Utilizing Arghel extract as corrosion inhibitor for reinforced steel in concrete

Inhibition of the corrosion of reinforced steel in concrete in 0.5 M NaCl by Arghel extract has been studied employing different electrochemical techniques in conjunction with optical images photo. Potential‐time measurements showed that introducing of Arghel extract into concrete shifts the potential of reinforced steel to more positive values. Potentiodynamic polarization curves measurements manifested that Arghel extract acts as anodic type inhibitor. Nyquist plots were characterized by a distinct charge transfer and diffusion components. A proposed equivalent circuit was used to analyze the impedance spectra of reinforced steel in concrete in 0.5 M NaCl. Optical images for the cracked lollipops samples of the reinforced steel in concrete that is immersed in 0.5 M NaCl for 18 months showed no corrosion attack even in the presence of a low concentration of Arghel which is in good agreement with the results obtained from the electrochemical techniques.     

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.     

Corrosion and Corrosion Inhibition of Reinforcing Steel: II. Embedded In Concrete

Abstract

Reinforcing steel, whether embedded in Portland concrete or Portland cement-blast furnace slag concrete and mixed with distilled or tap water, becomes passivated. On the other hand, when the concrete is mixed with sea water, the steel corrodes severely, and when Helwan mineral water is used for mixing, a borderline condition is obtained. Portland cement-blast furnace slag concrete had poorer corrosion resistance compared with ordinary Portland cement concrete.

Steel passivity is not impaired when Portland cement concrete or Portland cement-blast furnace slag concrete is admixed with up to 8% of sulphates. However, when cement extract is used, the passivity is impaired when as little as 0·2% of sodium sulphate is added.

Additions of some anodic inhibitors such as benzoate, chromate, nitrite, phosphate and stearate to a corrosive concrete medium are efficient in preventing the corrosion of reinforcing steel. The critical concentration for inhibition is higher in the case of Portland cement-blast furnace slag concrete than that of Portland cement concrete. Coating the steel with Portland cement slurry alone or Portland cement slurry containing inhibitors improves the corrosion resistance of steel to some extent but does not inhibit the corrosion in strong attacking media.     

Microstructural properties of the bulk matrix and the steel/cement paste interface in reinforced concrete,maintained in conditions of corrosion and cathodic protection

Although rarely considered, especially within the investigation of steel corrosion phenomena or electrochemical protection techniques in reinforced concrete structures, the concrete bulk matrix has a significant contribution in the global performance of the system “reinforced concrete.” This is especially the case when chloride‐induced corrosion or electrical current flow [as within impressed current cathodic protection (CP)] are involved. In the latter cases, the concrete bulk matrix undergoes significant alterations in chemical composition, electrical properties, and microstructures, thus influencing the overall performance of the system. This work reports on the microstructural investigation of the bulk concrete matrix and the steel/cement paste interface in reinforced concrete, previously subjected to corrosion and CP for 460 days. The emphasis hereby is to evaluate the altered structural properties, i.e., porosity, pore size, permeability of the bulk cement matrix, and the steel/cement paste interface (translated to bond strength) as a result of chloride‐induced corrosion and two types of CP (conventional and pulse), compared to control (non‐corroding, non‐protected) conditions. The research revealed a major contribution and close dependence of all microlevel interfaces on the global performance of reinforced concrete. The electrical current flow (as in CP applications) was found to bring about unfavorable modifications to the material structure, both in the bulk matrix (reducing porosity) and at the steel/cement paste interface (enlarging interfacial gaps). The derived microstructural parameters show that the conventional CP leads to a higher level of structural heterogeneity, whereas the pulse CP exerts minimal or no effects, maintaining the material properties close to the reference (control) conditions, the underlying mechanism being a more homogeneous material microstructure.     

钢筋阻锈剂的阻锈机理及性能评价的研究进展

钢筋腐蚀是引起钢筋混凝土构筑物提前失效的主要因素,应用钢筋阻锈剂是主要的防腐蚀措施之一。重点介绍了海洋环境中,氯盐的侵蚀机理和阻锈剂的作用机理;讨论了阻锈剂的性能评价方法和应用现状;指出高效且环境友好复合型阻锈剂的合成是今后研究的主要方向,这对于提高我国钢筋混凝土结构耐久性具有重要意义。     

Initiation of chloride‐induced corrosion of steel in concrete: role of the interfacial zone

This paper provides a brief review of research aimed at characterising the steel–concrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH ～12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride‐induced corrosion because it counters the generation of ‘anodic acidity’ that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full‐scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non‐traditional cements.     

