Search Results (65)

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

The accurate measurement of a crack width in concrete infrastructure is essential for structural safety assessment and maintenance. However, existing image-based methods either suffer from overestimation in complex geometries or are computationally inefficient. This paper proposes a novel hybrid approach combining a fast skeleton-pruning algorithm and a crack-width measurement technique called edge-OrthoBoundary (EOB). The skeleton-pruning algorithm prunes the skeleton, viewed as the longest branch in a tree structure, using a depth-first search (DFS) approach. Additionally, an intersection removal algorithm based on dilation replaces the midpoint circle algorithm to segment the crack skeleton into computable parts. The EOB method combines the OrthoBoundary and edge shortest distance (ESD) techniques, effectively correcting the propagation direction of the skeleton points while accounting for their width. The validation of real cracks shows the skeleton-pruning algorithm’s effectiveness, eliminating the need for a specified threshold and reducing time complexity. Experimental results with both actual and synthetic cracks demonstrate that the EOB method achieves the smallest RMS, MAE, and R values, confirming its accuracy and stability compared to the orthogonal projection (OP), OrthoBoundary, and ESD methods. 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

This paper presents a standardized apparatus and method for testing the accuracy of mobile phone apps designed to measure concrete crack widths. The apparatus comprises a standardized crack-width calibration plate (CWCP) and a simulated wall (SW), along with a pose adjusting and fixing device (PAFD) and a spatial distance measuring assemblage (SDMA). The test method employs an innovative two-stage procedure associated with the SDMA to calculate the distances (K_i) from the phone’s four corners to the SW. The phone’s position is adjusted using the PAFD until the four monitored K_i values match the target K_i. An app installed on the phone then measures crack widths on the CWCP. A standard experimental procedure was established to assess the accuracy of a preliminary Android app in measuring concrete crack widths, with results presented and discussed. This apparatus and method, grounded in their underlying physical meaning, can realistically simulate actual engineering conditions precisely and cost-effectively. Full article

Superabsorbent polymers have been introduced into cementitious materials to solve issues related to early-age cracking, caused by shrinkage, and manual repair. A general improvement of autogenous healing is noticed, while the extent and effectiveness depend on the type of hydrogel and the amount included. To evaluate the self-healing effectiveness, the regain of mechanical performance needs to be assessed. However, such evaluation requires destructive testing, meaning that the healing progress cannot be followed over time. As a solution, air-coupled ultrasonic testing was used within this study, adopting a novel laser interferometer as a receiver, to estimate the regained properties of cementitious mixtures with and without superabsorbent polymers. The sensitivity of ultrasonic waves to the elastic properties of the material under study allows us to monitor the crack healing progress, while the semi-contactless nature of the procedure enables an easy and reliable measurement. Up to 80% recovery in ultrasonic velocity was achieved with reference concrete, while SAP concrete demonstrated up to 100% recovery after wet–dry curing. Following microscopic analysis, up to 19% visual crack closure was obtained for reference concrete, compared to a maximum of 50% for SAP mixtures, for average crack widths between 250 µm and 450 µm. Full article

This study investigates the influence of crack width on the time to chloride-induced corrosion initiation in reinforced concrete (RC) bridge decks, incorporating climate change projections through the year 2100 under IPCC scenarios (RCP2.6 and RCP8.5). A probabilistic modelling approach using Monte Carlo simulations (MCSs) was applied to assess corrosion initiation across a range of environmental and structural conditions, including normal and high-performance concrete (HPC), varying concrete cover depths, and the use of supplementary cementing materials (SCMs). The results indicate that increasing the crack width significantly accelerates chloride ingress, reducing the time to corrosion initiation by up to 41% compared with that under uncracked conditions. HPC demonstrated superior durability, delaying corrosion initiation by nearly twice as long as normal concrete under identical chloride exposure. Elevated temperatures projected under high-emission scenarios further reduce service life by increasing chloride diffusion rates. Polynomial regression models were developed to relate crack width and concrete cover to corrosion initiation time, offering practical tools for durability-based design and service life prediction. These findings highlight the importance of enhanced crack control, climate-adaptive material selection, and updated durability standards to improve the resilience of RC bridge infrastructure in the face of climate change. Full article

