电阻法在钢筋腐蚀中的适用性研究

钢筋的腐蚀是混凝土结构服役过程中遇到最为常见的病害问题,为解决传统失重法要求破损检测以至于应用受到限制的问题,提出应用电阻法测定混凝土中钢筋的腐蚀。基于加速腐蚀试验,通过电阻法和失重法测定混凝土中钢筋的腐蚀,对比钢筋电阻的变化和腐蚀速率,运用假设检验对其进行显著性分析。最终得出,电阻法测定钢筋的腐蚀不仅可以反映钢筋腐蚀的结果,又能分析其腐蚀的过程,能够很好的反应钢筋的腐蚀速率,在实际工程中具有很好的适用性。     

模拟混凝土孔隙液中钢筋腐蚀行为的恒电量法监测

利用恒电量法监测了钢筋在不同ｐＨ 值的模拟混凝土孔隙液中的极化电阻、钝化膜电阻Ｒｐ、Ｒｆ 值,并与电位法监测值进行了比较,结果表明,恒电量法更加准确和更具定量性,适用于钢筋的腐蚀监测。     

混凝土中钢筋腐蚀的测定与评价方法

综述了混凝土中钢筋腐蚀的测定与评价方法,包括腐蚀面积率、失重率、断面缩减率、自然电位、线性极化电阻、交流阻抗谱(EIS)、腐蚀电流、混凝土比电阻和四极法等,介绍了各种方法的特点与应用过程中存在的问题,以及国内外的研究现状.研究认为,评价混凝土中钢筋腐蚀应选择合理的测定与评价方法,四极法可以在不破坏混凝土结构的情况下监控混凝土中钢筋锈蚀过程,是未来研究的热点之一.     

电阻探针腐蚀监测技术的研究进展

介绍了电阻探针腐蚀监测系统和监测原理,综述了当前国内外电阻探针腐蚀监测技术的研究进展,重点分析了有关电阻探针腐蚀监测系统在电阻探针、监测数据处理和监测数据传输方向的研究现状,总结了电阻探针腐蚀监测技术在大气环境、水环境和土壤环境3种不同环境下应用的研究进展,最后对电阻探针腐蚀监测技术进行了展望,以为电阻探针腐蚀监测技术的发展和应用提供新的思路和指导意义。     

亚硝酸钙对混凝土结构中钢筋氯腐蚀的缓蚀作用

以模拟环境研究钢筋混凝土结构中钢筋阻锈剂，通过圆柱形试样海水部分浸泡试验及立方试样间浸试验，测得了６个月内添加不同浓度的氯化钠及亚硝酸钙的混凝土试样中钢筋自腐蚀电位及腐蚀电流，并用线性极化方法测定了极化电阻，结果表明亚硝酸钙是一种有效的阳极型阻锈剂。     

电阻探针技术和挂片失重法腐蚀监测结果的对比分析

目前,传统的腐蚀挂片法已不能满足腐蚀行业对于数据量的需求,为此研究了电阻探针监测技术和传统的挂片失重法在武汉大气环境下腐蚀速率的相关性.结果表明:在5℃≤θ≤35℃且相对湿度RH≥60％的大气环境中,腐蚀挂片法得到的腐蚀速率是电阻探针法的1.3倍.在上述温度和湿度范围内,温度和湿度越高,腐蚀速率也就越高,两者的交互作用对腐蚀速率有正向影响.相比较腐蚀挂片法,电阻探针技术有较好的实时监测效果.     

海洋潮汐区暴露700 d带裂缝混凝土中耐蚀钢筋的锈蚀行为

裂缝是混凝土结构物承载力及耐久性降低的主要原因。本研究利用青岛小麦岛实海暴露站,将不同裂缝宽度、裂缝类型及裂缝间距的钢筋混凝土在海洋潮汐区腐蚀700 d,利用电化学阻抗谱法研究带裂缝混凝土中耐蚀钢筋的锈蚀行为,拟合获得钢筋极化阻值并通过Stern-Geary公式和法拉第定律计算出腐蚀电流密度和腐蚀速率,通过对极化阻值的线性拟合,获取钢筋的脱钝时间,分析裂缝对钢筋锈蚀的影响规律。结果表明:由于混凝土的自愈合效应,当裂缝宽度小于0. 15 mm时,钢筋的腐蚀速率不受裂缝宽度的影响;当裂缝宽度超过0. 15 mm后,随着混凝土裂缝宽度的增大,钢筋的腐蚀速率增大。与单裂缝混凝土试件相比,双裂缝混凝土中的钢筋更容易锈蚀,且裂缝间距越小,钢筋的腐蚀速率越大。在裂缝宽度相同的情况下,纵向裂缝混凝土中的钢筋比横向裂缝混凝土中的钢筋更容易锈蚀。     

