Corrosion-induced Cover Cracking Research Articles

Creep Effect on Time to Corrosion-Induced Cracking of Concrete Cover

This paper presents an innovative method to include creep deformations in the prediction of time to corrosion-induced cover cracking. Using experimental results, creep and cracking criteria used in this method are verified. It is argued in the paper that the cover cracking problem under corrosion is close to a relaxation problem and the conventional creep formulations based on the effective elastic modulus cannot be adopted. It is found in the paper that accurate consideration of creep deformation would lead to about 30–40% longer time to cover cracking when compared to no consideration of creep deformations whilst for the currently practiced methods, the time can be up to 200% longer, which is unconservative in predicting time to cover cracking. Results in this paper open the debate on modelling of creep in the analysis of corrosion-affected structures and serve as an important step towards the accurate prediction of corrosion-induced concrete cracking.

Phase-field method for modeling non-uniform corrosion-induced cracking in concrete

Non-uniform corrosion of rebar leads to the cracking of the concrete cover, which reduces the reliability of structures and increases maintenance costs. In this paper, we present a coupled phase-field model at the mesoscale to investigate the time-dependent process of non-uniform corrosion-induced cover cracking. This model couples chloride and oxygen diffusion, electrochemical reaction, and concrete cover cracking. A time-dependent non-uniform corrosion model is established based on chloride diffusion and electrochemical theory by considering the cracking effect. The cracking behavior of the concrete cover is described using a phase-field regularized cohesive zone model. The model was verified against several experiments available in the literature. Parametric studies were conducted to observe the effects of the crack and chloride diffusion coefficient, the interaction between the corrosion of multiple rebars, and the crack characteristics in three dimensions.

Safety Analysis of Rebar Corrosion Depth at the Moment of Corrosion-Induced Cover Cracking

Concrete cover cracking induced by reinforcement corrosion is an important indication of the durability limit state for reinforced concrete (RC) structures and can be used to determine the structural service life. The process of rebar corrosion from the beginning of rusting to the occurrence of cover cracking due to corrosion expansion can be divided into two phases: the phase of the free expansion of the corrosion product and the phase of cover cracking. Based on the assumption of the uniform corrosion of the reinforcement, one model for predicting the reinforcement corrosion depth from corrosion initiation to cover cracking was established according to the cylindrical cavity expansion theory. The main factors affecting the reinforcement corrosion depth were analyzed. The main factors affecting the corrosion depth of reinforcement were analyzed. The quantitative sensitivity analysis of the factors influencing the calculation formula shows that the depth of reinforcement corrosion and the thickness of the concrete protective layer are approximately linearly increasing, with a growth rate of 0.2366 μm/mm; the diameter of the reinforcement is approximately linearly decreasing, with a decrease rate of 0.2122 μm/mm; the volume expansion rate of rust is approximately power function decreasing; the overall influence range of the yield criterion selection parameter is 0.15 μm; for the concrete strength grade, the overall influence range is 0.1 μm. The coefficient of determination R2 is 0.87, and the overall accuracy of the calculated formula is high, which can be used to predict the service life of reinforced concrete structures and guide the durability design in combination with the research results on the corrosion rate of reinforcement under different environments.

Investigation on the prediction of reinforcement corrosion-induced cover time-vary cracking from multi-scale

Invasion or penetration of chloride ions in concrete will cause reinforcement corrosion, and the corrosion substances accumulated expansion will lead to the cracking of concrete cover, which will affect the durability and service life of reinforced concrete (RC) structures. Combined with the environmental characteristics, the prediction model of corrosion-induced cover time-vary cracking was established by considering the pore distribution characteristics of concrete. Subsequently, the cracking behavior of concrete under corrosion of cover and corner reinforcement was simulated, which the cracking mechanism was discussed. Simultaneously, the equivalent modeling was established for the time-vary evaluation on mechanical properties of RC structures. The calculation results can directly describe the corrosion process of reinforcement at different times, which the cracking behavior of concrete caused by reinforcement corrosion can be obtained. The heterogeneous characteristics of concrete determine the cracking initiation and development in concrete, which controlling and reducing initial damage of concrete is the key to reducing the corrosion-induced cover cracking of concrete. As the corrosion deepens, the corrosion products fill the interfacial transition zones and accumulate as the rust layer simultaneously. Then, as the corrosion deepens and the diffusion process of chloride ions, the corrosion substances accumulated each other to squeeze concrete for cracking.

