Early-age concrete undergoes strongly coupled interactions among hydration, heat transfer, moisture transport, and mechanical response. To rigorously capture these coupled processes, a unified chemo-thermo-hygro-mechanical framework is established, ensuring thermodynamic consistency through the Coleman-Noll procedure. An explicit free-energy density function is introduced, from which the governing equations and constitutive relations of the coupled system are derived. Special emphasis is placed on an anisotropic viscoelastic creep law that distinguishes between tensile and compressive responses. Key material parameters are calibrated for predictive reliability, and validation against experimental data confirms accurate reproduction of the spatiotemporal evolution of temperature and stress alongside hydration and humidity fields. The framework further enables creep-induced stress analysis, highlighting the role of anisotropic creep and the distinct effects of short-term and long-term creep parameters on stress redistribution and cracking risk under restraint. Overall, the proposed energy-based formulation provides a robust foundation for analyzing time-dependent viscoelastic behavior and offers practical guidance for durability design of concrete structures.

Early-age cracking is common in mass reinforced concrete due to the coupled effects of cement hydration heat, temperature gradients, shrinkage, and mechanical restraint, leading to reduced durability and accelerated steel corrosion. The influence of steel reinforcement is not limited to macroscopic crack patterns, but fundamentally lies in its regulation of early-age damage initiation and evolution. However, existing experimental methods and conventional numerical models have difficulty capturing the continuous transition from damage to cracking, which hinders a mechanistic understanding of reinforcement effects. To address this limitation, a fully coupled chemo-thermo-mechanical-damage model based on a phase-field approach is developed. The model is derived from a unified free-energy functional and satisfies the second law of thermodynamics, enabling a continuous description of damage initiation, evolution, and crack formation within a single framework. The model is implemented in ABAQUS using UMAT and UMATHT subroutines and validated against a mass concrete wall experiment, demonstrating good internal consistency. Further analyses reveal that steel reinforcement primarily regulates damage evolution by modifying internal restraint and stress redistribution, rather than merely delaying damage initiation. In contrast, expansive agents mainly postpone damage onset through stress adjustment, while their influence on subsequent damage evolution remains limited. The proposed framework provides a mechanistic basis for understanding and quantitatively analyzing reinforcement-controlled early-age damage and cracking, and offers theoretical support for early-age damage regulation toward long-term durability.

Ultrasonic tomography is widely used to image the internal defects in hardened concrete. However, the application of ultrasonic tomography on hydration monitoring has been rarely reported. The heterogeneity and attenuation of fresh concrete cause variations in ultrasonic velocity, which reduce the robustness and accuracy of defect imaging. This disturbance is unacceptable for large-diameter pile foundations, especially at early ages when the concrete exhibits high heterogeneity. To this end, two innovative works are presented in this paper. First, testing equipment is specially developed to produce the ultrasonic tomography of super pile foundations with a diameter of 4 m, a length of 92 m, and submerged in 63-m-deep water. Second, the isolation forest algorithm is introduced to detect and locate the defects in the ultrasonic image based on adaptive thresholds. Cavities with diameters exceeding 10 cm and layered defects thicker than 18 cm can be robustly detected in the sharpened image, whereas no defects can be recognized in the original image. The feasibility and effectiveness of the proposed method are validated through simulation, full-scale experiments, and in-situ tests. The proposed method can facilitate the ultrasonic testing of large structures made of heterogeneous materials.

Ground penetration radar is the primary method used for internal detection of concrete. However, water interference prevents the ground penetration radar from operating effectively underwater. To overcome this limitation, this study presents an ultrasonic-based method for accurately detecting inclusions in concrete. The process begins by applying an adaptive window technique to full matrix data acquired from an ultrasonic array, aiming to suppress interfacial wave components. In addition, an amplitude-phase coherence factor is incorporated into the total focusing method to mitigate the effects of heterogeneous scattering. A dedicated algorithm is further developed to estimate the location and diameter of rebars. The process is validated through simulations, laboratory experiments, and field tests. Rebar diameter errors are 1.51 mm, 1.31 mm, and 1.38 mm, while localization errors are 4.15 mm, 7.01 mm, and 6.66 mm, respectively. This work demonstrates the feasibility of ultrasonic imaging for visualizing internal features in underwater concrete, contributing to nondestructive testing and structural health monitoring of concrete infrastructure.

