Search Results (275)

This study presents two independently optimised Extreme Gradient Boosting (XGBoost) regression models, one for predicting corrosion current density ($i_{corr}$) and one for predicting corrosion potential ($E_{corr}$) parameters of carbon steel rebar embedded in mortar and immersed in simulated pore solution. An experimental dataset consisting of 216 measurements was curated from a systematic potentiodynamic scan study covering six chloride contamination levels, two carbonation states (non-carbonated and carbonated), four moisture conditions for mortar (65%, 85%, 95% relative humidity, and submerged), and three conditioning durations for simulated pore solution (36 h, 72 h and 20 days). Hyperparameters of the XGBoost models were optimised using a Bayesian optimisation framework with the Tree-structured Parzen Estimator (TPE) sampler over 300 trials. Model performance was assessed using 5-fold cross-validation and a random 80:20 train–test split. The optimised models achieved cross-validation $R^2$ scores of 0.936 and 0.953 for $i_{corr}$ and $E_{corr}$, respectively. On the hold-out test set, $R^2$ values of 0.933 and 0.945 were obtained with test RMSE values of 0.2 log₁₀(µA/cm²) and 41.9 mV, respectively. The contribution of each input feature to model predictions was quantified and visualised using the SHapley Additive exPlanations (SHAP) methodology. SHAP analysis reveals that chloride content has the highest impact on $i_{corr}$, followed by carbonation state and the low-humidity condition, while for $E_{corr}$, chloride content and the Submerged condition have the greatest impact. An interactive web application was developed using Streamlit, enabling researchers and practitioners to obtain corrosion parameter predictions. The findings provide data-driven insights into the relative importance of environmental factors governing rebar corrosion, with direct implications for the development of accurate corrosion prediction models for reinforced concrete service life assessment. Full article

The bond strength (τ) of the interface between the anchor bolt and grouting body (or rebar–concrete) is a key indicator used to evaluate the bearing capacity of anchorage engineering. And when rebars are subject to corrosion, τ also serves as an important durability metric. However, traditional experimental measurement of τ is complex, time-consuming and labor-intensive. In this study, based on pullout test data from 429 rebar–concrete specimens, we develop a machine learning method to construct a prediction model with strong generalization ability. Fundamental features—including specimen geometry, dimensions, material strengths, and corrosion rate—are used as inputs. The Sparrow Search Algorithm (SSA) and Particle Swarm Optimization (PSO) are used to fine-tune the hyperparameters of three machine learning models which are Random Forest (RF), Least Squares Boosting (LSBoost), and Generalized Additive Model (GAM). We perform a comparative error analysis of each model and benchmark them against three empirical formulas for τ. The unoptimized models exhibit low predictive accuracy and clear overfitting. After optimization using SSA and PSO algorithms, the prediction accuracy and overfitting issues are significantly improved, with the PSO-LSBoost model achieving the best performance (R² = 0.93). The PSO-LSBoost model’s prediction accuracy for τ far exceeds that of the three empirical formulas. SHAP analysis reveals that the corrosion rate (C_w) contributes most to τ, while the rebar type (ST) contributes least. This work introduces a novel, efficient approach for predicting anchorage bond strength and assessing bolt durability, thereby enhancing the reliability of anchorage structures. Full article