Seismic assessment of corroded concrete bridges using incremental modal pushover analysis

An efficient yet accurate procedure was developed for the seismic assessment of reinforced concrete (RC) bridges subject to chloride-induced corrosion. The procedure involves using incremental modal pushover analysis to assess corroded bridges as an alternative and less computationally demanding approach to non-linear dynamic analysis. A multi-physics finite-element analysis is performed to evaluate the effects of chloride-induced corrosion on bridge columns. In doing so, chloride ingress in concrete is numerically simulated as a diffusion process by considering the effects of temperature, humidity, corrosion-induced cover cracking and concrete aging. The estimated chloride concentration is then employed to evaluate the corrosion current density, from which the effects of corrosion on reinforcement, cracked cover concrete, confinement and plastic hinge length can be determined for subsequent non-linear static analysis. A case study of a typical bridge structure is presented. The proposed procedure can be used to assess the seismic performance of irregular RC bridges exposed to severe corrosive environments.

A Durability Prediction Method for Historical Square Rebar Reinforced Concrete Buildings

Square rebars were developed and used for decades in the early development of reinforced concrete (RC) structures; however, the objectives of modern concrete structure durability analyses and standards are centered on round rebars in past decades, which are not suited for RC buildings utilizing square rebars. Considering the absence of proper evaluation techniques to evaluate the square rebar RC structures’ durability accurately, a novel durability prediction method has been proposed for this type of historical building. The method is based on major parts as in-situ investigation, finite element model simulation, component importance analysis, and structural durability prediction. The durability prediction calculation method was established on the experimental results of the realistic historical concrete tests and corrosion-induced cover cracking experiments for square rebar components. It was found that the carbonization-resistant ability of historical concretes was relatively weaker than that of current concretes and the calculation method for critical corrosion depth of square rebar was different from that of round rebar. Furthermore, two typical application cases are presented to introduce the procedure of the method in detail. Consequently, the research outcomes can be directly used on the durability prediction and protection works for historical RC buildings.

Square-rebar corrosion-induced cover cracking and its time prediction for historical reinforced concrete buildings in China

ABSTRACT Square-rebars have been used in many historical reinforced concrete buildings worldwide. The durability and structural behavior of such historical buildings should be evaluated regularly and accurately. The prediction of the corrosion-induced cracking time is a critical element for the durability evaluation work. This study demonstrates a mathematical model for the corrosion-induced cover cracking for square-rebars and its time prediction method. The research methodology includes theoretical derivation and experimental validation. First, a simplified model that describes the corrosion-induced cover cracking for square-rebars is proposed, and then, Faraday’s law is combined with the model to develop a time prediction model for corrosion-induced cover cracking. Finally, an accelerated corrosion experiment for square-rebars is performed to validate the applicability and accuracy of the prediction model.

Combined Effect of Stray Current and Sustained Compressive Loading on Chloride Transport in Concrete

As with the leakage of stray current in the surrounding medium, the chloride transport in concrete is influenced by the stray current and loading of the subway structure. This paper presents the results of the experimental study on the chloride transport properties of concrete under the combined action of stray current and sustained compressive loading. First, an experiment was setup to explore the chloride transport in the subway structure as the concrete specimen embedded with steel under test current and study the influence of the existence of steel on the chloride transport profiles in concrete under stray current. Then, to investigate the combined effect of stray current and loading on the chloride transport properties, an improved experiment was designed with stray current and sustained compressive loading. The chloride transport profiles were measured, respectively, subjected to different stray currents and compressive stress levels. The experimental results indicated that stray current and sustained compressive loading have a significant influence on the chloride transport properties of concrete, and the loading threshold existed as the turning point of the chloride transport rate. Based on the experimental data and migration theory, the prediction model of chloride transport in concrete under stray current and sustained compressive loading was established and verified by the experimental measurements, and the steel corrosion‐induced cover cracking was studied, and the comparison indicated that the numerical results were consistent with the experimental results.

Empirical models of corrosion rate prediction of steel in reinforced concrete structures

Corrosion rate is one of the most important input parameters in corrosion-induced damage prediction models as well as in calculation of service-life for reinforced concrete structures. In most cases, instantaneous measurements or constant corrosion rate values used in damage prediction models is irrelevant. The new factors appearing such as corrosion-induced cover cracking, concrete quality to change the corrosion rate should be taken into consideration. This study shows several empirical models to predict the corrosion rate and their limits of application. The predicted values of steel corrosion rate using four empirical models are compared with the measured values of a series of 55 experimental samples collected from the literature. The results show that the empirical models overestimated the experimental corrosion rate. Using model proposed by Liu and Weyers provided the best agreement with the experimental data.
 Keywords:
 corrosion rate; prediction model; reinforced concrete; chloride ions; reinforcement corrosion.

