Probability Of Corrosion Initiation Research Articles

Probabilistic analysis of chloride penetration in reinforced concrete subjected to pre-exposure static and fatigue loading and wetting-drying cycles

Abstract Reinforced concrete (RC) structures are subjected to environmental actions and loading that could significantly affect their serviceability and safety. Among these actions these paper focuses on the interaction between concrete cracking produced by static and fatigue loading and chloride ingress. Given the complexity of the problem and its related uncertainties, we carried out an experimental study that provided information for the probabilistic characterization of chloride ingress model parameters by accounting for static and fatigue loading effects. In the experimental part of the study RC specimens (beams) were subjected to pre-exposure loading and wetting-drying chloride exposure. At the end of the simulated chloride environmental attack, ϕ 100 × 120-mm cylinders were drilled out from the bottom side of the central zone of the beams and used to measure chloride profiles within the concrete cover. The probabilistic analysis of test results showed that static and fatigue loading increases both the mean and standard deviation of chloride content for concrete depths larger than 15 mm. In order to evaluate the effect of loading on modeling chloride ingress processes, experimental data was used to fit the surface chloride concentration and the chloride diffusion coefficient for an analytical chloride ingress model as random variables. The identified random variables are then used to determine the distribution of the time to corrosion initiation for the present experimental configuration and to evaluate the long-term probability of corrosion initiation for other environmental exposures and cover configurations. The overall results confirm that considering pre-exposure loading conditions has an important effect in lifetime assessment. This effect depends on the aggressiveness of the surrounding environment.

Effect of Climate Change on Service Life of High Volume Fly Ash Concrete Subjected to Carbonation—A Korean Case Study

The increase in CO2 concentrations and global warming will increase the carbonation depth of concrete. Furthermore, temperature rise will increase the rate of corrosion of steel rebar after carbonation. On the other hand, compared with normal concrete, high volume fly ash (HVFA) concrete is more vulnerable to carbonation-induced corrosion. Carbonation durability design with climate change is crucial to the rational use of HVFA concrete. This study presents a probabilistic approach that predicts the service life of HVFA concrete structures subjected to carbonation-induced corrosion resulting from increasing CO2 concentrations and temperatures. First, in the corrosion initiation stage, a hydration-carbonation integration model is used to evaluate the contents of the carbonatable material, porosity, and carbonation depth of HVFA concrete. The Monte Carlo method is adopted to determine the probability of corrosion initiation. Second, in the corrosion propagation stage, an updated model is proposed to evaluate the rate of corrosion, degree of corrosion for cover cracking of concrete, and probability of corrosion cracking. Third, the whole service life is determined considering both corrosion initiation stage and corrosion propagation stage. The analysis results show that climate change creates a significant impact on the service life of durable concrete.

Reliability‐based and life‐cycle cost‐oriented design recommendations for prestressed concrete bridge girders

AbstractThere are several methods available to decide appropriate design recommendations to prevent corrosion of reinforcing steel in prestressed concrete bridge girders. With respect to chloride‐induced corrosion, in the present study two methods are considered. The first one is based on the target probability of corrosion initiation and the initial cost. The other method is based on the life‐cycle cost that includes the initial cost, maintenance cost, and expected failure cost. This paper deals with the development of recommendations for durability design of structures in marine environments from the reliability point of view, taking into consideration the life‐cycle cost of a structure. In order to address the problem, the chloride diffusion coefficient of a cracked area under service load is obtained considering opening and closing motion of cracks. Utilizing the diffusion coefficient of a cracked area, the development over time of the chloride concentration at the surface of reinforcement can be predicted. This information is used to quantify the probability of initiation of corrosion of prestressing steel as well as the distribution of life‐cycle cost. Based on the findings, recommendations for durability design in various exposure environments are developed.

Improved Bayesian network configurations for random variable identification of concrete chlorination models

Relevant material and environmental parameters are required in modelling chloride ingress into concrete. They could be determined from experimental data (concrete cores taken during inspection) but in practice data availability is limited by time-consuming and expensive tests. Consequently, the main objective of this paper is to develop an approach based on Bayesian networks (BN) to improve the parameter identification when inspection data is limited. We aim at proposing appropriate inspection configurations that reduce inspection costs and identification errors for different exposure conditions and materials. It was found that it is possible to define an optimal number of inspection points in depth for allowed identification errors defined by decision makers. The optimal number of inspection points depends on both exposure and material properties. The random variables identified with the improved BN configurations are used to assess the probability of corrosion initiation. The results indicate that the improved BN configurations are useful to identify model parameters even from scarce inspection data.

