出版者・発行元：Corrosion Science  

The corrosion interaction mechanism of carbon steel was studied to address the mutual interference of carbon steels under coating defects in the atmospheric environment. The findings revealed that the electrochemical interactions between the carbon steels were primarily influenced by the solution resistance, cathode area, and cathode-to-anode area ratio. In addition, the upper limit of the accelerating effect of the macrocell current on the anodic corrosion rate was determined by theoretical deduction. Finally, the corrosion-accelerating effect of the macrocell current was determined to assess the corrosion rate of carbon steels with electrochemical interactions under defects.

DOI： 10.1016/j.corsci.2023.111730

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Scopus

出版者・発行元：Construction and Building Materials  

To assess the impact of corrosion on steel and the effectiveness of surface preparation techniques on the bonding behavior between carbon fiber reinforced polymer (CFRP) and steel, thirty bonded joint specimens were examined. These specimens were based on three distinct corrosion levels of steel and three conventional surface preparation techniques. Furthermore, various evaluation methods were employed to understand the steel surface characteristics, encompassing macro and microscale observations, analysis of topographical structures, and quantification of surface evaluation indices. These were performed to determine their correlations with the interfacial stress behavior. The findings revealed that when the target for repair shifted from a new steel substrate to a corroded one, the synergistic performance at the steel-adhesive interface decreased. This led to a decrease in the maximum shear stress at the plate end, and there was also an undesirable shift in the mode of failure. Both test parameters (i.e., the corrosion level and surface preparation), synergistically determined the surface cleanliness, topography, and bonding defects, all three of which directly influenced the bonding behavior. Finally, an improved model for predicting the debonding capacity of CFRP-corroded steel bonded joints was introduced, incorporating surface damage (k1) and surface topography (k2) coefficients. This model's applicability was also verified by collecting other test data from available literature.

DOI： 10.1016/j.conbuildmat.2023.134279

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記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

<p>　鋼部材と炭素繊維シートの接着特性は，素地調整法や養生温度などの施工条件により変化する．しかし，これらの条件が炭素繊維シートの接着特性に及ぼす影響については不明な点が多いため，補修・補強の設計や施工条件を最適化することは困難である．本研究では素地調整法が鋼素地の表面性状と付着特性に及ぼす影響を明らかにした上で，鋼板と炭素繊維シートのせん断強度を検討した．また，養生温度が含浸樹脂の硬化速度，機械的性質，熱特性および繊維への浸透性に及ぼす影響を検討した．さらに，初期等温硬化モデルを構築し，熱履歴に関する樹脂のガラス転移過程を推定することで，後硬化による樹脂の各物性の改善効果を評価した．これらの知見に基づき，CFRP補強部の接着性能を向上させるための施工条件を提案した．</p>

DOI： 10.2208/jscejj.23-00250

CiNii Research

記述言語：英語   出版者・発行元：Kyushu Association for Bridge and Structural Engineering  

Over the past decade, CFRP strips have been increasingly used worldwide to repair or strengthen steel bridges. However, a large number of researchers use uncorroded steel as the target object before attaching CFRP. This approach is somewhat unreasonable as most steel members that require repair have suffered corrosion damage to different degrees. Additionally, before CFRP retrofitting, the corroded steel should be cleaned first, and the level of steel surface cleanliness is dependent upon the rust-removal method used. Even so, it is difficult to entirely remove all corrosion rust from the steel surface in practical applications. This means that in some cases, interfacial defects are almost inevitably going to occur. Therefore, in this study, the effects of interfacial defects on the corroded steel surface, following three kinds of rust-removal methods (acid solvent, disk sander, and abrasive blast), were primarily evaluated by means of the debonding shear stress at the plate end. In addition, several interfacial defects such as air bubbles, kissing bonds, and secondary rust, were observed based on surface and cross-section analyses using SEM-EDX, respectively. Varying amounts of rust residues tend to induce rust-back, and over time, cause visible under-film corrosion based on the observation of fracture interface. These observations can also provide strong evidence to explain why there is a certain reduction in strengthening effectiveness when using CFRP strips to repair corroded steel, compared to uncorroded steel. Finally, the authors argued that the disk sander in a single way for rust removal was insufficient in the case of repairing corroded steel members with a lot of relatively deep corrosion pits. Because severe rust residues and under-film corrosion observed was likely the primary reason for the adhesive's separation from the steel surface, thereby causing very premature failure of CFRP retrofitting.

