Search Results (88)

The operation of heavy-haul railway trains with large loads results in significant cracking issues in reinforced concrete beams. Atmospheric carbon dioxide, oxygen, and moisture from the atmosphere penetrate into the beam interior through these cracks, accelerating the carbonation of the concrete and the corrosion of the steel bars. The rust-induced expansion of steel bars further exacerbates the cracking of the beam. The interaction between environmental factors and beam cracks leads to a rapid decline in the durability of the beam. To address this issue, a multi-physics field coupling durability assessment method was proposed, considering concrete beam cracking, concrete carbonation, and steel bar corrosion. The interaction among these three factors is achieved through sequential coupling, using crack width, carbonation passivation time, and steel bar corrosion rate as interaction parameters. Using this method, the deterioration morphology and stiffness degradation laws of 8 m reinforced concrete beams under different load conditions, including those of heavy and light trains in heavy-haul railways, are compared and assessed. The analysis reveals that within a 100-year service cycle, the maximum relative stiffness reduction for beams on the heavy train line is 20.0%, whereas for the light train line, it is only 7.4%. The degree of structural stiffness degradation is closely related to operational load levels, and beam cracking plays a critical role in this difference. Full article

This paper presents field experiments of mineral deposition on steel, induced by cathodic polarization in natural seawater, as a sustainable strategy for the life extension of marine steel structures. Although this approach is quite well known, the ability of the mineral deposit to both protect steel from corrosion in the absence of a cathodic current, thus operating as an inorganic coating, and provide an effective substrate for colonization by microorganisms still needs to be fully explained. To this end, two identical steel structure prototypes were installed at a depth of 20 m: one was submitted to cathodic polarization, while the other was left under free corrosion for comparison. After 6 months, the current supplied to the electrified structure was interrupted. A multidisciplinary approach was used to analyze the deposits on steel round bars installed in the prototypes over time, in the presence and in the absence of a cathodic current. Different investigation techniques were employed to provide the following information on the deposit: the composition in terms of elements, compounds and macro-biofouling; the morphology; the thickness and the degree of protection estimated by electrochemical impedance spectroscopy (EIS). The results showed that under cathodic polarization, the thickness of the deposit increased to 2.5 mm and then remained almost constant after the current was interrupted. Conversely, the surface impedance decreased from 3 kΩ cm² to about 1.5 kΩ cm² at the same time, and the aragonite–brucite ratio also decreased. This indicates a deterioration in the protection performance and soundness of the deposit, respectively. Considering the trends in thickness and impedance together, it can be concluded that the preformed mineral deposit does not undergo generalized deterioration after current interruption, which would result in a reduction in thickness, but rather localized degradation. This phenomenon was attributed to the burrowing action of marine organisms, which created porosities and/or capillary pathways through the deposit. Therefore, the corrosion protection offered by the mineral deposit without a cathodic current is insufficient because it loses its protective properties. However, the necessary current can be quite limited in the presence of the deposit, which in any case provides a suitable substrate for sustaining the colonization and growth of sessile marine organisms, thus promoting biodiversity. Full article

Bond behavior between steel bars and concrete is fundamental to the structural integrity and durability of reinforced concrete. However, corrosion-induced deterioration severely impairs bond performance, highlighting the need for advanced and reliable assessment methods. This paper pioneers an algorithm for an advanced ensemble learning framework to predict bond strength between corroded steel bars and concrete. In this framework, a novel Stacked Boosted Bond Model (SBBM) is developed, in which a Fusion-Based Feature Selection (FBFS) strategy is integrated to optimize input variables, and SHapley Additive exPlanations (SHAP) are employed to enhance interpretability. A merit of the framework is that it can effectively identify critical factors such as crack width, transverse confinement, and corrosion level, which have often been neglected by traditional models. The proposed SBBM achieves superior predictive performance, with a coefficient of determination (R²) of 0.94 and a mean absolute error (MAE) of 1.33 MPa. Compared to traditional machine learning and analytical models, it demonstrates enhanced accuracy, generalization, and interpretability. This paper provides a reliable and transparent tool for structural performance evaluation, service life prediction, and the design of strengthening measures for corroded reinforced concrete structures, contributing to safer and more durable concrete structures. Full article