Improved Bayesian network configurations for probabilistic identification of degradation mechanisms: application to chloride ingress

Probabilistic modelling of deterioration processes is an important task to plan and quantify maintenance operations of structures. Relevant material and environmental model parameters could be determined from inspection data; but in practice, the number of measures required for uncertainty quantification is conditioned by time-consuming and expensive tests. The main objective of this study was to propose a method based on Bayesian networks for improving the identification of uncertainties related to material and environmental parameters of deterioration models when there is limited available information. The outputs of the study are inspection configurations (in space and time) that could provide an optimal balance between accuracy and cost. The proposed methodology was applied to the identification of random variables for a chloride ingress model. It was found that there is an optimal discretisation for identifying each model parameter and that the combination of these configurations minimises identification errors. An illustration to the assessment of the probability of corrosion initiation showed that the approach is useful even if inspection data are limited.

Time-dependent probability assessment for chloride induced corrosion of RC structures using the third-moment method

This paper presents the time-dependent probability of chloride-induced corrosion of reinforced concrete (RC) structures in marine environments. By using the third-moment (TM) method with improved analytical solutions, the stochastic models of corrosion initiation of reinforcing steel, along with the consequent surface cracking of concrete cover are proposed. The different effects of various influencing factors (including early-age micro crack or initial defect of concrete, etc.) on the time-dependent probability of corrosion initiation and surface cracking are also discussed. It is shown that the TM method developed in the paper is simpler and more efficient than traditional approaches such as Monte Carlo (MC) in analyzing the corrosion-induced probability. It is also shown that the distribution of influencing factors has little or almost no effect on the failure probability, whereas the mean and the coefficient of variation of basic variables affect it to various extents. Based on the detailed analysis, some conclusions with implications for engineering practice are drawn.

Probabilistic Model of Corrosion in Reinforced Concrete Structures Considering Coupling Effects of Influence Factors

A probabilistic model of the chloride-induced corrosion process is provided in this paper. Based on the Third-moment method, the uncertainty of various influence factors and the coupling effects of them are concerned. Considering the corrosion process as a statistic process, the probability of corrosion initiation at certain time can be obtained. Moreover, the effect of micro-crack in chloride ingress is taken into account, too. Due to the results of stochastic analysis, the surface chloride concentration is the most important factor that affects the corrosion probability, while the thickness of concrete cover, chloride diffusion coefficient, environmental relative humidity, critical threshold chloride concentration, micro-crack rate, water-to-cement ratio and temperature are also important factors. And the Third-moment method is proved to be reasonable in the durability assessment of corrosion-induced concrete structure. The results in this paper can be used to predict the rest life of corrosion-induced concrete structures.

Reliability-Based Assessment of the Effect of Climatic Conditions and CO<sub>2</sub> Emissions on the Corrosion of RC Structures Subjected to Carbonation

carbonation rate of concrete structures are influenced by CO2 emissions and climate conditions. Carbonation depth prediction model was proposed and CO2 emission scenarios influence on concrete structures' carbonation damage was studied. As there are significant uncertainty and variability of CO2 emissions, deterioration mechanisms, material properties, dimensions and environments, the time-dependent structural reliability analysis was employed to predict the probability of corrosion initiation from 2000 to 2100, considering several IPCC future atmospheric CO2 emission scenarios. Results show:(1)carbonation depth in A1F1 and A1B scenarios is 36% higher than that invariant CO2 concentration, and A1B scenarios is 21%; (2)The corrosion initiation probability of RC structures in A1F1 and A1B scenarios are 84% and 67% higher than that invariant CO2 concentration , respectively.

A fuzzy-probabilistic durability concept for strain-hardening cement-based composites (SHCC) exposed to chlorides: Part 2 – Application example

In Part 1 of this treatise, a fuzzy-probabilistic approach for assessing the durability of SHCC exposed to chlorides is introduced. This approach may be considered as a framework for durability concepts for novel types of cementitious materials and different forms of environmental action. In this second part an application of this concept to crack-free SHCC exposed to a North Sea marine environment is presented. Special emphasis has been given to the transparent and reproducible quantification of input variables based on limited experimental investigations, literature review, and expert assessment. Based on these input variables, the buildup of chlorides at the depth of the steel bar reinforcement and development of the probability of corrosion initiation of the steel reinforcement over time were computed. It was found that the non-stochastic uncertainty due to information deficit is still significant. This currently precludes the concept from being used as a practical design tool. However, with the help of sensitivity analyses it was possible to identify the most influential input variables. It could be shown that with a reduction of this uncertainty, long service lives for SHCC members may be correctly demonstrated. This identification furthermore allows a targeting of future research efforts to reduce uncertainty in the most economical way.

