Einflußeiner Verzinkung auf die Korrosion von mit Zementmörtel beschichtetem Stahl in NaCl-Lösung

Effect of galvanizing on the corrosion of steel in concrete immersed in NaCl solution Galvanized or pickled steel sheet specimens were embedded in portland cement mortar of various water cement ratios and curing conditions and then wholly or partially immersed in 0.5 M NaCl solution for 1 to 5 yrs. Free corrosion potentials and electrical resistances have been measured. Immersion conditions and the presence of zinc have a significant effect on the corrosion resistance of the embedded steel sheets. The potentials of the wholly immersed specimens are very negative. Thus, these specimens cannot act as cathodes in corrosion cells, and the steel sheets within the mortar do not corrode. The partially immersed specimens, on the other hand, show very noble potentials. Also in the case of galvanized steel sheets the potentials are shifted to the same positive values in the course of exposure time. Thus, all these specimens can act as cathodes in corrosion cells. Localized corrosion generally occurs at the water/air line. In the case of pickled specimens the mortar is cracked due to growing corrosion products. In the case of galvanized steels the corrosion is retarded significantly. The test results are discussed in detail with respect to practical problems of cell formation, internal and external protection of pipes as well as the corrosion resistance of reinforced concrete.     

Untersuchung über die Auswirkung der Elementbildung zwischen Stahl in Beton und Stahl in Erdboden

Investigation of the effect of galvanic corrosion between steel in concrete and steel in soil The investigation of cathodic polarization of steel in concrete on samples of portland cement and blast furnace cement revealed that oxygen reduction on steel in portland cement is less hindered than on steel in blast furnace cement. As to the magnitude of the cathodic current the aeration of the samples is important. Dry stored samples before measuring case a higher current density than wet stored ones. A significant relationship of the cathodic current depending on the water/cement value and the storage time of concrete could not be ascertained. The polarization resistances for portland cement samples lie within 86 and 3000 kΩ · cm² and for blast furnace cement samples between 430 and 5100 kΩ · cm². The measurements of the anodic current densities on corrosion cells of steel in concrete/steel in solution and steel in wet sand respectively rendered, by varying the cathode/anode aspect ratio from 1000: 1 to 1: 1, values for portland cement samples between 560 and 1,2 μAJcm² (corresponding to an annual corrosion of 6,5 and 0,014 mm respectively), and for blast furnace cement samples values between 730 and 0,28 μA/cm² (corresponding to an annual corrosion rate of 8,5 and 0,003 mm respectively). A decrease of the anodic current density variable with time could not be observed during the 28 days of measurements. On account of the investigations the following conclusions can be made: A formation of a corrosion cell with steel in concrete/steel in soil is particularly then to be expected if the concrete is dry on one side, e.g. the foundation of a building where oxygen diffuses by way of the gas pores in the concrete from the inner side to the cathode. This is less serious if the concrete is fully embedded in soil and thoroughly moistened. In this case the transport of oxygen has to be carried via waterfilled pores.     

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.     

Untersuchungen zum kritischen korrosionsauslösenden Chloridgehalt von Stahlfasern in künstlicher Betonporenlösung

Investigations into the critical corrosion‐inducing chloride content of steel fibres in artificial concrete pore solution It is well known, that reinforcement steel in concrete is normally protected against corrosion due to the high pH‐value of the pore solution of the concrete. This alkalinity leads to a passive layer on the steel surface, which prevents further corrosion. The passive layer can be destroyed by chloride ions diffusing into the concrete. The concentration of chloride in the concrete which leads to a destruction of the passive layer and therefore to corrosion of the steel is defined as the critical chloride content. Investigations in artificial concrete pore solutions show that the critical chloride content of black steel is strongly dependent on the pH‐value of the solution: the higher the concentration of the OH⁻‐ions the higher the critical chloride content. For steel fibres earlier investigations have shown, that steel fibres do not corrode in concrete even at high chloride contents. Therefore it could be assumed, that the critical corrosion‐inducing chloride content of steel fibres in concrete is distinctly higher than of conventional reinforcing steel. To verify this assumption the corrosion‐inducing chloride content of steel fibres is investigated in artificial chloride‐containing concrete pore solutions at different pH‐values. 5 different types of steel fibres, 1 lashing wire and as reference 1 reinforcing steel are investigated at 3 different pH‐value ranges. The concentration of chloride within the pore solution is gradually increased in time steps of 12 h. The beginning of corrosion is determined by current as well as potential measurements. Furthermore additional investigations are carried out with intermediate products of the fibre production (steel wires with different diameters) to investigate if the critical chloride content of the wires is increasing gradually with decreasing diameter. The investigations show, that steel fibres in artificial chloride‐containing pore solutions indicate an distinctly increased resistance against chloride‐inducing corrosion compared with conventional reinforcing steel for high pH‐values. With decreasing diameter of wires the critical chloride content increases gradually.     

