Full surface inspection methods regarding reinforcement corrosion of concrete structures

For reinforced concrete structures a localisation of all significant critical areas can only be done by a full surface inspection. The economic advantages are obvious: uncritical areas have not to be repaired expensively 1 . The first step of the assessment should always be a visual inspection 2 . The range of deterioration causes can be limited and the degree of deterioration may be estimated roughly. The inspection program can be adjusted to the requirements. By means of a full surface potential mapping areas with a high risk for chloride induced reinforcement corrosion can be localised, although no deteriorations are visually detectable at the concrete surface. In combination with concrete cover depth and resistivity measurements areas with corrosion promoting exposure conditions can be localised even if the reinforcement is not yet depassivated. The following publication gives an overview about the essential full surface investigation methods to localise critical areas regarding corrosion of steel in concrete. The selection of methods is based on the inspection procedure given in 2 .     

Inspection strategies for reinforcement corrosion surveys

This paper describes the procedure of the assessment of the condition of concrete structures regarding reinforcement corrosion and selection criteria for the methods to be used for inspection. It is based on the European Standard EN 1504 on Repair of Concrete Structures and the experience of the members of the task group.     

Local detailed inspection methods to determine concrete properties on structures

During assessment of reinforced concrete structures, information about concrete properties can give a clearer insight into the prevailing reasons for premature degradation of structures. In this paper an overview is given of methods for local detailed inspection of concrete properties in corroding reinforced concrete structures. Recommended non‐destructive, semi‐destructive and destructive testing methods for determining mechanical and durability properties of concrete are given, together with some practical information about performing the method and analysing obtained results. Recommended criteria for evaluating concrete quality and potential risk of corrosion due to poor concrete performance are also given.     

Condition survey with embedded sensors regarding reinforcement corrosion

Besides visual inspections, taking cores or samples and measurements at the concrete surface, the use of embedded sensors can be an effective tool for the assessment of the condition of concrete structures. For new structures sensors can be placed in positions without the possibility of access during use and for existing structures sensors can be used to follow the condition of the structure at relevant selected points. Actually different types of sensor systems are available based on different electrochemical or other methods.     

Embeddable reference electrodes for corrosion monitoring of reinforced concrete structures

Mixed‐metal oxide (MMO), graphite and laboratory‐made Ag/AgCl electrodes were electrochemically characterized to be used as reference electrodes embedded in concrete structures. Electrodes were studied in both, aqueous solutions of pH ranging from 7 to 13.5 and embedded into cement mortars; and the electrochemical studies were carried out in the absence and presence of chloride ions. Potential evolution, polarisation behaviour, galvanostatic pulse response and impedance characteristics of the electrodes were carried out in aqueous solutions. Besides, the electrochemical stability of the electrodes embedded in mortar was studied for an exposure period of two years. It was found that the MMO pseudo‐reference electrode is pH‐sensitive, the graphite pseudo‐reference electrode is oxygen sensitive and the Ag/AgCl pseudo‐reference electrode is chloride sensitive. Then, regarding the corrosion monitoring of steel rebars, care should be taken to avoid misleading interpretations of the corrosion potential measurements. However, any of them can be used to measure the corrosion rate of the rebars by means of traditional electrochemical techniques.     

Cost effectiveness and application of online monitoring in reinforced concrete structures

The annual costs for the maintenance of the Swiss national road networks amount to SFr. 560–640 millions 1 . Due to the limited means and the large number of engineering structures at the critical age between 30 and 45 years cost‐effective solutions for the monitoring and the maintenance of these structures have to be found 2 . In this paper the life cycle costs of an engineering structure using a sensor network (online‐monitoring system) were investigated. These costs were compared to the costs of classical inspection techniques.     

