Rust Expansion Research Articles

Experimental research on the degradation law of the bond performance between steel bars and concrete with rust expansion cracking

Experimental research on the degradation law of the bond performance between steel bars and concrete with rust expansion cracking

Mechanics of durability of structural concrete: new approach to the phenomenon of degradation. Part 2. Corrosion of reinforcement

There are several models in which the corrosion rate, rust expansion, and resulting crack propagation around reinforcement can be assessed. The effect of crack-induced corrosion on the behavior of the structure can also be assessed. Several methods have been proposed to evaluate the mechanical performance of reinforced concrete structures with corroded reinforcing bars. Changes in the mechanical properties of reinforcing bars, concrete and their interactions need to be modeled based on the concept of analytical methods. The load-bearing capacity of reinforced concrete beams with reinforcement corrosion was calculated using the finite element method. The influence of reinforcement corrosion is considered from the point of view of changes in the mechanical properties of reinforcement and adhesion of reinforcement to concrete. Instead of reducing the cross-sectional area of the reinforcement, the Young’s modulus and yield strength of the corroded reinforcement are reduced. Numerical modeling of the structural performance of reinforced concrete structures with reinforcement corrosion using a finite element program has shown that modeling of structural deterioration, such as reinforcement corrosion and concrete cover cracking, sometimes has a large impact on the analytical results. The structural characteristics of reinforced concrete elements with reinforcement corrosion are calculated. Using this modeling method, an analysis of the degree of influence of corrosion on structural characteristics was carried out.

Study on Seismic Behavior and Component Vulnerability of Corroded RC Shear Walls Subjected to Flexural Shear Failure

ABSTRACT The impact of corrosion degree, axial compression ratio, reinforcement ratio of longitudinal bar and horizontal distribution rebar, and stirrup of boundary column on seismic performance of RC shear walls were investigated. The corrosion forms (rust expansion cracks and corroded steel bars), failure process, hysteretic characteristics, bearing capacity, and deformability were compared. Subsequently, a numerical model of corroded RC shear walls was established adopting shell elements. Finally, according to the numerical simulation method, considering the uncertainty of corrosion degree and material parameters, the vulnerability models of RC shear wall components with different corrosion degrees were built. The results show that the mechanical properties of the shear wall were seriously deteriorated due to the corrosion of steel bars, and the ultimate displacement and ductility coefficient of severely corroded specimens were reduced by 28.5% and 12.27% respectively, compared to non-corroded specimens. A proposed numerical modeling method for corroded RC shear walls based on shell element is accurate, and the bearing capacity error and energy dissipation error of the simulation and test results were less than 20%. As the degree of corrosion grew, the probability of shear wall components experiencing more severe failure added significantly. When the displacement angle was 1/120 (This is the limit value of elastic-plastic displacement angle specified in the code), the probability of DS3 and DS4 occurring in the shear wall with a corrosion degree of 0% were 56% and 39.44%, and the probability of DS4 and DS5 occurring in the shear wall with a corrosion degree of 10% were 41.1% and 38.44%.

Corrosion-Induced Cracking Model of Concrete Considering a Transverse Constraint.

The performance of corrosion-induced cracking of reinforced concrete members under transverse constraints was studied. Based on the theory of elastic-plastic mechanics and the hypothesis of uniform corrosion of a steel bar, a three-layer hollow cylinder model was established to predict the critical corrosion of the steel bar at the time of the cracking of the concrete cover. Taking the constraint of stirrups on surrounding concrete into consideration, it can be used to predict the corrosion rate of members with stirrups at the time of the cracking of the concrete cover, which further expands the application range of the corrosion-induced cracking models of concrete. On this basis, the critical corrosion rate of concrete under different stirrup ratios at the time of cracking was measured. The calculated results of the model are in accordance with experimental data. For corner steel bars, when the stirrup spacing is less than 100 mm, the existence of stirrups can effectively delay the occurrence of rust expansion cracks and enhance the durability of the structure. On the basis of this study, the problem of corrosion expansion and cracking of the concrete cover caused by non-uniform corrosion of steel bars along longitudinal and radial directions needs to be further studied in the future.

