Corrosion Initiation Time Research Articles

Deterministic and probabilistic approaches for corrosion in RC structures: A direct proposed model to total service life predictions

In this paper the negative effects of the chloride ions attack in reinforced concrete (RC) elements have been studied. For this the vertical and horizontal chloride diffusivity has been treated by several models to identify the more relevant factor affecting the chloride concentration. The pitting corrosion has been treated to define the resistance losses of the shear forces and bending moments. An alternative deterministic/probabilistic procedure, by a direct and systematic new model, has been proposed to estimate the total time of service life for RC elements at the design phase. Several detailing configurations of steel bars in a RC beam, water/cement ratio and level of aggressiveness have been analysed to compare the model predictions. In this sense, this paper should provide useful results for analysts in terms of probability of failure for resistance losses and time of corrosion initiation. The goal is not only to provide practical results but also to evaluate the issue in a more modern risk analysis throughout the proposed prediction model.

Fragility Assessment of RC Bridges Exposed to Seismic Loads and Corrosion over Time.

A methodology to estimate the structural fragility of RC bridges, considering the effects of seismic loadings and corrosion over time, is presented. Two scenarios are considered: (a) The structure is exposed only to seismic loads, (b) Both the effect of corrosion and seismic loads are present in the system. The uncertainties related to material properties, structural geometry, seismic occurrences, corrosion initiation time, cracking and corrosion evolution are considered. Different time stages, such as 0, 50, 75, 100, and 125 years are selected to evaluate the effect of both seismic loads and seismic loads plus corrosion. The calculation of fragility curves implies a structural design, nonlinear modeling of structures with simulated properties, estimation of both corrosion times and seismic occurrences, and evaluation of structural demand over time considering the effect of seismic loads and corrosion. An illustrative example is provided on an RC continuous bridge with AASHTO beams, cap beams and circular columns located in Acapulco, Guerrero, Mexico. A performance level equal to 0.002 is chosen for the design of the structure. Results show that the probability of exceeding the design performance levels for both cases (seismic and seismic plus corrosion) are similar at the stage of time equal to zero (a newly built bridge). However, such probabilities, after 150 years, are equal to 0.61 and 0.85 due to the cumulative damage caused by seismic and seismic plus corrosion, respectively. The estimation of the probability of exceeding a certain performance level, considering the effect of corrosion together with seismic loads, highlights the importance of considering more than one type of solicitation for these kinds of structural systems. Lastly, recommendations about design are given.

A numerical study on chloride transport in alkali-activated fly ash/slag concretes

Alkali-activated binders for concrete composites are emerging as the available low-embodied-carbon alternatives to ordinary Portland cement (OPC). Despite decades of research, the durability of alkali-activated concrete remains a concern, especially the issues related to chloride penetration and the potential for chloride-induced corrosion of embedded steel bars. In this study, a multi-phase, multi-component ionic numerical model is developed to investigate the chloride transport in alkali-activated fly ash/slag (AAFS) concretes. The model framework considers the porosity of concrete, the chloride binding, and the electrochemical coupling between multi-species. Based on the proposed model, the parametric studies of a series of influencing factors on both chloride transport and initiation time of reinforcement corrosion are performed and discussed. The results indicate that the slag content and the water to binder ratio are the dominant factors affecting chloride penetration and corrosion initiation time of steel bars in AAFS concretes due to their greater contributions to reduce the porosity, while the aggregate volume fraction presents a limited effect compared with other factors. The transport model proposed in this study brings insights to the prediction of the service life of alkali-activated reinforced concrete structures.

A prediction model for chloride-ion ingress in concrete sleepers

There are approximately 600 km (370 mi) of railway passing through the desert areas in Iran. One of the important challenges associated with the degradation of railway structures in desert areas is chloride-ion invasion of the concrete, which causes the corrosion and swelling of bars, leading to the total destruction of concrete sleepers. Although numerous studies have been conducted on the prediction of bar corrosion in various reinforced concrete structures, there is no specific study on the prediction of bar corrosion in B70 concrete sleepers. This study investigates chloride diffusion in concrete sleepers and develops a prediction model using field and laboratory measurements. Sample profiles were taken from the Bam–Zahedan railway line for the determination of diffusion coefficients and initial and surface chloride contents. The early-age diffusion coefficient in concrete samples was obtained, and a prediction model was developed based on these parameters. Finally, a sensitivity analysis was performed in order to investigate the influential parameters on the initiation time of the corrosion. The results indicate that the effects of the chloride diffusion coefficient and the concrete cover were the leading factors in the corrosion initiation time.