This study investigated how increased Cr and Ni contents affect the corrosion behavior and rust layer evolution of HRB500 rebar in chloride-containing environments. Corrosion of the Cr- and Ni-alloyed rebars was characterized by distinct stages: in the initial stage, before a stable rust layer formed, the corrosion rate increased; with continued immersion, corrosion products progressively covered the surface and became more compact, and the overall corrosion rate decreased. Higher Cr and Ni contents were found to mitigate overall corrosion damage, markedly suppress localized corrosion, and shift the corrosion morphology toward a more uniform attack. Electrochemical measurements showed a noble shift in corrosion potential, a reduction in corrosion current density, and significant increases in low-frequency impedance and charge transfer resistance, indicating enhanced barrier properties against charge transfer and ionic migration. With corrosion progression, rust layer phases evolved from an Fe₃O₄-dominated assemblage to enrichment in stable iron oxyhydroxides; the fraction of α-FeOOH increased, raising the α/γ* index and suggesting improved rust layer stability and protectiveness. Mechanistically, Cr and Ni enrichment was found to facilitate the conversion of metastable products to α-FeOOH and to promote the formation of compact spinel oxides FeCr₂O₄ and NiFe₂O₄, thereby hindering chloride ion ingress and interfacial corrosion reactions and markedly improving corrosion resistance. Overall, this work elucidated the Cr–Ni co-alloying mechanism for rust layer stabilization and pitting suppression. At 504 h, the high Cr–Ni rebar reduced the maximum pit depth by approximately 61.8% and lowered i_corr to approximately 43% of that of the low Cr–Ni rebar, thereby providing quantitative guidance for marine-grade rebar design. Full article

Compared to reinforcing concrete with steel bars, rebars—made of fiber-reinforced plastic—have a high potential for resource savings in the construction industry due to their corrosion resistance. For the large-volume market of reinforcement elements, efficient manufacturing processes must be developed to ensure the best possible bond behavior between concrete and rebar. In contrast to established FRP-rebars made with thermosetting materials, the use of a thermoplastic matrix enables surface profiling without severing the edge fibers as well as subsequent bending of the bar. The rebars to be produced in this study are based on the process of reactive thermoplastic pultrusion of continuously glass fiber reinforced aPA6. Their surface must enable a mechanical interlocking between the reinforcement bar and concrete. Concepts for a profiling device have been methodically developed and evaluated. The resulting concept of a double wheel embossing unit with a variable infeed and an infrared preheating section is built as a prototype, implemented in a pultrusion line, and further optimized. For a comprehensive understanding of the embossing process, reinforcement bars are manufactured, characterized, and evaluated under parameter variation according to a statistical experimental plan. The present study demonstrates the relationship between the infeed, preheating temperature, and haul-off speed with respect to the embossing depth, which is equivalent to the rib height. No degradation of the Young’s modulus was observed as a result of the profiling process. Full article

In accelerated bridge construction, precast concrete girders are connected to cast-in-place concrete slab using shear transfer reinforcement across the interface plane to ensure the composite action. The steel transverse reinforcement is prone to severe corrosion due to the extensive use of de-icing salts and severe environmental conditions. As glass fiber-reinforced polymer (GFRP) reinforcement has shown to be an effective alternative to conventional steel rebars as flexural and shear reinforcement, the present research work is exploring the performance of GFRP reinforcements as shear transfer reinforcement between precast and cast-in-place concretes. Experimental testing was carried out on forty large-scale push-off specimens. Each specimen consists of two L-shaped concrete blocks cast at different times, cold joints, where GFRP reinforcement was used as shear friction reinforcement across the interface with no special treatment applied to the concrete surface at the interface. The investigated parameters included the GFRP reinforcement shape (stirrups and headed bars), reinforcement ratio, axial stiffness, and the concrete compressive strength. The relative slip, reinforcement strain, ultimate strength, and failure modes were reported. The test results showed the effectiveness and competitive shear transfer performance of GFRP compared to steel rebars. A shear friction model for predicting the shear capacity of as-cast, cold concrete joints reinforced by GFRP reinforcement is introduced. Full article

This study examines the relationship between bond strength degradation in corroded reinforced concrete and Half-Cell Potential (HCP) measurements through a combined experimental and numerical approach. Fifty-four concrete specimens reinforced with D19 and D22 rebars underwent impressed-current corrosion to induce specific levels of mass loss. The experimental results showed a progressive reduction in bond strength with increasing corrosion; at approximately 20% mass loss, D19 specimens exhibited up to ~45% reduction, while D22 specimens showed a reduction in ~30%. Correspondingly, HCP values became more negative as corrosion intensified, shifting from around −200 mV at 0% corrosion to values below −900 mV at higher corrosion levels. Although HCP effectively reflected corrosion severity, it did not correlate linearly with bond strength degradation. Numerical simulations performed using COMSOL Multiphysics reproduced the observed electrochemical trends, demonstrating increasingly negative potential distributions with higher corrosion current densities. The findings confirm that HCP is a reliable indicator of corrosion activity but has limited predictive capacity for bond strength loss. This work contributes quantitative insight into the electrochemical–mechanical relationship in corroded reinforced concrete and supports the development of improved assessment frameworks for early maintenance and structural integrity evaluation. Full article

