Chloride-induced Corrosion Of Steel Reinforcement Research Articles

Time-dependent fragility analysis of a nuclear containment structure under internal pressure and chloride-induced corrosion

The prestressed concrete containment structure, serving as the ultimate barrier against nuclear fuel leakage, holds paramount importance in ensuring the uninterrupted operation of nuclear power plants. Particularly in the aftermath of the Fukushima nuclear disaster, the influence of material aging and degradation of containment structures has been emphasized. Consequently, a probabilistic performance assessment of containment structures under chloride-induced corrosion condition is of significant relevance. This study presents a method for time-dependent fragility analysis of nuclear containment structures subjected to internal pressure, considering the effect of chloride-induced corrosion of steel reinforcement. A highly efficient and accurate finite element model with multi-layered shell element is formulated for damage and failure analysis. Furthermore, a corrosion degradation model of reinforced concrete, aligned with the attributes of multi-layered shell elements, is derived to reduce the reduce parameter samples generated by Latin Hypercube sampling technique. Material uncertainties and time-dependent effects are jointly integrated into the finite element analysis process, culminating in the establishment of fragility curves for the containment structure under various service lifetimes. The results indicate that within first 40 years of service, the load-bearing capacity of the containment structure has slightly decreased, while the probabilities of functional and structural failures in the containment structure will significantly increase after 60 years of service.

Seismic fragility analysis of nuclear containment structure under chloride-induced reinforcing steel corrosion conditions

Chloride-induced corrosion of reinforcing steel is one of the critical degradation factors influence the life cycle performance of the containment structure. Therefore, it is of great significance to study the safety performance of containment structure under chloride-induced reinforcing steel corrosion condition. This study presents fragility evaluation of the containment structure under chloride-induced reinforcing steel corrosion condition. Nonlinear time history analysis of the containment structure under different reinforcing steel corrosion conditions is carried out considering various uncertainties including uncertainty in material strength, record to record uncertainty and uncertainty in corrosion parameters. Roof drift under different ground motion intensity levels and seismic fragility of the containment structure corresponding to different performance level with typical service life are analyzed. Results reveal that with the increase of the service life of the containment structure, the increasing rate for roof drift of the containment structure decreases, while the variability of roof drift of the containment structure changes slightly. Service life of the containment structure has different impacts on the fragility of the containment structure corresponding to different performance levels. With the increase of service life, the increasing rate for failure probability of containment structure increases.

Machine learning-based prediction for residual bearing capacity and failure modes of rectangular corroded RC columns

Chloride-induced corrosion of steel reinforcement is likely to change the failure modes of reinforced concrete (RC) columns in marine environments under the combined action of vertical and seismic load. This study was aimed to predict the residual horizontal bearing capacity and failure modes of corroded RC columns based on machine learning (ML) methods. First, a database (163 flexural failure, 26 flexural-shear failure, and 35 shear failure) of rectangular corroded RC columns was established according to predefined selection criteria. Then, 6 efficient ML algorithms, including support vector machine, artificial neural network, k-nearest neighbors, convolutional neural network, random forest, and categorical boosting, were employed to establish predictive models for evaluating the residual bearing capacity and failure modes of corroded RC columns. Based on the SHapley Additive exPlanations (SHAP) method, the importance of input characteristic parameters was ranked and how the input parameters make decisions to obtain the final output results explained. Finally, influences of stirrup corrosion level (ηt), shear-span ratio (λ), and axial load ratio (n) were investigated regarding the residual bearing capacity and failure mode evolution of corroded RC columns. The results show that the proposed ML models can effectively predict the residual bearing capacity and failure modes of corroded RC columns and exhibit great potential for describing the relationship between input variables and output results.