The application of rebar reinforced ultra-high-performance concrete (R-UHPC) has been increasingly adopted in engineering structures due to its exceptional mechanical performance and durability characteristics. Nevertheless, when subjected to combined saline and stray current conditions, R-UHPC remains vulnerable to severe corrosion degradation. This investigation examined the corrosion performance and tensile behavior evolution of R-UHPC containing 2.0 vol% copper-coated steel fiber content and HRB400 steel rebar with a reinforcement ratio of 3.1%. The accelerated corrosion process was induced through an impressed current method, followed by direct tensile tests at varying exposure periods. The findings revealed that the embedding of rebar in UHPC led to the formation of fiber-to-rebar (F-R) conductive pathways, generating radial cracks besides laminar cracks. The bonding between rebar and UHPC degraded as corrosion progressed, leading to the loss of characteristic multiple-cracking behavior of R-UHPC in tension. Meanwhile, R-UHPC load-bearing capacity, transitioning from gradual to accelerated deterioration phases with prolonged corrosion, aligns with steel fibers temporally. During the initial 4 days of corrosion, the specimens displayed surface-level corrosion features with negligible steel fiber loss, showing less than 4.0% reduction in ultimate bearing capacity. At 8 days of corrosion, the steel fiber decreased by 22.6%, accompanied by an 18.3% reduction in bearing capacity. By 16 days of corrosion, the steel fiber loss reached 41.5%, with a corresponding bearing capacity reduction of 29.1%. During the corrosion process, corrosion cracks and load-bearing degradation in R-UHPC could be indicated by the ultrasonic damage factor. Full article

Tunnel lining structures, which are subjected to the combined effects of water and soil pressure as well as a water-rich erosion environment, undergo a corrosion-induced damage and degradation process in the reinforced concrete, gradually leading to structural failure and a significant decline in service performance. By introducing the Cohesive Zone Model (CZM) and the concrete damage plastic model (CDP), a three-dimensional numerical model of the tunnel lining structure in mining method tunnels was established. This model takes into account the multiple effects caused by steel reinforcement corrosion, including the degradation of the reinforcement’s performance, the loss of an effective concrete cross section, and the deterioration of the bond between the steel reinforcement and the concrete. Through this model, the deformation, internal forces, damage evolution, and degradation characteristics of the structure under the effects of the surrounding rock water–soil pressure and steel reinforcement corrosion are identified. The simulation results reveal the following: (1) Corrosion leads to a reduction in the stiffness of the lining structure, exacerbating its deformation. For example, under high water pressure conditions, the displacement at the vault of the lining before and after corrosion is 4.31 mm and 7.14 mm, respectively, with an additional displacement increase of 65.7% due to corrosion. (2) The reinforced concrete lining structure, which is affected by the surrounding rock loads and expansion due to steel reinforcement corrosion, experiences progressive degradation, resulting in a redistribution of internal forces within the structure. The overall axial force in the lining slightly increases, while the bending moment at the vault, spandrel, and invert decreases and the bending moment at the hance and arch foot increases. (3) The damage range of the tunnel lining structure continuously increases as corrosion progresses, with significant differences between the surrounding rock side and the free face side. Among the various parts of the lining, the vault exhibits the greatest damage depth and the widest cracks. (4) Water pressure significantly impacts the internal forces and crack width of the lining structure. As the water level drops, both the bending moment and the axial force diminish, while the damage range and crack width increase, with crack width increasing by 15.1% under low water pressure conditions. Full article

This study focuses on the nameplate of Vila D. Bosco, a modern building in Macau from the time of Portuguese rule, and looks at the types of metal materials and surface coatings used, as well as how they corrode due to the tropical marine climate affecting the building’s metal parts. The study uses different techniques, such as X-ray fluorescence spectroscopy (XRF), scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), attenuated total internal reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and cross-sectional microscopic analysis, to carefully look at the metal, corrosion products, and coating of the nameplate. The results show that (1) the nameplate matrix is a resulfurized steel with a high sulfur content (Fe up to 97.3% and S up to 1.98%), and the sulfur element is evenly distributed inside, which is one of the internal factors that induce corrosion. (2) Rust is composed of polycrystalline iron oxides such as goethite (α-FeOOH), hematite (α-Fe₂O₃), and magnetite (Fe₃O₄) and has typical characteristics of atmospheric oxidation. (3) The white and yellow-green coatings on the nameplate are oil-modified alkyd resin paints, and the color pigments are TiO₂, PbCrO₄, etc. The surface layer of the letters is protected by a polyvinyl alcohol layer. The paint application process leads to differences in the thickness of the paint in different regions, which directly affects the anti-rust performance. The study reveals the deterioration mechanism of resulfurized steel components in a subtropical polluted environment and puts forward repair suggestions that consider both material compatibility and reversibility, providing a reference for the protection practice of modern and contemporary architectural metal heritage in Macau and even in similar geographical environments. Full article