Composite materials have been extensively used across numerous industries due to their exceptional specific strength and corrosive resistance. However, ensuring their mechanical performance and structural integrity remains a critical challenge. This study provides an in-depth investigation into the damage mechanisms occurring in composite rebars manufactured via a modified pultrusion process, with a special emphasis on carbon, glass, and hybrid continuous fiber-reinforced polymers with epoxy resin matrix subjected to static tensile loading. To reveal the damage development, the acoustic emission (AE) technique was employed. Given the inherent complexity of composite microstructures, multiple failure modes can occur simultaneously, often masked by background noise and attenuation effects. Therefore, the core objective of this research is to evaluate and quantify the influence of acoustic attenuation on damage assessment in composite materials. This study introduces an optimization approach to minimize discrepancies between signals captured by different sensors, thereby enhancing the reliability of AE data interpretation. Results reveal that attenuation is strongly dependent on signal travel distance, frequency spectrum, and sensor type. Importantly, a data correction methodology is proposed to mitigate these effects, improving the accuracy of damage detection. Among the analyzed AE parameters, the initial frequency emerged as the most reliable feature for identifying the origin of acoustic events within hybrid composite structures. This finding represents a significant step toward more precise, attenuation-compensated acoustic emission monitoring, offering improved insight into failure mechanisms and contributing to the development of smarter diagnostic tools for composite materials. Full article

The Korean Highway Bridge Design Code introduced requirements for sufficient tensile lap-splice lengths in 2005. Bridge piers designed before 2005 might not have enough tensile lap-splice length. In addition to that, old structures are susceptible to corrosion due to several environmental factors. Thus, to investigate the effect of lap-splice lengths on the bending behavior of the old piers, twelve reinforced concrete (RC) beams were fabricated with sufficient and insufficient tensile lap-splice length, electrochemically corroded and tested under bending. Six of these beams, with sufficient lap-splice lengths, failed in a ductile manner after reinforcement bar (rebar) yielding occurred, whereas the remaining six, with insufficient lap-splice lengths, failed in a brittle manner owing to lap-splice bond failure before rebar yielding. The tested low-corrosion (< 4% by mass) beams exhibited significantly higher load-carrying capacities than non-corroded counterparts tested in our previous study. These results correlated with previously reported results by other researchers, indicating that low corrosion levels do not critically compromise the flexural performance of RC piers. Nevertheless, piers featuring insufficient lap-splice lengths must be rehabilitated to ensure seismically sufficient ductile flexural behavior. Full article

The paper addresses a critical gap in early-stage corrosion detection in reinforced concrete, a leading cause of structural failures with significant impacts on humans, the economy, and the environment. It presents the M5 (Magnetic Force-Induced Vibration Evaluation) method, an innovative Structural Health Monitoring (SHM) approach that avoids damping in concrete by using electromagnetic excitation and transferring rebar vibrations through magnetic coupling over the sample. By inducing and analyzing natural vibrations directly in reinforcement, M5 enables sensitive, non-destructive evaluation (NDE) of corrosion before deterioration occurs. The study follows a systematic literature review based on PRISMA standards and utilizes EmbedSLR v1.0 free software. The methodology combines NDE with IoT deployment using Low-Power Wide Area Networks (LPWANs) and advanced machine learning (ARA) to detect frequency changes caused by corrosion, ensuring continuous monitoring. Findings suggest that M5 has the potential to enhance sustainable asset management by extending infrastructure lifespan, optimizing maintenance, and reducing waste. Its practical implications are significant for urban planners and engineers aiming to align infrastructure management with smart city strategies. The originality of this work lies in integrating electromagnetic NDT with IoT and data-driven decision-making, offering new insights at the intersection of engineering and sustainable smart city management. Full article

