Performance of galvanized and stainless steel rebars in concrete under macrocell corrosion conditions

In the recent past, the damage caused by rebar corrosion in concrete structures has been considered as one of the major durability problems affecting the service life of concrete structures. In order to prevent corrosion of steel reinforcement, various types of protective methods have been adopted. One of the protective measures is using galvanized reinforcement in concrete to enhance the service life. In the present study various types of galvanized rebars namely bare – Cold Twisted Deformed (CTD), bare – Thermo Mechanically Treated (TMT), galvanized – Cold Twisted Deformed, Galvanized – Thermo Mechanically Treated, galvanized and chromated – Cold Twisted Deformed, galvanized and chromated – Thermo Mechanically Treated and stainless steel rebars have been evaluated for their corrosion resistance in M30 grade concrete under macro cell corrosion condition over a period of one year. From the studies it has been observed that TMT bars performed better when compared to CTD bars. Among the rebars tested, stainless steel rebar has shown negligible corrosion in chloride contaminated concrete.     

接触网部件材料在模拟典型大气环境介质中的腐蚀——热浸镀锌材料的腐蚀(I)

采用腐蚀失重法与显微镜技术,研究了电气化铁路接触网热浸镀锌部件材料在模拟典型大气环境(海洋环境、工业环境、城市环境)介质中的腐蚀及其形貌。结果表明,热浸镀锌材料在模拟城市大气环境介质中的腐蚀最为严重,工业环境次之,海洋环境腐蚀最轻。二次加工与成型会引起镀锌层局部破损致使基材局部暴露与镀锌层形成电偶对,会加重热浸镀锌部件的腐蚀,且破损面积越大腐蚀越严重。同样,热浸镀锌部件与不锈钢紧固件耦接会形成电偶腐蚀,也会加重热浸镀锌部件的腐蚀。建议针对电气化铁路各段不同的大气环境,选择不同的接触网零部件材料、或者采用相应的防腐措施。在接触网构件加工和装配过程中,建议改进加工工艺程序,避免热浸镀锌部件的二次加工或者成型;建议采用绝缘措施,以达到热浸镀锌部件与不锈钢紧固件之间的绝缘耦接,避免电偶腐蚀发生。     

镀锌钢在不同大气环境中的腐蚀行为

通过镀锌钢在全国13个大气腐蚀试验站8a的现场暴露试验,观察了镀锌钢的表面形貌,进行了表面评级,测试了腐蚀速率,并计算了碳钢与镀锌钢的腐蚀速率比值。结果表明:所有镀锌钢板均出现表面变暗的现象,在拉萨、敦煌等站其表面变化较小,在青岛、江津等站其腐蚀较为严重,表面存在一定程度的锈蚀,在万宁站其表面锈蚀最严重;在13个站点镀锌钢的腐蚀速率由大到小依次为万宁武汉青岛沈阳广州江津北京琼海西双版纳库尔勒漠河敦煌拉萨;通过计算,碳钢与镀锌钢的腐蚀速率之比为9.2~2 000.0。在实际应用中,镀锌钢在不同环境中的厚度应不同。     