Corrosion-Fatigue Life Prediction of the U-Shaped Beam in Urban Rail Transit under a Chloride Attack Environment.

The coupled effect of the chloride attack environment and train load seriously affects the safety and durability of urban rail transit viaducts and dramatically reduces their service life. In this research, a corrosion-fatigue life prediction model of the prestressed concrete (PC) beam under the coupled effect of the chloride attack environment and train load was developed. This proposed model was illustrated by a 30 m-span PC U-shaped beam in an urban rail transit viaduct. The competitive relationship between concrete fatigue cracking time, non-prestressed reinforcement corrosion initiation time, and concrete corrosion-induced cracking time was discussed. The effects of train frequency, the chloride attack environment grade, and the environmental temperature and relative humidity were investigated on corrosion-fatigue life. Results indicate that train frequency, the chloride attack environment grade, and the environmental temperature can reduce the corrosion-fatigue life of a U-shaped beam by up to 30.0%, 50.7%, and 21.5%, respectively. A coupled chloride attack environment and train frequency can reduce the corrosion-fatigue life by up to 61.2%. Distinct from the environmental temperature, the change of relative humidity has little effect on the corrosion-fatigue life of the U-shaped beam.

Effect of limestone powder addition on corrosion initiation time of reinforced concrete

This work aimed to evaluate the effects of limestone powder (LP) replacement fraction (8–24 wt%) on chloride diffusion and chloride threshold (Cth) for corrosion initiation. Depassivation of steel was diagnosed by monitoring the self-corrosion potential and corrosion current density using open circuit potential and AC impedance tests, respectively. Corrosion initiation time (Tini) was estimated based on the measured Cth coupled with a dual time-varying diffusion model. The results indicate that the chloride diffusion coefficient decreases with 8 wt% LP addition, though further increase in LP content reverses the trend. With increasing exposure duration, both the surface chloride concentration and diffusion coefficient vary remarkably at first and eventually tend to be stable. As the cover depth decreases from 55 mm to 45 mm, Tini is found to decrease by 30.0%–42.9%. Incorporation of LP appreciably decreases Cth regardless of its replacement fraction, consequently leading to a decreased Tini, despite a low chloride diffusivity can be obtained with appropriate LP addition.

Numerical Solutions for Chloride Diffusion Fluctuation in RC Elements from Corrosion Probability Assessments

Mechanical diffusion of chloride ions in reinforced concrete (RC) structures varies in time and space, and depends on uncertain factors such as material properties, temperature, humidity, and aging. In this paper, different scenarios considering the time of corrosion initiation and the influence of the chloride diffusion coefficient for different loadings (i.e., constant, sinusoidal, Gaussian, and random) were proposed. Stochastic analyses were carried out to estimate the probability of failure of steel bars, and to evaluate the influences of the internal and external factors. Advanced numerical solutions were developed to account for these influences under non-constant diffusion coefficient and non-steady-state condition. Results show that the chloride content can assume low values by using the oscillations of the generic function (e.g., sinusoidal and general) instead of constant function. The influence of the temperature appears relevant. The 3D analyses, considering the random variability, show that chloride content can be higher than ~1.50 compared to chloride content using traditional approaches. Stochastic approaches plus advanced solutions allow, in a more complete way, the sustainability decision-making process during the design phase, maintenance, inspections, and repair.

Time-Dependent Seismic Performance of Coastal Bridges Reinforced with Hybrid FRP and Steel Bars.

To increase the durability and seismic resilience of coastal bridges, a hybrid reinforced concrete (HRC) bridge that incorporates both glass fiber-reinforced polymer (GFRP) bars and steel bars is proposed. The time-dependent seismic performance of the HRC bridge is comprehensively investigated at three levels, namely the material, bridge column and bridge structure levels. First, the decrease of tensile strength of GFRP bars over time is analyzed based on the Arrhenius theory, and corrosion initiation time and performance deterioration of steel bars are determined by Fick’s second law and an empirical formula. Second, an efficient finite element modeling method for aging HRC bridge columns is proposed. Simulation of the compression/tension behavior and the fracture failure of the GFRP bar is described. Hysteretic analysis is further conducted to investigate the time-dependent energy dissipation, ductility, residual displacement, bearing capacity and post-yield stiffness ratio. Meanwhile, comparisons of HRC bridge columns to reinforced concrete (RC) references are provided. Third, the seismic demand and damage evolution of deteriorated HRC bridge structures are investigated through dynamic time-history analysis. The results indicate that the corrosion-resistant GFRP bars contribute to improving the bearing capacity and to reducing the residual displacement of the HRC bridge. With an increase in service time, the seismic damage to the bridge column, abutment and expansion bearing increases, but the damage to fixed bearing decreases. Research results presented herein show that the HRC bridge is a promising alternative structure scheme in the marine environment.