해저 콘크리트 구조물의 신뢰성 이론에 의한 시간 의존적 내구수명 평가

This study predicted the probability of corrosion initiation of reinforced concrete tunnel boxes structures using the Monte Carlo Simulation. For the inner wall and outer wall in the tunnel boxes, exposed to airborne chloride ion and seawater directly respectively, statistical values of parameters like diffusion coefficient D, surface chloride content , cover depth c, and the chloride threshold level were examined from experiment or literature review. Their average values accounted for , 3.0% by weight of cement, 94.7mm and 45.5mm for outer wall and inner wall, respectively, and 0.69% by weight of cement for D, , c, and , respectively. With these parametric values, the distribution of chloride contents at rebar with time and the probability of corrosion initiation of the tunnel boxes, inner wall and outer wall, was examined by considering time dependency of chloride transport. From the examination, the histogram of chloride contents at rebar is closer to a gamma distribution, and the mean value increases with time, while the coefficient of variance decreases with time. It was found that the probability of corrosion initiation and the time to corrosion were dependent on the time dependency of chloride transport. Time independent model predicted time to corrosion initiation of inner wall and outer wall as 8 and 12 years, respectively, while 178 and 283 years of time to corrosion was calculated by time dependent model for inner wall and outer wall, respectively. For time independent model, the probability of corrosion at 100 years of exposure for inner wall and outer wall was ranged 59.5 and 95.5%, respectively, while time dependent model indicated 2.9 and 0.2% of the probability corrosion, respectively. Finally, impact of , including values specified in current codes, on the probability of corrosion initiation and corrosion free life is discussed.

Climate change impact and risks of concrete infrastructure deterioration

Atmospheric CO2 is a major cause of reinforcement corrosion in bridges, buildings, wharves, and other concrete infrastructure in Australia, United States, United Kingdom and most other countries. The increase in CO2 levels associated with global warming will increase the likelihood of carbonation-induced corrosion. Moreover, temperature rises will increase corrosion rates. Clearly, the impact of climate change on existing and new infrastructure is considerable, as corrosion damage is disruptive to society and costly to repair. The paper describes a probabilistic and reliability-based approach that predicts the probability of corrosion initiation and damage (severe cracking) for concrete infrastructure subjected to carbonation and chloride-induced corrosion resulting from elevated CO2 levels and temperatures. The atmospheric CO2 concentration and local temperature and relative humidity changes with time over the next 100 years in the Australian cities of Sydney and Darwin are projected based on nine General Circulation Models (GCMs) under (i) high CO2 emission scenario, (ii) medium CO2 emission scenario, and (iii) CO2 emission reduction scenario based on policy intervention. The probabilistic analysis included the uncertainty of CO2 concentration, deterioration processes, material properties, dimensions, and predictive models. It was found that carbonation-induced damage risks can increase by over 400% over a time period to 2100 for some regions in Australia. Damage risks for chloride-induced corrosion increase by no more than 15% over the same time period due to temperature increase, but without consideration of ocean acidity change in marine exposure. Corrosion loss of reinforcement is not significant. The results were most sensitive to increases in atmospheric CO2.

Coupling effects of influence factors on probability of corrosion initiation time of reinforced concrete

The coupling model of major influence factors such as environmental relative humidity, load-induced crack and stress state affecting the chloride diffusion process in concrete is discussed. The probability distributions of the critical chloride concentration CC, the chloride diffusion coefficient D, and the surface chloride concentration Cs were determined based on the collected natural exposure data. And the estimation of probability of corrosion initiation considering the coupling effects of influence factors is presented. It is found that the relative humidity and curing time are the most effective factors affecting the probability of corrosion initiation before and after 10 years of exposure time. At the same exposure time, the influence of load-induced crack and stress state on the probability of corrosion initiation is obvious, in which the effect of crack is the most one.