Comparative study on induced macrocell corrosion phenomenon in repaired ordinary reinforced and self-compacting concrete structures

Abstract

This paper aimed at an experimental investigation of the comparative corrosion phenomenon in the reinforcing steel of repaired chloride contaminated self-compacting concrete (SCRC) and ordinary concrete (OC) patches. This research is a continuation of a previous study in which macrocell specimens were prepared with OC having different chloride contaminations simulating the actual patch repair in the construction field. Here, in this research, the same specimens were prepared with SCRC to investigate more deeply the macrocell phenomenon in SCRC, which received limited attention in the past. Four prismatic specimens with two sets of 5 and 3% chloride contaminated SCRC at the two ends were prepared respectively, and the middle portion of these specimens was cast after 24 h with uncontaminated SCRC simulating the actual patch repair in the field. After 1 year of experimental observations of corrosion potentials and corrosion rates, interesting and novel results were obtained in comparison with OC and SCRC specimens.     

Modelling reinforcement corrosion – usability of a factorial approach for modelling resistivity of concrete

As part of the macro cell corrosion process of reinforcement steel, the resistivity of concrete plays a crucial role. In order to investigate the influence parameters on the resistivity of concrete, the results of a discrete quantification were presented and implemented into a factorial approach for modelling corrosion propagation. First results delivered significant deviations from values obtained by measuring. Using Gauss' method of least mean squares provided a decrease in deviations. The hereby obtained deviations were lower than the scatter of the measuring results. A usability of the proposed factorial approach could therefore be approved.     

Evaluation of the corrosion inhibition of salts of organic acids in alkaline solutions and chloride contaminated concrete

This paper summarizes the results of testing on salts of organic acids for evaluating their use as inhibitors of rebar corrosion in chloride‐contaminated concrete. Initially a screening based on electrochemical tests in alkalinized calcium hydroxide solutions was performed on a number of carboxylic acid salts with different number of carbon atoms in the chain and carboxylic groups, also covering substances with hydroxyl and amine group substituents. The screening was completed by testing on carbon steel rebars in concretes with chlorides and substances added at 1:1 molar ratio, focused on sodium lactate, sodium oxalate and sodium borate for comparison. The monitoring of free corrosion potential and linear polarization resistance of steel bars have confirmed significant inhibition only for lactate. Corrosion was only restricted to occluded zones where the access of substance was limited by disadvantageous geometry, producing shallow attacks. Results of further tests in saturated calcium hydroxide solution are reported in order to assess the inhibition ability of lactate as a function of its content, chloride content and pH.     

Models for the propagation phase of reinforcement corrosion – an overview

The deterioration of a concrete structure by reinforcement corrosion proceeds in two phases: the initiation stage and the propagation stage. The first stage describes the time to onset of corrosion due to carbonation of the concrete or chloride ingress. The second stage is the actual deterioration stage. Most methods for life time assessments refer only to the first stage, what is on the safe side with respect to design of structures, but also a model for the second stage can be of interest, e.g. if the remaining life time of an existing structure has to be estimated. This paper presents and discusses the state‐of‐the‐art of models for the propagation stage with regard to their different approaches.     

Stray current-induced corrosion in cathodic protection installations of steel-reinforced concrete structures: FEM study of the critical parameters

A wide range of parameters was investigated by numerical calculations concerning their impact on DC stray current corrosion of reinforced concrete (RC) structures. A simplified model geometry was used to extract the relevant parameters and their interaction in terms of stray current-affected structures. This study mainly focuses on RC structures that are fitted with cathodic protection installations. The findings reveal a complex interaction between the investigated parameters. The possible relevance of further parameters, which is not the subject of this study, was emphasised.     

Modelling of reinforcement corrosion – Corrosion with extensive cathodes

Reinforcement corrosion is the most common reason for the premature deterioration of a concrete structure. In case of a partial depassivation of the reinforcement macrocells are formed with considerable metal removal rates. Thus an assessment of the macrocell current becomes of great concern. To find out, whether this can be achieved by numerical calculations, specimens have been fabricated and simulated by the use of a boundary element program. In this paper the results of the calculations are presented and compared to electrochemical measurements on the real specimens.     