Korrosionsverhalten feuerverzinkter Baustähle in überwiegend sandhaltigen Böden

Corrosion behaviour of galvanized steel in mainly sandy grounds In mainly sandy grounds with different portions of fine parts < 0,06 mm (2,5–20,4%) specimens of ungalvanized and galvanized steel were stored outside and in the laboratory. Besides the composition of the ground, the salinity and the temperature of the ground were varied too. The corrosion rate and, for ungalvanized specimens, the behaviour to pitting corrosion were determined. Furthermore the factors characterising the corrosion behaviour such as specific resistance of soil and corrosion potential were investigated continuously. The loss in weight of metal was much greater for ungalvanized than for galvanized specimens and increased for ungalvanized specimens with an increasing portion of fine parts in the ground. Additions of salt at the beginning of the tests produced an increased amount of metal wastage, but for galvanized specimens they only had an influence upon initial corrosion. The increased removals of material started since contents of 3 · 10^?3 MolCl^? + SO/kg. If salts were added to the ground after 2 years (after the formation of a surface layer), they increased the wastage of material for ungalvanized but not for galvanized specimens. Apart from ungalvanized bars in the soil with a fineness portion of 20,4%, corrosion, after an acceleration at the beginning, slowed down owing to the formation of a surface layer. Ungalvanized specimens were attacked by a strong pitting corrosion and that more in aerated than in dense and, thus, water-containing grounds. The additions of salt accelerate more an uniform corrosion of material than a pitting corrosion. As for galvanized specimens after a local removal of zinc under extreme conditions the steel base had been hardly corroded away. The parts free of zinc were protected cathodically by the still existing zinc. The corrosion of steel depends upon the temperature: by increasing the temperature from 4 to 20°C increases of corrosion up to 100% were stated. As for galvanized surfaces temperature has only a small influence upon corrosion.     

电力铁塔角钢镀锌层在NaCl介质中的腐蚀行为研究

采用Tafel直线外推法、加速腐蚀试验,研究了角钢镀锌层在NaCl溶液中的腐蚀行为,利用SEM和XRD表征角钢镀锌层的腐蚀形貌及腐蚀产物.结果表明:随着NaCl溶液温度和浓度升高,角钢镀锌层腐蚀电流密度增大;加速腐蚀试验的产物可阻碍Cl-腐蚀,使得角钢锌层的腐蚀速率随试验时间的延长而减小;锌层的氧浓差腐蚀为慢腐蚀过程,...     

镀锌层破损输电杆塔用镀锌钢在干湿交替作用下的腐蚀行为

采用自制大气腐蚀模拟试实验装置,并结合电化学阻抗及开路电位测试技术,研究了在干湿交替作用下,不同破损面积的输电杆塔用镀锌钢在NaCl和NaHSO₃腐蚀介质共同污染下的腐蚀行为。结果表明,随着破损面积以及暴露时间的增加,电极的开路电位逐渐正移,同时电极的腐蚀速率也会随着破损面积的增加而增加,不同破损面积的样品的腐蚀速率在初期随暴露时间的增加而增加,后期逐渐减小。     

Microbial corrosion of galvanized steel by a freshwater strain of sulphate reducing bacteria (Desulfovibrio sp.)

Microbially influenced corrosion of galvanized steel was investigated exposing coupons (2.0 × 2.0 cm) to culture of sulphate reducing bacteria strain Desulfovibrio sp. The coupons were exposed to the SRB culture for 4, 8, 24, 72, 96, 168, 360 and 744 h along with a control set in uninoculated medium. The results from the present study suggest that SRB were responsible for the corrosion of the galvanized steel. The corrosion rate of galvanized steel was not be correlated with the number of sessile SRB cells. Also Desulfovibrio sp. had an ability to produce EPS (Extracellular Polimeric Substances) and biodegrade the carbohydrate, that is the predominant component of the EPS produced by them. When Desulfovibrio sp. cells were in logarithmic phase, the concentration of dissolved zinc in the bulk solution was very toxic for Desulfovibrio desulfuricans.     

Outdoor atmospheric corrosion of carbon steel and weathering steel exposed to the tropical-coastal climate of Thailand

This study focuses on atmospheric corrosion of carbon steel and weathering steel exposed at two different locations with dissimilar meteorological parameters and airborne pollutants in Thailand. The samples are subjected to an outdoor atmosphere for up to 36 months at Rayong, close to the Gulf of Thailand, and Phangnga, near the Andaman Sea. Thickness loss (µm), corrosion rate (µm/year) together with corrosion product morphology and composition are systematically analyzed using X-ray diffraction and a scanning electron microscope. Corrosion resistance of the tested steels exposed at both locations is discussed based on the above-mentioned parameters and calculated corrosion kinetics. The results indicate that the total time of wetness, amount of rainfall and chloride deposition rate play an important role in corrosion behavior of the tested steels. Alloying elements, copper, chromium and nickel, are shown to improve corrosion resistance of the samples when exposed at the location with a higher chloride concentration.     