Optimum preventative maintenance strategies using genetic algorithms and Bayesian updating

Preventative maintenance (PM) includes proactive maintenance actions that aim to prevent or delay a deterioration process that may lead to failure. This type of maintenance can be justified on economic grounds because it can extend the life of bridges and avoid the need for unplanned essential maintenance. Due to the high importance of the effective integration of PM measures in the maintenance strategies of bridges, the authors have developed an optimisation methodology based on genetic algorithm (GA) principles, which links the probabilistic effectiveness of various PM measures with their costs in order to develop optimum PM strategies. To further improve the reliability of estimating the degree of deterioration of an element, which is a key element in predicting optimum PM strategies using the GA methodology, Bayesian updating is utilised. The use of Bayesian updating enables the updating of the probability of failure based on data from site inspection or laboratory experiments and the adjustment, if necessary, of the timing of subsequent PM interventions. For the case study presented in this paper, the probability of failure is expressed as the probability of corrosion initiation of a reinforced concrete element due to de-icing salt.

Effect of Reinforcement Geometry on the Probability of Corrosion Initiation in Reinforced Concrete Structures

During the last decade, major developments have been made to include durability of reinforced concrete structures into the design process. As corrosion of reinforcement steel is considered the major threat, special attention has been given to models for chloride ingress into concrete. However, mostly analytical expressions based on Fick's second law of diffusion are used and consequently this introduces major limitations. In this paper the genometrical constraints imposed by embedded reinforcing bars is addressed. To this end, numerical calculations have been performed to quantify the effect of physical hindrance of chloride ingress on the corrosion initiation time. Based on the findings, it is concluded that the common approach assuming a unilaterial undisturbed ingress presents too optimistic results. Consequently, it is advocated to include the reinforcement geometry into service life calculations so as to achieve a more realistic assessment of the performance of reinforced concrete structures over time.

CORROSION INITIATION TIME FOR REINFORCED CONCRETE MEMBERS ALONG INDIAN COASTS: EFFECTS OF TEMPERATURE AND RELATIVE HUMIDITY — A PROBABILISTIC APPROACH

Corrosion initiation time of steel reinforcement for partially saturated concrete members subjected to chloride ingress is investigated at five places along Indian coasts using simplified probabilistic analysis and sensitivity of the parameters to reinforcement corrosion is studied. Previously proposed diffusion based chloride ingress model for constant surface chloride concentration and variable diffusion coefficient is used. Corrosion is initiated when the chloride concentration on steel reinforcement exceeds a threshold value. The various input parameters considered in the model are surface chloride concentration (Cs), chloride threshold value (Cth), Concrete cover (X), reference diffusion coefficient (Dref), age (t), reference age (tref), diffusion decay index (m) and monthly temperature and relative humidity correction factors f(T) and f(h) respectively; to reference diffusion coefficient. For prediction of corrosion initiation time temperature and relative humidity data collected by India metrological Department is used and all other parameters are assumed same. A large variation in corrosion initiation time is found and therefore it becomes necessary to consider the temperature and relative humidity data in a region. Life-365 considers fully saturated condition of concrete and thus underestimates the corrosion initiation time of a reinforced concrete member. The deterministic approach uses mean values of the parameters and provides a 50% probability of corrosion initiation but the probabilistic approach provides expected time of first corrosion for chosen risk of corrosion and also gives sensitivity of parameters to probability of corrosion. Corrosion initiation time in ascending order is found at Colaba, Kanyakumari, Santacruz, Chennai and Vishakhapatnam. Corrosion initiation time is useful for owner, designer, or to an organization to take decision in time of priority of repairs, repair strategy, corrosion protection in order to optimize maintenance planning and budgeting. Planned maintenance at the optimum time is the safest and most cost effective approach.

Reliability Assessment of Corrosion Initiation of Harbor Concrete Structure Using FOSM

Due to the uncertainty of variables in durability model, the probabilistic approach is increasing. Monte Carlo Simulation (MCS) is an easily accessible method, but requires a lot of repeated operations. This paper evaluated the effectiveness of First Order Second Moment method (FOSM), which is more convenient and time saving method than MCS, to predict the corrosion initiation in harbor concrete structure. Mean Value First Order Second Moment method (MV FOSM) and Advanced First Order Second Moment method (AFOSM) are applied to the error function solution of Fick's second law modeling chloride diffusion. Reliability index and failure probability based on MV FOSM and AFOSM are compared with the results by MCS. The comparison showed that AFOSM and MCS predict similar reliability indexes and MV FOSM underestimates the probability of corrosion initiation by chloride attack. Also, the sensitivity of variables in durability model to failure probability was evaluated on the basis of AFOSM. The results showed that AFOSM is a simple and efficient method to estimate the possibility of corrosion initiation in harbor concrete structures.