提高海洋环境钢筋混凝土构筑物耐久性措施综述

针对海洋环境钢筋混凝土构筑物过早腐蚀破坏,从混凝土防护、钢筋保护、包覆隔离保护、施工技术四个方面综述目前国内外对海洋环境下保护钢筋减少腐蚀、延长构筑物服役寿命所采取的技术措施,内容涉及:高性能混凝土、抗海水腐蚀水泥、阻锈剂、混凝土表面涂层、提高保护层厚度、钢筋涂层、耐腐筋、电化学保护、纤维玻璃钢或钢护筒包覆隔离、预防早期开裂、透水模板。重点讨论各措施的基本原理、特点、主要缺点和发展方向及工程应用。其中海工高性能混凝土是最经济、最基本和不可替代的,其他作为高性能混凝土基本措施的有效补充。     

The study of the La(NO;3)3 inhibition on X70 pipeline steel in 3.0(wt.%) NaCl solution

Lanthanum nitrate has been investigated as corrosion inhibitor of X70 pipeline steel in 3.0 (wt.%) NaCl solution using electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in conjunction with scanning electron microscopy (SEM) and energy dispersive X‐ray detector (EDX) techniques. The results showed that La(NO₃)₃ belonged to the film‐formed mixed inhibitors, which can form a compact network over the whole surface of X70 pipeline steel. The inhibition effect of La(NO₃)₃ on X70 steel reinforced with the increase of the concentration itself. The EDX analysis showed that lanthanum ions were found to participate in the network film formed on the sample surface.     

Corrosion of steel reinforcement in structural concrete with carbon material addition

Different types of carbonaceous materials have been added to concrete mixes and their effect on the corrosion of embedded steel has been studied. Using a constant water/cement ratio of 0.42 and different amounts of carbonaceous materials and different curing periods the evolution of the corrosion process in the embedded reinforced bars has been determined. The addition of small quantities of carbonaceous materials to the mixture produces a reduction of the concrete permeability. Tests demonstrate that a decrease of the corrosion level occurs when the content ratio of carbon material addition is increased.     

Chloride threshold for rebar corrosion in concrete with addition of silica fume

The effect of silica fume on the chloride threshold for the initiation of pitting corrosion of steel in concrete was investigated. Laboratory tests were carried out in concrete specimens made with ordinary Portland cement and with 10% of silica fume. Chloride contents up to 2% by mass of cement were added to the mixes, in order to investigate the corrosion rate of embedded bars made of both strengthened and mild steel. A lower chloride threshold was observed in the bars which were embedded in concrete with silica fume compared to those embedded in concrete made of Portland cement.     

酸性气氛下钢筋混凝土结构腐蚀行为及其机理

对工业酸性气氛环境下经过10年使用的工厂钢筋混凝土采样,用EDS、XRD和SEM,以及力学性能测试等手段观测了钢筋的腐蚀产物成分和基体成分、混凝土的主要化学组成、微观形貌结构及钢筋的力学性能;另外,还定量分析了钢筋混凝土所处的大气环境中主要腐蚀性气体的含量进行了定量分析.结果表明,含S的酸性气体在箍筋表面的吸附与沉积是钢筋混凝土遭受破坏的主要原因,钢筋腐蚀的发生与C l-诱发的点蚀不同;大量酸性含S及CO2的气体导致混凝土的水泥水化产物和其微观结构发生了变化,特别是含S气体的存在对钢筋混凝土的中性化起重要作用.     

Impedance spectroscopy: An efficient tool to determine the non‐steady‐state chloride diffusion coefficient in building materials

One of the most important problems of reinforced steel concrete in marine environments is the corrosion of the reinforcing bars. Most of the times, this corrosion is a consequence of the local destruction of the passive layer formed on the surface of the embedded steel, due to the arrival of chlorides present in the environment. Many efforts have been made to determine the chloride diffusion coefficient in concrete structures, both using natural diffusion methods, and accelerated migration methods. This coefficient determines the velocity of ingress of chlorides, and as a consequence the life time of the structures. In this work it is presented the possibility of using the technique of impedance spectroscopy, that is, very simple to use and requires no chemical or conductivity measurement, to determine the value of the non‐steady‐state diffusion coefficient. This technique, together with the equivalent circuits proposed for the interpretation of the measurements, allows the determination of the chloride saturation of a concrete or mortar sample. Pores of the material that are initially filled with water have high resistivity, and as the chlorides penetrate into the sample the value of the resistivity decreases. This diminution can be determined in situ, and permits the calculation of the diffusion coefficient saving experimental time and efforts. The results have been obtained both with concrete and mortar samples, and using different cement types.     

Einfluß einer Feuerverzinkung und PVC-Beschichtung von Bewehrungsstählen und von Inhibitoren auf die Korrosion von Stahl in gerissenem Beton

Influence of galvanizing and PVC-coating of reinforcing steels and of inhibitors on steel corrosion in cracked concrete Cracked concrete beams of concrete quality B15 and B35 with carbonized cracks were exposed in artificial seawater, under frost and deicing salt conditions and in industrial climate. The reinforcement was composed of black steel, galvanized and PVC-coated steel. For the purpose of additional protection the concrete was partly mixed with an inhibitor Ca(NO₂)₂. The concrete cover was 1,5 till 5,0 cm. It was found that the inhibitor protects satisfactorily only in the case of the higher concrete quality, cover 1,5 cm and not to high crack width. A protective effect of galvanizing is given by not to high chloride contents (< 1,5% relative to cement) and crack widths. The chosen PVC-coating failed because of chemical instability in the alcaline medium 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.     