In this experiment, a novel designed Mn-N-bearing, nearly Ni-free, TRIP-aided economical 19Cr (Fe-18.9Cr-10.1Mn-0.3Ni-0.26N-0.03C) duplex stainless steel (DSS) was prepared, and it exhibited a good combination of strength and toughness after suitable solution treatment, showing good application potential. The deformation mechanisms of ferrite and austenite are different during tensile deformation at room temperature: the ferrite phase was deformed by a dislocation slip mechanism and formed a cell structure due to its higher stacking fault energy; the lower stacking fault energy of austenite resulted in a strain-induced martensite phase transformation mechanism. With an increase in aging time from 1 h to 7 h at 750 °C in air, the σ phase precipitates in the ferrite triple grain boundary junction, which leads to an increase in ultimate tensile strength, acts as an obstacle to the dislocation motion and decreases the ductility, deteriorating the pitting corrosion resistance in 3.5 wt.% NaCl solution at the same time. The σ phase precipitation behavior does not alter the deformation mechanism of the phases of the solution-treated TRIP-aided economical DSS. Full article

The inefficiency of unreinforced concrete beams as flexural members poses a challenge because concrete’s tensile strength is significantly lower than its compressive strength. In response to this challenge, reinforcement bars are commonly employed near the tension zone of reinforced concrete (RC) beams. Nonetheless, structures constructed with RC face challenges such as reduced live load capacity, concrete deterioration, and the corrosion of reinforcement bars over time. To address this, ongoing research is exploring maintenance and retrofitting techniques using high-strength, lightweight fiber-reinforced polymer (FRP) composite materials such as carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP). In this study, the flexural performance of corroded RC beams was enhanced through retrofitting with CFRP plates and sheets. The corroded RC beams were fabricated using an applied-current method with a 5% NaCl solution to induce a 10% target corrosion level under controlled laboratory conditions. Flexural tests were conducted to evaluate the structural performance, failure modes, load–displacement relationships, and energy dissipation capacities. The results showed that CFRP reinforcement mitigates the adverse effects of corrosion-induced reduction in rebar cross-sectional areas, leading to increased stiffness and improved load-carrying capacity. In particular, CFRP reinforcement increased the yield load by up to 36.5% and the peak load by up to 90% in corroded specimens. The accumulated energy dissipation capacity also increased by 92%. These enhancements are attributed to the effective load-sharing behavior between the corroded rebar and the CFRP reinforcement. Full article

Steel structures exposed to estuarine regions near the sea are susceptible to high-velocity and sediment-laden flows induced by runoff and tides, as well as storm surges, leading to significant erosion. This erosion causes defects in the protective coatings on steel surfaces, resulting in the accelerated corrosion of their components. However, damage to the protective coating of steel components is a relatively long process and is not easy to monitor in real time. This paper conducts an accelerated deterioration test of protective coatings under water and sediment erosion to explore the damage laws of the protective coatings of steel components under different test conditions. This study reveals that the adhesion of the protective coating decreased rapidly initially and then slowly with prolonged erosion time. In the early stage of erosion, scratches and pits are easily formed on the coating surface, while the damage tends to be uniform in the later stage. The damage characteristic values and damage rate of the protective coating were obtained based on the image recognition method. The characteristic value of scratch lengths ranged from 5 to 25 mm, and for pit diameters, they ranged from 1 to 4 mm. The maximum damage rate was 9.8%, and the damage rate showed a trend that approximately followed a logarithmic function with erosion time. It was also found that the sediment concentration had the greatest influence on the damage rate, followed by the erosion velocity, and the erosion angle had the least influence. Additionally, the relationships between adhesion and damage rate, as well as the relationship between adhesion and erosion depth, were established. It was found that the mean erosion depth exhibits a linear functional relationship with the damage rate, while adhesion exhibits a logarithmic functional relationship with both the damage rate and the erosion depth. The empirical formula proposed can provide a theoretical basis for quantitatively describing the surface defect conditions of the coating. Full article