Sampling-based seismic reliability analysis of the corroded reinforced concrete bridge bent

This study presents a sampling-based reliability sensitivity analysis to identify the random variables that are most influential on the seismic reliability of a corroded reinforced concrete (RC) bridge bent. To this end, a nonlinear finite element (FE) model of a scaled RC bent is developed, which accounts for the corrosion initiation and pitting corrosion models, as well impact of corrosion on the cover concrete, core concrete, reinforcing bars, and bond-slip behavior considering underlying uncertainties. Ground motion records are selected using conditional spectrum (CS) method. Pushover analysis is conducted on RC bent in discrete time points to evaluate the corrosion-dependent drift limit for different damage states. Seismic reliability analysis of the RC bent is conducted using Monte Carlo sampling (MCS) method in different damage states and time points. Results indicate the severe decrease in the seismic reliability index of the RC bent after 30 years of exposure to chloride, especially in the higher damage states. Finally, importance vectors are developed based on sensitivity analyses. The obtained results demonstrate that the importance of underlying random variables depends on the corrosion level and intended damage state. The obtained importance vectors show that the random variable related to the seismic input is the most influential variable on the seismic reliability of the corroded RC bent. It is also found that variables related to corrosion initiation time contribute the most to the seismic reliability of the RC bent in the first 15 years, while in the last 15 years the structural variables are the important ones.

Three-dimensional corrosion propagation in steel rebars of RC columns with early-age cracks

• Research developed a numerical framework incorporating finite element analysis (FEA) and random processes to simulate chloride-induced corrosion and rust formation in reinforcing steel embedded in RC members having early-age cracks. • The multiphysics phenomena of corrosion initiation and propagation are modelled through adequate considerations of chloride diffusion through cracked concrete, heat and moisture transport, polarization of steel rebars, and rust formation. • FEA of a RC column with randomly distributed vertical, horizontal and inclined early-age cracks shows lower corrosion initiation times of steel rebars in the vicinity of cracks and time-evolution of corrosion pit along the length and periphery of rebars. • Research outcome signifies the strong influences of early-age cracks in induction and propagation of pitting corrosion in RC members. This paper presents numerical simulation of chloride-induced corrosion and rust formation on steel rebars embedded in RC members with early-age surface cracks. A finite element analysis (FEA) framework, which integrates physiochemical and electrochemical processes of rebar corrosion with random generation of early-age cracks, is adopted to predict temporal progression of corrosion pit along the length and periphery of rebars. The multiphysics phenomena of corrosion initiation and propagation are modelled through adequate considerations of chloride diffusion through cracked concrete, heat and moisture transport, polarization of steel rebars, and rust formation. FEA of a RC column with randomly distributed vertical, horizontal and inclined early-age cracks shows lower depassivation times (i.e., corrosion initiation times) of steel rebars in the vicinity of cracks. This results in higher reduction of rebar diameter at crack zones in comparison with that observed at distant locations from cracks where uniform corrosion of rebars prevails. Based on the observed trajectories of time-evolving rust formation along the length of rebars, for different crack patterns, an average pitting length of 140 mm is observed. Research outcome signifies the strong influences of early-age cracks in induction and propagation of pitting corrosion in RC members.

Evaluation of Preventative Methods against Rebar Corrosion in Concrete

Prevention of rebar corrosion is achieved in the design and construction phases, by means of suitable mix design, casting and curing, and adequate cover depth; this approach have been introduced in international standards (EN 206) and design codes (Eurocode 2). Additional protection methods (cathodic protection, stainless steel or galvanised rebars, corrosion inhibitors, concrete coatings) can be used in very aggressive environment, especially in presence of chlorides, or when increased service life is required. In this work a simplified performance-based approach, based on Monte Carlo simulation, has been used to evaluate the service life (initiation time of corrosion) in chloride containing environments. The results confirmed that cathodic prevention and stainless steels are the most effective protection methods to guarantee a safe working condition in a severe environment. The use of pozzolanic or slag cement is confirmed as an effective way to slow chloride transport and by this way to increase the service life.

