Seismic strengthening of reinforced concrete columns damaged by rebar corrosion using combined CFRP and steel jacket

In order to study the effectiveness of combined carbon fiber-reinforced polymer （CFRP） sheets and steel jacket in strengthening the seismic performance of corrosion-damaged reinforced concrete （RC） columns, twelve reinforced concrete columns are tested under combined lateral cyclic displacement excursions and constant axial load. The variables studied in this program include effects of corrosion degree of the rebars, level of axial load, the amount of CFRP sheets and steel jacket. The results indicate that the combined CFRP and steel jacket retrofitting technique is effective in improving load-carrying, ductility and energy absorption capacity of the columns. Compared with the corrosion-damaged RC column, the lateral load and the ductility factor of many strengthened columns increase more than 90% and 100%, respectively. The formulae for the calculation of the yielding load, the maximum lateral load and the displacement ductility factor of the strengthened columns under combined constant axial load and cyclically increasing lateral loading are developed. The test results are also compared with the results obtained from the proposed formulae. A good agreement between calculated values and experimental results is observed.

Probabilistic Lifetime Assessment of Marine Reinforced Concrete with Steel Corrosion and Cover Cracking

In order to study the durability behavior of marine reinforced concrete structure suffering from chloride attack, the structural service life is assumed to be divided into three critical stages, which can be characterized by steel corrosion and cover cracking. For each stage, a calculated model used to predict the lifetime is developed. Based on the definition of durability limit state, a probabilistic lifetime model and its time-dependent reliability analytical method are proposed considering the random natures of influencing factors. Then, the probabilistic lifetime prediction models are applied to a bridge pier located in the Hangzhou Bay with Monte Carlo simulation. It is found that the time to corrosion initiation to follows a lognormal distribution, while that the time from corrosion initiation to cover cracking t~ and the time for crack to develop from hairline crack to a limit crack width t2 can be described by Weibull distributions. With the permitted failure probability of 5.0%, it is also observed that the structural durability lifetime mainly depends on the durability life to and that the percentage of participation of the life to to the total service life grows from 61.5% to 83.6% when the cover thickness increases from 40 mm to 80 mm. Therefore, for any part of the marine RC bridge, the lifetime predictions and maintenance efforts should also be directed toward controlling the stage of corrosion initiation induced by chloride ion.

The Effects of Degradation Phenomena of the Steel-Concrete Interface in Reinforced Concrete Structures

Reinforced concrete (RC) constructions are the innovation of sustainable constructions replacing masonry constructions. Despite this, the use of concrete and steel to improve the performance of structural members in service is a recurring problem due to the immediate or overtime appearance of cracks. The objective of this work was therefore to assess the damage phenomena of the steel-concrete interface in order to assess the performance of an RC structure. Samples of approximately 30 cm of reinforcement attacked by rust were taken from broken reinforced concrete columns and beams in order to determine the impact of corrosion on high adhesion steel (HA) and therefore on its ability to resist. The experimental results have shown that the corrosion degradation rates of reinforcing bars of different diameters increase as the diameter of the reinforcing bars decreases: 5% for HA12;23.75% for HA8 and 50% for HA6. Using the approach proposed by Mangat and Elgalf on the bearing capacity as a function of the progress of the corrosion phenomenon, these rates made it possible to assess the new fracture limits of corroded HA steels. For HA6 respectively HA8 and HA12, their initial limit resistances will decrease by 4/4, 3/4 and 1/4. Based on the results of this study and in order to guarantee their durability, an RC structure can be dimensioned by taking into account the effects of reinforcement corrosion.

Influence of mill scale and rust layer on the corrosion resistance of low-alloy steel in simulated concrete pore solution

Electrochemical impedance spectroscopy, cyclic potentiodynamic polarization measurements, and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy were used to investigate the influence of mill scale and rust layer on the passivation capability and chloride-induced corrosion behaviors of conventional low-carbon（LC） steel and low-alloy（LA） steel in simulated concrete pore solution. The results show that mill scale exerts different influences on the corrosion resistance of both steels at various electrochemical stages. We propose that the high long-term corrosion resistance of LA steel is mainly achieved through the synergistic effect of a gradually formed compact, adherent and well-distributed Cr-enriched inner rust layer and the physical barrier protection effect of mill scale.

