Corrosion of steel bars in saturated Ca(OH)2 and concrete pore solution

Testing steel in solution has the advantage of avoiding the long time necessary for chlorides to penetrate the concrete cover.  It is well known that steel in high alkaline environments is passive and the protective capability of the passive film increases with pH.  The pH of saturated calcium hydroxide solution is lower than concrete pore solution which does induce passivation but not to the degree encountered by steel in good quality concrete.  Nevertheless, saturated calcium hydroxide has been used in many studies of rebar corrosion as a substitute for pore solution.  This paper discusses the electrochemical behavior of low carbon steel bars is chloride free and chloride contaminated pore solution and saturated calcium hydroxide solution.  Results show that the passive film on the steel immersed in pore solution and saturated Ca(OH)2 have similar composition.  However, as a result of lower pH in saturated Ca(OH)2 solution, the passive layer formed in this solution is less protective and does not offer enough passivity to steel to simulate a realistic concrete environment

Finite Element Modeling of Concrete Based on Quantitative Computed Tomography (QCT)

Models have been used before to predict the mechanical and transport behavior of concrete. In most of these studies, aggregates were considered either circle or sphere and the impact of the aggregates geometry and in-homogeneities in concrete structure is ignored. The objective of this study is to develop a novel method for accurate prediction of the mechanical behavior of concrete using quantitative computed tomography (QCT)-based finite element analysis. Concrete cylinders were cast and cured for 28 days. The QCT scans were carried out on the samples using a clinical CT scanner. An image processing method was applied to detect aggregates, paste content and the air voids. The distribution of each phase then calculated in each image slice (2D) and in the bulk material (3D). The processed QCT images were directly converted into voxel-based 3D FE models for linear and nonlinear analyses. The FE models were generated by conversion of each voxel into an 8-noded brick element. Air void content of the cylinders (2D and 3D) was determined. In addition, the aggregates content was estimated using the image analysis. In both cases, the results obtained by the image analysis and the actual measurement and ASTM method are in very good agreement

FEA of the galvanostatic technique with guard ring in cracked concrete

Uncertainty of the polarized area of reinforcing steel is one of the major sources of error when measuring corrosion rate of steel in concrete.  To overcome this problem, instruments equipped with the guard ring, aimed at limiting the polarized area, have been introduced and are available commercially.  However, some limitations and disadvantages of the guard ring equipment have been reported. The function of this system on measuring the corrosion in sound concrete was analyzed experimentally and mathematically [1].  This paper explains the function the guard ring equipment in cracked concrete by using finite element analysis (FEA)

FEA of the galvanostatic technique with guard ring in cracked concrete

Uncertainty of the polarized area of reinforcing steel is one of the major sources of error when measuring corrosion rate of steel in concrete.  To overcome this problem, instruments equipped with the guard ring, aimed at limiting the polarized area, have been introduced and are available commercially.  However, some limitations and disadvantages of the guard ring equipment have been reported. The function of this system on measuring the corrosion in sound concrete was analyzed experimentally and mathematically [1].  This paper explains the function the guard ring equipment in cracked concrete by using finite element analysis (FEA)

The Role of Cracks in Chloride-Induced Corrosion of Carbon Steel in Concrete—Review

The majority of works in the field of chloride-indued corrosion of steel in concrete are focused on the cracks formed by the corrosion products. However, the number of studies on the influence of cracks (pre-cracked concrete) on corrosion is limited. Cracks create preferential/free paths for the penetration of chlorides, water, and oxygen into concrete; thus, the presence of cracks in concrete can intensify chloride-induced corrosion of steel reinforcement. This paper presents a review of the effects of cracking on the corrosion of steel in concrete. It was widely reported in the reviewed papers that cracks have a negative impact on concrete durability. They influence the chloride penetration and the chloride-induced corrosion of reinforcement in terms of the initiation and propagation stages. This influence is a complex function of many factors, including mix design, exposure conditions, crack frequency, crack orientation, crack width, and cover depth. Although there is a general agreement on the effects of cracks on the initiation of corrosion, the role of cracks and their widths on the propagation of corrosion in the long term is still under debate