Tunnel linings are exposed to harsh service environments, where long-term effects such as groundwater ingress, train-induced vibrations, and material degradation can significantly reduce their structural capacity and durability. A novel nested arch reinforcement system employing corrugated basalt fiber-reinforced polymer (BFRP) plates was proposed and evaluated to overcome the corrosion and maintenance limitations of steel-based systems. Ten reduced-scale reinforced concrete (RC) arch segments were subjected to four-point bending to examine the effects of reinforcement ratio, BFRP plate thickness, and filling density. A refined finite element model (FEM) was established and validated against the experimental results. The ultimate load capacity of the strengthened system increased by 61-102% and its flexural stiffness by 200-358%, while residual deformation was reduced by up to 75%. According to the FEM results, an increase in reinforcement ratio reduced the damage growth in the original specimens but intensified damage in the nested arch, thereby enhancing its tensile contribution. At yielding, the stress distribution in the corrugated BFRP plates became more uniform, indicating that the lining provides greater contribution by high-reinforcement. Furthermore, the ultimate capacities obtained from the proposed analytical method exhibited an average error of about 10-15% compared with the test results, demonstrating its applicability for practical design. These results provide a practical basis for the design and implementation of lightweight, durable, and rapidly installable strengthening solutions for deteriorated tunnel linings.

Basalt fiber-reinforced polymer (BFRP) composite laminates are increasingly used in wind turbine blades due to their lightweight, high specific strength, and environmental benefits. But the brittle epoxy makes them susceptible to delamination and fiber fracture under high-velocity ballistic loads like hailstones, which reduces flexural strength by up to 60% and compromises structural load-bearing capacity. While experimental ballistic testing using light gas guns is accurate, it is extremely costly, time-consuming, and struggles to capture internal damage initiation. This study adopts a high-efficiency sequential multiscale simulation framework that balances prediction accuracy and computational cost for plain-woven BFRP laminates. A microscale representative volume element (RVE) model with hexagonal fiber packing is constructed to derive elastic constants and strength parameters under periodic boundary conditions coupled with a fracture energy-based damage evolution criterion. These properties are then transferred to a mesoscale RVE model replicating the actual plain-woven architecture to obtain material properties for the macroscale composite laminate. At the macroscale, a user-defined material subroutine integrating Hashin criterion and bilinear cohesive zone model is implemented to simulate multi-mode damage initiation, including fiber tensile/compressive/shear failure, matrix damage, and interlaminar delamination, and damage evolution supported by an exponential stiffness degradation model. By validating against the experimental ballistic limit, the simulations accurately capture the entire impact-induced damage, energy dissipation, and ballistic limit. This approach provides a reliable, low-cost computational tool for the design and performance evaluation of BFRP composite and emerging FRP composites in wind turbine blades under extreme impact conditions, reducing reliance on extensive physical testing.

Guardrails can prevent vehicles from crashing into the opposite lane, thereby reducing the risk of fatalities. However, the burial depth may be insufficient when the underlying soil is hard. The detection of the burial depth of guardrail posts mainly relies on the impact-echo method. According to the time-of-flight of the bottom echo, the burial depth is calculated based on wave velocity. However, since the frequency of guided waves cannot be precisely controlled by hammer impact and guided wave velocity is related to the frequency, the impact echo method suffers from insufficient accuracy for detecting burial depth. Therefore, this paper utilizes transducers to replace the impact hammer to excite guided waves. An automatic identification method is developed based on the Sparse Bayesian learning to compensate for the dispersion of guided waves and to recognize the bottom echo. The burial depth is determined based on a Bayesian model that utilizes multiple transducer pairs without prior knowledge of material properties and wave velocities. The detection accuracy is examined for different burial depths in simulations, experiments, and field tests. Simulation results show a mean relative error of 3.23% and experimental results show a mean relative error of 8.43%. The proposed method promotes the maintenance of highway infrastructures.

Quantitative measurement of apparent defects using underwater vision-based techniques is essential for structural inspection of submerged bridge components. However, measurement accuracy is greatly limited by nonlinear imaging distortions caused by multi-medium refraction and viewport deformation under hydrostatic pressure. To overcome these challenges, this paper introduces a multi-refraction correction model that accounts for refractive interface deformation. A nonlinear underwater imaging framework is established by integrating a spatial coordinate transformation-based calibration method with deformation analysis of the viewport. The feasibility and accuracy of the proposed approach are validated through underwater checkerboard corner-detection experiments. Compared with traditional multi-plane refraction correction method, the proposed model enhances measurement precision by more than 40 %. Additional experiments on submerged bridge pier components show that the measurement errors for apparent defect dimensions consistently remain below 5 %, highlighting the strong potential of the method for practical implementation in underwater visual inspection of bridge infrastructure.