水性硅酸盐溶胶型涂料对钢筋混凝土耐久性的影响

分析了钢筋混凝土腐蚀破坏的主要原因是钢筋腐蚀导致的混凝土胀裂.为保护钢筋混凝土研制了一种水性硅酸盐溶胶型涂料并研究了该涂料对混凝土内置网筋的保护作用及经涂料涂覆的混凝土氯离子渗透性和高压渗水性能.结果表明,涂履水性硅酸盐溶胶型涂料可明显提高与改善混凝土的耐久性.     

The effect of temperature on the corrosion of steel in concrete. Part 1: Simulated polarization resistance tests and model development

The effect of temperature on the corrosion rate of steel corrosion in concrete is investigated through simulated polarization resistance experiments. The simulated experiments are based on the numerical solution of the Laplace’s equation with predefined boundary conditions of the problem and have been designed to establish independent correlations among corrosion rate, temperature, kinetic parameters, concrete resistivity and limiting current density for a wide range of possible anode/cathode (A/C) distributions on the reinforcement. The results, which successfully capture the resistance and diffusion control mechanisms of corrosion as well as the effect of temperature on the kinetic parameters and concrete/pore solution properties, have been used to develop a closed-form regression model for the prediction of the corrosion rate of steel in concrete.     

Effect of Long-Term Service on the Structural Strength of Reinforcing Wire

The main factors influencing the structural strength of high-strength reinforcing wire serving for a long period under the conditions of preliminarily stressed structures of reinforced concrete bridges are considered. The processes of local corrosion of reinforcing wire, softening due to relaxation in the metal, and lowering of the crack resistance due to hydrogen saturation of the steel are considered.     

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.      

Shear performance of reinforced concrete beams with corroded stirrups in chloride environment

Experiments were conducted for the investigation of the influence of reinforcing steel corrosion on the shear capacity of reinforced concrete beams. The shear performance of RC beams with different corrosion levels in both longitudinal reinforcing steel bars and stirrups was examined. Relationships of corrosion-induced crack widths in concrete cover with the corrosion level of the reinforcing steel bars were obtained. Engineering approaches were developed to predict the residual shear strength of the corroded beams.     

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.     

Epoxy‐coated bars as corrosion control in cracked reinforced concrete

One of the most common corrosion protection methods in reinforcing concrete bars is the application of fusion‐bonded epoxy coatings. Although considerable research has been carried out on the performance of epoxy‐coated bars (ECR), there are still many uncertainties about their performance in cracked concrete. In this experimental program, reinforcing steel bars with six types of epoxy coatings embedded in concrete slabs with a 0.4 mm wide preformed crack intersecting the reinforcing steel at right angles were tested. Results of corrosion potentials, corrosion current density, coating adhesion tests, chloride content, and visual examination after 68 months of exposure to a simulated marine environment are reported. Results revealed that under the studied conditions the ECR did not provide total protection of steel reinforcement in cracked concrete. Their use however, tended to reduce significantly the damage caused by the chloride‐induced corrosion when compared with the uncoated bars embedded in concrete with similar characteristics.     

