Application of electrochemical techniques for the control of cracks and steel corrosion in concrete

Electrochemical techniques are becoming increasingly popular as a means of rehabilitating deteriorated reinforced concrete. In this paper we explore the possibility of using an electrodeposition technique for repairs of land-based cracked concrete structures and investigate the effect of this technique on various concrete properties. Concrete specimens reinforced with steel rebars were used as test specimens in this study. The specimens were first precracked by exposing rebars to chloride-induced corrosion, and then immersed in a solution of zinc sulfate and subjected to a constant d.c. current. The current was applied between the reinforcing steel in the concrete and an external electrode immersed in the solution for eight weeks. The degree of crack closure, water permeability, condition of reinforcing steel, and chloride concentration were investigated in order to assess the effectiveness of this method as a potential rehabilitation technique. The results indicate that the formation of electrodeposits caused the closure of cracks and led to improvement of the concrete watertightness. In addition, the investigation shows that the application of the electrical current increases the passivity of steel in concrete.     

人工加速锈蚀钢筋混凝土构件中钢筋锈蚀率与锈蚀电流的关系研究

本文针对人工加速锈蚀钢筋混凝土构件中钢筋锈蚀率与锈蚀电流的关系展开研究.首先采用串联方式进行多根钢筋混凝土梁的人工加速锈蚀试验,并通过破型获得梁内钢筋的真实锈蚀率.其次将串联连接人工加速锈蚀电路简化为电阻串并联模式,通过比较计算钢筋内电流密度及实际电流密度来确定其合理性.最后基于试验数据进行曲线拟合工作,修正了传统的锈蚀率与锈蚀电流间关系公式,并采用其他相关试验数据加以验证,验证结果表明该修正公式是有效的.     

Comparison between surface and bulk hydrophobic treatment against corrosion of galvanized reinforcing steel in concrete

The effectiveness of bulk hydrophobic treatment against corrosion of galvanized steel reinforcement in concrete specimens with w/c = 0.45 and w/c = 0.75 was compared with that of surface treatment, even in the presence of cracks 0.5 and 1 mm wide in the concrete cover. In this case surface hydrophobic treatments were applied both before and after cracking as a preventive and a restorative method against reinforced concrete deterioration, respectively. The obtained results in terms of water absorption, electrochemical measurements, chlorides penetration, and visual observations carried out on reinforced concrete specimens during the exposure to wet–dry cycles in 10% NaCl solution showed that bulk hydrophobization is the most effective treatment in improving the corrosion resistance of galvanized steel reinforcements in concrete also in the presence of cracks. Surface hydrophobization is very effective just in the first few exposure cycles to the aggressive environment and when used as a restorative method which is able to cancel the deleterious effect of cracks only 0.5 mm wide.     

Chloride induced corrosion of reinforcing steel evaluated by concrete resistivity measurements

The chloride threshold (Cl_TH) concentration for rebar corrosion initiation has received extensive attention over the last years. The chloride threshold concentration depends on several factors involving concrete composition and quality, exposure conditions and rebar surface characteristics. As a consequence, many researchers have proposed Cl_TH ranges that take into account the relative influence of each of these many factors. On the other hand, the electrical resistivity of concrete has proven to be an effective parameter that can be used to estimate the risk of reinforcing steel corrosion, particularly when corrosion is induced by chloride attack. The present study is based on a correlation of electrochemical parameters such as corrosion potential (E_corr) and current density (i_corr) together with concrete resistivity (ρ) and chloride concentration data. A relationship between chloride threshold values for rebar corrosion initiation and resistivity values (indicative of concrete quality) is proposed. According to this correlation, when the electrical resistivity of concrete increases from 2 to 100 kΩ cm, the value of Cl_TH increases from 0.44 to 2.32% relative to the weight of cement.     