Research on multi-apparent defects detection of concrete bridges based on YOLOR

To enhance the accuracy of detecting apparent defects in concrete bridges, this study proposes an improved model based on the YOLOR. Initially, a concrete bridges defect (CBD) dataset comprising 7009 images was established, encompassing nine distinct types of defects: pockmark, spalling, cavity, whitening, reticular crack, single crack, rust expansion, exposed rebar and leakage. Subsequently, using the CBD dataset, performance comparison experiments involving YOLOv3, YOLOv4, YOLOR-640, and YOLOR-1280 were conducted to select the optimal model. Based on the characteristics of the apparent defects in bridges, the anchor boxes and localization loss function were optimized respectively, thereby proposing an improved model named YOLOR-BDIM. The results indicate that the mAP of YOLOR-BDIM increased by 2.7 % compared with initial model. Furthermore, YOLOR-BDIM achieved a detection accuracy of 97.5 % during the random tests, showing excellent detection performance even in complex environments.

Analysis of Bonding Properties of Corroded Reinforcement Concrete

In order to investigate the degradation of bonding properties between corroded steel bars and concrete, this study employs the half-beam method to conduct bond-slip tests between corroded steel bars and concrete after impressed-current accelerated corrosion of the steel bars in concrete. The effects of steel corrosion rate, steel bar diameter, steel bar strength grade, and concrete strength grade on the bonding properties between concrete and corroded steel bars were analyzed. The influence of different corrosion rates on specimens’ bonding strength and bond-slip curves was determined, and a constitutive relationship for bond-slip between corroded steel bars and concrete was proposed. The results indicate that the ultimate bonding strength of corroded reinforced concrete specimens decreases with increasing corrosion rate. Additionally, an increase in corrosive crack width leads to a linear decrease in bonding strength. Evaluating the decline in adhesive properties through rust expansion crack width in engineering applications is feasible. Furthermore, a bond-slip constitutive relationship between corroded steel bars and concrete was established using relative bond stress and relative slip values, which aligned well with the experimental findings.

Simulation and analysis of rust expansion cracking of reinforced concrete

Reinforced concrete is used in complex environment, and the damage of concrete protective layer caused by steel corrosion will seriously reduce the durability of the structure. In order to deal with the different corrosion morphology of steel bars in engineering, three different function expressions are proposed to describe the uniform and non-uniform corrosion of steel bars. Based on PF_CZM phase field model and adaptive refinement mesh technology, the cracking of concrete protective layer caused by different corrosion types of steel bars is simulated. The simulation results are close to the experimental or actual observed crack propagation. The research shows that the non-uniform corrosion coefficient (α) of steel bars affects the crack propagation form of protective layer. When α=1,2, the thinnest part of the protective layer will be penetrated by the main crack, and two secondary cracks will be produced on both sides. The characteristic displacement in the process of crack propagation is similar, and the maximum expansion displacement of steel bar is less than 125 μm when there is obvious crack in the protective layer. When α=4,8, the protective layer will produce two main cracks. The corrosion characteristic displacement is also similar, and the maximum expansion displacement of steel bars exceeds 180 μm when there are obvious cracks in the protective layer. However, with the increase of non-uniform corrosion coefficient, the amount of steel corrosion required for obvious damage and cracks gradually decreases, and the structure is more likely to be damaged. When non-uniform corrosion occurs in both longitudinal and transverse directions of steel bars, cracks will originate from the most serious corrosion of steel bars and spread to both sides. Compared with the two-dimensional simulation results, the simulated crack propagation morphology and the predicted structural durability results are more accurate. The coarse mesh is used to verify the adaptability of the method to the project, which provides reference for the engineering design and durability research of concrete structures.

Multiphysics and multiphase mesoscopic study on electrochemical corrosion of reinforcement caused by chloride salt

Reinforcement corrosion caused by chloride attack is one of the main reasons for the degradation of reinforced concrete (RC) structures, especially those exposed to marine environment. To study the effect of chloride attack on the electrochemical corrosion behavior of reinforcement, a 2D meso-numerical model coupling ion transport and electrochemical corrosion was established by modifying the anode Tafel slope in this paper. More importantly, gaussian function model with clear physical meaning is proposed to describe the distribution of reinforcement corrosion layer. The reliability of the proposed model is further verified by compared with the third-party experiments data. Furthermore, the effects of electric field effect, meso-structure, maximum corrosion depth and corrosion rate on the distribution of reinforcement corrosion layer are investigated based on the proposed model. The numerical simulation results show that the influence of electric field effect and interfacial transition zone (ITZ) on corrosion morphology cannot be ignored. Moreover, the novel gaussian distribution model with physically meaningful parameters has wide applicability through comparison with experiments. Specially, a simulation of chloride diffusion trajectories in concrete meso-structures reveals how ITZ promotes chloride diffusion. The research of this paper provides theoretical support for the rust expansion cracking and service life prediction of reinforced concrete structures.