Research on Flexural Behavior of Coral Aggregate Reinforced Concrete Beams

Through the flexural behavior test of coral aggregate reinforced concrete beams(CARCB) and ordinary Portland reinforced concrete beams(OPRCB), and based on the parameters of concrete types, concrete strength grades and reinforcement ratios, the crack development, failure mode, midspan deflection and flexural capacity were studied, the relationships of bending moment-midspan deflection, load-longitudinal tensile reinforcement strain, load-maximum crack width were established, and a calculation model for the flexural capacity of CARCB was suggested. The results showed that with the increase in the reinforcement ratio and concrete strength grade, the crack bending moment(Mcr)and ultimate bending moment(Mu) of CARCB gradually increased. The characteristics of CARCB and OPRCB are basically the same. Furthermore, through increasing the concrete strength grade and reinforcement ratio, Mcr/Mu could be increased to delay the cracking of CARCB. As the load increased, crack width(w) would also increase. At the beginning of the loading, w increased slowly. And then it increased rapidly when the load reached to the ultimate load, which then led to beam failure. Meanwhile, with a comprehensive consideration of the effects of steel corrosion on the loss of steel section and the decrease of steel yield strength, a more reasonable calculation model for the flexural capacity of CARCB was proposed.

Utilization of waste vehicle tires in concrete and its effect on the corrosion behavior of reinforcing steels

The mechanical and physical properties of concrete specimens obtained from replacing natural coarse aggregate with waste vehi- cle rubber tires at levels of 2vol%, 5vol%, 7vol%, and 10vol% were studied, and the corrosion behavior of reinforcing steels was investigated in these specimens. Corrosion rates were determined by measuring the galvanic current between steel-reinforced concrete specimens both with and without chloride addition. The change in electrode potential of reinforcing steels in these concrete specimens was measured daily for a period of 60 d in accordance with the testing method in ASTM C876. The results show that the use of waste vehicle tires in concrete instead of coarse aggregate decreases the mechanical strength of the specimens, and increases the corrosion rates of the reinforcing steels embedded in the concretes.

Finite element model of reinforcement corrosion in concrete

A nonlinear finite element model （FEM） of the corrosion of steel reinforcement in concrete has been successfully developed on the basis of mathematical analysis of the electrochemical process of steel corrosion in concrete. The influences of the area ratio and the Tafel constants of the anode and cathode on the potential and corrosion current density have been examined with the model. It has been found that the finite element calculation is more suitable for assessing the corrosion condition of steel reinforcement than ordinary electrochemical techniques due to the fact that FEM can obtain the distributions of potential and corrosion current density on the steel surface. In addition, the local corrosion of steel reinforcement in concrete is strengthened with the decrease of both the area ratio and the Tafel constants. These results provide valuable information to the researchers who investigate steel corrosion.

Characterization of the Reinforcing Steel Corrosion by Potentialdynamic Scan Approach

Reinforcement corrosion is the major cause of damage and early failure of reinforced concrete structures worldwide with subsequent enormous costs for maintenance, restoration and replacement. Many methods used today for assessment of reinforcement corrosion are based on electrochemical techniques that determine the free corrosion potential or polarization resistance. Most of these methods always consider the B value in Stern-Geary equation as constant. However, B changes with different condition. In this paper, potentialdynamic method is used to characterize the corrosion of reinforcing steel. The corrosion rate of Q235 carbon steel is measured with concrete environment. B is calculated real-time. By this way, the error of reinforcement corrosion rate is minimized.

Durability of Reinforced Concrete Beams under Simultaneous Flexural Load in Corrosive Environment

The deterioration of concrete over time is the result of various mechanical, physical, chemical and biological processes, with the corrosion of reinforcement being the most serious problem of durability of reinforced concrete structures. Over the last 50 years, a tremendous effort has been spent by the international scientific community with laboratory research and experimental field studies in order to increase the resistance of concrete over corrosion. This paper presents an experimental study of the corrosion behaviour of reinforced concrete beams with simultaneous sustained flexural loading. For this purpose, 40 reinforced concrete beams of 5 different compositions were constructed and exposed in simulated harmful environmental conditions in 3 different stress ratios for a total period of 42 months. Their behavior against corrosion was determined via regular measurements of the electrical resistance of concrete (according to ASTM G57) and the corrosion potential of the steel-reinforced bars with the use of copper sulphate (CSE) as reference electrode (according to ASTM C876). A theoretical calculation of the corrosion rate was conducted based on the electrochemical measurements of the beams. The results indicate that the corrosion potential of steel decreased in time and more rapidly after the initiation of the corrosion process;the electrical resistance firstly increased, remained stable for a short period and then decreased with the corrosion development, as expected. An inversely proportional relationship of the water/cement ratio of a composition with its corrosion behaviour as well as an analogous relationship between the cement content of a composition and its corrosion behaviour was observed. Also, the corrosion rate of steel is increased gradually with increasing load.