DOI： 10.60345/kabse.39.0_85

CiNii Research

出版者・発行元：Structures  

Resin-impregnated carbon fiber fabric reinforced polymer (CFRP) is a novel material for steel structure reinforcement, but its performance is influenced by moisture and temperature. This study investigates the irreversible degradation of CFRP–steel adhesive joints in a hydrothermal setting, focusing on resin hydrothermal aging behavior. Moisture absorption tests, Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) were conducted to assess moisture's impact on resin matrix's properties. Results indicate that moisture absorption behavior is partially reversible through physical drying, while hydrolysis resulting from moisture absorption is irreversible. The partially reversible aspect of moisture absorption leads to a partial restoration of the thermodynamic properties of the resin matrix. Additionally, the mechanical performance of resin specimens and CFRP-steel adhesive joints in hydrothermal conditions was assessed using tensile and pull-off tests. Findings show that elevated temperatures accelerate the moisture absorption rate of resin while increasing the maximum moisture absorption capacity. The moisture absorption affects the fracture surface morphology of the resin matrix, with aging time negatively correlated with adhesion strength. Compared to the hydrothermally aged state, there is a slight recovery in the mechanical performance of CFRP–steel adhesive joints after drying desorption. The saline environment with no significant promotion aging compared to the distilled water environment. These findings provide insights for evaluating CFRP–steel adhesive joints’ durability in atmospheric or marine environments.

DOI： 10.1016/j.istruc.2023.105581

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出版者・発行元：Construction and Building Materials  

Atmospheric corrosion is one of the most critical issues in steel structures. To improve the structure's durability and reduce its cost, hot-dip coatings are a significant method for steel protection. The corrosion behavior of Al-based hot-dip coatings has been extensively studied. Galvanic corrosion usually occurs when steel members are coated with different hot-dip coatings and placed in direct contact. In this study, galvanic corrosion of an Al coating in contact with a 55Al–Zn coating in an atmospheric environment was investigated through electrochemical and exposure tests. The galvanic corrosion and its mechanism were studied based on open circuit potential (OCP), galvanic current, and X-ray diffraction (XRD) analyses. This study verified the galvanic corrosion of bolt joints in the actual application by the long-term exposure test. The results suggests that 55Al–Zn coating is a good substitute for Zn coating used for bolted joints in contact with Al-coated steel plate.

DOI： 10.1016/j.conbuildmat.2023.132694

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記述言語：英語   出版者・発行元：公益社団法人 腐食防食学会  

<p>高湿度環境や海洋環境における炭素繊維補強された鋼構造物では，ガルバニック腐食が発生しやすくなる．本研究では，炭素繊維と普通鋼の接触によるガルバニック腐食に影響を及ぼす主要因である，一方向性炭素繊維（CF）の電気化学的特性，異種材料間の接触状態，および環境温度について検討した．その結果，炭素繊維と炭素繊維束は，繊維方向に対して均質な抵抗器と見なせることを明らかにした．ただし，炭素繊維が金属粗面に接触する場合には，異種材料間の導電経路が最適化され，接触面積が増大することで，表面抵抗が著しく低下する．また，アレニウス方程式に基づき，高温環境における腐食促進作用を説明するための簡略化モデルを構築し，温度変化がガルバニック腐食に及ぼす影響は，普通鋼の腐食に比して顕著であることを明らかにした．</p>

DOI： 10.3323/jcorr.72.202

CiNii Research

出版者・発行元：Lecture Notes in Civil Engineering  

It is commonly duplex layers partially placed on a thermal sprayed coating when narrow parts are difficult to thermal spray. In a previous study, it was shown that when the duplex layer has a defect, thermal spray coating deteriorates faster than the single-layer coating. It is critical to evaluate and anticipate the occurrence and progression of duplex layer degradation and blistering in order to execute effective maintenance management for steel structures. In this investigation, specimens with duplex layers were exposed to the atmosphere and corrosion environment was monitored using ACM-type corrosion sensors and temperature-humidity sensors. Based on these findings, we proposed a method to evaluate the deterioration and blister progression of duplex layer between Al-5Mg thermal sprayed coating and heavy-duty paint coating in an environment without rain-washing action of adhered sea salt.

DOI： 10.1007/978-981-19-4293-8_38

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出版者・発行元：Lecture Notes in Civil Engineering  

A high-power continuous-wave laser is applied in this study as a replaceable surface treatment method for steel structures. Various forms of corrosion pits will affect the laser treatment efficiency for surface preparation of severely corroded steel structures. In order to evaluate the effect of laser treatment on the steel surface with corrosion pits, carbon steels with artificial pits of various depths and widths were performed and treated by laser irradiation. SEM-EDX analysis distinctly identified laser-treated areas under conditions by mapping elements. Results indicate the laser beam can reach the bottom of pits, promising cleaning efficiency of laser irradiation is still worth expecting.

DOI： 10.1007/978-981-19-4293-8_34

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出版者・発行元：Lecture Notes in Mechanical Engineering  

A new cathodic protection method including a sacrificial anode and a water swelling rubber was developed and applied to steel members in boundary with ground in the environment of stagnant water and dryness. To ensure applicability, the water swelling rubber was considered as the electrolyte carrier. The reliabilities in water absorption and retention capacity of the rubber were verified by an immersion and drying test. In addition, an electrochemical test was conducted to evaluate the applicability of the water swelling rubber under different environmental conditions. The test results demonstrated that the water absorption and retention performance of the rubber are associated with electrolyte concentration. And the method with the rubber is suitable for immersed and dry environments.