含氯混凝土中钢筋宏电池腐蚀的研究

为了确定含氯混凝土中钢筋的宏电池腐蚀的特性 ,研究了钢筋腐蚀速度与混凝土电阻间的关系。在宏电池阴阳极之间串联可变电阻来模拟混凝土电阻的变化。实验结果显示钢筋腐蚀反应的自然腐蚀电位主要为阳极反应决定 ,而腐蚀反应速度为阴极反应控制。混凝土电阻对钢筋腐蚀反应速度影响很大。     

含氯混凝土中钢筋宏电池腐蚀的研究

为了确定含氯混凝土中钢筋的宏电池腐蚀的特性,研究了钢筋腐蚀速度与混凝土电阻间的关系。在宏电池阴阳极之间串联可变电阻来模拟混凝土电阻的变化。实验结果显示钢筋腐蚀反应的自然腐蚀电位主要为阳极反应决定,而腐蚀反应速度为阴极反应控制。混凝土电阻对钢筋腐蚀反应速度影响很大。     

潮差/飞溅区钢筋混凝土牺牲阳极防腐系统及远程控制监测系统的开发

本文介绍了一种钢筋混凝土牺牲阳极防腐系统,该系统由高活性锌合金牺牲阳极、导电砂浆填充料和复合材料防护套组成,可应用于潮差区和飞溅区的钢筋混凝土阴极保护,其防护效果达到相关国际标准要求。同时,本文还介绍了一种钢筋混凝土阴极保护远程控制监测系统,该系统不仅能够有效评估牺牲阳极保护效果,而且容易无损、原位地监测钢筋的极化电位、自腐蚀电位、线性极化电阻、混凝土的电阻率、氯离子浓度、钢筋的环境温度及阳极发生电流等阴极保护腐蚀参数。     

钢筋混凝土腐蚀监测技术及其应用

混凝土中的钢筋腐蚀是影响混凝土结构耐久性的主要因素.对钢筋腐蚀进行监测,是钢筋混凝土安全服役的重要保障手段之一.叙述了钢筋腐蚀监测几种常用的电化学测量和物理方法测量技术.分析了各种方法的原理及特点,介绍了各种方法技术在钢筋混凝土腐蚀监测上的应用.并对今后的发展趋势进行了展望.     

A critical discussion on rebar electrical continuity and usual interpretation thresholds in the field of half-cell potential measurements in steel reinforced concrete

Corrosion of steel in reinforced concrete structures is a recurrent problem affecting civil engineering structures and costing the world billions of dollars per year. This physical phenomenon mainly results from chloride ingress or concrete carbonation. Corrosion can be diagnosed through a nondestructive method such as half-cell potential measurements. The present paper studies this method on a reinforced concrete wall containing eighteen unconnected steel bars and subjected to chloride-induced macrocell corrosion. Three corrosion systems with different configurations of connections between the steel bars are generated, involving three different anode-to-cathode surface ratios. Then, half-cell potential variations are observed versus macrocell corrosion current. The results lead to a critical discussion regarding the physical relevance of the usual potential threshold method to detect corroding rebars in reinforced concrete structures. In addition, the experiments demonstrate that electrical continuity between reinforcing steel bars is not necessary to get meaningful information about the macrocell corrosion system. At last, the paper show that the electric field (potential gradient) relative to a macrocell corrosion system may be measured by connecting the measurement system (reference electrode?+?voltmeter) to any electrochemical system in electrolytic contact with the concrete.     