Early-age internal visualization is critical for timely assessing the quality of pile foundations, especially as super cross-sea bridges increase the diameter and length of pile foundations beyond the capabilities of traditional cross-hole sonic logging (CSL). This article introduces two innovations. First, ultrasonic instruments are specially developed to transmit waves through a concrete pile with a diameter of 4 m, a length of 92 m, and a water depth of 63 m, before the full hardening of concrete. Second, an imaging method is proposed to upgrade traditional CSL from 1D detection to 3D visualization. Both large-scale experiments and field tests are tested in the first 7 days after the concrete casting. The experiments successfully visualize typical construction defects, achieving a detection resolution of 18 cm for layered defects and 15 cm for void defects. During the field test, a low-pixel region is observed at the pile head, extending approximately 2.1 m deep, attributed to mud floating up during concrete casting into the steel casing. These developments in instrument technology and visualization methods provide essential tools for the quality evaluation of super pile foundations. Furthermore, the visualization data can support digital twin modeling in subsequent stages of construction and maintenance planning.

Precast segmental self-centering bridge columns (PSC-SCBCs) typically use full-length steel tendons, which demand high prestressing forces, large tendon sizes, and complex anchorages, leading to inefficient stress distribution along the column height. This study presents a comprehensive numerical investigation into the seismic performance of PSC-SCBCs incorporating two novel tendon optimization strategies: intermediate anchorage of tendons and hybrid steel-FRP tendon systems. A detailed finite element model was developed and validated in ABAQUS to evaluate the influence of tendon anchorage height, material composition, and axial prestress level on the columns' lateral strength, damage pattern, energy dissipation, and residual drift. Three groups of specimens were analyzed. Groups I and II replaced one-third or two-thirds of full-length steel tendons with intermediate-length tendons anchored at H/3, H/2, or 2H/3. Group III employed a hybrid system combining steel, carbon FRP (CFRP), and basalt FRP (BFRP) tendons at designated heights and with varied prestressing levels. The results indicate that intermediate anchorage improves prestress distribution, enhances structural performance, enables easier tendon inspection, and reduces material demand. The hybrid steel-FRP tendon systems further increased lateral strength by up to 50 % and reduced residual drift by 44 % at higher prestress levels, while maintaining energy dissipation comparable to conventional systems. Tendon stress analysis revealed that anchoring high-stiffness steel tendons at low elevations risks premature yielding, whereas FRP tendons safely operated below 73 % of their ultimate capacity at 5.5 % drift. These findings validate the proposed tendon strategies as practical, efficient, and resilient solutions for advancing seismic bridge design.

Basalt fiber and basalt fiber-reinforced polymer (BFRP) material are known for their high mechanical performance, excellent durability, and sustainability features. In this study, the embodied carbon emissions of basalt fiber, BFRP grid, and BFRP bar are calculated and compared with those of other fibers and FRPs. Then, the carbon emissions of a FRP grid-strengthened structure and a FRP bar-reinforced concrete structure are evaluated. It is estimated that the emission factor (EF) of basalt fiber ranges from 0.98 to 3.87 kgCO2e/kg, depending on the manufacturing method and scale, which is significantly lower than that of carbon and aramid fibers. With the novel automatic continuous weaving-molding (ACWM) manufacturing method, the EF of BFRP grid is 3.27 kgCO2e/kg. In the FRP grid-strengthening case study, it is found that a thicker FRP grid significantly reduces the carbon emissions for unit flexural capacity enhancement. For 5 mm-thick CFRP, GFRP, and BFRP grid-strengthened structures, the carbon emissions for unit flexural capacity enhancement are reduced to 6.26, 8.39, and 6.90 kgCO2e/kN/m, respectively, from 8.57 kgCO2e/kN/m for the section enlarged structure. In another case study of an offshore reinforced structure, under the stiffness equivalent substitution, the life-cycle carbon emissions for CFRP, AFRP, GFRP, BFRP, and steel reinforced concrete are 1448, 1795, 1749, 1460, and 1530 tCO2e, respectively.