Experimental study on cyclic flexural behaviour of GFRP-reinforced seawater sea-sand concrete slabs with synthetic fibres

Seawater and sea-sand (SWSS) concrete is a new type of concrete with many economic and environmental benefits. However, chloride-induced corrosion of steel reinforcement is a major problem associated with this type of concrete. Due to its excellent resistance in chloride environments glass fibre reinforced polymer (GFRP) reinforcement could be utilized in SWSS concrete as an alternative to steel Adding fibres can also improve the concrete properties reinforced with GFRP bars. Fibres can affect the post-crack response and failure mode of GFRP reinforced concrete and also improve the bond between rebar and concrete. This study focused on the flexural behaviour of GFRP reinforced SWSS concrete slabs with or without fibre incorporation which has not yet been fully addressed in the literature. Polypropylene (PP) and polyvinyl alcohol (PVA) fibres were used for the concrete reinforcement. Under-reinforced (ρ < ρb) and over-reinforced (ρ > ρb) GFRP reinforced concrete (RC) slabs were prepared and subjected to four-point cyclic bending loads. The results show that GFRP bar is a promising alternative to steel for SWSS concrete reinforcement. The GFRP RC slabs with plain SWSS concrete had a cracking moment which was 13% lower than the values predicted by the ACI 440.1R-15 provisions. However, adding fibres, particularly PP fibres, could successfully compensate for this reduction. Variation in GFRP reinforcement ratio had almost no effect on cracking moment. With the addition of fibres, the cracking moment and ultimate strength of the slabs were both improved. Crack width and crack spacing were reduced in fibre-reinforced SWSS concrete slabs compared with the plain concrete counterparts. Fibres reduced the residual deflection of the slabs at the end of each cycle. Comparing experimental deflection results with the values predicted by different models revealed that there is no available model could satisfactorily predict deflection for all the GFRP reinforced SWSS slabs.

The Role of Cracks in Chloride-Induced Corrosion of Carbon Steel in Concrete—Review

The majority of works in the field of chloride-indued corrosion of steel in concrete are focused on the cracks formed by the corrosion products. However, the number of studies on the influence of cracks (pre-cracked concrete) on corrosion is limited. Cracks create preferential/free paths for the penetration of chlorides, water, and oxygen into concrete; thus, the presence of cracks in concrete can intensify chloride-induced corrosion of steel reinforcement. This paper presents a review of the effects of cracking on the corrosion of steel in concrete. It was widely reported in the reviewed papers that cracks have a negative impact on concrete durability. They influence the chloride penetration and the chloride-induced corrosion of reinforcement in terms of the initiation and propagation stages. This influence is a complex function of many factors, including mix design, exposure conditions, crack frequency, crack orientation, crack width, and cover depth. Although there is a general agreement on the effects of cracks on the initiation of corrosion, the role of cracks and their widths on the propagation of corrosion in the long term is still under debate.

Chloride-induced corrosion of steel reinforcement in mortars manufactured with alternative environmentally-friendly binders

There is increasing interest in exploring the durability of structures manufactured with cements that are more environmentally friendly than traditional Portland. Accordingly, protection against chloride-induced corrosion of carbon steel reinforcement in mortars manufactured with environmentally friendly hybrid cements and alkali-activated materials (AAM) needs to be analyzed in-depth. Hybrid cements are innovative alternative binders with reduced amount of clinker in their formulation (20–30%). Their precursors are aluminosilicate wastes and they are very feasible in-construction implantation because they are not activated neither with liquid solutions of strong alkalinity nor external heating. In this research, AAM mortars were manufactured using slag from industrial by-products activated with sodium silicate. Hybrid mortars were manufactured either from fly ash or from slag, and activated with Na2SO4. Portland cement (CEM IV) mortars were also included in this study as reference. Chlorides were made to penetrate into the four different mortars under study by diffusion. The porosity and chloride penetration were evaluated and related to the different materials. The electrochemical behavior of the steel reinforced mortar specimens was monitored by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The corrosion rate values obtained for steel embedded in AAM were similar to conventional CEM IV mortars, and the morphology of the attack is less localized.

