Baupraktische Erfahrungen bei der Instandsetzung chloridbelasteter Parkhäuser aus Stahlbeton. Schadensdiagnose,Instandsetzungsmaßnahmen,Erfahrungen

Experiences in practice in the repair of concrete structures for car park constructions damaged by chloride induced corrosion Investigations, possibilities of repair, experiences at several constructions In chloride contaminated steel reinforced concrete structures there are several parameters which determine the risk of corrosion and the intensity of a chloride induced corrosion of the reinforcing steel. The content of chloride in the concrete is the most important parameter. Caused by the methods of repair and caused by the different situations of constructions it is unavoidable that areas with high concentrations of chloride may remain in the repaired steel reinforced concrete structures. Up to now there are no long term experiences available to give an answer to the question how different methods of repair have been sucessful in practice. Therefore we will report upon our experiences in different methods of repair in case of chloride induced corrosion of steel reinforced concrete car park structures. The repaired structures reported have been successful over a period of eight to fifteen years in practice. These car park structures are actually in use without any harm or restrictions.     

Corrosion of reinforcing steel in simulated concrete pore solutions: Effect of carbonation and chloride content

The corrosion susceptibility of as-received reinforcing steel bars (rebars) in solutions simulating the pore liquid of alkaline and carbonated concrete has been studied by means of potentiodynamic polarisation tests and polarisation resistance measurements. The effect of different degrees of carbonation and the presence of several chloride contents in the simulated pore solutions was investigated. Results show the beneficial effect of high alkalinity on the localised corrosion of steel caused by chloride ions. From the results of the potentiodynamic tests a critical chloride concentration above which pitting could take place was evaluated for each solution. The chloride threshold values here found are of the same order than those previously reported in the literature for film-free steel. The results obtained in solutions simulating carbonated concrete showed that under weak carbonation conditions carbon steel does not passivate while in the presence of high levels of carbonate and bicarbonate the resistance to localised corrosion is improved.     

国内外混凝土钢筋阻锈剂研究进展

混凝土中钢筋的腐蚀是钢筋混凝土建筑过早损坏的主要原因。氯离子的进入是加速此种腐蚀的关键因素。文章着重介绍阻止钢筋混凝土腐蚀的阻锈剂的发展及迁移型阻锈剂的行为特点。阻锈剂技术的发展趋势和今后的研究工作需要进一步的探究。     

Considerations on reproducibility of potential and corrosion rate measurements in reinforced concrete

This communication analyses information supplied by the electrochemical parameters related to rebar corrosion in reinforced concrete structures (RCS). Corrosion potential and corrosion current density are determined for different sets of conditions. Tests are performed to gather data on conflictive aspects of the two electrochemical parameters, with regard to evaluating the results of RCS inspections. Consideration is made of the limitations of potential measurements if not accompanied by complementary indications such as concrete resistivity, rebar surface area involved in the measurements, or the instrumentally determined corrosion current. The capacity of galvanostatic pulses applied directly on large RCS to offer a reliable guide to corrosion rate of steel reinforcements is discussed.     

NO_2~-和Cl~-对模拟混凝土孔隙液中钢筋腐蚀行为的影响

应用极化曲线法和电化学阻抗技术研究了NO_2~-和Cl~-对钢筋在不同pH值的模拟混凝土孔隙液中的腐蚀行为,结果表明,钢筋耐蚀性与溶液的pH值,以及NO_2~-和Cl~-的浓度相关,pH值的降低和Cl~-浓度的增高都会使钢筋的耐蚀性降低。在含Cl~-的模拟液中,随着NO_2~-浓度升高,钢筋腐蚀速率降低,在pH值为12.50和10.50的溶液中,当[NO_2~-]/[Cl~-]≥0.4时,NO_2~-对钢筋具有良好的阻锈作用。     

混凝土保护涂层抗氯离子渗透性研究

在NaCl溶液中对混凝土保护涂层进行干/湿循环加速腐蚀实验,用电化学循环极化法和高压渗水法对混凝土保护涂层的防护效果进行了研究,并将两种方法研究结果进行对比.结果表明：氯盐环境中,混凝土保护涂层可以有效提高混凝土的抗渗性,降低氯盐对钢筋的腐蚀破坏;循环极化测试法可用于研究钢筋钝化膜的溶解特性和钢筋的锈蚀趋势.      