Bolted joints with low efficiency in pultruded unidirectional (UD) FRP members hinder material strength utilization. To address this limitation, this study explores innovative enhancement strategies for multi-bolt joints in square tubes: material strengthening via multi-directional (MD) fiber architecture, global structural optimization through bilateral constraint, and local hole reinforcement using bonded inserts. Results show that MD lay-up introduces off-axis fiber tie action, transforming shear-dominant UD failure to bearing failure. Bilateral constraints confine stresses within the tube-wall plane, expanding the uniform load-carrying area. Bonded inserts establish continuous full-perimeter load-transfer paths in sleeved joints, promoting uniform multi-bolt load distribution. Accordingly, these individual mechanisms increase joint strength by up to 58.5% over corresponding control cases. Furthermore, fiber architecture-constraint-bonded insert interaction mechanisms are revealed for the first time: under unilateral constraint, long inserts delay premature UD failure from throughthickness stress non-uniformity by resisting bending compared to short inserts, whereas multi-axial stress diffusion in MD mitigates sensitivity to stress non-uniformity, minimizing the effect of insert length. By contrast, bilateral constraint enforces upright insert posture in both UD and MD cases, ensuring uniform through-thickness stresses and thus comparable performance across insert configurations. The synergistic combination "MD lay-up + bilateral constraint + long insert" doubles the strength of unilaterally constrained conventional UD joints. Finally, a strength prediction method incorporating insert and constraint effects is developed based on design codes, showing agreement with experimental results within 10% deviation.

Inspection of concealed underwater bridge piers faces challenges such as inaccessibility, poor visibility, and low measurement accuracy, limiting safety assessment and maintenance planning. This paper proposes a highprecision visual 3D measurement framework for detecting defects on underwater bridge piers in highturbidity water, integrating a binocular system with a clean-water hood mounted on an ROV, a multi-medium refraction correction model, and a multi-sequence point cloud stitching method. Validation shows the cleanwater hood preserves over 80% of point cloud reconstruction at 120 NTU turbidity, while refraction correction reduces checkerboard corner and cylindrical surface errors to within 0.2 mm and 0.8 mm, respectively. The point cloud stitching method improves accuracy by 50%. Field tests demonstrate over 60% improvement in defect size measurement along x and y directions. These results show that reliable 3D defect quantification is feasible in turbid underwater environments when turbidity, refraction, and stitching errors are jointly controlled.

The FRP-grid–concrete interface governs stress transfer and damage development in FRP-grid-strengthened reinforced concrete members, yet existing models rarely combine mixed-mode interaction, grid-node restraint, and loading-history effects within one formulation. This study proposes a three-dimensional mixed-mode zero-thickness interface element for monotonic and repetitive progressive loading (RPL). The model describes tangential slip, normal opening and closure, tangential–normal coupling, unloading stiffness degradation, strength degradation, residual-slip accumulation, and the additional restraint associated with grid intersections through an equivalent node-influence zone. The formulation is implemented in Abaqus as a user-defined element, while a Python preprocessor automates interface insertion, local-coordinate assignment, node-zone identification, and parameter allocation. Model parameters are established from pull-out tests and subsequently examined using published monotonic cases not included in calibration and held-out RPL specimens. The numerical results reproduce the principal load–slip characteristics, damage localization, pinched hysteresis, and progressive peak-load degradation observed in the tests. The proposed framework provides an efficient and physically interpretable means of representing FRP-grid–concrete interaction in nonlinear finite element analysis.

In this paper, a stress wave velocity imaging technology for an ultra-large deep-water pile foundation is proposed and investigated, in which an optical fiber distributed acoustic sensing (DAS) system is employed for the detection of stress wave inside a pile foundation and a stress wave velocity imaging method based on cross-correlation time-shift stacking is developed for the early online monitoring of pile integrity during construction period. Based on this, the stress wave detection scheme was designed and implemented at Dongwuyang cross-sea bridge by embedding sensing fiber cable into a 92-meter deep-water pile foundation during the construction period to capture the stress wave generated by a percussion drill at an adjacent well. The results demonstrate that the wave velocity distribution along the pile foundation after the solidification period can be obtained through the proposed scheme that exhibits good consistency with a fluctuation range from 3636 m/s to 4000 m/s between the depths of 35 and 90 m, which is in accord with the results of the acoustic wave transmission method. Finally, the possibility of pile integrity monitoring through stress wave velocity imaging is also explored and evaluated based on simulation and above detection results, which indicates a potential method for pile defect detection during the construction period.