Blast fragility analysis of RC columns considering chloride-induced corrosion of steel reinforcement

Chloride-induced corrosion of steel reinforcement is one of the key factors that influences the life cycle performance and load-carrying capacities of concrete structures. For concrete structures that might be subjected to explosion hazards during the service life, the fragility analysis with the consideration of chloride-induced rebar corrosion provides quantitative information on lifecycle performance of structures against blast loading. This study performs the fragility analysis of reinforced concrete (RC) columns considering chloride-induced corrosion of steel reinforcement subjected to blast loading. General corrosion and pitting corrosion are considered in this study. Monte Carlo simulations are carried out in the study to calculate the failure probabilities. The mean and standard deviation of the degraded diameter and yield stress of the reinforcement up to 90 years after the corrosion initiation is established, which is incorporated in the existing empirical formulae for constructing the P-I curves of RC columns to predict its deteriorated blast loading-resistance capacity with time. In the analysis the blasting scaled distance is used as the demand intensity measure, random fluctuations of the peak reflected pressure, positive blast loading duration, concrete compressive strength, thickness of the concrete cover, diameter and yield stress of steel reinforcement are considered in the simulations. The blast fragility curves of typical RC columns are generated with respect to different damage levels corresponding to the number of years after corrosion initiation. It is found that the damage probability of RC columns increases significantly with steel reinforcement corrosion deterioration. Parametric analyses have shown that the column size is a more dominant factor, in comparison with the reinforcement ratio, of the RC columns on the blast resistance capacity corresponding to the minor damage levels. It is also found that the longitudinal reinforcement ratio is a less dominant factor than transverse reinforcement ratio on blast fragility curves of RC columns to resist blast loading. The blast resistance capacity of RC columns deteriorates significantly with corrosion damage.

A study on effectiveness of inorganic and organic corrosion inhibitors on rebar corrosion in concrete: A review

Reinforced concrete is the most extensively used building material in the construction industry. Generally, well-made concrete provides good physical and chemical protection to the embedded steel bar against an aggressive environment. The highly alkaline concrete pore solution protects the steel reinforcement from aggressive ions by forming a passive oxide layer over the steel surface. However, the passive film can be destroyed, and corrosion of steel reinforcement can be initiated either due to carbonation or due to the presence of a sufficient amount of chloride ions at the rebar level. Chloride induced corrosion of steel reinforcement affects the durability and decreases the service life of reinforced concrete structures exposed to aggressive environments, which results in huge repair and maintenance costs. By keeping in view, the substantial economic loss incurred due to corrosion of steel reinforcement in reinforced concrete structures, it is necessary to adopt adequate measures to minimize the corrosion of steel reinforcement in concrete. The most common corrosion prevention technique is the use of corrosion inhibitors in concrete. Several research works have been reported in the literature to evaluate the efficiency of corrosion inhibitors against chloride-induced corrosion of steel reinforcement in concrete. Corrosion inhibitors are typically introduced either as an admixture during the preparation of fresh concrete mixes or as a surface application on the hardened concrete to prevent the onset of corrosion of steel reinforcement or extend the corrosion initiation time in reinforced concrete structures. This review article summarizes the reported research works on inhibiting the behaviour of organic and inorganic corrosion inhibitors against chloride-induced corrosion of steel reinforcement in simulated concrete pore solution such as saturated calcium hydroxide solution containing varying concentrations of chloride ions as well as in cementitious composites. Further, the reported research works on the effect of corrosion inhibitors on the mechanical properties of cementitious composites are also are reviewed and discussed.

The Effect of Durability and Corrosion Behavior on the Concrete Treated with Chemical Inhibitor

Chloride-induced corrosion of steel reinforcement and the reaction of atmospheric carbon dioxide with cement paste are the most important causes of premature failure in marine-reinforced concrete structures. Among the available methods, corrosion inhibitors offer a simple and costeffective technique in reducing the chloride-induced corrosion on the steel reinforced concrete.