Influence of crack width,cover depth and concrete quality on corrosion of steel in HPC containing corrosion inhibiting admixtures and fly ash

In this study the influence of crack width, cover depth and concrete quality on corrosion of steel in high performance concrete was investigated. Three mixtures, one control and two more containing corrosion inhibiting admixtures, Calcium Nitrite and Disodium Tetrapropenyl Succinate, in combination with 20% fly ash replacement with respect to the cement weight were prepared. Specimens were concrete cylinders measuring 100 mm in diameter and 65 and 105 mm in length, with a 16-mm steel bar centrally placed at two concrete covers of 25 and 45 mm. Before being exposed to a simulated marine environment, the specimens were pre-cracked under a controlled splitting test with crack widths ranging from 90 to 330 μm formed perpendicularly to the reinforcing bars. During a 16-month exposure, the corrosion risk of the reinforcing bars was evaluated by half-cell corrosion potentials and the corrosion rate by linear polarization method. Also, the total integrated corrosion current was estimated. Results show that, albeit to different degrees, cracking was found to be an influencing factor in promoting corrosion of the steel in concrete with either 25 mm or 45 mm concrete cover; nevertheless, the effectiveness of the concrete cover depended greatly on the crack thickness. Results also revealed that corrosion inhibitors and fly ash were effective in delaying corrosion even in cracked concrete.     

Pitting corrosion and structural reliability of corroding RC structures: Experimental data and probabilistic analysis

A stochastic analysis is developed to assess the temporal and spatial variability of pitting corrosion on the reliability of corroding reinforced concrete (RC) structures. The structure considered herein is a singly reinforced RC beam with Y16 or Y27 reinforcing bars. Experimental data obtained from corrosion tests are used to characterise the probability distribution of pit depth. The RC beam is discretised into a series of small elements and maximum pit depths are generated for each reinforcing steel bar in each element. The loss of cross-sectional area, reduction in yield strength and reduction in flexural resistance are then inferred. The analysis considers various member spans, loading ratios, bar diameters and numbers of bars in a given cross-section, and moment diagrams. It was found that the maximum corrosion loss in a reinforcing bar conditional on beam collapse was no more than 16%. The probabilities of failure considering spatial variability of pitting corrosion were up to 200% higher than probabilities of failure obtained from a non-spatial analysis after 50 years of corrosion. This shows the importance of considering spatial variability in a structural reliability analysis for deteriorating structures, particularly for corroding RC beams in flexure.     

Shear strength of concrete beams reinforced with steel bars milled from scrap metals

The paper reports a study on the shear resistance of concrete beams reinforced with mild steel bars that are milled from scrap metal such as old vehicle parts and obsolete machinery. It has been previously reported that because the chemical compositions of carbon, sulphur and phosphorus in these reinforcing steel bars exceed the maximum allowable limits, the characteristic tensile strengths are too high and ductility too low for standard mild steel. Concrete beams reinforced with such bars to resist flexural tensile and shear stresses were tested under a two-point loading system to provide a central constant moment region and outer shear spans. Tested beams exhibited little deflection and very low ductility prior to collapse. Experimental failure loads for the beams averaged 123% of the theoretical failure load, which was generally governed by either shear or yielding of the tension steel. Shear failure was mostly initiated by diagonal tension cracks, followed by either crushing of the concrete, or splitting of the concrete over the longitudinal tensile bars near the supports. Failure of the beams was brittle and the post-cracking strain energy absorption averaged 357.9 Nm. At failure the maximum crack width in the beams ranged from 1.12 to 5.0 mm, the largest sizes forming in the diagonal shear cracks.     

Corrosion Process and Mechanisms of Corrosion‐Induced Cracks in Reinforced Concrete identified by AE Analysis

Abstract: Concrete structures could suffer from the corrosion of reinforcing steel bars (rebars) because of the penetration of chloride ions. For crack detection and damage evaluation in concrete, acoustic emission (AE) techniques have been extensively applied to concrete and concrete structures. In the corrosion process of reinforced concrete, it is demonstrated that continuous AE monitoring is available to identify the onset of corrosion and the nucleation of concrete cracking because of the expansion of corrosion products. At the latter stage, the expansion of corrosion products generates corrosion‐induced cracks in concrete. The generating mechanisms of these cracks are studied in accelerated corrosion tests of reinforced concrete beams. Kinematics of microcracks are identified by SiGMA (Simplified Green’s functions for Moment tensor Analysis) analysis of AE. It is demonstrated that AE activity at the onset of corrosion and at the nucleation of corrosion‐induced cracks is in remarkable agreement with the phenomenological model of the corrosion process in steel. Then, mechanisms of corrosion‐induced cracks are visually and quantitatively investigated by the SiGMA analysis.     