Cracking time and prediction model of low-alloy steel reinforced seawater sea-sand concrete based on DIC technology

The cracking of seawater sea-sand concrete (SSC) cover due to the corrosion of low-alloy steel (LS) is a critical factor affecting its serviceability and durability. To analyze the cracking behavior of the SSC cover, a thick-walled cylinder model was developed in this study. The cylinder was divided into multiple coaxial rings of equal thickness, and damage variables were introduced to determine the extent of damage for each cracked ring based on the position of the rust expansion crack front. A predictive model for the cracking time of SSC cover was established by using the displacement compatibility equation at the interface of reinforcing steel and cover concrete, in combination with Faraday's law. To verify the accuracy of the model, the Digital Image Correlation (DIC) technique was utilized to determine the timings of two pivotal stages: the initial cracking and complete cracking of the cover. The comparison between the predictive outcomes and experimental results showed an error range of 4 %–10 %, indicating that the predictive model is relatively accurate.

Damage prediction of RC columns with various levels of corrosion deteriorations subjected to blast loading

Coastal structures are often exposed to harsh environmental conditions such as saltwater, high humidity, and coastal winds, leading to corrosion damage to the reinforcing steel and degradation of concrete. The blast risk is characterized by a relatively low likelihood but a significant consequence. The blast resistance of structural members with deteriorated properties due to corrosion and the corresponding post-blast performance is of significance to evaluate the lifecycle structural safety facing explosion threats. In this study, the damage of reinforced concrete (RC) columns of coastal structures with various corrosion degrees subjected to blast loading is investigated. The corrosion effect was modelled by considering the deterioration of rebar diameter and yield strength, bond strength between rebar and concrete, and rust expansion pressure effect. The numerical model was validated by simulating drop weight impact tests of RC beams with different corrosion degrees. Based on the validated model, the finite element (FE) models of corroded RC columns with the maximum corrosion degree of 15% were established and their responses and damage to blast loads of various blasting scenarios were calculated. It is found that the blast response of the column increases with the degree of corrosion. The blast damage mode may change from combined shear and flexural damage to concrete spalling damage with the increment of corrosion degree. Furthermore, the residual axial loading capacity and stiffness of post-blast columns were calculated and it is found that they degrade as the corrosion degree increases. A blast damage index is defined in terms of the residual axial loading capacity of the column, which is found to increase with the corrosion degree. The damage amplification factor due to corrosion deterioration (CAF) is then proposed as a function of corrosion degree, TNT equivalent mass, standoff distance, concrete strength, and reinforcement ratio to predict the blast damage of corroded columns.

Nanoindentation analysis of corrosion products and induced expansion stress in reinforced concrete exposed to marine environments

Reinforced concretes are widely used in construction owing to their ultrahigh mechanical properties and long-term durability. However, the corrosion of steel bar within concrete poses a substantial threat to the structural integrity of buildings, impeding advancements in ocean engineering and necessitating expensive maintenance measures. In this study, the corrosion mechanisms of reinforced concrete under marine environments were investigated. The elastic modulus of corrosion products and the identification of rust compositions in different corrosive environments were comprehensively investigated using nano indentation technique and microscopic characterizations. The average young's modulus of rust products in chloride, sulfate, and chloride-sulfate composite solutions were measured to be 47.6 GPa, 37.59 GPa, and 61.52 GPa, respectively. And the analysis identified the presence of two distinct layers of rust product, providing valuable insights into the corrosion process. In addition, the real-time and in-situ monitor of corrosion expansion stress shows that the rust expansion stress generated in chloride solution was almost twice as high as that under sulfate solution and 1.3 times higher than that in the composite solution. The advanced wire beam electrode technique was employed to compare and analyze the different stages of depassivation, pitting corrosion and corrosion rate during the whole process. The corrosion process under chloride solution showed larger and more serious corrosion than under sulfate solution, with the anodic peak current spreading and reaching 4.00 μA cm-2 after 300 days. This work reveals valuable insights into the corrosion behaviour of reinforced concrete in three corrosive conditions and can be used to inform the development of strategies for corrosion prevention and mitigation.