Inhibitor efficiency of migratory corrosion inhibitors to reduce corrosion in reinforced concrete exposed to high chloride environment

Chloride-induced corrosion of steel reinforcement is the most important cause of premature failure of reinforced concrete structures. Corrosion inhibitors have proven to be an effective method to reduce corrosion rate in terms of application and cost-effectiveness. Various types of inhibitors are present such as organo-functional silanes, Amino-alcohol and Surfactant & amine salts-based inhibitors. The inhibitor efficiency of six major commercial migratory corrosion inhibitors, for reinforced concrete available in UK, was investigated using electrochemical study and permeability measurements to determine the most efficient inhibitor to protect steel in concrete with high chloride environment. It is showed that these compounds are effective inhibitors for reinforced concrete structures. Out of the tested inhibitors, organo-functional based inhibitors showed the best inhibitor efficiency and barrier properties.

A Markov chain-based model for structural vulnerability assessmentof corrosion-damaged reinforced concrete bridges.

The deterioration and cracking of reinforced concrete (RC) bridges due to the chloride-induced corrosion of steel reinforcement is an inherently time-dependent stochastic phenomenon. In the current practice of bridge management systems, however, the determination of the condition states of deteriorated bridges is highly dependent on the opinion of experienced inspectors. Taking such complexity into account, the current paper presents a new stochastic predictive methodology using a non-homogeneous Markov process, which directly relates the visual inspection data (corrosion rate and crack widths) to the structural vulnerability of deteriorated concrete bridges. This methodology predicts the future condition of corrosion-induced damage (concrete cracking) by linking structural vulnerability analysis and a discrete-time Markov chain model. The application of the proposed methodology is demonstrated through a case-study corrosion-damaged RC bridge pier.This article is part of a discussion meeting issue ‘A cracking approach to inventing new tough materials: fracture stranger than friction’.

Coupled multi-physics simulation of chloride diffusion in saturated and unsaturated concrete

Chloride-induced corrosion of steel reinforcement is one of the major long-term deterioration mechanisms for reinforced concrete infrastructures. Chloride transport through cement-based materials is a complex chemo-physical process involving ionic diffusion in concentrated solution, pore structure, chemistry, membrane permeability of the matrix, cracking, and the variation of the internal and external environmental conditions. Although in the literature there are plenty of both simplistic phenomenological models and sophisticated models, in this study, a new model is developed taking aim at capturing the fundamental physics and, at the same time, having a formulation as simple as possible that it can be effectively calibrated and validated using available limited experimental data. The model couples the ionic diffusion process with the concrete micro-structure evolution due to continued hydration accounting for hygro-thermal variations and their effects on both the diffusion and hydration processes. The formulation is implemented in a semi-discrete conduit transport network that mimics the internal heterogeneity of the cementitious material by connecting the matrix space between coarse aggregate pieces. This allows the model to replicate naturally the meso-scale tortuosity effect which is an important feature towards representing realistically the heterogeneity-induced variations of chloride concentration within the concrete. The limited model parameters are carefully calibrated and the formulation is validated by simulating multiple experiments ranging from diffusion through pastes to large concrete cylinders. The results of numerical simulations show the ability of the model to describe spatial and temporal evolution of the chloride concentration within the samples under varying chloride concentrations and temperature boundary conditions within both saturated and unsaturated concrete.

Methods of accelerating chloride-induced corrosion in steel-reinforced concrete: A comparative review

Rebar corrosion has been recognized as a major durability issue of the reinforced concrete (RC) structures over recent decades, prompting the necessity to study the corrosion behavior of steel in concrete during the service life. To estimate service life of RC structure, the corrosion of reinforcing steel is generally accelerated by means of the impressed current technique in limited available time. In the literature, several accelerated laboratory corrosion methods have been proposed, however the results varied greatly as chloride concentrations and testing conditions were different. Researchers are unsure which testing methods can be used to give reliable results to simulate the real-life corroded RC structure. This review paper aims to systematically compare and evaluate different methods of accelerating chloride-induced corrosion of steel reinforcement in concrete. First, the accelerated methods categorized into three groups namely, the impressed current (IC), the chloride ion diffusion (CID) and the artificial climate environment (ACE) are briefly discussed. Then, the key influencing factors (i.e. current density, salt concentration, service load) affecting the corrosion results in different methods are compared and evaluated. Finally, the corrosion products and acceleration method are comprehensively discussed. By this comparative review, it is believed that researchers can have a better understanding of different accelerated corrosion methods along with the influencing factors. So they could select or even develop the most suitable techniques to yield reliable corrosion test results.