锈蚀钢筋混凝土柱的修正压-剪-弯分析模型研究

随着服役时间的增加,混凝土结构中钢筋易发生锈蚀,引起混凝土结构承载性能下降,严重影响工程结构的继续使用。该文在分析纵筋锈蚀后的屈曲效应、箍筋锈蚀后的约束效应、混凝土和钢筋材料性能劣化的基础上,建议了考虑锈蚀影响的钢筋、混凝土及锈蚀钢筋与混凝土界面粘结性能的本构模型,以锈蚀钢筋混凝土柱为研究对象,对反复荷载作用下钢筋混凝土柱的分析模型进行修正,建立了锈蚀钢筋混凝土柱压-剪-弯交互作用下极限承载力计算模型,并通过21根锈蚀混凝土柱的试验结果对建议分析模型进行了验证。研究结果表明:锈蚀钢筋混凝土柱极限承载力试验值与计算值之比的平均值为1.021,方差为0.014,建议模型极限承载力预测值与试验结果吻合较好,可用于低周反复荷载作用下锈蚀钢筋混凝土柱的承载力分析。     

Flexural behaviour of concrete slabs reinforced with steel sheet

This is a report on tests carried out on concrete slabs reinforced with bonded steel sheet, where flexural stiffness and ultimate capacity were improved versus conventional r. c. slabs. In the case of sheet metal, which has biaxial strength properties, the steel is far better utilized than in that of the uniaxial reinforcing bars, hence the slab structure is more economical. Fire- and corrosion protection is provided by a 10 mm coating of fire-shield plaster (or some other insulating agent).     

The effect of ribs on the mechanical behavior of corroded reinforcing steel bars S500s under low-cycle fatigue

An experimental study has been carried out to assess the effects of gradually accumulating corrosion damage on the low-cycle fatigue behavior of smoothed concrete reinforcing steel bars S500s. Low-cycle fatigue loading may simulate in a satisfactory way the loading applied to the reinforcement of structures during seismic actions. Profiled (ribbed) concrete reinforcing steel bars have been tested after the removal of the ribs by means of filing. The fatigue behavior of the smoothed bars is compared against that of profiled steel bars, which are widely used as concrete reinforcement. The low-cycle fatigue tests performed indicate that the presence of ribs greatly reduces the performance of the steel bars under cyclic loading. A significant increase of the number of cycles to failure, as well as of the dissipated energy, has been observed, whereas there was only a minor reduction of the load-carrying ability of the bars due to the reduction of the ribs. The results indicate that the use of non-profiled steel bars could be considered in certain areas of reinforced concrete frames, especially for structures located in seismically active areas, which suffer the most from earthquake loadings.     

Effect of steel manufacturing process and atmospheric corrosion on the corrosion-resistance of steel bars in concrete

This paper presents results of a study conducted to evaluate the effect of steel manufacturing process and the surface condition of reinforcing steel on their corrosion-resistance when embedded in concrete. Steel bars produced by water quenching and air-cooling were utilized. The corrosion-resistance of fresh bars, i.e., those that were clean and shiny, and those exposed to atmosphere and accelerated salt spray, when embedded in concrete, was evaluated. The corrosion-resistance of the clean and corroded reinforcing steel bars was assessed by measuring corrosion potentials and corrosion current density. Accelerated impressed current technique was also utilized to evaluate the corrosion-resistance of clean and corroded reinforcing steel bars in concrete. A longer time-to-initiation and lower rate of reinforcement corrosion was noted in the concrete specimens prepared with water-quenched steel bars compared to similar bars manufactured by the hot-rolling process. Similarly, the rate of reinforcement corrosion in the concrete specimens prepared with corroded steel bars, exposed to atmosphere for 12 months and salt spray, was less than that on the unexposed bars. The data developed in this study also indicate that the surface layer formed on the water-quenched steel bars, due to the cooling process, provides protection to the metal substrate as against the loose mill scale formed on the steel bars produced by the air-cooling process.