Estimating chloride exposure of reinforced concrete bridges using vehicle spray and splash mechanisms

Reinforced concrete (RC) bridges located in cold climates are typically exposed to large amounts of deicing salts during winter, which causes corrosion-related deterioration of RC bridges. Vehicle spray and splash are the major mechanisms of transporting deicing salts from the road to the exterior bridge surfaces. However, a systematic method for incorporating these mechanisms in the estimation of chloride exposure of an RC bridge is not available in the literature. This article aims to fill this knowledge gap. An analytical method is proposed to estimate the surface chloride concentration for an RC bridge, considering snow precipitation, salt application, vehicle type, vehicle speed, traffic volume, and distance to the roadside. The proposed method is demonstrated using an example RC bridge, and the results are compared with reported data from field tests. A parametric study investigating the effects of various model parameters on the results is also included in this article. The proposed method is expected to improve the determination of corrosion initiation time in service life estimation models for RC bridges.

Formation Factor Concept for Non-Destructive Evaluation of Concrete's chloride diffusion coefficients

Estimation of chloride diffusion coefficient (Drcm) is an integral part of service life assessment of vulnerable concrete structures due to chloride induced corrosion. This study focuses on the suitability of an alternate non-destructive, low-cost approach of estimating diffusion coefficients through electrical resistivity and formation factor as a replacement of conventional destructive migration tests. The variation in formation factor for 60 concrete mixes with different Supplementary Cementitious Materials (SCM) types (fly-ash, slag) and proportions (0–40%) along with multiple mix parameters (w/cm ratio and target slump) were studied after 365 days of curing. Drcm values predicted from formation factor approach were found to be in close proximity to the coefficients obtained from migration test but however, required certain modifications to ensure conservative estimations. Tentative modification factors were developed for each binder separately as well as for all blended mixes. Based on the obtained factored Drcm values using the modification factor, it was demonstrated that it is possible to ensure reliable and conservative estimation of corrosion initiation time of any mixes without the requirement of destructive testing.

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 graphene orientation on permeability and corrosion initiation under composite coatings

The unique anisotropic properties of graphene, particularly impermeability, have made it a promising candidate for further advances in corrosion prevention applications. Despite the large number of experimental works divulging the use of graphene in anticorrosion coatings, there is no report on the numerical modelling and simulation of the relationships between the orientation of graphene sheets in composite coatings and the introduced corrosion protection efficiency, to our knowledge. Herein, it is tried to model the influence of the orientation of graphene sheets dispersed in organic coatings on the diffusivity and flux of corrosive substances besides the corrosion initiation time of the protected substrates. To discover the relationship between the graphene orientation and corrosion-related phenomena, this study introduces a novel model consisting of a trigonometric factor named unprotected projected surface area proportion, which calculates corrosion-related parameters based on the principal Fick’s laws. The model reveals that the decrease in the angle between graphene sheets and the substrate is highly beneficial for postponing the corrosion onset. It is accordingly estimated that a mismatch angle of 10° can slow down the diffusion process significantly and delay the corrosion initiation by around 65 times in a 100 μm thick epoxy/graphene composite coating in comparison to the counterpart with the perpendicular alignment. The predicted corrosion parameters were in a good agreement with the experimental data, indicating the merit of the proposed model. Thus, this model can be further employed as the fundamental of future research on the optimum graphene orientation in anticorrosion composite coatings.

Reinforced Concrete Structure Performance in Marine Structures: Analyzing Durability Indexes to Obtain More Accurate Corrosion Initiation Time Predictions.

This paper presents a comparison of six index properties collected during durability inspections of five Mexican seaports. Typical durability indicators such as compressive strength, saturated electrical resistivity, ultrasonic pulse velocity, percent total void content, capillary porosity, and chloride concentration profiles were analyzed to obtain empirical correlations with the non-steady-state chloride diffusion coefficient. These indices were compared to determine correlation coefficients that are the most important for obtaining better corrosion initiation forecasting. Two models of corrosion initiation time (ti) were used: Fick’s second law of diffusion and the reported UNE-83994-2 (Spanish Association for Standardization, UNE) in which electrical resistivity was used to calculate concrete service life. The data from both models were cleaned using correlated variables, and the initial variables were compared with ti. The main result achieved was the verification of the feasibility of using correlations of variables to clean unnecessary data in order to calculate ti. Additionally, electrical resistivity was identified as one of the main durability indexes for in-service concrete structures exposed to marine environments. This is important because electrical resistivity is a non-destructive and reliable test that can be measured both in the laboratory and in the field very easily.

