共查询到20条相似文献，搜索用时 15 毫秒
1.
A strong interest for the durability of reinforced concrete structures currently exists in industry and research [1]. Against the background of immense costs for maintaining reinforced concrete structures and repairing damage caused by corroding reinforcement steel, this interest lead to a German joint research project. The aim of this network‐based (www.bam.de/dfg537.htm) research group is, to deliver the basic knowledge of the corrosion propagation and to make a probabilistic tool available for engineers so that a complete design for durability, concerning reinforcement corrosion, will be possible. 相似文献
2.
Over the last 25 years, cathodic protection (CP) of reinforced concrete structures suffering from chloride induced reinforcement corrosion has shown to be successful and durable. CP current causes steel polarisation, electrochemical reactions and ion transport in the concrete. CP systems are designed based on experience, which results in conservative designs and their performance is a matter of wait‐and‐see. CP systems can be designed for critical aspects and made more economical using numerical models for current and polarisation distribution. Previously, principles of numerical calculations for design of CP systems were reported. The results were satisfactory, except in terms of current density for active corroding systems. This was suggested to be due to neglecting beneficial effects of CP current flow. One of the beneficial effects is pH increase at the steel surface due to oxygen reduction. As the pH increases, the corrosion rate decreases and the current demand decreases. A simple model was set up for this transient process, suggesting that such effects should occur on the time scale of hours to days. This model was validated from start up data of a CP field trial system on part of a bridge. Field results confirmed the modelling proposed here. 相似文献
3.
4.
J. Gulikers 《工业材料与腐蚀》2005,56(6):393-403
Traditionally, the assessment of service life of steel reinforced concrete structures has been focused on the prediction of the time required to achieve a transition from passive to active corrosion rather than to accurately estimate the subsequent corrosion rates. However, the propagation period, i.e. the time during which the reinforcing steel is actively corroding, may add significantly to the service life. Consequently, ignoring the propagation period may prove to be a conservative approach. On the other hand the prediction of the corrosion rate may result in a very complex task in view of the electrochemical nature of corrosion and the numerous parameters involved. In order to account for the various influences an essentially empirical model has been introduced in which the electrolytic resistivity of the concrete environment serves as the major parameter. This model will be discussed for carbonation‐induced corrosion based on the commonly accepted theory of aqueous corrosion. An alternative model for microcell corrosion is proposed which is based on the commonly accepted view that anodic and cathodic sites are microscopic and their locations change randomly with time. In line with this view electrolytic resistivity can be incorporated and thus may play a significant role in the kinetics of the corrosion process. For a wide range of corrosion current densities the relationship between corrosion current density, log(icorr), and concrete resistance, log(Rcon), can then be approximated by an almost ideal linear relationship. Assuming a fixed geometrical arrangement of anodic and cathodic sites on the steel surface, this linear relationship is also valid for concrete resistivity, ρcon. However, from the theoretical treatment of the electrochemical processes underlying reinforcement corrosion it becomes evident that a linear relationship between corrosion current density and concrete resistivity does not necessarily imply that concrete resistance is dominating the overall corrosion cell resistance. In most cases a significant portion of the driving voltage of the corrosion cell will be consumed by the transfer of electrical charge involved in cathodic reactions, i.e. cathodic activation control will dominate. 相似文献
5.
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. 相似文献
6.
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. 相似文献
7.
Since the initiation stage of the damage process due to reinforcement corrosion had been successfully investigated in the recent past, the damage progress in the propagation stage is currently in the focus of research. This work deals with the mechanisms of cracking and spalling due to corrosion of reinforcement and aims for the development of an analytic prediction model of the damage process. On this occasion the influence of shrinkage and creep on the stress condition within the concrete cover is of major importance to the subsequent analysis of the crack formation due to reinforcement corrosion in the early propagation stage. 相似文献
8.
M. Raupach K. Reichling J. Broomfield J. Gulikers U. Schneck M. Serdar I. Pepenar 《工业材料与腐蚀》2013,64(2):111-115
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. 相似文献
9.
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. 相似文献
10.
Muazzam G. Sohail Stéphane Laurens Fabrice Deby Jean P. Balayssac Nasser Al Nuaimi 《工业材料与腐蚀》2021,72(12):1854-1871
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. 相似文献
11.
This paper, describes experiments that form the basis of an invention that aims at improving the durability of conventional (mechanical) repairs to concrete structures suffering from chloride induced corrosion of reinforcing steel. The invention comprises application of a short term, low voltage, DC current before or after concrete is broken out and before repair material is applied. It is an additional step in conventional concrete repair. The application of current will last typically 24 h at a current density of typically 5 A/m2 of steel surface area. In laboratory experiments corrosion pits are simulated by placing highly concentrated iron(II)chloride solution in contact with a mortar surface, after which current is applied. The results indicate that this treatment is able to remove 90% or more of the chloride from the simulated pit solutions. Furthermore, the pH has increased from about 3 to more than 12. The combined reduction of chloride content and increase of pH strongly reduces the chloride to hydroxyl ratio of the pore solution and thus the aggressive conditions at the reinforcing steel. After applying alkaline chloride free repair material, this will result in a longer life of the repair, thus reducing the life cycle costs of repaired structures. The process is named EAR, electro active repair. 相似文献
12.
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. 相似文献
13.
This paper describes the results of the calculations on Case Study 1 which have been performed within the activities of the EFC Task Group on modelling of corrosion of steel in concrete. These calculations have been performed by six researchers from different institutes, each of them using his favourite tools and assumptions. Case Study 1 was intended to obtain a preliminary impression of the corrosion models used by researchers as well as to gain information on the underlying scientific backgrounds. It has to be noted that these calculations already have been carried out in 2000 and 2001 and some of the models might have been more or less improved in the meantime. Also only selected details are described in this paper, because the discussion on the details within the EFC task group has shown, that a full scientific discussion of the models including all relevant assumptions is not possible within the framework of this paper. However, it also should be noted that it has never been intended to find the “best” model or to rank the models, but to get an overview and learn from each other. Finally, the participants of the EFC task group came to the conclusion, that all types of models have their advantages, depending on the complexity of the corrosion system to be simulated. 相似文献
14.