Corrosion inhibitor systems for remedial treatment of reinforced concrete. Part 2: sodium monofluorophosphate

Sodium monofluorophosphate (MFP) has been applied in the form of concentrated aqueous solutions to the surfaces of concrete structures with the aim of inhibiting corrosion of embedded reinforcing steel which has become depassivated as a consequence of carbonation and/or chloride contamination. To evaluate the effectiveness of such treatments, a series of laboratory investigations was undertaken with reinforced concrete specimens that were chloride-contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately 18 months thereafter. Gravimetric measurements of the quantities and distribution of corrosion on the steel were also made on completion of the exposure tests. It has been found that there were no marked reductions in the corrosion rates of the steel under the conditions investigated. Analysis of aqueous extracts from the treated concrete specimens by means of ion chromatography revealed that negligible penetration of soluble MFP ions had occurred into any of the specimens. Hydrolysis products of MFP (phosphate and fluoride) were present at significant depths in aqueous extracts of the carbonated concrete specimens but only fluoride was detectable in similarly obtained aqueous extracts of non-carbonated specimens.     

Electrochemical realkalisation for rehabilitation of reinforced concrete structures

In steel reinforced and prestressed concrete structures depassivation of the reinforcing steel can take place due to carbonation of the concrete cover. Depending on humidity and oxygen availability subsequent corrosion reactions will be initiated. Such conditions require measures to exclude corrosion induced damages during the designed lifetime of the structure. In the last few years an electrochemical realkalisation treatment has been proposed as adequate rehabilitation technique for carbonated concrete. This temporary treatment should increase the pH-value of the concrete pore water solution due to penetration of alkaline electrolyte from the concrete surface as well as repassivate the reinforcement due to electro chemical reactions at the steel surface. In order to clarify the different mechanisms taking place during electrochemical realkalisation laboratory tests have been carried out using carbonated reinforced mortar specimens. The investigations were aimed at checking the influence of various parameters, e.g. treatment time and current density, as well as the efficiency and long-term durability of this rehabilitation method.     

Stainless steel reinforcing bars – reason for their high pitting corrosion resistance

In harsh chloride bearing environments stainless steel reinforcing bars offer excellent corrosion resistance and very long service life for concrete structures, but the high costs limit a more widespread use. Manganese bearing nickel‐free stainless steels could be a cost‐effective alternative. Whereas the corrosion behavior of stainless steels in alkaline solutions, mortar and concrete is quite well established, only little information on the reasons for the high pitting resistance are available. This work reports the results of pitting potential measurements in solutions simulating alkaline and carbonated concrete on black steel, stainless steel DIN 1.4301, duplex steel DIN 1.4462, and nickel‐free stainless steel DIN 1.4456. Duplex and nickel‐free stainless steels are fully resistant even in 4 M NaCl solutions with pH 13 or higher, the lower grade DIN 1.4301 shows a wide scatter between fully resistant and pitting potentials as low as +0.2 V SCE. In carbonated solutions with pH 9 the nickel‐free DIN 1.4456 shows pitting corrosion at chloride concentrations ≥3 M. This ranking of the pitting resistance can be rationalized based on XPS surface analysis results: both the increase of the Cr(III)oxy‐hydroxide and Mo(VI) contents in the passive film and a marked nickel enrichment beneath the film improve the pitting resistance. The duplex DIN 1.4462 shows the highest pitting resistance, which can be attributed to the very high Cr(III)oxy‐hydroxide, to a medium Mo(VI) content in the film and to a nickel enrichment beneath the film. Upon time, the protective properties of the surface film improve. This beneficial effect of ageing (transformation of the passive film to a less Fe²⁺ containing, more hydrated film) will lead to higher pitting potentials. It can be concluded that short‐term solution experiments give conservative results in terms of resistance to chloride‐induced corrosion in reinforced concrete structures.     

Behaviour of stainless steel in simulated concrete pore solution

Abstract

The localised corrosion behaviour of austenitic, martensitic, and duplex stainless steels has been studied in several solutions simulating the liquid present in the pores of both alkaline and carbonated concrete in the presence of chloride ions. The work aimed to evaluate the suitability of these types of stainless steel as rebars in reinforced concrete structures exposed to very aggressive environments. Electrochemical tests have been performed in solutions with pH values in the range 7·6-13·9, chloride concentration in the range 0-10%, and temperatures of 20 and 40°C. The adverse effect of a decrese in pH on the critical chloride content is discussed, as a function of stainless steel composition and temperature, and the inhibitive effect of high carbonate/bicarbonate concentrations is also shown.     

Study and characterization by acoustic emission and electrochemical measurements of concrete deterioration caused by reinforcement steel corrosion

The durability of reinforced concrete structures becomes a matter of concern, due primarily to the increase of damage by the corrosion of steel reinforcements. This corrosion is not only related to the composition and to the procedure of concrete manufacturing (water/cement, sand/cement, etc.), but also to the aggressive agents as chlorides, carbon dioxide, etc. present in the surrounding medium (Cl⁻, CO₂, etc.). It is well known that the first kind of rebar corrosion (chloride) is more detrimental and that this process contains three basic components: chloride diffusion, electrochemical corrosion and concrete fracture. Therefore the early detection of possible degradation of structures by means of non-destructive testing is essential in order to ensure the functionality of these structures.