The durability degradation of concrete structures in marine and urban underground environments is largely governed by chloride-induced corrosion. This process becomes significantly more severe under the coupled action of external loading and drying–wetting cycles, which accelerate chloride transport and structural deterioration. However, the existing research often isolates the effects of mechanical loading or environmental exposure, failing to comprehensively capture the synergistic interaction between these factors. This lack of understanding of chloride ingress under simultaneous mechanical and environmental loading limits the development of reliable service life prediction models for concrete structures. In this study, a self-made loading system was employed to simulate this coupled environment, combining external loading with 108 days of drying–wetting cycles. Chloride profiles were obtained to assess the combined effects of stress level, water/binder ratio, and fiber content on chloride penetration in fiber-reinforced cementitious composites (FRCCs). To further extend the analysis, a Crank–Nicolson-based finite difference approach was developed for the numerical assessment of chloride diffusion in concrete structures after repair. This model enables the point-wise treatment of nonlinear chloride concentration profiles and provides space- and time-dependent chloride concentration distributions. The results show that using an FRCC as a repair material significantly enhances the service life of chloride-contaminated concrete structures. The remaining service life of the repaired concrete was extended by 36.82% compared to the unrepaired case, demonstrating the clear practical value of FRCC repairs in aggressive environments. Full article

Concrete structures in marine environments face significant degradation due to reinforcement corrosion caused by chloride ingress and sulfate attack. Poor construction quality, inadequate standards, and suboptimal design can further accelerate deterioration. Non-destructive testing (NDT) has proven valuable for durability assessment, yet its application remains limited due to the complex microstructural characteristics of concrete. This study establishes a comprehensive procedure for evaluating precast concrete degradation in marine environments using multiple characterization techniques. Two precast concrete elements with different cement types, CEM II A-L 42.5R and CEM I 42.5 R/SR, were analyzed through compressive strength tests, open porosity measurements, mercury intrusion porosimetry (MIP), ultrasonic wave transmission, and scanning electron microscopy (SEM). The results indicate that CEM I 42.5 R/SR exhibits superior compressive strength and lower porosity, making it more durable and suitable for load-bearing applications. Higher ultrasonic pulse velocity (UPV) further confirms its resilience. In contrast, CEM II A-L 42.5R shows lower mechanical performance and greater susceptibility to marine-induced degradation. Over time, pore size distribution shifts, potentially compromising mechanical integrity. SEM analysis reveals gypsum and brucite formation in degraded regions, demonstrating microstructural changes due to seawater exposure. A strong negative correlation between porosity and UPV underscores the detrimental effect of increased porosity on material density and structural stability. This study highlights the effectiveness of UPV and porosity analysis as reliable NDT techniques for assessing concrete deterioration. The strong correlation between UPV and porosity trends suggests that UPV serves as an early indicator of durability loss, enabling timely maintenance interventions. These findings provide valuable insights into material selection for enhanced structural performance in marine environments and emphasize the role of NDT in long-term structural health monitoring. Full article

Through alternating high–low temperature and humid heat tests, six sets of different humidity cycle numbers were applied to Q235B low-carbon steel and Q345B low-alloy steel. Monotonic tensile tests were conducted to compare the differences in monotonic performance degradations. The influence of humidity cycle numbers on the hysteretic and fatigue performance of Q235 steel was investigated through cyclic loading tests. A cyclic constitutive model based on the mixed hardening model was established and validated. The results show that the humid heat environment causes corrosion of the steel, and the degree of corrosion follows a power-law relationship with the number of humid heat cycles. Under monotonic loading, as the number of humid heat cycles increases, the strength and deformation performance of both steels degrade linearly, with Q345 low-alloy steel exhibiting more significant performance deterioration. The corrosion damage induced by the humid heat environment greatly reduces the low-cycle fatigue life of Q235 steel, and the more severe the corrosion, the lower the fatigue life. However, there is no significant effect on the development of the hysteretic curve shape. Under variable amplitude cyclic loading, as the corrosion degree increases, the hysteretic energy dissipation and energy dissipation rate continuously decrease. The two-segment backbone curve considering mass loss rate and the material hardening parameters based on the mixed hardening model can accurately describe the hysteretic characteristics of Q235 low-carbon steel under the humid heat environment. Full article

