Depassivation Of Reinforcement Research Articles

Electro-chemo-physical analysis for long-term reinforcement corrosion within the reactive system of concrete

This paper presents an electro-chemo-physical model for analyzing long-term chloride-induced reinforcement corrosion in concrete structures. The integration of electrochemical and thermodynamic analyses enables the proposed model to capture the influence of simultaneous reactions within concrete on the corrosion process. The model is validated against experiments, where the necessity of considering the complicated reactions within concrete in long-term corrosion modeling is underscored. Building upon experimental observations and numerical explorations, a potential corrosion acceleration effect resulting from Friedel's salt dissolution in a longer term of corrosion propagation is discovered. Thereafter, a new qualitative model for describing the reinforcement depassivation process in concrete is proposed, along with discussions on governing mechanisms. From a computational perspective, the study also identifies hematite and magnetite as thermodynamically stable rusts under different concentrations of Fe2+ and O2. The proposed model and discoveries are poised to contribute significantly to scientifically robust predictions of deterioration and remaining service life for aging reinforced concrete structures.

Electrochemical realkalisation of carbonated cementitious matrix: characterization research to influence of time and current density

The depassivation of reinforcement caused by the reduction of concrete alkalinity due to the concrete carbonation process can induce the appearance of steel corrosion. The restoration of alkalinity can be done by chemical realkalinization (CRA) or electrochemical realkalinization (ERA) methods. In this context, the present work aims to evaluate the influence of the application time and the current density used in the electrochemical realkalinization process. For the development of the research, mortar samples were molded with a reinforced bar for electrical connection and remained for 24 months in a carbonation chamber. After this period, the carbonation depth that occurred was verified and then the specimens were submitted to the electrochemical realkalinization process using 3 different current values, 0.5, 1.0 and 1.5A/m2 and remained at different periods (7 , 14 and 21 days) in the recovery process. Additional tests of absorption, compressive strength, carbonation depth measurements, mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TGA) were also carried out on reference, carbonated and realkalinized specimens. Based on the results of the tests, it was observed that the recovery process starts after 7 days with the lowest current density used. A better current density x application time ratio was also observed considering the results of the mercury intrusion porosimetry and thermogravimetric analysis tests in conjunction with the realkalinization process.

Service Life Design of Concrete Structures Made of High-Volume Limestone Powder Concrete—Case of the Carbonation-Induced Corrosion

One of the paths to CO2 emissions reduction in the concrete industry is to use low-clinker cements, providing at the same time the performance of concrete that is adequate for application in concrete structures. This paper explores the impact of the clinker replacement with high amounts of limestone powder (21–70% in the powder phase) on concrete carbonation resistance. To quantify this impact, the empirical relationship between the carbonation resistance and the compressive strength of the high-volume limestone powder concrete (HVLPC) was established. For that purpose, the regression analysis was applied on the experimental results collected from the published research. The service life analysis based on the full probabilistic approach was performed using the fib Model Code 2010 prediction model and proposed empirical relationship. The first-order reliability method (FORM) was applied to solve the limit state function of reinforcement depassivation with a reliability index equal to 1.3. The obtained minimum concrete cover depths were 40–110% higher compared to those prescribed in the current European standard EN 1992-1-1:2004 for indicative strength classes. Based on the full probabilistic analysis, recommended cover depths are given for all carbonation exposure classes, commonly applied concrete strength classes, and service lives of 50 and 100 years.

Comparative Analysis of Engineering Carbonation Model Extensions to Account for Pre-Existing Cracks.

Cracks in reinforced concrete structures can accelerate the local depassivation of reinforcement due to carbonation. Different approaches have been proposed to account for pre-existing cracks within engineering models to predict the carbonation depth. In this study, we provide a detailed comparative analysis of different extensions available for the fib carbonation model to account for cracks, viz., crack influence factor (CIF) approaches, a diffusion-based model and the crack depth adaption. The model extensions are first validated against a dataset of lab data collected from the literature and additional experiments performed as the part of this study. The CIF approaches achieved the highest accuracy for the carbonation depth prediction when compared against lab data. The diffusion-based model was inaccurate for low CO2 concentrations. The crack depth adaption provides overly conservative results. No model was found to be best performing, and large scatter was observed between predicted and experimental values. This emphasizes the need for more detailed multi-physics-based models to achieve accurate predictions. For further comparison, service life predictions were conducted for two structural scales, viz., the whole structure and the cracked area. It is concluded that the choice of model extension and the structural scale of analysis have a large influence on predicted probability of failure.