镀锌钢在东莞大气及模拟大气中的腐蚀行为

采用失重法、金相检验、扫描电镜法(SEM)、X射线衍射法(XRD)、能量色散谱法(EDS)以及电化学阻抗谱法(EIS)研究了镀锌钢在东莞大气环境和模拟大气环境中暴露不同时间后的腐蚀行为。结果显示:在东莞大气中,镀锌钢在暴露早期发生了局部腐蚀,随着暴露时间的延长,腐蚀速率先迅速降低然后逐步稳定,耐蚀性先降低后增强;腐蚀12个月后,主要腐蚀产物为ZnO和Zn4SO4(OH)6;在模拟大气环境中,镀锌钢的腐蚀速率和耐蚀性随时间的变化规律和东莞实地大气暴露试验的结果具有良好相关性。     

国产镀锌钢在不同水环境中的腐蚀行为:II反渗透水和调质水

利用开路电位测量、电化学阻抗谱测试技术,结合微观形貌观察,对比研究了国产镀锌钢板在不同反渗透水中的腐蚀行为,镀锌钢在不同进水盐度所得的反渗透水中的腐蚀失效表现出了相似的电化学特征,通过CaCl2、NaCl和NaHCO3等对反渗透水的水质进行调整,改变了镀锌钢的腐蚀失效历程,这可能与腐蚀产物膜的脱落和附着密切相关。     

Corrosion of Bare and Galvanized Mild Steel in Arabian Gulf Environment

Corrosion performance of bare and galvanized mild steel in atmospheric, soil and splash zone exposure conditions was evaluated at a Khaleej Mardumah test station (KMTS) in Jubail Industrial City (JIC) located at Arabian Gulf coast. The samples were exposed for a period of 15 months. During the exposure, the environmental conditions were periodically monitored by analysis of air, soil, groundwater, and seawater samples. The corroded mild steel and galvanized steel samples were examined by SEM, XRD and XRF to identify the corrosion products and study their surface morphology. Weight loss method was employed to determine the corrosion rates. The experimental results showed that intense temperature and humidity variations as well as high chloride and sulfate concentrations in the region result in severe corrosion of bare mild steel especially under the splash zone conditions. A comparison with the corrosion data for other parts of the world shows that atmospheric and soil environments at the selected test site are significantly corrosive to mild steel. The splash zone, on the other hand, is much more corrosive to mild and galvanized steel than the other parts of the world.     

Effect of concrete carbonation process on the passivating products of galvanized steel reinforcements

The composition of passivating products on galvanized steel reinforcement in concrete during carbonation was studied. Cube‐shaped concrete specimens were manufactured with Portland 52.5 R cement and reinforced with hot‐dip galvanized steel sheets obtained from pure Zn and Zn? Sn? Bi? Ni alloy bath. The concrete specimens were exposed to air curing for 28 days and then to the carbonation chamber. Corrosion rate and potential measurements were performed both during the curing in air and exposure in a carbonation chamber. At defined periods of time, some concrete specimens were broken and the galvanized steel sheets were submitted to XRD, SEM observations and EDX analysis. The growth of the passivation products was evaluated by integrating the diffraction peaks. XRD analysis and SEM observations show that the layer of calcium hydroxyzincate (CaHZn), formed on the galvanized sheets during the air curing, is destroyed by the concrete carbonation process. However, potential measurements indicate that the galvanized steel always remains in the passive state. X‐ray diffractometry was not able to identify the new passivating product; EDX maps suggest the presence of zinc carbonates.     