Reinforced concrete structures deteriorate over time when exposed to environmental effects throughout their service life, resulting in a loss of structural performance and ultimately a reduction in service life. One of the most critical deterioration mechanisms in this process is the corrosion of the reinforcement steel. The initiation and propagation of corrosion adversely affect the load-bearing capacity, bond strength, and overall structural behavior of reinforced concrete elements, thereby threatening the structural safety. Therefore, understanding the corrosion process and accurately predicting the service life of reinforced concrete structures is critical to ensuring their long-term durability. This study comprehensively examines the effects of chloride-induced rebar corrosion on the service life of reinforced concrete structures. Various mathematical models used to predict corrosion initiation and propagation times are analyzed in detail. These models provide a scientific basis for understanding the effects of environmental conditions and structural properties on the corrosion process and estimating how these effects affect the service life. In particular, the study investigates the effect of parameters such as concrete cover thickness, rebar diameter, crack presence, corrosion rate, and environmental conditions on the corrosion process, all of which also affect structural performance. Cracks in reinforced concrete elements shorten the corrosion initiation period depending on their thickness. Considering that the presence of cracks also changes the structural behavior, it is recommended to use the Kwon model, which takes the presence of cracks into account, in the service life calculations. The presence of cracks is ineffective in the corrosion propagation period, and it is recommended to use the Morinaga model for this period. For reinforced concrete elements exposed to aggressive environments, increasing the thickness of the concrete cover and the diameter of the reinforcement has been shown to increase the service life. Columns with larger diameter reinforcement showed a longer service life than beams with smaller diameter reinforcement. Therefore, evaluating each element separately in service life calculations will ensure that a safer approach is taken. In conclusion, this study serves as a valuable resource for developing design strategies to improve the long-term durability of reinforced concrete structures and to minimize the adverse effects of corrosion on structural performance. It provides design and field engineers with guidance to make more accurate service life assessments and implement effective decisions to improve structural performance. Full article

The composite performance of steel fiber-reinforced concrete (SFRC) is excellent, and its application potential in subsea tunnel engineering has gradually emerged. This paper discusses three types of laboratory testing methods for studying the corrosion of SFRC induced by chlorides: the ion diffusion method, electric field migration method, and pre-corrosion method. The similar relationship between short-term accelerated deterioration tests and the natural corrosion process, as well as the experimental setup for simulating the coupling effect of multiple factors, requires further exploration. Furthermore, the mechanisms of steel fibers influencing the chloride corrosion resistance of SFRC are explored from four aspects: type, coating, shape, and dosage. Finally, by examining practical case studies of SFRC in subsea tunnel applications, the challenges posed by the multi-directionality of chloride ion corrosion, the diversity of corrosion sources, and the uneven distribution of steel fibers are highlighted. Future research should focus on enhancing the application of SFRC in subsea tunnel linings. This study provides a reference and basis for promoting the application of SFRC in subsea tunnel engineering and indicates future development directions. Full article

The absence of carbon fiber-reinforced rebar performance standards in Korea has limited its reliability. This study investigates the durability performance of carbon fiber-reinforced polymer rebar as an alternative to traditional steel reinforcement in concrete structures. Concrete beams reinforced with carbon fiber-reinforced polymer rebar were exposed to chloride environments for durations of 35 and 70 days and then subjected to bending tests to evaluate their durability. The results demonstrate that the strong bond between the carbon fiber-reinforced polymer and concrete effectively prevented brittle fracture, even under exposure to harsh chloride. A scanning electron microscope analysis of the specimens exposed to chloride showed no deterioration of the carbon fiber-reinforced polymer rebar, highlighting its exceptional resistance to corrosion. Furthermore, durability tests were conducted in a carbonation chamber for 8 and 12 weeks, with no signs of degradation in the carbon fiber-reinforced polymer rebar. These findings suggest that carbon fiber-reinforced polymer rebar offers excellent resistance to both chloride-induced corrosion and carbonation, making it a promising solution to enhance the longevity and durability of reinforced concrete structures exposed to aggressive environmental conditions. Full article