Corrosion-induced cracking poses a significant threat to the longevity of reinforced concrete (RC) structures, yet precisely forecasting its advancement continues to be a considerable scientific obstacle. The principal shortcoming of current numerical models is their excessive simplification, frequently presuming totally saturated conditions and disregarding the dynamic interplay between environmental (hygro-thermal) variations and developing mesoscale damage. This study presents a thorough hygro-thermo-electro-chemo-mechanical (HTECM) phase-field model to fill this research need. The model uniquely combines dynamic unsaturated hygro-thermal transport with multi-ion reactive electrochemistry and meso-scale fracture mechanics. A rigorous comparison with published experimental data validates the model’s exceptional accuracy. The anticipated progression of fracture width exhibited remarkable concordance with experimental data, indicating a substantial enhancement in precision compared to uncoupled, saturated-state models. A key finding is the quantification of the damage-induced “transport-corrosion” positive feedback loop: initial corrosion-induced microcracks significantly expedite the transport of local moisture and corrosive agents, leading to nonlinear structural degradation. This work presents a high-fidelity numerical platform that enhances the understanding of linked deterioration in materials science and improves the durability design of reinforced concrete structures. Full article

This study investigates the deterioration of corroded reinforced concrete pipes and their restoration using ultra-high performance concrete (UHPC), utilizing Three-Edge Bearing Tests and 3D finite element analysis under uniform corrosion-induced wall thinning. Unrepaired pipes exhibit elastic behavior, crack propagation, and yield stages, with failure driven by concrete cracking and rebar yielding. UHPC repair mitigates load drop during crack propagation, extends the yield phase, and enhances plastic deformation capacity. Pipe load-bearing capacity is negatively correlated with corrosion thickness and positively correlated with repair thickness (R² > 0.979) and repair compensation ratio. Interfacial performance analysis indicates natural bond degradation under sustained loading, transitioning the pipe to a unitized structure. Embedding steel nails significantly improves interfacial bond strength, increasing failure bearing capacity by 2.91 and 3.56 times compared to natural and PE film interfaces, respectively. Numerical simulations reveal that interface shear strength is five times more influential on bearing capacity decay than interface fracture energy, underscoring its critical role in durability design. An optimization strategy is proposed: reinforce stress-concentrated areas with nails to enhance shear strength and prioritize monitoring interfacial slip to ensure service safety. Full article

This study investigates the corrosion performance of reinforced steel in concrete subjected to carbonation and chloride ingress. Four systems were examined: normal concrete (NC15), chloride-exposed (ClC15), carbonated (COC15), and chloride-exposed carbonated concrete (COClC15). A comprehensive assessment was carried out using electrochemical testing, gravimetric weight loss, chloride profiling, Temkin adsorption isotherm modeling, and SEM analysis. Electrochemical results showed a marked increase in corrosion activity under combined chloride–carbonation exposure. The highest corrosion current density (i_corr) was obtained in COClC15 (0.4779 µA/cm²), compared with only 0.0106 µA/cm² for NC15. Gravimetric analysis confirmed these findings, with COClC15 exhibiting a corrosion rate nearly 1.5 times greater than ClC15 and 52 times higher than NC15 after 120 days. Chloride profiling revealed reduced binding efficiency in carbonated concrete; at 5 mm depth, COClC15 bound only 0.06% chloride, while ClC15 retained 0.43%. The Temkin adsorption isotherm further quantified the weakened binding capacity. The binding coefficient (β) of COClC15 was considerably lower than ClC15 and NC15, reflecting the impact of C–S–H decalcification and aluminate phase transformation into carboaluminates, which restrict Friedel’s salt formation. SEM micrographs corroborated these observations, showing extensive microstructural degradation in COClC15. This study revealed that the synergy of carbonation and chloride ingress reduces chloride-binding capacity, accelerates depassivation, and severely compromises the durability of reinforced concrete in aggressive environments. Full article