A probabilistic model for corrosion prediction of steel reinforcement

A path probability model (PPM) for predicting the probability distribution of steel reinforcement subject to chloride ingress is presented in this paper to evaluate the corrosion level in a probability way. The whole corrosion history of given service period is divided into a series of paths formed by initiation phase and propagation phrase, which are respectively associated to the probability of corrosion initiation and the conditional probability of steel corrosion ratio when the corrosion has initiated. Based on PPM, a dynamic simulation has been performed to predict the time-dependent probability density function of corrosion ratio using Monte Carlo simulation technique. The efficiency of PPM is shown in some practical engineering cases. Sensitivity analysis of input parameters was also performed. The simulation results show that reinforcement corrosion ratio is related to the level of corrosion development and the quality of simulation results depends on the accuracy of statistical parameters from onsite experiments. PPM offers a new way to exhibit the evolution of reinforcement corrosion ratio during its service time.

Pore Corrosion Model for Gold-Plated Copper Contacts

The goal of this study is to model the electrical response of gold plated copper electrical contacts exposed to a mixed flowing gas stream consisting of air containing 10ppb H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S at 30degC and a relative humidity of 70%. This environment accelerates the attack normally observed in a light industrial environment (essentially a simplified version of the Battelle class 2 environment). Corrosion rates were quantified by measuring the corrosion site density, size distribution, and the macroscopic electrical resistance of the aged surface as a function of exposure time. A pore corrosion numerical model was used to predict both the growth of copper sulfide corrosion product which blooms through defects in the gold layer and the resulting electrical contact resistance of the aged surface. Assumptions about the distribution of defects in the noble metal plating and the mechanism for how corrosion blooms affect electrical contact resistance were needed to close the numerical model. Comparisons are made to the experimentally observed number density of corrosion sites, the size distribution of corrosion product blooms, and the cumulative probability distribution of the electrical contact resistance. Experimentally, the bloom site density increases as a function of time, whereas the bloom size distribution remains relatively independent of time. These two effects are included in the numerical model by adding a corrosion initiation probability proportional to the surface area along with a probability for bloom-growth extinction proportional to the corrosion product bloom volume. The cumulative probability distribution of electrical resistance becomes skewed as exposure time increases. While the electrical contact resistance increases as a function of time for a fraction of the bloom population, the median value remains relatively unchanged. In order to model this behavior, the resistance calculated for large blooms has been weighted more heavily.

Probabilistic evaluation of initiation time of chloride-induced corrosion

The paper presents a model for chloride ingress into concrete. The model accounts for two mechanisms which control the chloride ingress—diffusion and convection. Using one-dimensional (1-D) formulation of the model, the influence of chloride binding and ambient humidity on chloride ingress into concrete has been investigated. Based on results of this investigation parameters for probabilistic analysis have been selected. Probabilistic evaluation of the time to corrosion initiation has then been carried out for a reinforced concrete (RC) wall (1-D problem) and a RC column (2-D problem) in a marine environment. Results of the analysis show that for the same thickness of the concrete cover the probability of corrosion initiation in the corner reinforcing bars of the RC column is much higher than in reinforcing bars in the middle part of the RC wall. The results demonstrate the importance of 2-D modelling for correct prediction of corrosion initiation in such RC elements as columns and beams.

Corner effect on chloride ion diffusion in rectangular concrete media

Chloride ion diffusion at the corner of rectangular concrete structures is presented. At the corner of a rectangular concrete, chloride ion diffusion occurs in a two-dimensional process. Chloride ions accumulate from two orthogonal directions, so that the corrosion-free life of concrete structures is significantly reduced. A numerical procedure based on the finite element method is used to solve the two-dimensional diffusion process. The orthotropic property of the diffusion coefficient of concrete is considered, and the chloride ion profile obtained from numerical analysis is used to produce the transformed diffusion coefficient. Comparisons of experimental data are also carried out to show the reliability of the proposed numerical analysis. From two-dimensional chloride diffusion, the corrosion-free life of concrete structures is estimated using the probability of corrosion initiation. In addition, monographs that produce the transformed diffusion coefficient and the corrosion-free life of concrete structures are made for maintenance purposes.