Concrete is widely used for its high strength and durability. At early ages, hydration, heat transfer, and moisture transport are the main causes of stress. These processes may lead to nonuniform deformation, high tensile stress, and early cracking, which make prediction difficult. Previous chemo-thermo-hygral models often depended on empirical relations or weak coupling assumptions and lacked thermodynamic consistency. As a result, their theoretical rigor and applicability were limited. In this study, a new free energy density function is proposed within a thermodynamically consistent framework, and a strongly coupled chemo-thermo-hygral model for early-age concrete is developed. The governing equations are derived strictly from thermodynamic principles to describe the spatial and temporal evolution of hydration, temperature, and relative humidity. The model is validated by two-dimensional and three-dimensional simulations and experimental data. The results show that the model can accurately capture the evolution of temperature-humidity coupling and has good predictive ability. A parameter analysis shows that the evolution of relative humidity is sensitive and complex, which highlights its key role in the early-age behavior of concrete. The proposed framework overcomes the limitations of existing models and provides a unified and solid basis for the study of coupled reactive porous media, with important implications for structural design, crack control, and durability improvement.

Despite significant advancements in the field of structural health monitoring (SHM), there have been significant challenges in the development of a full-lifecycle SHM. To enable a reliable, comprehensive and accurate full-lifecycle SHM, even under extreme conditions, this study proposes a novel Dual-Stage Adaptive Long-Gauge Fiber Optic Strain Sensor (DS-LGFS). This sensor seamlessly transitions between high-precision monitoring in small strains and reliable sensing during large deformations. A hybrid deployment scheme, integrating conventional LGFSs with the new DS-LGFSs, is designed to facilitate a full-lifecycle SHM. We establish a comprehensive theoretical framework to clarify the relationship between key design parameters and the sensor’s dual-stage behavior. Furthermore, a dual-stage temperature compensation strategy and an error analysis are developed to ensure measurement reliability. Experimental results demonstrate an ultimate strain measurement capability of 2%, a 178% improvement over standard bare FBG sensors, alongside exceptional repeatability and stability. These findings underscore the DS-LGFS’s significant potential for accurate, reliable, and practical full-lifecycle SHM.

Crumb rubber concrete (CRC) offers environmental benefits through the recycling of waste tires, enhancing flexibility, durability, and impact resistance. However, its application is often limited by a reduction in mechanical strength. This study investigates the novel combination of crumb rubber (CR) aggregate and basalt minibars fiber (BMF) to mitigate these drawbacks and enhance the overall performance. An experimental program was conducted to evaluate the effect of rubber replacement ratios (5

The increasing accumulation of fly ash and ground granulated blast-furnace slag (GGBFS) presents significant environmental and land-use challenges. Valorizing these industrial by-products as alkali-activated geopolymer mortar (AGM) offers a sustainable waste management strategy while reducing the carbon footprint of construction repair. This study adopts a two-stage approach to investigate the effects of activator-to-binder ratio (A/B), slag-to-total binder ratio (S/B), and fiber type (basalt and polypropylene) on the fluidity, mechanical properties, and shrinkage of AGM. Results showed that appropriate A/B and S/B optimize overall performance. The optimal Group A40S3 (A/B = 0.40, S/B = 0.30) exhibited a setting time of 80 min, 7d flexural strength of 6.06 MPa, and compressive strength of 35.53 MPa. Fiber incorporation further enhanced flexural strength by over 25% and reduced drying shrinkage by 26.3–36.7%, with both fiber types showing comparable effectiveness. From a waste management perspective, the optimized AGM reduced embodied carbon by 50%, embodied energy by 17%, and material cost by 13% compared to equivalent OPC mortar, while diverting 760 kg of solid waste per cubic meter from landfills. This study provides a waste‑to‑resource solution that combines early‑age performance with quantifiable environmental and economic benefits for rapid repair engineering.

Underground grain silos offer advantages such as space efficiency, low energy consumption, and concealment, but their long-term exposure to complex geotechnical environments makes them vulnerable to concealed, multimode, and spatially distributed water leakage. To address the limitations of existing detection and monitoring methods, this study proposes a frequency-modulated actively heated fiber-optic sensing method for distributed water leakage monitoring in underground grain silos. Based on transient heat conduction theory, a one-dimensional finite element heat transfer model and a parametric numerical simulation framework were developed to investigate the effects of infiltrated water thickness, heating power, and excitation duration on temperature responses. A sensing indicator system and evaluation framework were then established to enable multimode leakage identification and quantitative assessment of leakage parameters, including leakage amount, grain moisture content, and moist layer thickness. Laboratory model tests under 12 leakage conditions verified the effectiveness of the proposed method. The leakage mode identification accuracy reached 100%, and the experimental indicators showed good agreement with the optimal excitation curves, with R² values greater than 0.963. The inverted grain moisture content errors were within 1% for all conditions, and the moist layer thickness errors were less than 1 mm in 11 conditions, with a maximum error of 1.56 mm. These results demonstrate that the proposed method provides an effective technical approach for accurate identification and assessment of concealed multimode leakage in underground grain silos.