The construction of large-scale infrastructure, such as power facilities, requires extensive use of reinforced concrete. The durability degradation of reinforced concrete structures in chloride environments involves multi-physics coupling effects, chloride ion diffusion, rebar corrosion, and concrete damage. Existing models neglect the coupling mechanisms among these processes and the influence of mesoscale structural characteristics. Therefore, this study proposes a diffusive–mechanical coupled phase field by integrating the phase field, chloride ion diffusion, and mechanical equivalence for rebar corrosion, establishing a multi-physics coupling analysis framework at the mesoscale. The model incorporates heterogeneous meso-structure of concrete and constructs a dynamic coupling function between the phase field damage variable and chloride diffusion coefficient, enabling full-process simulation of corrosion-induced cracking under chloride erosion. Numerical results demonstrate that mesoscale heterogeneity significantly affects crack propagation paths, with increased aggregate content delaying the initiation of rebar corrosion. Moreover, the case with corner-positioned rebar exhibits earlier cracking compared to the case with centrally located rebar. Furthermore, larger clear spacing delays delamination failure. Comparisons with the damage mechanics model and experimental data confirm that the proposed model more accurately captures tortuous crack propagation behavior, especially suitable for evaluating the durability of reinforced concrete components in facilities such as transmission tower foundations, substation structures, and marine power facilities. This research provides a highly accurate numerical tool for predicting the service life of reinforced concrete power infrastructure in chloride environments. Full article

Pullout bond tests using specimens with an expansion-agent-filled pipe (EAFP) simulating the cracking due to rebar corrosion were conducted to evaluate the deterioration of bond behavior when the crack width is not uniformly distributed along the longitudinal direction. The primary specimens for the pullout test are designed with a bond length equal to 20 times the bar diameter. To investigate the distribution of bond stress along the rebar in detail, a bond analysis was performed using the local bond stress–slip model as a function of the induced crack width that is developed based on the pullout test of the specimens with a bond length of four times the rebar diameter. The EAFP simulation showed a tendency for larger crack widths at the free end, likely due to filling the expansion agent from the load-end side. From the results of the pullout bond test, as the induced crack width increases, the maximum bond stress decreases. The results of the bond analysis, assuming the five patterns of crack width distributions along the longitudinal direction, showed that the bond stress–slip curve is little affected by the difference in the crack width distribution. Within a bonded length up to 20 times the rebar diameter, the differences in crack width variations had little effect on the distribution of the local bond stress. It is possible to evaluate the bond behavior based on the average crack width. Full article

Thousands of coastal reinforced concrete structures using HRB400 bars have served for over three decades in China. Their reinforcement simultaneously endures chloride corrosion and seismic action, yet studies on performance degradation remain limited. This paper investigates the low-cycle fatigue (LCF) behavior of HRB400 bars under various strain amplitudes, systematically analyzing corrosion morphology, cyclic stress–strain response, fatigue life, and underlying mechanisms. Corrosion is induced by an adjusted accelerated method that replicates field conditions. Observations reveal that corrosion pits act as primary crack initiation sites. Crack paths and fracture surfaces progressively follow the local pit geometry as strain and corrosion grow. The detrimental effect of corrosion on LCF life is more pronounced for smaller bars. At a γ of around 8%, 20 mm bars lose 60.7% of the half cycles to failure at ε = ±1.5%, but only 37.5% at ε = ±5.0%. Predictive corrosion-inclusive strain amplitude (ε_a)–fatigue life models are proposed, yielding R² = 0.952 (16 mm) and 0.928 (20 mm). A unified LCF predictive model, calibrated on a database of 310 corroded/uncorroded bar tests, is established. The final model comprehensively considers the characteristics of rebars, seismic action, and corrosion damage, improving the conventional relationship between LCF life and seismic loading. This work contributes to the understanding of the fatigue behavior of HRB400 bars and provides support for time-dependent seismic reliability analysis of aging reinforced concrete structures in corrosive environments. Full article