To optimize the design of concrete beams and assess the performance of new materials, four-point bending tests were conducted to examine the bending behavior of alkali-activated concrete (ALAC) beams with different reinforcement ratios. The cracking load, displacement, and crack width were measured using the Digital Image Correlation (DIC) method and compared with results obtained through traditional methods. The findings demonstrate that DIC significantly outperforms traditional techniques in determining crack load, displacement, and crack width, particularly in capturing crack initiation and propagation. As the reinforcement ratio increases, the mid-span displacement at the peak load decreases for ALAC beams. At the same reinforcement ratio, the ALAC beam exhibits 1.07 times the bearing capacity, 1.4 times the mid-span displacement, and 0.72 times the maximum crack width compared to ordinary Portland cement concrete (PCC) beams. The cracking load, calculated using a plasticity coefficient of 1.17 for the section resistance moment, aligns closely with the experimental results. Furthermore, the formulas for mid-span displacement and maximum crack width in ordinary concrete beams can also predict the corresponding properties of ALAC beams. These findings validate the mechanical behavior and application potential of ALAC beams under various reinforcement ratios. Full article

Concrete is widely used in different types of buildings and bridges; however, one of the major issues for concrete structures is crack formation and propagation during its service life. These cracks can potentially introduce harmful agents into concrete, resulting in a reduction in the overall lifespan of concrete structures. Traditional methods for crack detection primarily hinge on manual visual inspection, which relies on the experience and expertise of inspectors using tools such as magnifying glasses and microscopes. To address this issue, computer vision is one of the most innovative solutions for concrete cracking evaluation, and its application has been an area of research interest in the past few years. This study focuses on the utilization of the lightweight MobileNetV2 neural network for concrete crack detection. A dataset including 40,000 images was adopted and preprocessed using various thresholding techniques, of which adaptive thresholding was selected for developing the crack evaluation algorithm. While both the convolutional neural network (CNN) and MobileNetV2 indicated comparable accuracy levels in crack detection, the MobileNetV2 model’s significantly smaller size makes it a more efficient selection for crack detection using mobile devices. In addition, an advanced algorithm was developed to detect cracks and evaluate crack widths in high-resolution images. The effectiveness and reliability of both the selected method and the developed algorithm were subsequently assessed through experimental validation. Full article

The current design methods employed for composite pavement structures predominantly rely on cement concrete slabs, which unfortunately lack established design standards and associated control indicators for determining the appropriate thickness of the asphalt layer. Therefore, the emergence of reflective cracks at the bottom of the asphalt layer has become a prevalent issue in composite pavement. This article aims to enhance the existing design methodology for composite pavement structures by proposing the inclusion of “cracking at the bottom of the asphalt layer” as a design indicator. An extensive analysis was conducted to assess the influence of various factors, including the elastic modulus and thickness of the asphalt layer, the elastic modulus, and thicknesses of the cement concrete slab, as well as the dimensions of the cement concrete slab (length and width), foundation reaction modulus, and joint width, on the comprehensive stress at the bottom of the asphalt layer. Additionally, formulas were derived to calculate the temperature warping stress and load stress, and a formula was also provided for determining the equivalent modulus of the structure, taking into account the stress-absorbing layer. Subsequently, the proposed methodology was applied to the Weixu Expressway. The results suggest adopting a surface structure design scheme consisting of a 6 cm asphalt concrete + 2 cm stress absorption layer. This study found that, when the thickness of the stress-absorbing layer is less than 2 cm, the load stress is highly sensitive to changes in the thickness of this layer. Specifically, a 1 cm thick stress-absorbing layer reduces the maximum tensile stress at the bottom of the asphalt layer by approximately 69.7%, decreases the equivalent stress by about 34.1%, and lowers the maximum shear stress by around 30.9%. However, once the thickness exceeds 2 cm, the load stress remains relatively constant. Thus, it was advisable to utilize an optimal stress-absorbing layer thickness of 2 cm. Full article