Parallel Finite Element Model for Multispecies Transport in Nonsaturated Concrete Structures.

The chloride-induced corrosion of steel reinforcement embedded in concrete is undoubtedly one of the most important durability problems of reinforced concrete structures. The chloride ions as well as other ionic species (Na+, Ca2+, K+, OH−) come from various deicing salts and they are transported from the environment into concrete. To investigate the transport mechanism of the multispecies, complex scientific methods and accurate mathematical models are needed. The purpose of this study is to develop a more robust mathematical model and better computational technique to characterize the coupled effect of ionic transport mechanisms as well as the influence of interaction of ionic species. The new mathematical model was developed based on the Nernst–Planck equation and null current condition to solve the ionic-induced electrostatic potential, and the model was implemented by a parallel finite element algorithm. The verification of mathematical model was done by comparing the model prediction with experimental results for ionic transport in saturated concrete. The comparisons showed good results. The model prediction of the multispecies transport in partially saturated concrete demonstrated that the ionic species dissolved in pore solution could be carried by the moisture movement and pressure gradient. Therefore, the multispecies transport model based on the parallel finite element method is effective, accurate, and can be used for solving the partial differential equations for ionic species transport in concrete.

Structural and durability assessment of ECC/concrete dual-layer system for tall wind turbine towers

The increasing consumption of wind energy necessitates the development of taller concrete turbines towers with larger installed rotors. A previous study demonstrated that a dual layer system that incorporates protective layers made from engineered cementitious composites (ECC) improves the durability performance of these towers (Jin and Li, 2019 [1]). However, the introduction of ECC layers could affect the tower design due to its low elastic modulus relative to concrete. This paper first studies the structural impacts of the concrete towers with added ECC layers. An iterative method is employed to examine the requirements of strength, deflection, natural frequency and fatigue. The results show that ECC protective layer produces nonconsequential effects on tall concrete towers with less than 4% increase in tower diameter. After satisfying the aforementioned requirements, a durability analysis is conducted to compare the tower designs with and without ECC layers. The results indicate that the application of ECC layers significantly delays the initiation of chloride-induced corrosion of steel reinforcement and prolongs the service life of concrete wind turbine towers by four times. Therefore, this study allays the concerns that ECC protective layers may compromise the tower’s structural performance and confirms its potential application in tall wind turbine towers for improved durability performance.

Prediction model of chloride diffusion in concrete considering the coupling effects of coarse aggregate and steel reinforcement exposed to marine tidal environment

Abstract Chloride-induced corrosion of steel reinforcement is one of the significant factors for the durability of the reinforced concrete structures exposed to marine environments. Reinforced concrete is a multiphase composite material composed of mortar, coarse aggregate, and rebar. The coarse aggregate and rebar can both affect the chloride diffusion characteristics of concrete. Nevertheless, the current researches related to the effects of the aforementioned two impact factors on chloride diffusion in concrete either considered the coarse aggregate only, or taken into account the steel bar separately. The coupling effects of coarse aggregate and steel reinforcement on chloride transport in concrete required to be further explored and discussed. In this paper, an in-door physical experiment for chloride diffusion in plain and reinforced concrete specimens exposed to marine tidal environment was carried out. The specimens were cast using different volume fractions of coarse aggregate and diameters of steel reinforcement. The chloride concentrations for experimental specimens were measured at various exposure times, and these measurements were adopted to further investigate the common influences of coarse aggregate volume fraction and blocking effect of rebar on chloride diffusion in concrete. Using the impact factors of coarse aggregate volume fraction f(v), the direct and indirect blocking effect coefficients of rebar α(v), βr(Φ/c) to improve the analytical solution of Fick’s second law, a prediction model of chloride diffusion in concrete considering the coupling effects of coarse aggregate and steel reinforcement was proposed. The accuracy of this proposed prediction model was validated by comparing the chloride concentrations evaluated by the prediction model with the experimental measurements. The findings are expected to be useful in realistically predicting the durability of reinforced concrete structures.