A Monte Carlo-Based Approach to Assess the Reinforcement Depassivation Probability of RC Structures: Simulation and Analysis

In this work, an approach is presented to assess the reinforcement depassivation probability of reinforced concrete structures under corrosion induced by carbonation or chloride diffusion. The model consists of coupling mathematical formulations of CO2 and Cl− diffusion with Monte Carlo simulation (MCS). Random events were generated using MCS to create several design life and environmental scenarios. A case study was performed by simulating five Brazilian environmental conditions and distinct mixes of concrete. The effect of input parameters on the reinforcement concrete depassivation probability was evaluated. The results point out that the depassivation probability due to carbonation is more significant in urban centers, and the compressive strength of concrete has the main influence on the depassivation probability. Results also showed that the depassivation probability due to chloride ingress is influenced by, in order of importance, the chloride content on the surface (61.4%), concrete cover (20.3%), compressive strength (7.1%), relative humidity (6.1%), and temperature (5.1%). In addition, an increase in the compressive strength of concrete, from 30 to 50 MPa, can reduce depassivation probability by up to 70%, resulting in a concrete structure that attends the durability limit state. Thus, by incorporating probabilistic approaches, this model can be a valuable tool in the civil construction industry for studying the improvement of durability, reliability, and safety of reinforced concrete structures.

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.

Assessment of the effect of changes in consolidation conditions in the advance of the carbonation front in cementitious matrix composites

ABSTRACT: Carbonation is one of the main deleterious effects of reinforced concrete structures, as it creates a favorable condition for the reinforcement depassivation and, thus, facilitates the onset of the corrosive process. The phenomenon is directly influenced by the material void’s structure, which is affected by the consolidation of the mass in the fresh state, subject evaluated in this study. For this purpose, samples were made using two water to cement ratios and defining two different consolidation methods. Compressive strength tests were carried out for the mechanical characterization of the specimens, in addition to accelerated carbonation tests, monitoring the progress of the carbonated thickness using the phenolphthalein colorimetric indicator, during 98 days. Microstructural differences were evaluated by scanning electron microscopy (SEM). The results indicate that the lower the workability of the mixture, the greater the impacts on the compressive strength of the material, resulting from failures in the consolidation stage. Nevertheless, another behavior is observed when evaluating this effect in the advancement of the carbonation front, indicating that the voids structure of the material should not be evaluated only according to its volume, but also in terms of the pattern of its distribution, its morphology and its connectivity.

Chloride Transport in Cracked Concrete Subjected to Wetting – Drying Cycles: Numerical Simulations and Measurements on Bridges Exposed to De-Icing Salts

Although many models for service life predictions have been developed, their application to existing bridges is still not at a satisfactory level. The here presented coupled 3D chemo-hygro-thermo mechanical (CHTM) model can realistically simulate both corrosion phases: initiation and propagation. The focus of this research is the transport processes in cracked and un-cracked concrete before reinforcement depassivation. Realistic environmental conditions with the surface water and chloride contents variable in time are simulated based on the meteorological data for a mountain region where case studies bridges are located. Application of the large quantities of de-icing salts in combination with the poorly designed and executed details resulted in a high chloride content in concrete of the superstructure of both bridges: at the reinforcement level chloride content in cracked concrete elements exceeds the threshold value up to 10 times. Numerical results match well with the chloride content measured on the bridges after 11 and 14 years of service. Accounting for the realistic environmental conditions (wetting-drying cycles, application of de-icing salts only in the winter season, etc.) in the numerical simulations results in the continuous transport processes in concrete and higher chloride content in deeper concrete layers as opposed to the finite element models with the constant boundary conditions.