Effect of organic silicon quaternary ammonium salts on mitigating corrosion of reinforced steel induced by SRB in mild alkaline simulated concrete pore solution

The corrosion damage of 20 SiMn steel by sulphate-reducing bacteria(SRB)and the mitigation effect of organic silicon quaternary ammonium salt(OSA)were studied in sterilized mild alkaline simulated concrete pore solution(STR)with different additions of SRB and OSA at pH 9.35 for 28 days.Uniform corrosion occurs in STR medium while slight localized corrosion is observed in STR+OSA medium,and localized pitting corrosion occurs in STR+SRB and STR+SRB+OSA media.The largest pit depth reduces from 36.70μm in STR+SRB medium to 3.31μm in STR+SRB+OSA medium due to the mitigation effect of OSA.The corrosion rate reflected by weight loss and electrochemical impedance spectroscopy(EIS)results presents the order of STR<STR+OSA<STR+SRB+OSA<STR+SRB,which also proves that the presence of SRB can accelerate corrosion in a carbonated medium.However,OSA as an efficient bacteriostatic agent can reduce the excessive growth of SRB and thus reduce corrosion.

Corrosion Behaviour and Chloride Attack of Reinforcing Steel in Presence of Concrete Admixtures

Corrosion and electrochemical behaviour of reinforcing steel embedded in cement pastes with and without concrete admixtures used in Egypt to modify concrete properties have been studied. The influence of the admixtures on the corrosion resistance of the steel against chloride attack has been studied by using impressed current and impressed voltage techniques. The results indicate that the type and concentration of the used admixture have an important effect on the extent of chloride induced corrosion of the steel. The mechanism of corrosion of steel due to chloride attack was discussed. (Edited author abstract) 16 Refs.

A State-of-the-Art Review of Electrochemical Chloride Extraction for Concrete Structures

Electrochemical chloride extraction is a promising technique for the rehabilitation of concrete structures under chloride induced corrosion. This study consists of an extensive literature review of this treatment including application cases. It is found that the rate of chlorides removed is affected by the total charge passed, whereas increasing charge in a range between 1500 to 2000 Ah/m2 increases the amount of chlorides removed and this can be more effective by increasing current density instead of duration of treatment. Bound chlorides are extracted during treatment and, water works better than Ca(OH)2 as an electrolyte, possibly due to modifications on the concrete pore structure. Moreover, ECE is not efficient in repassivate structures but is efficient in its purpose of removing chlorides if treatment setup is well planned, which justifies the need for better international standards on the topic.

Tensile Strength and Oxide Analysis of Carbon Steel in Concrete Exposed in Atmospheric Environment for 53 Years

The tensile strength of a corroded rebar in a 53-year-old concrete structure was studied. The microstructure of the metallic substrate, the fracture surface, and the corrosion product layers were investigated. Metallographic observation results showed that the carbon steel was constituted of ferrite and some pearlite. The tensile test results indicated that the corroded rebar presented low strength and elongation. In addition, the fracture surface of the rebar in the tensile test displayed dimple fracture behavior. The Raman spectroscopy results indicated that corrosion products at the general corrosion zone were obviously different from those at the localized corrosion zone. The rust layer at the general corrosion zone was composed of goethite （α-FeOOH）, magnetite （Fe304）, and hematite （α-Fe203）, while that of the pitting zone was made of feroxyhyte （δ-FeOOH）, goethite （α-FeOOH）, and hematite （α-Fe203）. However, the general tendencies that the corrosion products were constituted of a mix of oxides and hydroxides, the oxides mainly existed in the internal part and the hydroxides more presented in the external layer were observed.

框架结构考虑钢筋腐蚀的地震风险评估方法

为科学评估框架结构考虑钢筋腐蚀的地震风险,研究了钢筋腐蚀及混凝土开裂对框架结构抗倒塌性能的影响,将结构倒塌极限状态对应的结构变形能力均值定义为时间的函数,考虑老化时间对结构倒塌年均失效概率式积分,得到考虑钢筋腐蚀效应的结构地震倒塌概率;提出了考虑结构老化效应的地震风险评估方法,将该方法应用于不同设防烈度的锈蚀RC框架结构,研究了在接近倒塌极限状态下考虑结构老化效应对地震风险的影响。结果表明:6、7、8度设防的框架结构锈蚀50年比未锈蚀结构的倒塌储备系数(CMR)分别小18.7%、31.0%、19.4%;6、7、8度设防的框架结构考虑老化效应50年的年均倒塌超越概率比不考虑老化效应结构的年均倒塌超越概率分别大28.6%、59.8%、32.6%;建议在不同烈度区RC框架结构的地震风险评估中考虑结构老化效应的影响。

对人工接地装置材料选择要求的探讨

依据电化学腐蚀的原理对人工接地装置材质选择的要求进行研究,着重分析以镀锌扁钢为代表的不同材质的人工接地埋地敷设时的腐蚀过程,并针对不同的工程情况提出相应的解决方案。