This paper presents the results of an experimental investigation on the use of acoustic emission during the corrosion of steel rebars embedded in mortar and immersed in sodium chloride solution. The process of corrosion is accelerated by various imposed potentials and is followed by acoustic emission coupled to electrochemical techniques. The experimental results show that electrochemical techniques can evaluate the corrosive character of the medium used. The acoustic emission showed an activity characteristic of the corrosion initiation phase and the corrosion propagation phase. Thus, it was significantly possible to highlight the acoustic signature of the concrete damage related to the porosity of the mortar and to chloride concentration. The results also show a perfect correlation between the evolution of the acoustic activity and the current of corrosion density.     

矿物掺合料对钢筋氯盐腐蚀行为的影响及其作用机理

用水泥提取液模拟混凝土孔隙液,用自腐蚀电位、动电位极化和电化学阻抗技术,研究单掺粉煤灰或矿粉、复掺粉煤灰和矿粉对混凝土中钢筋氯盐腐蚀行为的影响.结果表明,粉煤灰和矿粉均能有效降低钢筋受氯离子腐蚀的风险,减小腐蚀速率,并能不同程度地提高钢筋腐蚀的临界氯离子浓度.抑制氯离子腐蚀能力由强到弱依次为:矿粉>矿粉+粉煤灰>粉煤灰>水泥.且随氯离子浓度的增大,矿粉和粉煤灰的阻锈效率会有不同程度的下降.用矿粉和粉煤灰按适当比例复掺的方法来对抗氯离子腐蚀不仅经济,而且有不错的阻锈效果.     

Investigations of an ethanolamine‐based corrosion inhibitor system for surface treatment of reinforced concrete

Laboratory investigations were performed to assess the efficacy of a proprietary ethanolamine‐based corrosion inhibitor system when applied to the surface of reinforced concrete specimens that were chloride‐contaminated to varying extents in the presence or absence of carbonation. The corrosion responses of embedded steel bars at various depths of cover were monitored electrochemically during a controlled programme of cyclic wetting and drying undertaken for several months prior to the inhibitor treatment and for approximately eighteen months thereafter. Gravimetric measurements of the quantities and distribution of corrosion on the steel were also made on completion of the exposure tests. Analysis of aqueous extracts from treated concrete revealed that the ethanolamine component of the inhibitor system penetrated to depths of more than 15 mm within the concrete. It was found that, for inhibitor‐treated specimens, there was some reduction in the corrosion rate of pre‐corroding steel at low cover depths in non‐carbonated concrete with modest levels of chloride contamination. At higher levels of chloride contamination and in carbonated specimens, however, the ethanolamine‐based inhibitor was apparently ineffective under the conditions investigated.     

Monitoring of corrosion processes in chloride contaminated mortar by electrochemical measurements and X‐ray tomography

Corrosion of steel reinforcement in concrete exposed to chloride containing environments is a serious problem in civil engineering practice. Electrochemical methods, e.g., potential mapping, provide information whether the steel reinforcement is still passive or depassivation has been initiated. By applying such techniques no information on the type of corrosion, its extent and distribution of corrosion products is available. Particular the corrosion progress is a significant problem. Especially in the case of macrocell corrosion in reinforced concrete structures, the development at the anode cannot be separated into corrosion damage resulting from macrocell corrosion or self‐corrosion. Until now also in laboratory tests it is impossible to collect such information without destroying specimens after electrochemical testing was performed. To overcome this problem it was tried to study the steel surface within the mortar specimens by X‐ray tomography (CT). Within the scope of these investigations it could be shown, that X‐ray tomography is suitable to make corrosion pits and their development visible which are embedded in a mortar with a cover thickness of about 35 mm. In this publication the time‐dependent corrosion damage of reinforced steel is documented by X‐ray tomography.     

Electrochemical chloride removal from reinforced concrete structures and its ability to repassivate prerusted steel surfaces

Gravimetric and electrochemical measurements were used to expose the relationship between the degree of prerusting of reinforcements embedded in chloride‐contaminated mortar or concrete and the efficiency with which they are repassivated once depassivating ions are removed. The results show that, above a certain, ill‐defined rusting threshold, the electrochemical chloride removal does not ensure effective repassivation of reinforcements in the steel/concrete system. Once the passivity of reinforcements embedded in reinforced concrete structures (RCS) is overcome, the typical corrosion rates of the active state seemingly suffice to maintain an acid pH at the metal/rust interface in the bulk of such a strongly alkaline material as concrete. After this local acidification, the metal inside pits probably behaves similarly as it would in an acid solution. As a result, it does not suffice to remove the rusting agent in RCS in order to stop corrosion; rather, the agent must be removed before the first visible signs of deterioration appear.     