DOI： 10.1007/978-981-19-6841-9_22

Scopus

記述言語：日本語   出版者・発行元：公益社団法人 土木学会  

<p>　鋼道路橋において，溶射皮膜上に塗装が塗布され，重ね皮膜になる場合があるが，その重ね皮膜の耐久・防食特性については不明な点が多い．そこで，本研究ではAlとZnの溶射と重防食塗装の重ね皮膜部の耐久・防食特性を解明するために，クロスカット傷を導入した溶射単膜，および溶射と塗装の重ね皮膜部を有する鋼板試験体を用いて複合サイクル腐食促進試験を行った．また，重ね皮膜部の膨れ性状の測定，分極特性などの電気化学測定，SEM-EDXによる断面元素分析およびXRDによる生成物の同定分析を実施した．これらの結果から，溶射と塗装の重ね皮膜では，Al溶射の重ね皮膜がZn溶射に比べて早期に劣化し，耐久性が低下することなどを明らかにした．また，塩類に曝される腐食性の高い環境におけるAlとZnの溶射と塗装の重ね皮膜の劣化機構を示した．</p>

DOI： 10.2208/jscejj.22-00288

CiNii Research

出版者・発行元：International Journal of Steel Structures  

Steel box girders are easily subjected to fatigue cracking under the vehicle loading, and the crack initiating from arc notch of diaphragm is one of the typical fatigue details. The stress characteristics of diaphragm and U-rib in real bridge under the vehicle loading were analysed, as well as the deformation characteristics. Experimental work on fatigue crack propagation and bearing capacity was conducted. Simulations using the finite-element method were undertaken, and the crack propagation behaviours were studied. It is found that the out-of-plane deformation is the main cause of crack propagation at arc notch of diaphragm in real bridge. Fatigue testing data of 9 diaphragm-rib specimens carried out by the vibration fatigue test system and results of FEM simulations show that the rate and path of fatigue crack propagation changed significantly during the fatigue crack propagation. The fatigue crack initiates as a tensile-shear mixed mode crack and turns to single tensile mode with the increase of crack length.

DOI： 10.1007/s13296-022-00637-8

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出版者・発行元：Composites Part B: Engineering  

This study focused on the interfacial bond behavior of steel-CFRP (carbon fiber-reinforced polymer) adhesion joint associations with different steel surface treatments through typical pull-off and shear tests. The specimens were fabricated based on wet layup laminating CFRP and clean/corroded steel plates. Four types of surface treatments and two kinds of pre-coating processes were investigated to optimize the interfacial bond behavior. Meanwhile, the conventional rust removal methods were also studied by clarifying the physical and chemical characteristics of steel surfaces. Test results evaluated the topography, microstructure, and surface composition of clean and corroded steel specimens, and qualitatively established their relation to bonding behaviors and failure modes. A strong correlation existed between the surface geometry properties and the tensile/shear strength, however, for clean and corroded steel surfaces their fracture mechanisms differ. Various physical property parameters of the corroded surface related to surface treatment will further affect the bond performance. The corresponding adhesion mechanisms were mathematically demonstrated based on the surface energy principle. The present experimental results provide new insights into the interfacial bond mechanism between corroded steel structures and adhesive or CFRP composites.

DOI： 10.1016/j.compositesb.2022.110280

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出版者・発行元：Engineering Failure Analysis  

Finger-type expansion joints (FJs) have been extensively used in highway bridges and are exposed to the repeated impacts of traffic loading and corrosive environments. In this study, the corrosion and cracking behaviors of FJs serving in bridges for more than 25 years were investigated. The microstructure, electrochemical properties, and dynamic response of the FJs were investigated to analyze the fracture mechanism. The results showed that the crack-induced mechanisms of the two main failure modes were different because the synergistic effect of corrosion with residual stress changed depending on the degree of corrosion. First, considerable residual tensile stress, which enhanced the effective stress range, was the critical cause of fatigue crack initiation in the less corroded heat-affected zone (HAZ). Second, the dominant mechanism for cracking was the applied stress to the severely eroded FJ bottom, which was accelerated by galvanic corrosion. Crack-inducing factors included a combination of stress concentration and dynamic springback behavior.

DOI： 10.1016/j.engfailanal.2021.105894

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出版者・発行元：Lecture Notes in Civil Engineering  

Hot-dip Al coating is an effective and economical protection method for steel structures. Hot-dip Al coated steel members have also been used in the case that contact with concrete. Al is an amphoteric metal that can react with acid and alkaline. Concrete is an alkaline material. The corrosion behavior of hot-dip Al coating contact with concrete is studied by measurement OCP and monitoring the change of pH during the hardening process of concrete. And the atmospheric test that simulates the actual structures. The corrosion products are analyzed by the diffraction of X-rays (XRD). The hot-dip Al coating can be dissolved during the hardening process. With the decreasing pH of concrete, the Al coating also has a relatively stable due to the passivation effect. In the dry and no stagnant water environment, the hot-dip Al coating has a better anti-corrosion behavior due to the passivation and shielding effect of complex calcium-aluminum compounds.

DOI： 10.1007/978-981-16-6932-3_21

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