Quality of steel-concrete interface and corrosion of reinforcing steel

This article deals with the influence of steel-concrete interface defects on reinforcing steel corrosion. The defects that are analyzed in this paper relate to the gaps caused by bleeding, settlement and segregation of fresh concrete under horizontal reinforcing bars. These defects are increasing with the concrete depth below the horizontal reinforcement and depend on the bleeding capacity of concrete mixture. Various concrete mixtures including self-compacting concrete (SCC) were tested. The defects at the interface were characterized by the ultimate bond strength recorded in a pullout test and by the defect length under the reinforcement measured with a videomicroscope. The results indicate a good correlation between these two characterization methods. The corrosion was measured by the resistance of polarization and corroded surface area. The results allow us to conclude that the quality of concrete and steel-concrete interface, decreasing with height of concrete section, affects directly the corrosion rate.     

Adhesive-bonded steel/concrete composite construction

The development of a new form of roadway deck for bridges is described. This consists of a concrete core bonded to a steel soffit plate using epoxy resin adhesive. The durability of structural joints made with a number of adhesives and with steel, concrete, and aluminium adherends is being investigated. There is a marked difference in resistance to damp conditions between different grades of epoxy resin. A search for further potential structural applications continues.     

The performance of a migrating corrosion inhibitor suitable for reinforced concrete

The protection provided by a migrating corrosion inhibitor (MCI) based on an alkylaminoalcohol was tested on concrete specimens containing reinforcing steel bar (rebar) segments. Two inhibitor dosages were investigated, together with two water/cement ratios and various chloride contents. The inhibition efficiency was followed over a period of 1000 days measuring electrical and electrochemical parameters such as the corrosion potential, the corrosion current density, the electrical resistance and performing electrochemical impedance spectra. The inhibitor was able to reduce the corrosion rate only when the initial chloride content was below 0.16 wt.% (percent weight relative to cement content). The efficiency increased as the water/cement ratio increased. There was no beneficial effect when the initial chloride content was greater than 0.43 wt.%. The efficiency of the product increased when the amount of inhibitor being applied doubled.     

建筑增强用聚丙烯腈纤维的耐海水腐蚀性研究

模拟混凝土应用的海洋环境,在常温(25℃)、氯化物浓度为5610 mg/L的海水中对建筑增强用聚丙烯腈(PAN)纤维进行浸泡处理,研究建筑增强用PAN纤维的耐海水腐蚀性,并与聚对苯二甲酸乙二醇酯(PET)增强纤维和聚丙烯(PP)增强纤维进行对比。结果表明:海水浸泡50 d后,建筑增强用PAN纤维的主要吸收特征峰无明显变化,且无新的吸收特征峰出现,纤维超分子结构变化较小,晶区取向度基本保持不变,结晶度略有增加;海水浸泡50 d后,建筑增强用PAN纤维的拉伸强度为1261 MPa、降幅0.63%,初始模量为18.6 GPa、增幅8.14%,其拉伸强度与PET增强纤维相当、约为PP增强纤维的1.8倍,初始模量约是PET增强纤维的1.4倍、PP增强纤维的3.2倍;建筑增强用PAN纤维、PET增强纤维、PP增强纤维的拉伸强度耐蚀系数分别为99.4%,99.2%,100.0%,建筑增强用PAN纤维的耐海水腐蚀性介于PP增强纤维和PET增强纤维之间,但其在海水中环境中具有优异的模量保持优势,可以更好地提高混凝土在海水环境中的耐受力。     

混凝土劣化的检测与修复

介绍了混凝土劣化检测和修复的方法,研究表明:钢筋锈蚀、冻融循环、碱骨料反应和酸碱侵蚀是造成混凝土劣化的四个主要原因;现代化技术能够准确检测混凝土裂缝和钢筋锈蚀等劣化问题,主要非破损检测方法有:打击法、超声法、放射法、红外分析、瑞利波频谱、雷达和抗渗性检测等;混凝土劣化的修复要针对其劣化的原因来开展,主要有钢筋锈蚀修复、裂缝修复、剥落或蜂窝麻面修复、渗漏修复、补强几个方面。     

Effective monitoring of corrosion in reinforcing steel in concrete constructions by a multifunctional sensor