Corrosion Behavior of Epoxy-Coated Rebar with Pinhole Defect in Seawater Concrete

Experiments were carried out to investigate the corrosion behavior of epoxy-coated rebar(ECR) with pinhole defect(diameter in hundreds of microns) immersed in the uncarbonated/carbonated simulated pore solution(SPS) of seawater concrete. Corrosion behavior was analyzed by electrochemical impedance spectroscopy. The composition and morphology of corrosion products were characterized by X-ray diffraction, energy-dispersive spectrometry and scanning electron microscopy. Meanwhile, oxide film produced by preheating before spray coating was investigated by X-ray photoelectron spectroscopy and Mott–Schottky technology. Results indicated that corrosion behavior of ECR with pinhole defect exhibited three stages when immersed in the uncarbonated/carbonated SPS. In the initial stage, steel in defect was passivated when exposed in the uncarbonated SPS and corroded when exposed in the carbonated SPS, due to competitive adsorption between chloride and hydroxyl ions. In the second stage, the oxide film under coating reconstituted(the thickness and defects density decreasing) in the uncarbonated SPS, which was caused by the synergy between high hydroxide and chloride activity, while in the carbonated SPS, crevice corrosion happened under the coating around pinhole,because of the different oxygen concentrations cell at the coating/steel interface. In the third stage, localized corrosion occurred under the coating around the pinhole in the uncarbonated SPS, which was probably induced by ion diffusion at the nano-scale coating/steel interface. The corrosion products adjacent to the defects were re-oxidized from FeCl_2·4H_2O and Fe_2(OH)_3Cl to Fe_2O_3·H_2O, and the corrosion area was expanded outward in the carbonated SPS.     

Monitoring of corrosion in reinforced concrete structure using Bragg grating sensing

Corrosion in reinforced concrete structures is a major problem that seriously affects the service life of the structures. In order to detect rebar corrosion, a fiber optic corrosion sensor (FOCS) made of one fiber Bragg grating (FBG) sensor and twin steel rebar elements was designed and packaged up with concrete. Subsequently, a series of experiments were carried out to verify its feasibility. A constant current accelerated corrosion test was performed on five fiber optic corrosion sensors and the relationship between reflected wavelength change from the grating and the weight loss rate of rebar was obtained by the gravimetric weight loss method. The experiment shows that it is feasible to monitor the degree of corrosion of reinforced steel in reinforced concrete structures using FOCS.     

丙烯酸系乳胶用于钢筋混凝土的防腐蚀研究

用电化学阻抗谱研究了丙烯酸系乳胶作为混凝土添加剂或钢筋表面涂层时对钢筋腐蚀行为的影响,加速腐蚀试验结果表明混凝土中添加乳胶后能够延缓钢筋表面钝化层的破坏,而对混凝土的渗透性能影响不大,乳胶涂层能够显著减小钢筋腐蚀速率,涂层的存在改变了钢筋表面的腐蚀状态,在此基础上提出了改善钢筋混凝土抗蚀能力的措施。     

On the effectiveness of realkalisation as a rehabilitation method for corroded reinforced concrete structures

Based on available experience with the use of electrochemical realkalisation (ERA), a fairly recent method for rehabilitating reinforced concrete structures (RCS), carbonated concrete can undoubtedly be realkalised. To the authors' minds, however, the following questions remain unanswered: (a) does ERA always effectively repassivates reinforcements?; (b) can ERA be considered an end or just a means to ensuring RCS durability?; and (c) what is the use of ERA if it cannot stop corrosion? This work was aimed at answering the previous, controversial questions. To this aim, the behaviour in a Ca(OH)₂ saturated solution, and in a sound uncarbonated mortar consisting of 1:3:0.5 cement, sand and water, of reinforcing bars from an RCS that failed through carbonation after 29 years of service life was examined.     

Effect of electrode orientation on linear polarisation measurements using sensor controlled guard ring

Abstract

Use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The sensors are used to monitor potential differences measured on the concrete surface above the reinforcing steel. These data are then used to confine the corrosion measurement to a known area of reinforcing steel. The role of the sensors is paramount in maintaining adequate confinement of the perturbation applied to the reinforcing steel. Experiments were conducted on reinforced concrete specimens containing both active and passive zones of reinforcing steel. Polarisation resistance measurements were taken using both a potentiostatically controlled guard ring device developed at the University of Liverpool and a galvanostatically controlled commercial device. Both devices indicated that the orientation of the sensor electrodes can affect the polarisation resistance determined when taking measurements on passive steel next to actively corroding areas. The sensor orientation was not observed to affect the polarisation resistance measurements taken on actively corroding steel next to passive steel.