X80钢在干湿交替与水饱和哈密土壤环境下的腐蚀行为

目的揭示X80钢在干湿交替与水饱和哈密土壤环境下的腐蚀行为与规律。方法采用失重实验和电化学测试分析腐蚀速率与阴阳极电化学过程的变化规律,利用金相分析观察母材和焊缝的组织特征,通过SEM、EDS、XRD等微观分析手段观察腐蚀产物形貌、元素含量与物相组成,从而研究干湿交替与水饱和土壤环境对X80钢腐蚀行为的影响。结果 X80钢在干湿交替环境下的腐蚀速率是水饱和下的2～3倍,其在干湿交替与水饱和哈密土壤环境下的腐蚀产物物相均由Fe3O4、FeOOH、FeS所构成。X80钢在干湿交替环境下,表面的腐蚀产物膜出现大量凹坑与裂隙,使O2在试样表面分布不均,形成氧浓差电池,并且该凹坑与裂隙有利于腐蚀性离子进入,加剧局部腐蚀。在同一环境下,由于焊接接头各区域组织差异引起的微电偶腐蚀,X80钢焊缝的腐蚀速率明显高于母材。结论干湿交替环境与土壤中大量存在的Cl-显著加速了X80钢母材及焊缝的局部腐蚀,且X80焊缝耐蚀性明显低于母材,其腐蚀机理均为氧浓差电池和局部腐蚀自催化效应共同作用,腐蚀形态也由以全面腐蚀为主(水饱和环境)转变为以点蚀+溃疡状腐蚀为主(干湿交替环境)。     

Polarisation behaviour of steel bar samples in concrete in seawater. Part 1: Experimental measurement of polarisation curves of steel in concrete

The most widely used technique for the investigation of corrosion of reinforcing steel in concrete is the linear polarisation resistance (LPR) method, which however needs to assume the Tafel slopes or the B constant for calculation of the corrosion rate. This paper aims to explore the use of a polarisation curve technique to study the polarisation behaviour and to evaluate simultaneously the corrosion rate and Tafel slopes of steel samples in concrete. As the first part of the study, this paper reviews the relevant literature, and examines the effect of the experimental technique on the measured polarisation curves of steel in concrete in seawater. In particular, differences in the results obtained by two different test procedures are examined. A comparison of the experimental polarisation curves with the theoretical curves based on charge transfer reactions is made.     

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.     

Q235钢/导电混凝土在3种典型土壤环境中腐蚀的灰色关联度分析

采用动电位扫描和电化学阻抗谱(EIS)技术,研究了Q235钢/导电混凝土在盐碱土、黄棕壤、红壤中的腐蚀行为,分析了土壤环境因素对腐蚀过程的影响规律,并基于灰色关联度理论计算了土壤中各离子对导电混凝土中Q235钢腐蚀过程的影响权重.结果 表明,加速腐蚀45 d后,Q235钢/导电混凝土表面出现孔洞、边缘出现细微裂纹.Q2...     

不同表面状态下钢筋的腐蚀行为研究

采用实验室加速腐蚀试验、电化学测量技术研究了不同表面状态下钢筋的腐蚀行为。结果表明:表面带有氧化皮的钢筋的腐蚀行为明显区别于裸表面钢筋。在气相加速腐蚀试验中,裸表面钢筋比氧化皮钢筋有较大的腐蚀失重量;在混凝土模拟孔隙液中,带氧化皮钢筋和端面钢筋(裸钢筋)一样可以在高碱性环境中完全钝化,但随着溶液中Cl-含量上升,钢筋裸表面的钝化膜更易受到破坏,氧化皮钢筋相对端面钢筋维钝电流密度明显减小,破裂电位明显正移,表现出较好的抗Cl-性能。     

Wasserstoffinduzierte Spannungsrißkorrosion an unverzinkten und verzinkten Baustählen

Hydrogen induced stress corrosion cracking of non galvanized and galvanized construction steels The processes of atmospheric corrosion and corrosion in collected water which may lead to hydrogen induced stress corrosion cracking of high-strength reinforcing steels in casing tubes before injection with concrete are discussed. Hydrogen uptake during corrosion occurs in weakly acid solutions as well as in neutral or alkaline aqueous solutions. The hydrogen uptake by proton discharge in acid solutions decreases with increasing pH of the electrolyte. Hydrogen can also be absorbed in neutral to weakly alkaline solutions if steels are plastically deformed and water reacts with the fresh iron surface. In alkaline solutions, hydrogen uptake is possible if, at the generally passivated steel surface, localized corrosion (pitting or crevice corrosion), local galvanic cells and a sufficient decrease in the pH of the pit electrolyte occurs. In the case of galvanized steels with damaged zinc layers, hydrogen uptake may result from the cathodic polarization of the free steel surface by zinc dissolution. The absorbed hydrogen interacts with the microstructure of the steels and weakens the bonds between the iron atoms. The influence of the microstructure of high-strength steels on the fracture behaviour is discussed on the basic of the so-called decohesion theory.     