Crack detection and quantification play crucial roles in assessing the condition of concrete structures. Herein, a novel real-time crack detection and quantification method that leverages binocular vision and a lightweight deep learning model is proposed. In this methodology, the proposed method based on the following four modules is adopted: a lightweight classification algorithm, a high-precision segmentation algorithm, a semi-global block matching algorithm (SGBM), and a crack quantification technique. Based on the crack segmentation results, a framework is developed for quantitative analysis of the major geometric parameters, including crack length, crack width, and crack angle of orientation at the pixel level. Results indicate that, by incorporating channel attention and spatial attention mechanisms in the MBConv module, the detection accuracy of the improved EfficientNetV2 increased by 1.6% compared with the original EfficientNetV2. Results indicate that using the proposed quantification method can achieve low quantification errors of 2%, 4.5%, and 4% for the crack length, width, and angle of orientation, respectively. The proposed method can contribute to crack detection and quantification in practical use by being deployed on smart devices. Full article

Concrete columns are considered critical elements with respect to the stability of buildings during earthquakes. To improve the accuracy of column damage and collapse risk estimates using numerical simulations, it is important to develop a methodology to quantify the effect of displacement history on column force–deformation modeling parameters. Addressing this knowledge gap systematically and comprehensively through experimentation is difficult due to the prohibitive cost. The primary objective of this study was to develop guidelines to simulate the lateral cyclic behavior and axial collapse of concrete columns with different modes of failure using continuum finite element (FE) models, such that wider parametric studies can be conducted numerically to improve the accuracy of assessment methodologies for critical columns. This study expands on existing FEM research by addressing the complex behavior of columns that experience multiple failure modes, including axial collapse following flexure–shear, shear, and flexure degradation, a topic which has been underexplored in previous works. Nonlinear FE models were constructed and calibrated to experimental tests for 21 columns that sustained flexure, flexure–shear, and shear failures, followed by axial failure, when subjected to cyclic and monotonic lateral displacement protocols. The selected columns represented a range of axial loads, shear stresses, transverse reinforcement ratios, longitudinal reinforcement ratios, and shear span-to-depth ratios. Recommendations on optimal material model parameters obtained from a parametric study are presented. Metrics used for optimization include crack widths, damage in concrete and reinforcement, drift at initiation of axial and lateral strength degradation, and peak lateral strength. The capacities of shear–critical columns calculated with the optimized numerical models are compared with experimental results and standard equations from ASCE 41-17 and ACI 318-19. The optimized finite element models were found to reliably predict peak strength and deformation at the onset of both lateral and axial strength failure, independent of the mode of lateral strength degradation. Also, current standard shear capacity provisions were found to be conservative in most cases, while the FE models estimated shear strength with greater accuracy. Full article

A top-chord-free Vierendeel-truss composite slab (TVCS) comprises a concrete slab, several vertical webs, and a steel bottom chord. In this study, static tests and finite element analyses were conducted based on an actual project to investigate the deformation, crack characteristics, ultimate bearing capacity, and failure mode of the composite slab. The findings indicated that the loading process of this type of floor can be divided into elastic, elastoplastic, and failure stages. The section stress distribution in the elastic stage was further analyzed. The crack development pattern exhibited a fine density in the pure bending sections of the concrete slabs, while demonstrating good overall flexural bearing capacity and ductility for the composite slab. Experimental results were compared with the ANSYS finite element model simulation to validate the accuracy of the simulation. Parametric analysis was conducted to assess the impact of concrete strength, steel strength, vertical web width, and distance ratios on the mechanical characteristics of the composite slab. By introducing an adjustment coefficient for the vertical web distance ratio, a revised calculation formula for flexural bearing capacity was proposed, which aligned well with the finite element analysis. Full article