Numerical and Experimental Analysis of Self‐Protection in Reinforced Concrete due to Application of Mg–Al–NO2Layered Double Hydroxides

Concrete possesses an intrinsic chloride binding capacity. Chloride ions from the environment bind with the hydrated cementitious phases in the form of bound chlorides. The contribution of chemically bound chlorides toward increasing the service life of concrete structures is vital as they help in slowing down the chloride diffusion in the concrete thereby delaying reinforcement depassivation. The authors attempt to increase the chloride binding capacity of concrete by adding a small amount of Mg–Al–NO2layered double hydroxides (LDHs) with the objective to delay reinforcement corrosion and by this to considerably extend the service life of concrete structures situated in harsh environments. This study presents numerical and experimental analysis of the action of LDH in concrete. Formation factor is used to determine the effective chloride diffusion coefficient. In addition, the chloride binding isotherms together with Poisson–Nernst–Planck equations are used to model the chloride ingress. A comparable chloride binding is observed for concrete with and without Mg–Al–NO2, depicting only a slight chloride uptake by Mg–Al–NO2. Further investigations are conducted to understand this behavior by studying the stability and chloride entrapping capacity Mg–Al–NO2in concrete.

Application of the 3D chemo-hygro-thermo mechanical model on existing bridges exposed to chlorides and mechanical damages

Bridge engineering world practice has showed that implicit method of service life prediction, relying on sufficient quality and depth of concrete cover, do not guarantee a 100- year structure lifetime without major, complex and expensive repair works. Bridges exposed to harsh combination of mechanical (static, dynamic, cyclic loading) and environmental (sea salts, de-icing agencies, freeze - thawing cycles, etc.) actions are particularly vulnerable. Two such case studies: Krk Bridge and Maslenica Bridge located in aggressive maritime environment will be analysed in the paper including in-service performance and comparison between measured values on bridges and numerical results obtained by two numerical models for service life prediction: the 3D chemo-hygro-thermo mechanical (3D CHTM) model implemented into the finite element code MASA and the Life-365 model. Both models are capable to realistically predict chloride content in concrete after long-term exposure to seawater. However, the 3D CHTM model, which considers cracks and damage in concrete, anticipates the beginning of steel reinforcement depassivation much more precisely than the other model which doesn’t take concrete damage and cracks into account.

Chloride ions transportation behavior and binding capacity of concrete exposed to different marine corrosion zones

Transport of chloride ion into concrete can induce depassivation of reinforcement, which seriously threatens the durability of concrete subjected to marine environment. In this paper, the chloride ion transport and binding capacity of different concrete samples located in marine atmosphere zone, splash zone, tidal zone and submerged zone for 9 and 13 months were tested. And the chloride ion profiles of one whole concrete sample exposed to all the corrosion zones for 13 months was also detected. The effect of fly ash and ground granulated blast furnace slag (GGBS) on the chloride ion transport and binding capacity of all the concrete samples were studied and the optimized replacement ratios of mineral admixtures in marine environment was proposed. The contents of Ca(OH)2 and Friedel’s salt in paste exposed to different corrosion zones were also tested by XRD and DSC-TG. Results showed chloride ion content in separate concrete samples exposed to splash zone and atmosphere zone were lower than that of the other zones, but the opposite results were observed for one whole concrete sample throughout all the corrosion zones. For separate samples, the chloride binding capacity of concrete in atmosphere zone was the lowest, and would decrease with corrosion time in marine environment. The washing effect by tidal action would lead to the loss of Ca(OH)2, abrasion of surface, and decrease of compressive strength of concrete.