Rust expansion cracking behaviour of new Cr alloy-reinforced coral aggregate concrete

The rust expansion cracking behaviour of Cr alloy-reinforced coral aggregate concrete (CAC) was studied by theoretic and experimental methods to analyse the serviceability limit state of concrete. The corrosion product composition of the Cr alloy rebar was analysed to determine the stability and protection of the rust layer. The critical corrosion ratio model of Cr alloy-reinforced concrete was established by considering the influence of water–binder ratio, admixtures and fibres, relative protective layer thickness, Cr alloy reinforcement type and reinforcement placement. The results demonstrated that owing to the loose and porous characteristics of CAC, the corrosion products filled the concrete, resulting in critical corrosion ratio of the rebar being much larger than that of ordinary concrete (OC). When Cr alloy was added to a carbon rebar, the rust layer structure and corrosion products of Cr alloy rebars changed significantly, thereby improving the stability and protection of the rust layer. The protection coefficients of HPB300, Cr1, CrAl, Cr3, Cr5, and Cr8 rebars were 0.211, 0.286, 0.304, 0.490, 0.670, and 0.964, respectively. The rust layer density of the Cr alloy rebar was high, hindering the erosion of the harmful medium in concrete. The critical corrosion ratios of Cr1, CrAl, Cr3, Cr5, and Cr8 reinforcements increased by 0.72%, 1.81%, 4.01%, 11.60%, and 29.35%, respectively. When Cr (5%–8%) was added to the rebar, the corrosion time of reinforcement began to rust and concrete cracking was prolonged. This was beneficial for preventing concrete cracking caused by rebar corrosion.

NUMERICAL SIMULATION OF NON – UNIFORM CORROSION INDUCED CRACKING

This research is focused on modeling the damage of concrete due to corrosion. The load used in this paper is only focused on the internal load due to rust expansion. In this study, corrosion was modeled uniformly and non-uniformly to investigate the difference between these two configurations to the damage in concrete. The simulation in this study was carried out using the 3DNLFEA program. The results show that numerical simulation provides predictions that are in line with experimental and numerical modeling results performed by the previous study in terms of pressure and corrosion cracking patterns. From the crack analysis, the pattern found that a non-uniform corrosion model can be used to express a realistic rust corrosion development around the reinforcement. Meanwhile, uniform corrosion requires a larger loss of steel area to reach the damage stage. Therefore, for non-uniform corrosion, the corrosion rate cause cracks and reaches a limiting crack width at earlier times in the service life of the corroded part.

Durability degradation simulation of RC structure based on gamma process considering two-dimensional chloride diffusion and life probabilistic prediction

In this paper, based on the gamma process, a new method for predicting the life of reinforced concrete (RC) structures eroded by chloride is presented considering two-dimensional (2D) chloride diffusion. First, according to the chloride diffusion theory, an analytical model and a finite difference numerical model considering 2D chloride diffusion under the action of multiple factors were established. Based on this, the Monte Carlo method and method proposed in this study were employed to predict the initial rust time of RC structures eroded by chloride. Histograms of the initial rust time and probability density function obtained using the two methods mentioned above were compared and analyzed to verify the validity of the proposed method. Finally, the life prediction model of the RC structure considering the initial rust time T1, rust expansion cracking time T2, and time when the concrete surface crack width reaches the limit crack width T3 was established, and its applicability was verified through an analysis of an engineering example. The research indicates that the gamma process-based probability models can approximately predict the time required for rebar corrosion of an RC structure eroded by chloride considering 2D diffusion.

Corrosion Analysis of RCC Beam using Simplified FEM Model

The durability of the reinforced concrete structures highly influenced by many important factors including steel corrosion. Corrosion starts off with the availability of the water and oxygen, products formed due to this get deposited in the interface between the concrete and steel. As the depositing corrosion volume increases, an expansive pressure at the interface exerts on the surrounding concrete and eventually causes structural degradation, which reduces concrete and steel bond. This work focuses on a parametric study on rust expansion pressure to understand the effect of grade of concrete, diameter of the rebar, position of the rebar and c/d ratio using ABAQUS software. After the analysis, it is found that rust expansion pressure increases as the grade of concrete and c/d ratio increases, which means the pressure required to cause surface cracks due to corrosion is more in higher grades concrete and high c/d ratio. Position of the bar did not affect the corrosion pressure requirement to cause surface cracks. As the corrosion level increased, deflection of the beam also increased. But position of the corroded reinforcing bars in the beam slightly affects the deflection of the beam.

Predicting corrosion in reinforced UHPC members through time-dependent multi-physics numerical simulation