Durability assessment of a tunnel structure with two‐sided chloride ingress—A case study located in a tropical environment

AbstractReinforced concrete structures are the backbone of the transportation infrastructure. Their structural safety and functional performance are critical to sustaining a globalized economy. Corrosion of steel reinforcement is typically triggered by chloride contamination and carbonation, becoming a primary factor in reinforced concrete deterioration. This paper presents a durability assessment of a tunnel structure located in a tropical marine environment. The condition assessment included visual examination, crack survey, cover depth measurements, half‐cell potential mapping, and concrete coring. The chloride profiles showed that the tunnel walls are subjected to chloride attack from both surfaces, an unusual finding in the literature. A stochastic approach is implemented to estimate the probability of corrosion initiation for chlorides and carbonation, including an innovative model for two‐sided chloride diffusion. The results indicate that two‐sided chloride exposure significantly reduces the corrosion initiation time.

Probabilistic Seismic Demand Models and Life-Cycle Fragility Estimates for High-Rise Buildings

This paper presents a probabilistic framework for estimating the time-variant seismic fragility of high-rise buildings under carbonation-induced corrosion with a multiple damage model. A 42-story steel frame RC core tube (SFRCT) building was selected as a representative high-rise building to illustrate the proposed method. The main novelties of this study are that (1) a Bayesian updating method is used to determine the posterior probability distributions of the unknown parameters in the time-varying demand models of the maximum interstory drift and the residual drift at the top floor, (2) an analytical derivation method is used to compute the probability distribution of the corrosion initiation time in reinforcements, (3) the uncertainties associated with the corrosion initiation time and unknown parameters in demand models are incorporated into fragility estimates based on total probability theory, and (4) the elliptical copula and Archimedean copula are used to develop bivariate fragility estimates that consider the correlations among the limit states associated with maximum drifts and residual drifts, respectively. The results indicate that the seismic demand and fragility estimates of this high-rise building increase as the corrosion initiation time, which highlights the necessity of accounting for the uncertainty in the corrosion initiation time. In addition, the Gaussian copula and the Clayton copula (special cases of the elliptical copula and the Archimedean copula, respectively) produce similar joint probability distributions for the two-dimensional limit states; however, the Clayton copula can be used in a more general condition. The proposed methodology is applicable for evaluating the seismic life-cycle fragility of both existing and new high-rise buildings under multicriteria performance indicators.

Carbonation model for concretes with fly ash, slag, and limestone calcined clay - using accelerated and five - year natural exposure data

Supplementary cementitious materials (SCMs) can be used in concrete to enhance sustainability and reduce the concrete industry's carbon footprint. However, some negative perceptions about their long-term carbonation resistance are obstacles for large-scale implementation of such concretes. This study evaluated the carbonation resistance of 34 concretes (with Ordinary Portland Cement, fly ash, blast furnace slag, and limestone calcined clay) in natural tropical exposure conditions (Open and Sheltered) for 5 years and in accelerated exposure conditions (1 and 3% CO2) for 112 days. Using these data and the square root of time function, the carbonation coefficients (KCO2, natl and KCO2, accl) of these concretes were estimated and a good correlation between them could not be observed. Hence, a more generic model (named as “A-to-N model”) to estimate the KCO2, natl using the KCO2, accl, CO2 concentration, and mixture proportion of concrete was developed, for which the mean absolute percent error is about 12% (reasonable accuracy). Using the A-to-N model, the carbonation depth at 50 years was estimated for various concretes. SCM concretes with low water-binder ratio and optimal binder content showed high resistance against carbonation at later ages; such information along with the target cover depth must be used while selecting materials for concrete design. Based on the model developed, a relatively simple ‘service life design chart’ was developed. This chart can be used by engineers to set the target KCO2, natl or KCO2, accl, and select the cover depth and binder type to provide the target service life (i.e., corrosion initiation time). This paper clearly shows that SCMs can be used to design concretes with comparable long-term carbonation depth as OPC concretes.

Numerical Simulation of Non-Uniformly Distributed Corrosion in Reinforced Concrete Cross-Section.

Reinforced concrete structures can be strongly damaged by chloride corrosion of reinforcement. Rust accumulated around rebars involves a volumetric expansion, causing cracking of the surrounding concrete. To simulate the corrosion progress, the initiation phase of the corrosion process is first examined, taking into account the phenomena of oxygen and chloride transport as well as the corrosion current flow. This makes it possible to estimate the mass of produced rust, whereby a corrosion level is defined. A combination of three numerical methods is used to solve the coupled problem. The example object of the research is a beam cross-section with four reinforcement bars. The proposed methodology allows one to predict evolving chloride concentration and time to reinforcement depassivation, depending on the reinforcement position and on the location of a point on the bar surface. Moreover, the dependence of the corrosion initiation time on the chloride diffusion coefficient, chloride threshold, and reinforcement cover thickness is examined.