氯离子含量对黄壤土中碳钢腐蚀行为的影响

利用极化曲线技术、电化学阻抗测试技术等方法,研究了氯离子含量对黄壤土中碳钢腐蚀行为的影响。实验结果表明,氯离子对黄壤土中碳钢腐蚀影响显著。碳钢的腐蚀速率随土壤中氯离子含量的增加而增加,当氯离子的质量百分含量增加到0.90%时,腐蚀速率达到最大,然后腐蚀速率随着氯离子含量增加有所减小。碳钢在低氯含量土壤中阻抗谱表现为单容抗弧,在高氯含量土壤中为双容抗弧。     

红壤中变电站接地网金属材料的腐蚀行为分析

采用扫描电镜 (SEM)、能谱 (EDS) 和X 射线衍射 (XRD) 等技术对红壤中变电站接地网服役长达13 a的镀锌扁钢进行了形貌分析和腐蚀产物分析。结果表明,该镀锌扁钢受到严重腐蚀,腐蚀产物主要由FeOOH,Fe₃O₄和Fe₂O₃等组成,腐蚀产物分层的原因是新生成的腐蚀产物沉积在金属/腐蚀产物层界面或腐蚀产物开裂处,同时S和Cl对内层腐蚀产物具有较大的影响。Tafel测试结果表明,在腐蚀电流峰值附近,SO₄^2-与Cl^-的百分比为1∶2时,两者对镀锌Q235碳钢在该红壤中的腐蚀性影响具有等效作用。通过室内加速实验模拟镀锌Q235碳钢在该红壤中的腐蚀发现,镀锌Q235碳钢的腐蚀速率呈现先增大后减小的规律,该加速实验在未改变镀锌Q235碳钢腐蚀机理的同时具有较好的加速效果。     

Study of corrosion evolution of carbon steel exposed to an industrial atmosphere

ABSTRACT

The corrosion evolution of carbon steel exposed to an actual industrial atmosphere was investigated. The characteristics of the rust that formed on the steel were analysed by mass-loss measurement, X-ray diffraction, scanning electron microscopy and electrochemical techniques. Mass-loss results showed that the long-term corrosion kinetics of carbon steel can be divided into four stages, and that the corrosion rate varies during the different corrosion stages. This corrosion-rate fluctuation is attributed to the increase in the ambient temperature and the change in the composition of the rust layer formed on the steel surface. The reciprocal of charge transfer resistance (R_ct) can be used to represent the corrosion rate. The backward-facing specimens were found to be more suitable as the objects to investigate the corrosion evolution. The evolution of the rust layer that formed on the steel is also discussed.     

镀锌钢在红沿河大气环境中的腐蚀行为

目的研究镀锌钢在红沿河地区SO2和Cl-含量较高的大气环境中的腐蚀行为与机理。方法根据GB/T 6464—1997将制备好的试样在红沿河核电厂进行现场暴晒试验,分别暴晒4、12、18、24个月后取回试样。利用失重分析、X射线衍射(XRD)和扫描电镜(SEM)等技术,观察与分析试样暴晒后的腐蚀产物。结果镀锌钢腐蚀失重随暴晒时间的延长而线性增加;随着暴晒时间的延长,锌镀层表面形成的腐蚀产物成分变化不大,以Zn12(SO4)3Cl3(OH)15·5H2O和6Zn(OH)2·Zn SO4·4H2O为主;腐蚀产物随暴晒时间的延长逐渐增加,产物形貌略有变化,以球状和针状为主。暴晒18个月后,腐蚀产物分为双两层,内层致密,外层疏松;暴晒24个月后,腐蚀产物厚度稍有增加,疏松层向致密层转变。结论 SO2与Cl-是镀锌钢在红沿河地区的大气腐蚀过程的主要影响因子。镀锌钢表面形成的腐蚀产物对锌镀层的保护作用较差。     

Corrosion of galvanised steel under an electrolytic drop

Described here for the first time is an investigation of the local corrosion behaviour of galvanized steel using an electrolytic droplet comprising chloride and sulphate ions. The maximal height of the electrolytic layer and the diameter varied between 500-1100 μm with a total diameter between 1.47-3.35 mm, respectively. These measurements were possible by using microelectrodes as reference and counter electrodes, which could be inserted into the electrolyte droplet thus forming an electrochemical microcell. Polarization curves as well as electrochemical impedance spectroscopy plots were recorded under the electrolyte droplet configuration allowing the determination of the polarisation resistance R_p and the proportionality constant k of the Stern and Geary equation. The influence of temperature, chloride concentration, pH and the thickness of the electrolytic layer on the corrosion rate of galvanised steel were studied.     