A novel multifunctional sensor is developed for in situ and non-destructive monitoring of the corrosion current and open circuit potential of reinforcing steel, as well as the pH and Cl⁻ concentration of concrete. The pH and Cl⁻ sensors show good responses to the pH and Cl⁻ concentration of concrete pore solutions, respectively, and are able to monitor both the carbonization process of concrete and the ingress of Cl⁻ in concrete. Combined with measurements of the corrosion potential and corrosion current density, as well as the EIS spectra of reinforcing steel in concrete, this study demonstrates that the pH and the Cl⁻ concentration of concrete are two of the most crucial factors that determine the corrosion of reinforcing steel in concrete. The corrosion tendency and corrosion rate of reinforcing steel largely depend on the chemical environment in the concrete. The multifunctional sensor is a powerful tool for in situ monitoring corrosion of steel in concrete, and provides accurate details of the chemical condition of the concrete pore solution and the corrosion status of the reinforcing steel in concrete. These are essential for corrosion predictions and service life evaluations of concrete constructions.     

Monitoring of steel corrosion in concrete by electrode arrays and electrical resistance probes

In the present work two relatively new methods were implemented, in order to follow exactly the time and spatial evolution of steel corrosion in concrete. Measuring with a coupled electrode array is by some means the advancement of electrochemical noise (EN) with electrically connected micro-electrodes, which are spatially arranged, the assessment of anodic and cathodic currents distribution in time is possible. An electrical resistance (ER) probe can provide general corrosion rate, which is calculated from the thickness reduction; however, its response to localize corrosion is limited. The measurements were performed in concrete specimens, which were exposed to periodic wetting and drying cycles. The results of both used methods were compared and related to the conditions of the micro-electrodes and the ER probes after the test was finished. It was found that micro-electrode arrays can monitor the time and spatial evolution of steel corrosion in concrete. The measured currents reliable indicate the temporal anodic and cathodic activities of individual electrodes, and the assessment of general corrosion rates is also possible. Two characteristic fluctuations of the measured currents from the micro-electrode arrays were defined: slower fluctuations and shorter transients. It is believed that the slower fluctuations were generated by rather general corrosion of the electrodes, whereas the shorter transients were very probably generated by the initiation of pits. In accordance with the results of our previous study, it was confirmed that electrical resistance probes (ER) are able to measure reliably the cumulative corrosion damage, as well as the average general corrosion rate. The general corrosion rates obtained by using ER probes were generally slightly higher than those estimated from the measured currents. It should be mentioned that due to the relatively short duration of the experiments, the reliability of the methods for long-term practical applications still needs to be assessed.     

Macrocell and microcell corrosion of steel in ordinary Portland cement and high performance concretes

Microcell corrosion is the term given to the situation where active corrosion and the corresponding cathodic half-cell reaction take place at adjacent parts of the same metal. Macrocell corrosion can occur when the actively corroding bar is coupled to another bar which is passive, either because of its different composition or because of different environment. The present study was undertaken to determine the influence of concrete type and properties on the relative microcell and macrocell corrosion rates. The samples were monitored for more than 3 years and the results confirm that microcell corrosion is the major mechanism in corrosion of steel reinforcing bars in concrete. Furthermore, results show that, for high performance concrete, the difference between microcell and macrocell corrosion is far more significant than for ordinary Portland cement concrete because of its high resistance to ionic flow.     

Tests of epoxy-glued joints for a segmental precast bridge deck

Tests on epoxy glue carried out on site in connection with the construction of a new precast prestressed motorway bridge are described. The object of the tests was to determine the structural strength of the resultant glued joints and to examine the curing characteristics of the glue under normal site conditions. The tests showed that, provided suitable precautions are taken, no particular restrictions are necessary upon allowable stresses for post-tensioned glued segmental concrete sections as compared with normal monolithic concrete.     

Effects of cathodic prevention on the chloride threshold for steel corrosion in concrete

This paper presents the results of long-term experimental tests aimed at studying the effects of cathodic prevention on the critical chloride threshold for the onset of pitting corrosion on steel bars in concrete. Cathodic prevention is applied when the structure is new and rebars are still passive being in contact with alkaline and chloride-free concrete. The results obtained showed that even very low values of current densities can increase the critical chloride threshold and, therefore, contribute to increase the service life of reinforced concrete structures in chloride-bearing environments.     