一般大气环境下钢筋锈蚀深度的RBF神经网络预测模型研究

钢筋锈蚀深度预测是评估在役RC结构服役性能的基础。为建立一般大气环境RC构件中钢筋锈蚀深度预测模型,通过收集实测数据,分析影响钢筋锈蚀深度的主要参数及其影响规律,继而基于实测数据建立数值模型和RBF神经网络预测模型,并进行参数敏感性分析。研究结果表明:与数值模型相比,RBF神经网络对钢筋锈蚀深度预测效率与精度更高,能够有效映射各影响参数与钢筋锈蚀深度之间复杂的非线性关系。参数敏感性分析结果显示,钢筋混凝土表面锈胀裂缝宽度对钢筋锈蚀深度影响最大,钢筋直径、保护层厚度与钢筋直径之比和混凝土抗压强度等其他因素影响次之。所得模型可用于工程检测中钢筋锈蚀程度预测与RC构筑物剩余服役寿命评估。

Durability of Concrete Subjected to the Combined Actions of Flexural Stress,Freeze-thaw Cycles and Bittern Solutions

Freeze-thaw durabilities of three types of concretesnormal portland cement concrete （OPC）, high strength concrete （HSC） and steel fiber reinforced high strength concrete （SFRHSC） were systemically investigated under the attacks of chemical solution, and combination of external flexural stress and chemical solution. Four kinds of bitterns from salt lakes in Sinkiang, Qinghai, Inner Mongolia and Tibet provinces of China were used as chemical attack solutions. The relative dynamic modulus （RDM） was used as an index for evaluating the damage degree during the course of chemical attack and stress corrosion. The experimental results show that the freeze-thaw durability of concrete is visibly reduced in the present of the flexural stress, i e, stress accelerates the damage process. In order to quantify the stress accelerated effect, a stress accelerating coefficient was proposed. The stress accelerating coefficient is closely related with the types of bitterns and the numbers of freeze-thaw cycles is. The more numbers of freeze-thaw cycles is, the greater the stress accelerating coefficient for various concretes will be. In addition, there also exists a critical ratio of external stress to the maximum flexural stress. If the stress ratio exceeds the critical one, the freeze-thaw durability of various concretes will be greatly decreased compared to the responding concretes without applied stress. The critical stress ratio of OPC, HSC and SFRHSC is 0.30, 0.40 and 0.40, respectively, indicating that HSC and SFRHSC have advantages over OPC and are suitable to use in the bittern erosion regions.

牺牲阳极在核电站钢筋混凝土构筑物维修中的保护效果监测

国内核电站大多靠近海边,受海洋大气环境的影响,钢筋混凝土的腐蚀问题不容忽视,传统局部打补丁的修补方法维修效果不佳,将埋入式牺牲阳极应用于钢筋混凝土结构的局部维修,具有施工简单,无需维护管理,保护效果好等特点,能大大减少重复性维修。本文对局部采用牺牲阳极维修后混凝土中钢筋的电位进行了监测,发现在牺牲阳极布置区域内钢筋电位极化较为明显,钢筋受到了较好的保护,但在布置区域之外,牺牲阳极的保护范围有限。

钢筋混凝土梁锈胀开裂计算研究

【目的】钢筋锈蚀引起的钢筋混凝土构件锈胀开裂是混凝土结构退化的重要原因,有必要对锈胀裂缝机理进行探究。【方法】基于人工通电锈蚀试验对钢筋混凝土梁进行锈胀开裂计算,通过计算锈蚀钢筋混凝土梁锈胀开裂锈蚀深度,从而得到锈胀裂缝宽度值。【结果】研究结果表明,考虑电流腐蚀密度与电解液浓度的锈胀裂缝计算公式能有效预测钢筋混凝土梁的锈胀开裂宽度。【结论】钢筋混凝土梁的锈胀开裂机理十分复杂,裂缝宽度受到的影响较多,结合电流腐蚀密度与电解液浓度所修正的裂缝计算公式为裂缝研究提供了一种有效的思路。

螺纹钢的磷化处理对混凝土环境下耐蚀性的影响

文章旨在探讨螺纹钢的磷化处理对其在混凝土环境下耐蚀性的影响。螺纹钢因其出色的机械性能和黏结特性,在建筑结构中被广泛采用。然而,它在混凝土孔隙液环境中容易受到腐蚀,影响建筑结构的安全性和耐久性。因此,研究通过实验探讨了磷化处理对螺纹钢耐蚀性的影响。结果表明:磷化处理能在螺纹钢表面形成一层磷酸盐保护膜,显著提高其耐蚀性和抗氧化能力,进而提供了一种提高工程领域螺纹钢耐蚀性的有效方法,对提高螺纹钢在恶劣环境下的耐蚀性能具有重要的理论和实际意义。