Corrosion-induced cracking fragility of RC bridge with improved concrete carbonation and steel reinforcement corrosion models

Corrosion-induced cracking is one important limit state in the durability performance analysis of the reinforcement concrete (RC) structures. A comprehensive probabilistic approach is established for the corrosion-induced cracking fragility analysis of the RC bridge in the urban atmospheric condition with improved concrete carbonation and steel reinforcement corrosion models. The improved deterioration models have a probabilistic formation by adding correction and error terms to the existing deterministic models. The deterministic parts are selected from reviews and discussions on existing models. The correction terms are sets of explanatory functions representing the influencing factors related to the potential bias in the deterministic models. The statistical distributions of unknown model parameters are calibrated and the optimum collections of the explanatory functions are selected through the Bayesian rule based on long-term data from onsite tests or natural exposure experiments. The probabilistic analysis approach for the corrosion-induced cracking fragility are generated based on the improved deterioration models. Fragility curves, parameter sensitivities and random variable importance are achieved for the example RC bridge. The results show that increases on the concrete strength, cover depth and steel bar diameter, or decrease on the CO2 density, are efficient countermeasures to improve the durability performance of the RC bridge against corrosion-induced cover cracking and the uncertainty of the problem mainly comes from the concrete carbonation model.

Calculation method for the service life of Chinese historical reinforced concrete buildings

Almost all of the existed studies on the corrosion of rebars were based on round-section rebars. However, the square-section steel rebars were widely used in China from 1912 to 1949, and there was no specific calculation model or durability assessment method for this type of historical buildings. In this study, based on the original configuration design of this kind of structures, the experiments of the corrosion-induced cover cracking of a certain number of reinforced concrete members with square-section rebars were carried out with the electrochemical acceleration method. The average rust depths of the square-section rebars at the critical corrosion-induced cover cracking moment were obtained. Then, the calculation method of critical rust depth of steel rebars at the concrete cover cracking moment was presented with data fitting method. Finally, combining with predication of carbonization life of concrete, a calculation method of the service life for Chinese historical RC buildings using square-section rebars was proposed. The research results can provide the basis for the durability assessment and conservation for Chinese historical RC buildings.

Validation of thick-walled cylinder analogy for modelling corrosion-induced concrete cover cracking

The main objective of this paper is to validate the use of the thick-walled cylinder (TWC) analogy to model corrosion-induced crack propagation in reinforced concrete (RC) structures. The TWC analogy neglects the effects of member geometry to create an idealized axisymmetric stress state. Although this simple approach has been used by many researchers, its suitability to various geometries and reinforcement configurations has not been comprehensively investigated previously. To achieve this goal, four different geometries are modeled using finite element analysis. The finite element models are two-dimensional, and they consist of plane membrane, quadrilateral elements under plane-stress conditions. Corrosion-induced expansion at the rebar/concrete interface is simulated using truss elements subjected to an equivalent thermal load. As a part of this validation, the effect of an adjacent corroding rebar and asymmetry of geometry were also investigated. The results are compared against the analytical solutions found using the TWC analogy. This study found that, in general, the use of the TWC analogy to model corrosion-induced cover cracking is appropriate; however, its limitations are also discussed.

Development of an Improved Crack Propagation Model for Corrosion-Induced Cover Cracking in RC Structures

During the last two decades, reinforced concrete (RC) has been extensively used in most of the world as one of the common construction material due to its advantages and durability. However, RC structures exposed to marine environments are subjected to chloride attack. Chlorides from seawater penetrate into RC structures are not only causing severe corrosion problems but also affect the durability and serviceability of such structures. This paper investigates the influence of transverse reinforcement and spacing of reinforcing bars on concrete cover cracking of two-way RC slab specimens using accelerated corrosion tests. The experimental program involved the testing of four RC slab specimens and was generally designed to observe the crack width and the time of crack to propagate. An improved model for predicting the timing of crack propagation based on the experimental data was then developed.

Influences of Repair Materials Properties on Reinforcement Corrosion-Induced Cover Cracking Time

Cover cracking from reinforcement corrosion is one of the major causes of deteriorations in reinforced concrete structure. If the cover cracking time can be predicted, it would be useful for maintenance planning and budget allocation. The objective of this paper was to find the influence of repair materials on concrete cover cracking time. In this study, the corrosion of concrete reinforcement was accelerated by electricity. Using three types of materials, it was found that the cover cracking time of repair mortar was the shortest followed by those of concrete and non-shrink cement grout respectively. In addition, specimens simulating repaired concrete were prepared. The cracking times of the repaired specimens were found to be about the same and were of the same order as those of repair materials only.

Experimental and numerical analysis of corrosion-induced cover cracking in reinforced concrete sample

Corrosion of embedded reinforcing bars is recognized as being the major cause of deterioration of reinforced concrete structures. With regard to maintenance strategies of concrete nuclear structures, the monitoring of cracking remains of primary importance. Recently, authors have developed a post-treatment technique to extract crack features from continuous computations. In this paper, such technique is applied to carry out a numerical analysis of an accelerated corrosion test. Obtained results allow highlighting specific propagation and failure mechanisms that characterize corrosion-induced cracking.