In corrosive environments containing chloride and sulfate, the corrosion of steel bars is common along the base of squat RC shear walls (SRCSW) due to problems such as construction quality, concrete stress concentration, local defects, and accumulation of water and corrosive media. In this paper, three SRCSWs are designed and constructed and their mechanical properties assessed. One side of each SRCSW was exposed to a corrosive environment for 70 days, while the other side was subject to the same conditions over different corrosion times (i.e., 0 day, 42 days, and 70 days). Then, the corrosion-induced cracking process, the mechanical properties of SRCSWs corroded along the base, the relationship between the mass loss of total steel bars (MLTSB) in the corroded area and the wall mechanical properties, and the relationship between the average width of corrosion-induced cracks (CICs) and the wall mechanical properties were studied through an accelerated corrosion test and a loading failure test. The results indicate that the area of corrosion-induced cracking on SRCSWs increased with the corrosion time, and the cracking area on the different SRCSWs was approximately identical when the SRCSWs were exposed to the same corrosion time. When the degree of corrosion was different, the loading failure characteristics of the SRCSWs were obviously different, but the failure mode always corresponded to shear failure. The load–displacement curves of the SRCSWs with different degrees of corrosion along the base basically coincided and were linear when the loading was in the elastic stage. Compared to SW-1, the peak load of SW-2 decreased by 4.0%, but that of SW-3 increased by 2.7%. Compared to SW-1, the yield loads of SW-2 and SW-3 decreased by 22.4% and 11.8%, respectively. When the MLTSB increased from 13.05% to 16.71%, the crack, yield, and peak loads of the SRCSWs corroded along the base decreased by 8.8%, 22.4%, and 6.8%, respectively. The cracking, yield, and peak loads of the SRCSWs corroded along the base decreased linearly with the increase in MLTSB and the average width of the CICs, and the corresponding fitting relations were established. The results of this study can serve as a reference for the durability design of SRCSWs in corrosive environments. Full article

Prestressed concrete box girders are commonly employed in the development of high-speed railway bridge constructions. The prestressed strands in the girder may corrode due to long-term chloride erosion, leading to the degradation of its flexural performance. To examine the flexural performance of corrosion-affected simply supported prestressed concrete box girders, eight T-shaped mock-up beams related to the girders used in the construction of high-speed railway bridges were manufactured utilizing similarity theory. Seven of the beams underwent electrochemical accelerated corrosion, and then each beam was subjected to failure under the four-point load test method. Measurements recorded and analyzed in detail during the loading process included the following: crack propagation, crack width at various loads, crack load, ultimate load, deflection, and concrete strain of the mid-span section. The results demonstrate that a corrosion rate of just 8.31% has a considerable impact on the structural integrity of the beams, as evidenced by a pronounced reduction in flexural cracks and a tendency towards reduced reinforcement failure. Furthermore, the corrosive process has a detrimental effect on mid-span deflection, ductility, and ultimate flexural bearing capacity, which could have significant implications for bridge safety. This study provides valuable insights for the assessment of flexural performance and the development of appropriate maintenance strategies for corroded simply supported box girders in high-speed railways. Full article

An investigation was conducted to assess the efficacy of using waste rubber as a substitute for a portion of an aggregate to enhance concrete’s sustainability. For the purpose of accomplishing this objective, a total of 12 specimens were constructed and then subjected to a series of tests to investigate their bending behavior. The samples were constructed with the following dimensions: 1000 mm length and a 100 mm by 150 mm cross-sectional area. A few factors were selected, including the impacts of the longitudinal reinforcement ratio and the waste rubber ratio. Based on the volume of aggregates, rubber replacement rates of 0%, 5%, 10%, and 15% were investigated in this study. To assess the beam bending behavior, the stirrup width and spacing were kept constant at ∅6/10. The longitudinal reinforcement was composed of three diameters: ∅6 at the top (for all beams) and ∅8, ∅10, and ∅12 at the bottom. The experimental results demonstrated that the effects of varying amounts of waste rubber and tension reinforcement on the bending and cracking of reinforced concrete beams (RCBs) were varied. The findings indicate that the incorporation of waste rubber into concrete results in a reduction in both the load-carrying capacity and the level of deformation of the material. Additionally, it was shown that as the amount of waste rubber in the RCB increased, the energy absorption capacity and ultimate load decreased. There was a reduction in energy dissipation of 53.71%, 51.69%, and 40.55% for ∅8 when longitudinal reinforcement was applied at 5%, 10%, and 15% replacement, respectively. Additionally, there were reductions of 25.35%, 9.31%, and 58.15% for ∅10, and 38.69%, 57.79%, and 62.44% for ∅12, respectively. Full article