Three distinct corrosion morphologies were identified on the surfaces of three types of fibers owing to the difference in corrosion products. After 40 days of corrosion, the average bond strength of H fibers increased by 37.9% because of dense and rough rust layer, while those of C and M fibers deteriorated by 30.5% and 18.8% due to surficial groove loss and loose rust layer. The average bond strength of H, C, and M fibers improved by 12.4%, 11.7%, and 58.0% as the crack width increased from 0.1 to 0.3 mm, whereas significant reductions in pull-out energy and equivalent bond strength were obtained once the crack width exceeded 0.2 mm owing to fiber fracture. The corrosion-induced bond deterioration of M fibers became less severe as the embedded length increased up to 12 mm and remained unaffected thereafter.