Computational modeling for predicting corrosion initiation in reinforced concrete structures

Abstract This article presents a model for penetration of chloride by diffusion in reinforced concrete structures based on the solution of the Fick's 2nd Law, using the finite element method (FEM) in two-dimensional domain. This model predicts the time, in a given situation, so that a certain limit of chlorides for depassivation of reinforcement is reached, characterizing the end of service life. Several approaches for the chloride surface concentration and for the diffusion coefficient are used, parameter which must be corrected due to the effects of temperature, solar radiation, exposure time, and relative humidity. Moreover, a parametric analysis is carried out in order to study the factors involved and their impact on the ingress of chlorides by diffusion, contributing to a better understanding of the phenomenon. In addition, the developed model is applied to the cities of Vitória (ES) and Florianópolis (SC) to analyze the service life for different concrete covers, making a comparison with the Brazilian standard.

Passivity of embedded reinforcement in carbonated low-calcium fly ash-based geopolymer concrete

This paper investigates the carbonation of two low-calcium fly ash-based geopolymer concretes to assess the effect of alkali concentration in the activator, and the carbon dioxide concentration on the pH drop and passivity of the reinforcement. Chemical adsorption of carbon dioxide at different concentrations into an aqueous NaOH solution, as representative of the pore solution, is studied to predict the distribution of carbonate species and pH drop. pH profiles were obtained during the exposure period. X-ray diffraction (XRD) was conducted to identify the carbonate phases. Half-cell potential and polarization resistance of reinforced concrete samples were monitored to assess the passivity of embedded reinforcement. The carbonated binders remained rather highly alkaline during the accelerated carbonation test which was in agreement with the predicted values. No sign of depassivation of reinforcement was observed, even for the lower strength grade concrete, during the long exposure time of 500 days to 1% carbon dioxide.

ОСОБЕННОСТИ РАЗВИТИЯ ПИТТИНГОВОЙ КОРРОЗИИ СТАЛЬНОЙ АРМАТУРЫ ЖЕЛЕЗОБЕТОННЫХ ИЗГИБАЕМЫХ ЭЛЕМЕНТОВ

Two types of steel reinforcement depassivation process: carbonation of concrete and chloride penetration are considered in the article. The comparison between the corrosion due to carbonation of concrete and the chloride-induced corrosion was carried out. It was found out, that chlorides induced corrosion is potentially more dangerous than that resulting from carbonation. Method of durable tests of reinforced concrete structures under the action of the gravitational load and the corrosive chloride environment is described in the article. The results of experimental research on reinforced concrete structures with corrosive damages to steel reinforcement are given in the article. The properties of corrosion cracking in the case of the pitting corrosion were determined. The character of corrosive damage distribution along the reinforcement bars and its effect on the strength of reinforced concrete beams were determined.

Study of Fine-Grained Composites Exposed to Sulfuric Acid and Sodium Sulfate

The degradation of concrete due to ingress of sulfate ions from the environment plays an important role in the durability of concrete constructions, especially in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water and from biogenic activity of bacteria. During this process the pH of the surface of concrete sewer pipes is reduced and it may lead to the steel depassivation and results in the corrosion of steel reinforcement. Damage due to sulfate interaction can result in the cracking and softening, with loss of strength of concrete. This paper is focused on the sulfate attack on fine-grained concrete where the effect of one-year contact of 0.5% H2SO4, and 5% Na2SO4 on changes of pH and content of sulfates in 7 types of concrete has been analyzed. It was found that after one year of sulfate attack on concrete, significant growth of content of sulfates is observed in the lowermost layer of the samples. Samples treated by 5% Na2SO4 contain slightly more sulfates in the upper layers than samples treated by sulfuric acid. The reduction in pH of aqueous leaches occurred in all layers of the samples. However, even in the lower layers of the samples, the reduction of pH below 9.5 did not turn up (except for SRS sample), and thus the conditions for the depassivation of reinforcement were not met.