Galvanic Corrosion Study between Tensile-Stressed and Non-Stressed Carbon Steels in Simulated Concrete Pore Solution

The present study investigated the galvanic effect between tensile-stressed and non-stressed carbon steels, in addition to the influence of the tensile stress on the passivation and corrosion behavior of steel in a simulated concrete pore solution. Three different levels of tensile stress, ranging from elastic to plastic stress on the surface, were applied by adjusting the displacement of C-shape carbon steel rings. Different electrochemical measurements including the open circuit potential (OCP), the electrochemical impedance spectroscopy (EIS), the zero-resistance ammetry (ZRA), and the cyclic polarization were performed. Based on the results of EIS, the tensile stress degraded the resistance of the oxide film in moderate frequencies while enhancing the charge transfer resistance in low frequencies during passivation. As corrosion propagated, the stressed steel yielded a similar charge transfer resistance to or an even lower charge transfer resistance than the non-stressed steel, especially in the case of plastic tensile stress. The galvanic effect between the tensile-stressed and non-stressed steels increased the chloride threshold value of the tensile-stressed steel, although the susceptibility to pitting corrosion was exhibited after being corroded

Galvanic Corrosion Study between Tensile-Stressed and Non-Stressed Carbon Steels in Simulated Concrete Pore Solution

The present study investigated the galvanic effect between tensile-stressed and non-stressed carbon steels, in addition to the influence of the tensile stress on the passivation and corrosion behavior of steel in a simulated concrete pore solution. Three different levels of tensile stress, ranging from elastic to plastic stress on the surface, were applied by adjusting the displacement of C-shape carbon steel rings. Different electrochemical measurements including the open circuit potential (OCP), the electrochemical impedance spectroscopy (EIS), the zero-resistance ammetry (ZRA), and the cyclic polarization were performed. Based on the results of EIS, the tensile stress degraded the resistance of the oxide film in moderate frequencies while enhancing the charge transfer resistance in low frequencies during passivation. As corrosion propagated, the stressed steel yielded a similar charge transfer resistance to or an even lower charge transfer resistance than the non-stressed steel, especially in the case of plastic tensile stress. The galvanic effect between the tensile-stressed and non-stressed steels increased the chloride threshold value of the tensile-stressed steel, although the susceptibility to pitting corrosion was exhibited after being corroded

Unraveling the Corrosion of the Ti–6Al–4V Orthopedic Alloy in Phosphate-Buffered Saline (PBS) Solution: Influence of Frequency and Potential

This paper addresses the interplay between electrical fields in the human body and the corrosion behavior of Ti-6Al-4V alloy, a prevalent orthopedic material. The study investigates the impact of alternative electrical signals at different frequencies on the alloy’s electrochemical behavior in a simulated body environment. The human body always has natural sinusoidal potential due to, e.g., heart palpitations and brain/nervous system activities. Ignoring such natural activities may lead to underestimating the corrosion performance of the Ti-6Al-4V alloy in the body. By analyzing anodic and cathodic responses and the net faradaic current induced by alternating current potential, the research sheds light on the influence of electrical fields on corrosion rates. Understanding these dynamics could lead to improved implant materials, mitigating corrosion-related challenges and enhancing implant performance over the long term. Results of this work indicated that frequent oxidation and reduction at certain frequencies may induce corrosion and hinder biomimetic apatite formation, impacting osseointegration. Natural alternative currents in the body affect the corrosion performance of Ti-based implant alloys, highlighting the need for consideration in biomedical applications

Electrochemical behavior of a magnesium ZK60 alloy processed by high-pressure torsion

High-pressure torsion (HPT) was used to evaluate the effect of straining on the electrochemical properties of a ZK60 magnesium alloy. The samples were processed using HPT up to 20 turns and the electrochemical responses were examined through polarization, EIS, Mott–Schottky and hydrogen evolution tests. Electron back-scatter diffraction (EBSD) studies showed more homogeneity with finer average grain sizes accompanied by the evolution of a nobler texture when increasing the numbers of HPT turns. Ultimately, this led to improved corrosion behavior for the HPT-processed disks. Post corrosion observations revealed improved protective layers after higher turns of HPT.</p