Anodic polarisation measurements of corrosion and corrosion inhibition of Steel in concrete

Abstract

Anodic polarisation experiments were carried out on steel in concrete. The effects of surface treatment of the steel, medium of curing, as well as durations of curing were investigated.

Corrosion of steel in concrete due to the presence of the corroding chloride ions, either added to the mixing water or diffusing from the external attacking medium, was also investigated. The chloride ions when present in the mixing water are more effective in destroying the passivation of steel than when present in the outside medium. In the former case a minimum concentration of 1 % is required for this action, while in the latter case 4% is required.

Anodic corrosion inhibitors like nitrite, chromate, phosphate, benzoate and silicate were tried in order to suppress the action of the corrodent. The minimum concentration required of the inhibitor to stifle the corrosion is generally lower in the case when it is added to the mixing water of concrete. Possible mechanisms of corrosion and corrosion inhibition are discussed in the light of the current views on both processes.     

三峡地区材料33年土壤腐蚀行为研究

综合分析钢铁、水泥制品、塑料等四类材料在三峡地区埋设33年的土壤腐蚀数据、总结了材料在三峡土壤中的腐蚀规律,讨论了三峡地区土壤的腐蚀性,提出了选材与防护建议     

Long‐time behavior of non‐galvanized and galvanized steels for geotechnical stabilization applications

The contribution is dedicated to the durability of geotechnical stabilization applications. The long‐term corrosion behavior of unprotected and galvanized thread‐bars for micro‐piles and nails in different soils is described. The bars in the ground are embedded in an up to 20 mm thick cement mortar, which may be cracked and locally destructed. First, the corrosion‐affecting parameters of the steel corrosion in the ground are described and soil classes are defined. Furthermore, an estimation of the long‐term (up to 50 years) corrosion behavior was assessed on the base of information from the literature. Here the corrosion of the thread‐bar in direct contact with the soil was in the center of interest. The corrosion protection of the cement mortar cover was not taken into consideration, in order to be on the safe side. On the other hand, a macrocell‐corrosion of the thread‐bars cannot be completely excluded, if the cement mortar casing exhibits defects and constructional and environmental corrosive conditions in the ground are fulfilled. Two cases are discussed: ? element formation between sections along the thread‐bar, ? element formation between the thread‐bar and other reinforced concrete parts.     

A study of organic substances as inhibitors for chloride-induced corrosion in concrete

Chloride-induced corrosion of carbon steel reinforcement is the most important cause of premature failure on reinforced concrete structures. Among available methods, corrosion inhibitors offer a simple and cost effective prevention technique, primarily to prevent and stop chloride-induced corrosion. Nevertheless, performance of commercial inhibitors is only partially satisfactory. This paper deals with a basic study on the inhibitive action of organic substances toward chloride-induced corrosion on carbon steel rebar in alkaline environment. The effect of aminic and carboxylic groups was investigated through electrochemical potentiodynamic polarisation tests in simulating concrete pore solution in the presence of chlorides, to ascertain inhibitor effectiveness to increase pitting potential. Results are discussed taking into account the most likely mechanism of inhibition, in relation to the functional group of tested organic compounds.     

Electrochemical rehabilitation methods for reinforced concrete structures: advantages and pitfalls

Abstract

There are still many unresolved issues concerning the efficiency of electrochemical realkalisation and electrochemical chloride removal as electrochemical rehabilitation methods for corroding reinforced concrete structures. The present paper seeks to answer a number of questions which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic communities, despite the vast amount of work that has been devoted to research on corrosion in concrete embedded steel, such as whether corrosion can be stopped once it has started, whether corroded reinforced concrete structures can be repassivated, and whether it is sufficient to remove the sources of corrosion in order to stop rusting. A discussion is conducted on the relationship between the prerusting grade of rebars and the possibility of their repassivation; on whether electrochemical rehabilitation methods treatments are efficient, and if so, when and on whether a simple potential measurement can determine the passive or active state of a rebar. For this purpose an analysis is made, using electrochemical, gravimetric and metallographic techniques, of the response of clean and previously corroded steel electrodes in a Ca(OH)₂ saturated solution with and without a sodium nitrite corrosion inhibitor and in cement mortar. The effectiveness of electrochemical realkalisation and electrochemical chloride removal for repassivating prerusted steel in concrete is found to depend heavily on the prerusting grade.     

硫脲-二乙烯三胺缩聚物对混凝土中钢筋的缓蚀作用

用动电位极化曲线及电化学阻抗谱研究了硫脲－二乙烯三胺缩聚物在浊凝土孔隙模拟液及混凝土中对钢筋腐蚀的抑制作用。结果表明它是一种混合型缓蚀风筋的点蚀有较好的抑制作用。在模拟液中添加１％的该缓蚀剂就可以使对氯离子的容忍度从０．０２ｍｏｌ／Ｌ提高到０．１ｍｏｌ／Ｌ。它与ＮａＮｏ３有交好的协同作用。它妈能吸附于钢筋表面,又能提高混凝土密实程度,减缓腐蚀介质向混凝土内的渗透。能谱分析的结果表明它能够富集于钢筋