Structural capacity assessment of corroded RC bridge piers

A new numerical model is developed that enables simulation of the non-linear flexural response of reinforced concrete (RC) components and sections with corroded reinforcement. The numerical model employs a displacement-based beam–column element using the classical Hermitian shape function. Material non-linearity is accounted for by updating element stiffness matrices using the moment–curvature response of the element section considering uniform stiffness over the element. The cover concrete strength is adjusted to account for corrosion-induced cover cracking and the core confined concrete strength and ductility are adjusted to account for corrosion-induced damage to the transverse reinforcement. The numerical model is validated against a benchmark experiment on a corroded RC column subject to lateral cyclic loading. The verified model is then used to explore the impact of corrosion on the inelastic response and the residual capacity of corroded RC sections. The results show that considering the effect of corrosion damage on RC sections changes the failure mode of RC columns.

Corrosion induced cover cracking studied by X-ray computed tomography, nanoindentation, and energy dispersive X-ray spectrometry (EDS)

In this study, several experimental techniques are utilized to study different aspects of cracking of the protective cover due to reinforcing steel corrosion. Firstly, micro-computed X-ray tomography technique (CT-scanning) is used for monitoring rust formation during accelerated corrosion of reinforcement, and subsequent cover cracking. Secondly, the nanoindentation technique is employed to determine mechanical properties of the rust layer, which is an important input parameter for numerical models. Finally, energy dispersive X-ray spectrometry is used for elemental mapping around the steel–cement paste interface. Also, as a part of the study, the resistance of a strain hardening cementitious composite (SHCC) to corrosion induced cover cracking is examined. It was found that CT-scanning can be successfully utilized in non-destructive monitoring of the corrosion process in reinforced specimens. The nanoindentation study showed that the Young modulus of rust is highly dependent on the level of confinement provided to the rust layer by the surrounding cement paste. And, finally, SHCC proved to be an excellent alternative to brittle cementitious materials when corrosion induced cracking of the cover is a concern.

Numerical modeling of time to corrosion induced cover cracking in reinforced concrete using soft-computing based methods

Reinforced concrete (RC) is one of the most commonly used composite materials in construction industry. Corrosion of reinforcing steel embedded in concrete is a crucial issue leading deterioration of RC structure. In this study, mathematical formulations that predict the time from corrosion initiation to corrosion cracking in RC elements subjected to accelerated corrosion test are presented. For this, the time to corrosion cracking t cr in RC elements is evaluated and developed using soft-computing techniques, namely, genetic algorithms and artificial neural networks. In the models, nine critical estimation parameters were considered. The experimental inputs are mix design properties of the concretes, curing conditions, testing age, mechanical properties of concrete, and cover thickness of RC elements. The dataset was formed by collecting 126 experimental data samples reported in the technical literature. The dataset was randomly separated into three parts for training, testing, and validating the models. Through the numerical study, the influences of various experimental factors on the duration and extent of RC corrosion-induced cracking were shown. It was found that the soft-computing based models gave reasonable predictions of t cr in RC elements. However, the neural network model performed better and the highest correlation coefficient (R) between predicted and experimental t cr values was computed as 0.998.

Concrete cover cracking due to uniform reinforcement corrosion

Service life design (SLD) is an important tool for civil engineers to ensure that the structural integrity and functionality of the structure is not compromised within a given time frame, i.e. the service life. In SLD of reinforced concrete structures, reinforcement corrosion is of major concern and reinforcement de-passivation is a frequently used limit state. The present paper investigates an alternative limit state: corrosion-induced cover cracking. Results from numerical simulations of concrete cover cracking due to reinforcement corrosion are presented. The potential additional service life is calculated using literature data on corrosion rate and Faraday’s law. The parameters varied comprise reinforcement diameter, concrete cover thickness and concrete material properties, viz. concrete tensile strength and ductility (plain concrete and fibre reinforced concrete). Results obtained from the numerical simulations reveal that, depending on the serviceability limit state applied, the service life of a reinforced concrete structure can be increased significantly by allowing minor damage of the cover.

Analytical modeling for corrosion-induced cover cracking of corrosive reinforced concrete structures

An analytical model for predicting the corrosion-induced cracking of concrete cover of reinforced concrete (RC) structures was developed. The effects of influence factors such as practical initial defects, corrosion rate, strength and elastic modulus of concrete on the corrosion-induced cracking of concrete cover were investigated. It was found that the size of practical initial defects was the most effective factor. Therefore, improving the compactness of concrete is an effective way to improve the durability of RC structures. It was also demonstrated that the accelerated corrosion tests may be unfavorable in the study of the relationship between cracking time and crack width.