Sulfuric Acid Attack on Various Types of Fine Grained Concrete

Sulfate corrosion is one of the major threats for durability of concrete constructions and it becomes a major destructor in sewage collection systems where the concrete sewer pipes are exposed to sulfates from wastewater as well as from biogenic activity of bacteria. During this process the pH of the surface of concrete sewer pipes is reduced and it may lead to steel depassivation and results in the corrosion of this steel reinforcement. This paper is focused on the sulfate attack on fine grained concrete where the effect of 0.5% sulfuric acid, simulating biogenic sulfuric acid corrosion, on changes of pH and content of sulfates in various types of concrete has been investigated. After 3 and 6 months of the corrosive treatment, the content of sulfate ions and pH values in several layers of specimens were determined. It was found that the sulfate ions penetrate into concrete to the maximum depth of 20 mm and the pH of the aqueous leaches of particular layers of the samples was reduced to 11.4 at the most. Thus, the conditions for the depassivation of reinforcement were not met. The GL and GBFS concrete samples showed the least changes of their pH and therefore they had the best resistivity to the six months sulfate attack.

Acoustic emission monitoring of early corrosion in prestressed concrete piles

SUMMARY Prestressed concrete (PC) piles in marine environments are vulnerable to corrosion damage especially at their tidal zone because of the concurrent exposure of steel reinforcement to moisture, chlorides, and oxygen. Early detection of corrosion in prestressed strands is desirable to enable the effective planning and prioritizing of maintenance operations. This paper reports on experiments aimed at testing the hypothesis that acoustic emission (AE) monitoring is suitable to recognize and classify early corrosion damage in PC piles exposed to saltwater. In fact, AE is sensitive to the formation and growth of microcracks in both steel and concrete, which may develop upon depassivation of reinforcement and buildup of corrosion by-products. In addition, the influence of AE signals produced through flexural cracks in the concrete is of less concern for PC piles as such cracks are seldom produced under service loads. Five specimens representative of full-scale portions of PC piles were designed to accelerate corrosion and subjected for 1 year to wet/dry cycles in saltwater simulating tidal action. The specimens were monitored continuously with AE sensors. Benchmark electrochemical measurements were routinely performed to understand when depassivation of the steel strands occurred. Visual evidence of early corrosion was collected from strands removed from two decommissioned specimens. It is shown that AE intensity analysis is more effective than AE signal strength and cumulative signal strength analysis in recognizing corrosion damage. Intensity analysis-based criteria for the assessment of early corrosion damage are proposed, complementing previously developed criteria for more severe corrosion damage in steel strands. Copyright © 2014 John Wiley & Sons, Ltd. Received 22 May 2014; Revised 15 September 2014; Accepted 2 November 2014

THE EFFECT OF WATER/CEMENT RATIO ON THE SULFATE CORROSION OF FINE GRAINED CONCRETE

Sulfate corrosion is one of the major threats for durability of concrete constructions and it becomes a major destructor in sewage collection systems where concrete sewer pipes are exposed to sulfates from waste water as well as from biogenic activity of bacteria. The second type of corrosion is termed microbiologically induced concrete corrosion (MICC) and during this process the pH of the surface of concrete sewer pipes is reduced and it may lead to steel depassivation and results in the corrosion of this steel reinforcement. This paper is focused on the sulfate attack on fine grained concrete where the effect of 0.5% sulfuric acid emulating MICC and also effect of solution simulating sewage water on the concrete samples with three different water/cement ratios (w/c = 0.4, 0.45 and 0.5) have been investigated. After 1, 3 and 6 months of the corrosive treatment the content of sulfate ions and pH values in several layers of specimens were determined. It was found that the sulfate ions penetrate into concrete to maximum depth of 20 mm and the pH of the aqueous leaches of particular layers of the samples was reduced to 11.92 at the most. Thus, the conditions for the depassivation of reinforcement were not met.

Stochastic Assessment for Chloride Penetration in Reinforced Concrete Structures under Corrosive Environments

In the paper, the improved coupling convection and diffusion model of chloride ion penetration in reinforced concrete (RC) structures under corrosive environments is presented, in which many major influence factors such as environmental temperature and relative humidity, water ratio of concrete, and stress state etc are considered. Based on Fourth-Moment stochastic simulation theory, the estimation of the depassivation probability of reinforcement in corrosive RC is analyzed. And many important conclusions on depassivation of reinforcement is gained, which will be useful for repair, rehabilitation, and replacement of RC structures in corrosive environments.

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.