Cerium-tannic acid passivation treatment on galvamzed steel

A novel cerium-tannic acid passivation treatment was performed on galvanized steel. The corrosion resistance of cerium-tannic passivated samples was tested by dropping test with 0.5 wt.% CuSO4 aqueous solution. The mass loss per unit area of passivated samples was measured after the corrosion in 0.5 mol/L NaCl + 0.005 mol/L H2SO4 at room temperature for 96 h. The electrochemical behaviors of cerium, tannic acid, and cerium-tannic acid passivated samples on galvanized steel in 0.5 mol/L NaCI solution were investigated by polarization curves and electrochemical impendence spectra. The corrosion equivalent circuit was established according to the impedance characteristics. The results show that cerium-tannic acid treated samples exhibit better corrosion resistance than the sole cerium or tannic acid treated samples under the same condition. The mechanism of synergistic effect for cerium-tannic acid passivation on galvanized steel was discussed.     

Corrosion of stainless steels and carbon steel by molten mixtures of commercial nitrate salts

The isothermal corrosion behavior of two stainless steels and a carbon (C) steel in mixtures of NaNO₃ and KNO₃ was evaluated to determine if the impurities found in commodity grades of alkali nitrates aggravate corrosivity as applicable to an advanced solar thermal energy system. Corrosion tests were conducted for approximately 7000 hours with Types 304 and 316 stainless steels at 570 °C and A36 C steel at 316 °C in seven mixtures of NaNO₃ and KNO₃ containing variations in impurity concentrations. Corrosion tests were also conducted in a ternary mixture of NaNO₃, KNO₃, and Ca(NO₃)₂. Corrosion rates were determined by descaled weight losses while oxidation products were examined by scanning electron microscopy (SEM), electron microprobe analysis (EPMA), and x-ray diffraction (XRD). The nitrate mixtures were periodically analyzed for changes in impurity concentrations and for soluble corrosion products. Results of these tests indicated that the short-term corrosion rates of the stainless steel specimens in many of the mixtures could be described in terms of parabolic kinetics. However, no single rate law could be assigned to the corrosion kinetics resulting from exposure in all of the mixtures. For engineering applications, corrosion rates over the entire exposure period are best described as linear with respect to time. In the binary nitrate mixtures, the annualized rates of metal loss were found to be between 6 and 15 μm/year for the stainless steel specimens at 570 °C depending on the particular mixture. Metal loss for the C steel specimens immersed in these same mixtures at 316 °C extrapolated to approximately 1–4 μm/year. SEM and XRD revealed that the complex, multiphase surface oxides formed on the stainless steel coupons were composed primarily of iron-chromium spinel, iron oxides, and sodium ferrite. Magnetite was the principal corrosion product formed on the carbon steel specimens. Overall, for the typical range of impurities in commercially available nitrate salts, corrosion rates for solar thermal energy applications remained acceptable for all of the materials examined.     

Cerium-tannic acid passivation treatment on galvanized steel

A novel cerium-tannic acid passivation treatment was performed on galvanized steel. The corrosion resistance of cerium-tannic passivated samples was tested by dropping test with 0.5 wt.% CuSO₄ aqueous solution. The mass loss per unit area of passivated samples was measured after the corrosion in 0.5 mol/L NaCl + 0.005 mol/L H₂SO₄ at room temperature for 96 h. The electrochemical behaviors of cerium, tannic acid, and cerium-tannic acid passivated samples on galvanized steel in 0.5 mol/L NaCl solution were investigated by polarization curves and electrochemical impendence spectra. The corrosion equivalent circuit was established according to the impedance characteristics. The results show that cerium-tannic acid treated samples exhibit better corrosion resistance than the sole cerium or tannic acid treated samples under the same condition. The mechanism of synergistic effect for cerium-tannic acid passivation on galvanized steel was discussed.