Ultra-high-performance concrete (UHPC) has superior durability characteristics over traditional concrete. Improved durability behavior of UHPC has been attributed to the dense material property, which effectively constrains harmful material ingress and oxygen supply. However, the corrosion performance of reinforced UHPC under sustained mechanical loading, which may induce cracking, in addition to environmental conditioning is still not well characterized. This study investigates the electrochemical-mechanical coupling effects on deterioration mechanisms of reinforced UHPC beams subjected to service loading conditions and chloride attack through multi-physics simulation techniques. Finite element models were simulated considering the cracking induced by service loads and deformations caused by rust expansion on the cementitious matrix. Material transport properties such as chloride and oxygen penetration parameters were updated in each step of the time-dependent process based on cracking conditions. The simulation results show that there is substantial steel cross section and yielding load capacity loss, initial stiffness reduction, and damage area increase in reinforced concrete members while UHPC members showed relatively small cross section loss, negligible increase in UHPC damage, no observable reduction in initial stiffness, and minimal loss in yield load capacity. The effect of oxygen supply level on the corrosion performance is also explored showing that the corrosion rate of reinforced UHPC specimens were limited due to depleted oxygen at the steel-UHPC surface. Numerical simulation results were verified against experimental trends on corrosion performance of reinforced UHPC specimens. Further, the numerical framework herein provides an alternative way in predicting deterioration processes and evaluating service life performance of ductile reinforced concrete infrastructures in a computationally efficient manner.

Crack development of rebar rust in rubberized concrete using mesoscale model

Reinforcement rust will lead to cracking of rubberized concrete and reduce durability of rubberized concrete structure. Therefore, the fracture morphology of rubberized concrete, which is caused by corrosion and expansion of reinforcement in rubberized concrete is studied by means of meso numerical simulation. The results show that: (1) The fracture morphology of rubberized concrete is little affected by the thickness of the protective layer of reinforcement. (2) The occurrence timing of the inflection point of the rust expansion reaction around the reinforcement can reflect the difficulty of cracking rubberized concrete. (3) The smaller the thickness of the protective layer and the larger the diameter of the reinforcement, the more easily the rubberized concrete will crack. (4) The diameter of reinforcement will affect the expansion level of cracks in all directions. The increase of reinforcement diameter promotes the crack propagation degree in the direction of 180°, and inhibits the crack propagation degree near 90° and 270°. (5) The content of rubber affects the fracture morphology of reinforcement rust. As the content of rubber increases, the path of cracks formed inside the rubberized concrete decreases, and the penetration cracks inside the rubberized decrease. The results of this paper have guiding significance for the research of fracture morphology distribution and reaction force of rubberized concrete caused by reinforcement rust.

Corrosion mechanism and damage characteristic of steel fiber concrete under the effect of stray current and salt solution

Steel fiber reinforced concrete (SFRC) has been widely used in construction and transportation due to its superior mechanical properties. From the perspective of structure, SFRC is a potential solution to the problem of stray current induced corrosion in electrical railway systems. However, the corrosion mechanism of SFRC under the coupling effect of stray current and salt solution is not clear, and the change of mechanical properties in the process still lacks a quantitative description, so it is difficult to predict the structural life. In this paper, different corrosive media were selected for the stray current induced corrosion test of SFRC, in which the chloride concentration was adjusted to study its influence on the corrosion rate. Ultrasonic and electric current were combined to monitor the corrosion process. The colorimetric and titration method were used to measure the chloride depth and concentration in the specimen after corrosion, mercury intrusion porosimetry was employed to determine the pore structure. It is found that chloride is the most destructive to SFRC and dominates the corrosion process, while sulfate and caustic alkali contribute secondary effect. Chloride destroyed the passive film on the surface of the steel fiber and corroded it to form a local rust expansion area, causing concrete damage and reducing mechanical properties. In addition, if the damage degree reaches 0.3 ∼ 0.4, the structure will be destroyed. When the environmental chloride concentration reaches the threshold 0.6 mol/L, the higher the concentration, the faster the SFRC corrosion. The quantitative relationship between the main influencing factors (concentration of chloride, corrosion time and chloride penetration depth) and damage degree is proposed based on the experimental data. The research may provide reference for the application of SFRC in electric railway projects.

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.

Corrosion Cracking Process of Reinforced Concrete under the Coupled Effects of Chloride and Fatigue Loading

To study the corrosion cracking process of reinforced concrete under the combined effects of chloride and fatigue loading, the constan-current and dry-wet cycle accelerated corrosion method was used to corrosion the specimens under different stress levels for different time. The quality loss of reinforcement, the composition of corrosion products and the cracking of concrete are analyzed from the macro, micro and micro scales, and to obtain the spatial distribution as well as microscopic characteristics of corrosion products of the reinforcement bar under coupling conditions. Additionally, a model of steel rust cracking under the coupled action of chloride and fatigue loading is established. The results show that: under the same corrosion time, the concrete cracking and steel corrosion degree become more serious with the increase of stress level. The greater the stress level, the earlier corrosion occurs and the more corrosion products are, Moreover, due to the fatigue load, the concrete on the upper side of the steel bar has rust expansion cracks earlier than the lower side.