不同粘结剂基TiB_2-C复合阴极中碱金属的渗透迁移行为(英文)

在含K低温电解质熔体中,采用EDS及改进型电解膨胀率测试仪,分别研究电解过程中沥青、呋喃、酚醛、环氧基TiB2-C复合阴极中碱金属(K和Na)的渗透迁移路径。同时,计算并讨论相应的电解膨胀率、碱金属的扩散系数以及复合阴极的腐蚀率。结果表明:无论使用何种粘结剂,电解过程中,碱金属在阴极中表现出相似的渗透迁移路径:碱金属首先渗透进入阴极的孔隙当中,随后渗透进入粘结剂相中,随着电解的不断进行,最后渗透进入复合阴极的骨料相当中。渗透进入粘结剂相和炭质骨料相当中的K和Na均会引起复合阴极的电解膨胀,同时,K比Na有着更强的渗透力。树脂基复合阴极的电解膨胀率、碱金属在其中的扩散系数以及腐蚀率均小于沥青基复合阴极,即,树脂基复合阴极的抗碱金属渗透力强于沥青基复合阴极。而就树脂基TiB2-C复合阴极而言,酚醛基TiB2-C复合阴极的抗渗透力最强,碱金属在其中的渗透速率、扩散系数和相应的腐蚀率分别为4.72mm/h,2.24×10-5 cm2/s和2.31 mm/a.     

Corrosion of Carbon Steel and Corrosion-Resistant Rebars in Concrete Structures Under Chloride Ion Attack

Corrosion of reinforced concrete is the most challenging durability problem that threatens reinforced concrete structures, especially structures that are subject to severe environmental conditions (i.e., highway bridges, marine structures, etc.). Corrosion of reinforcing steel leads to cracking and spalling of the concrete cover and billions of dollars are spent every year on repairing such damaged structures. New types of reinforcements have been developed to avoid these high-cost repairs. Thus, it is important to study the corrosion behavior of these new types of reinforcements and compare them to the traditional carbon steel reinforcements. This study aimed at characterizing the corrosion behavior of three competing reinforcing steels; conventional carbon steel, micro-composite steel (MMFX-2) and 316LN stainless steel, through experiments in carbonated and non-carbonated concrete exposed to chloride-laden environments. Synthetic pore water solutions have been used to simulate both cases of sound and carbonated concrete under chloride ions attack. A three-electrode corrosion cell is used for determining the corrosion characteristics and rates. Multiple electrochemical techniques were applied using a Gamry PC4? potentiostat manufactured by Gamry Instruments (Warminster, PA). DC corrosion measurements were applied on samples subjected to fixed chloride concentration in the solution.     

Effect of Alloying Elements on Tensile Properties, Microstructure, and Corrosion Resistance of Reinforcing Bar Steel

The effect of copper, phosphorus, and chromium present in a semikilled reinforcing bar steel produced by in-line quenching [thermomechanical treatment (TMT)] process on the tensile properties, microstructure, and corrosion resistance of steel in simulated chloride environment has been investigated. The results have been compared with that of a semikilled C-Mn reinforcing bar steel without these alloying elements produced by the same process route. Though the amount of phosphorus (0.11 wt.%) was higher than that specified by ASTM A 706 standard, the Cu-P-Cr steel exhibited a composite microstructure, and good balance of yield stress, tensile stress, elongation, and ultimate tensile to yield stress ratio. Two conventional test methods, namely, the salt fog, and potentiodynamic polarization tests, were used for the corrosion test. The rust formed on Cu-P-Cr steel was adherent, and was of multiple colors, while the corrosion products formed on the C-Mn steel were weakly adherent and relatively darker blue. Also, the free corrosion potential of the Cu-P-Cr steel was nobler, and the corrosion current was markedly lower than that of a C-Mn rebar. The Cu-P-Cr steel did not develop any pits/deep grooves on its surface even after the prolonged exposure to salt fog. The improved corrosion resistance of the Cu-P-Cr steel has been attributed to the presence of copper, phosphorus, and small amount of chromium in the dense, adherent rust layer on the surface of reinforcing steel bar. A schematic mechanism of charge transfer has been proposed to explain the improved corrosion resistance of the Cu-P-Cr alloyed TMT rebar.