桥梁钢结构防腐蚀涂层配套和涂层使用寿命

介绍了桥梁钢结构防腐涂层设计的相关依据:ISO12944-5:2007、BS EN ISO14713:1999和JT/T722-2008。从防腐方法的选择、钢结构设计、涂层配套方案及膜厚确定、涂装管理、涂装设计以及完善的涂层维护计划的建立等方面对影响桥梁钢结构防腐效果的因素进行了探讨。     

局部锈蚀对钢筋混凝土梁承载性能的影响

局部锈蚀钢筋混凝土构件的承载性能及破坏形态与均匀锈蚀构件相比有很大差异,本文采用数值模拟方法对钢筋混凝土梁在跨中锈蚀、端部锈蚀、单侧锈蚀等情况下的受弯性能展开研究.研究结果表明:跨中锈蚀导致的粘结力损失对于混凝土梁承载力并无较大影响,但是会降低锈蚀构件的抗弯刚度;两端锈蚀导致的粘结力损失会严重影响钢筋在混凝土中的锚固效果,当锈蚀率较大时会导致锚固失效,使结构材料远未达到屈服强度构件就不能继续承担荷载;单侧锈蚀的钢筋混凝土梁,当锈蚀段在距离加载点附近时,且位于粘结应力较大值区段的起始位置处,对钢筋混凝土梁的承载性能影响最大.     

Influence of heat treatment on the corrosion of high speed steel

The corrosion behaviour of M2 high speed steel, as-received as well as heat-treated under different conditions, has been studied in 0.1 M KCl aqueous solution by corrosion potential measurements, Tafel curves and electrochemical impedance. Heat treatment leads to an increase of the corrosion resistance of high speed steel; the higher the tempering temperature after quenching, the higher the corrosion resistance of the steel. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy were also used to further understand the corrosion behaviour of the different samples. Based on these analyses, the microstructure of the different samples was correlated with their corrosion properties.     

跨海大桥钢结构防腐涂料设计方案

介绍了跨海大桥钢结构防护涂层(包括防锈底漆、中间漆和面漆)的选择标准、原则以及主桥钢箱梁热喷涂防腐蚀涂层体系和热喷涂锌、铝涂层钢铁防护标准.通过实例说明了跨海大桥钢箱梁防腐涂料体系设计方案及其涂装注意事项.论述了钢丝主缆涂装工艺及钢质护栏内、外表面防腐涂装方案.     

Study on the corrosion behavior of reinforcing steel in simulated concrete pore solutions using in situ Raman spectroscopy assisted by electrochemical techniques

In situ Raman spectroscopy, electrochemical impedance spectroscopy (EIS) and polarization curves were used to study the corrosion behavior of reinforcing steel in simulated concrete pore (SCP) solutions (saturated Ca(OH)₂ solutions). Results indicated that the reinforcing steel remained passive in chloride-free SCP solutions. However, the anodic polarization curve of the steel did not exhibit a stable passive region in the SCP solution with 0.5 M NaCl, the corrosion current density exceeded 0.1 μA cm⁻², the steel surface was unstable with chloride attack and localized corrosion appeared on it with FeCO₃ and Fe₂O₃ as the main corrosion products.     

Corrosion behavior of reinforcing steel in simulated concrete pore solutions: A scanning micro-reference electrode study

The scanning micro-reference electrode (SMRE) technique was used to study the corrosion behavior of reinforcing steel in simulated concrete pore (SCP) solutions with different pH values. The early stage as well as the propagation of the localized corrosion of reinforcing steel in different solutions was explored. The results indicated that the potential distribution on the reinforcing steel surface changed in homeostasis and the steel remained passive in the pure simulated concrete pore solution. The solution pH had a significant effect on the localized corrosion of reinforcing steel, and the critical pH value for localized corrosion of reinforcing steel in SCP solutions was between 11.46 and 11.31.