Cathodic protection (CP) has become a successful method for the rehabilitation of concrete structures affected by chloride-induced corrosion of reinforcing steel. CP involves applying an electrical current from an external anode through the concrete to the reinforcement. The current causes steel polarisation, electrochemical reactions and ion transport. Normally the anode is placed over relatively large surface areas, including those where the steel is passive. Conventional views assume that protection current will not significantly flow outside the anode area. In many cases this results in a conservative design. This paper presents principles and first results of numerical calculations for design of an example CP system by finite element modelling. The final objective is to develop a tool for more economical CP system design. In particular, a CP system for the protection of local damage in bridges (e.g. at leaking joints) has been simulated. The corroding area with respect to the size of the anode is varied. Current and potential distributions and depolarisation values are predicted, both close to and more distant from the anode. It appears that current densities required to achieve sufficient polarisation are much higher than those usually found in the field. Neglecting time-dependent repassivation processes is likely to be the main cause and further work is needed to include them. The present model can be used with reasonable confidence for preventive application to passive steel. 相似文献
16.
Potential mapping is a widely applied and accepted non-destructive measuring technique to assess the condition of concrete structures with respect to corrosion of the embedded reinforcement steel. Most often a single reference electrode is used to perform point measurements according to a predefined grid. At present there is much debate on the appropriate potential level to allow for a distinction between passive and actively corroding steel. In the RILEM recommendation for half-cell potential measurements, a statistical analysis of the results of potential mapping is advocated in order to arrive at an improved quantification of this potential region pertaining to the structure under investigation. However, the underlying calculation procedure has not been elaborated and consequently there is no practical and unambiguous guidance for the consulting engineer on how to perform such a statistical analysis. In this paper, the theory for the statistical analysis is presented based on the assumption that the potential distribution for both actively corroding and passive steel can be adequately described by a normal probability density distribution. This theory is applied to a number of situations to exemplify the procedure by clear graphs. The potential criteria derived will demonstrate a significantly smaller range as compared to the criteria presented in ASTM C 876. Moreover, with this statistical analysis any desired probability level of detection of corroding reinforcement steel can be chosen. 相似文献
17.
Both on‐site investigations and laboratory studies have shown that different corrosion rates are obtained when different commercially available corrosion rate instruments are used. The different electrochemical techniques and the measurement parameters used, i.e. polarisation current and time, are in some studies considered the main reasons for the variations. This paper presents an experimental study on the quantitative effect of polarisation time and current on the measured polarisation resistance – and thus the corrosion current density – of passively and actively corroding steel. Two electrochemical techniques often used in instruments for on‐site corrosion rate measurements are investigated. On passively corroding reinforcement the measured polarisation resistance was for both techniques found to be highly affected by the polarisation time and current and no plateaus at either short or long polarisation times, or low or high polarisation currents were identified. On actively corroding reinforcement a large effect of the polarisation time was also found, but only a minor effect of the polarisation current. The effect of the polarisation time was, however, practically independent of the corrosion rate for actively corroding steel. For both techniques guidelines for polarisation times and currents are given for (on‐site) non‐destructive corrosion rate measurements on reinforcement steel in concrete. 相似文献
18.
Chloride contents at the steel–mortar interface that initiate steel corrosion were determined for carbon steel in alkali-activated fly ash mortar for three different exposure conditions: exposure to 1 M NaCl solution; leaching in deionized water and then exposure to 1 M NaCl solution; and leaching in deionized water, aging in air at 20°C and natural CO2 concentration, and then exposure to 1 M NaCl solution. For comparison, a Portland cement mortar, exposed to 1 M NaCl solution, was studied. The median values of the corrosion-initiating chloride contents (average over the full length of the rebar) in the alkali-activated fly ash mortar varied between 0.35 and 1.05 wt% Cl with respect to binder, consistently lower than what was obtained for the Portland cement mortar, but with no clear trend regarding the exposure conditions. For most of the alkali-activated fly ash mortar specimens, preferential corrosion at the connection between the working electrode and the external measurement setup was observed, while preferential corrosion did not occur for the Portland cement mortar. Scanning electron microscopy and auxiliary experiments in synthetic solutions indicated that this behavior was caused by inhomogeneities at the steel–mortar interface in the alkali-activated mortar, likely due to its peculiar rheological properties in the fresh state. 相似文献
19.
The paper reports the results of numerical simulations carried out with FEM and aimed at evaluating the corrosion conditions of steel bars in concrete elements subjected to chlorides. Two case studies were analysed: a reinforced concrete element subjected to de‐icing salt in the presence of a crack and a concrete tunnel in a chloride‐contaminated, water saturated soil. Attention was focused on the selection of proper values of concrete resistivity and of the parameters suitable to describe the electrochemical behaviour of steel in the different conditions of exposure. The results allowed to quantify the effects of the galvanic coupling between active and passive areas on the corrosion rate of steel. 相似文献
20.
Against the background of huge costs for maintenance and repair it would be helpful to have a tool to assess the remaining life time of concrete structures. Deterioration is often caused by reinforcement corrosion and research projects have been carried out to develop models for the time‐dependent progress of the degradation. Although these projects have resulted in several steps forward, further work is still needed. This paper presents two actual research activities which deal with modeling of reinforcement corrosion: the first one is the RILEM Technical Committee MAI, the second is a German joint research project. 相似文献