Experimental and numerical study of accelerated corrosion of steel reinforcement in concrete: Transport of corrosion products

Chloride-induced corrosion of steel reinforcement in concrete is one of the major causes for deterioration of reinforced concrete (RC) structures. Currently, there are only a limited number of coupled 3D chemo-hygro-thermo-mechanical models capable to realistically simulate corrosion process in cracked concrete. Especially moisture behavior coupled with transport of corrosion products in cracked concrete and its effect on the corrosion induced damage has not been addressed so far. In the present paper experiments performed on concrete cylinders under accelerated conditions are presented and discussed. The experiments are simulated using recently developed chemo-hygro-thermo-mechanical model. Based on the experimental results the model is verified and calibrated with respect to the parameters that are responsible for transport of rust through pores and cracks of concrete.

Chloride-induced reinforcing steel corrosion in ternary concretes containing fly ash and untreated sugarcane bagasse ash

The corrosion of reinforced ternary concretes containing fly ash (FA) and untreated sugarcane bagasse ash (UtSCBA) was evaluated. Chloride-ion diffusion at 28 and 90 days, as well as microstructural properties, percentage of voids, and compressive strength (CS) in cylinders were evaluated at 2500 days of age. Moreover, corrosion was monitored in prismatic specimens exposed to a NaCl solution by corrosion potentials and linear polarization resistance techniques. Results show that the combination of FA plus UtSCBA decreased the chloride-ion diffusion and did not affect the compressive strength (CS) of the concrete. For the studied concretes, the combination of FA plus UtSCBA appears a suitable option against chloride-induced corrosion.

Prediction model of long-term chloride diffusion into plain concrete considering the effect of the heterogeneity of materials exposed to marine tidal zone

Long-term chloride-induced corrosion of steel reinforcement would make concrete structures vulnerable to deterioration and as a result shorten their service life. However, physical experiment of in-situ or laboratory may not be an effective way to determine long-term chloride profiles and diffusion behaviors into concrete attributed to its time-consuming and implementary difficulty. This study adopted the results of chloride concentration into mortar and corresponding concrete specimens from a filed experiment in marine tidal zone at exposure times of 60, 120, 240, 360, 480, and 600 d reported in literatures, and the meso-scopic finite element numerical simulation method, in which the concrete was modeled as a three-phase composite material composed of mortar, coarse aggregate, and interfacial transition zone (ITZ), was combined to develop a simplified empirical model for predicting long-term chloride diffusion into plain concrete considering the effect of the heterogeneity of materials exposed to marine tidal zone (with exposure limited to 20 years). Certainly, the accuracy, reasonability and reliability of the evaluated chloride profile results associated with this empirical prediction model were validated as well. The proposed empirical model is expected to be useful in realistically predicting the long-term diffusion of chloride into concrete.

Determination of critical anodic and cathodic areas in corrosion processes of steel reinforcement in concrete

Chloride-induced corrosion of steel reinforcement in concrete is one of the major reasons for deterioration of reinforced concrete (RC) structures. In the present paper the coupled 3D chemo-hygro-thermo-mechanical model for concrete is used to study the influence of the anode/cathode surface ratio on the corrosion rate and corrosion induced damage. It has been demonstrated that the position and size of anode and cathode strongly influences the crack pattern and the corrosion rate (Ožbolt et al., 2012, 2014). Currently there is no algorithm which can predict the combination between anode and cathode surfaces on reinforcement that results to the highest corrosion rate. Therefore, to investigate this influence the expression for maximum entropy production, deduced from irreversible thermodynamics, is formulated. The entropy is produced by dissipative processes, which are in this special case the flow of ions through the electrolyte, the anodic and cathodic polarization and the diffusion oxygen process. Through several numerical examples, in which the size and position of anodic and cathodic surfaces are varied, is demonstrated that maximum entropy leads to maximum corrosion rate.