Analysis of the parameters affecting probabilistic predictions of initiation time for carbonation‐induced corrosion of reinforced concrete structures

Probabilistic approaches are available for service life design of reinforced concrete structures subjected to reinforcement corrosion. The International Federation for Structural Concrete (fib) has proposed a model code where design equations and related parameters, involving materials properties, exposure conditions and construction details, are reported. This paper investigates the role of design parameters in the prediction of service life by applying the fib design procedure to existing structures suffering carbonation‐induced corrosion. Results of the modelling were compared to results of the inspection and a significant difference was observed. In order to investigate the reasons for this difference, the roles of concrete cover thickness and carbonation depth were considered separately in the modelling of service life. The concrete cover thickness had a significant effect on the output of the service life modelling, which however was not sufficient to explain the discrepancy between in situ and modelling results. The modelled values of carbonation depth were also affected by errors; sensitivity analysis showed that, although some parameters had higher influence than others, no single parameter had a predominant role.     

Modelling of reinforcement corrosion – Influence of concrete technology on corrosion development

Reinforcement corrosion is influenced by different parameters like resistivity of concrete, setting conditions and also by concrete technology. Moreover the presence of cathodic areas and the possibility of unhampered cathodic reaction influences the reinforcement corrosion. In this paper the development of corrosion without large cathodic areas, called self‐corrosion, considering different concrete parameters, is studied.     

Concrete cover cracking owing to reinforcement corrosion – theoretical considerations and practical experience

Reinforcement corrosion might lead to cracking and spalling of the concrete cover owing to the volume expansion associated with the deposition of some of the possible corrosion products. This is not only aesthetically unpleasing, it might also accelerate deterioration processes or become a safety issue for passing traffic. The present paper discusses first the mechanisms of carbonation‐ and chloride‐induced reinforcement corrosion and considers the chemistry of aqueous iron in order to identify the type of corrosion products as well as their location of formation. Furthermore, practical examples are summarised in order to compare the documented behaviour of a number of real structures with the theoretical considerations made. It is shown that for the case of purely chloride‐induced (pitting) corrosion, precipitation of corrosion products is strongly delayed or may even not occur. Implications are discussed with respect to time‐to‐corrosion prediction models and visual inspection of reinforced concrete structures. Both the theoretical considerations and the practical experience illustrate that relying on outwardly visible signs to detect internally on‐going corrosion must be done with caution if localised reinforcement corrosion cannot be excluded.     

Electrochemical corrosion parameters for active and passive reinforcing steel in carbonated and sound concrete

The electrochemical corrosion parameters, such as corrosion potential, corrosion current density, and the Tafel constants are necessary inputs for the corrosion modeling in reinforced concrete. Literature shows large variability in their values, whereas the data are scarce for the carbonated concrete. This paper presents a range of corrosion parameters for the active steel in carbonated and the passive steel in noncarbonated concrete. Forty-eight singly reinforced concrete cylinders were cast, of which 24 were carbonated and the others were sound samples. Potentiodynamic polarization curves were obtained at three different scan rates and extrapolated to extract the corrosion parameters. To validate these parameters, a macrocell corrosion system was simulated using FEM-based Comsol multiphysics® software. The numerical results were compared to two experimental studies. A natural dispersion in the values of corrosion parameters for both active and passive steels was observed. The average Stern–Geary constant was 54 and 47 mV for active and passive steels, respectively. Numerical simulations with the obtained parameters predicted the macrocell corrosion in partially carbonated concrete with a high accuracy. The presented values of corrosion parameters in this study could help researchers and engineers to simulate the corrosion phenomena in concrete accurately.     

Effects of Tafel slope,exchange current density and electrode potential on the corrosion of steel in concrete

A parametric study is carried out to investigate the effect of variations in anodic and cathodic Tafel slopes, exchange current densities and electrode potentials on the rate of steel corrosion in concrete. The main goal of this investigation is to identify the parameters that have significant influence on steel corrosion rate. Since there is a degree of uncertainty associated with the selection of these parameters, particularly during modelling exercises, it is intended that the results of this study will provide valuable information to engineers and researchers who simulate steel corrosion in concrete. To achieve this goal, the effect of a parameter on the corrosion rate of steel is studied while all other parameters are kept constant at a predefined base case. For each parameter, two extreme cases of anode‐to‐cathode ratio are studied. The investigation revealed that the variations in the anodic electrode potential have the greatest impact on the corrosion rate, followed by the variations in the cathodic Tafel slope.