The insufficient toughness of the epoxy-bonded interface between carbon fiber-reinforced polymer (CFRP) and steel readily results in a deterioration of the joint's interfacial fracture performance at elevated temperature. This study proposes a method to toughen the epoxy-bonded interface between CFRP and steel by incorporating thermoplastic polyamide nanofiber veils (Xantu.Layr). End notched flexure (ENF) tests were conducted to investigate the toughening effect of the nanofibers on the epoxy-bonded interface at room temperature (25 °C) and elevated temperatures (50 °C and 75 °C). The failure modes, load-displacement, R-curves were obtained. Simultaneously, three-dimensional digital image correlation (3D-DIC) technology was employed to monitor the strain evolution at the bonded interface during various loading stages. Subsequently, the mode II interfacial fracture toughness GIIC of the joints was calculated based on the classical beam theory (CBT), modified beam theory (MBT), and ouyang method (OYM) models. The results indicate that the nanofiber veils-modified bonded joints exhibited a mixed failure mode comprising steel-adhesive interfacial debonding and cohesive failure. Furthermore, the highest GIIC was obtained based on the OYM model since its comprehensive account of energy dissipation throughout the entire bonded region during interfacial fracture. According to the OYM calculations, the GIIC of joints with three layers of nanofiber veils increased by 23.0%, 26.7%, and 31.4% at 25 °C, 50 °C, and 75 °C, respectively, compared with unmodified joints, indicating a more pronounced toughening effect at higher temperatures. Finally, SEM microstructural fracture analysis revealed that the nanofibers enhanced the interfacial fracture toughness through multiple energy-dissipating mechanisms, including fiber bridging, pull-out, and fracture within the epoxy matrix.

Concrete-filled aluminum tubes (CFAT) have shown considerable potential for application in bridge structures with high durability requirements, particularly in coastal environments. However, it remains unclear whether the existing temperature gradient provisions for concrete-filled steel tubes (CFST) are directly applicable to CFAT members. To address this issue, over one year of natural exposure monitoring was conducted to obtain the temperature field of unobstructed CFAT members and the corresponding meteorological parameters. A validated numerical model was then employed to compare the temperature fields of CFAT and CFST members under representative sunny and rainy conditions, and to investigate the effects of tube diameter and wall thickness on the cross-sectional temperature gradient. The results show that, compared with CFST members of the same size, CFAT members exhibit a more uniform cross-sectional temperature field, with peak temperatures on sunny days approximately 3-6 degrees C lower. This indicates that the existing CFST temperature gradient provisions should not be directly applied to CFAT members. Parametric analysis further shows that, for a constant diameter, increasing wall thickness reduces the peak temperature, whereas for a constant wall thickness, increasing diameter increases the peak temperature and decreases the center temperature, although this influence gradually weakens with increasing diameter. Based on these results, a three-segment temperature gradient pattern for unobstructed CFAT members was proposed, together with recommended temperature gradient values and slope change point positions. The proposed results can provide a basis for the thermal action representation and design parameter selection of CFAT members under similar environmental conditions.

Effective shear stress transmission through weak shear planes is essential for realizing the full load-bearing potential of ultrahigh-performance fiber-reinforced concrete (UHPFRC) structures. This study investigates the underexplored size effects that govern the direct shear behavior of monolithic cast UHPFRC components through both experimental and theoretical analyses. A systematic experimental program involving 34 Z-shaped UHPFRC specimens was designed to evaluate the effects of critical parameters, including shear plane height and thickness, steel fiber content, and interfacial groove configurations. The results demonstrated that the shear stiffness increases proportionally with the decrease of the shear plane height, regardless of the presence of shear plane grooves. For every 1.0% increase in steel fiber content, the shear resistance of UHPFRC specimens showed an increase of 3.1-6.9 MPa. As the shear plane height increases from 50 to 450 mm, the strength of the intact specimen without grooves on the shear plane decreases by 24.5%, and that of slotted specimen with grooves on the shear plane decreases by 28.4%. Thickened shear planes (300 mm) exacerbate stress heterogeneity, reducing direct shear strength by 24.1% compared with thinner configurations (200 mm). The experimental insights are synthesized into a prediction equation for direct shear capacity that incorporates size effects, groove geometry, and the mesomechanical constitutive of UHPFRC, achieving prediction errors below 10% compared with experimental data. This work provides a mechanistic framework for optimizing the design of shear-critical UHPFRC components.

This study investigated the impact resistance of a low-carbon, low-shrinkage ultra-high-performance fiber-reinforced concrete (UHPFRC), and aimed to establish a unified characterization method. The UHPFRC was prepared by replacing 25% of the fine aggregate (by mass) with a particle size of 1 similar to 3 mm coal gangue and incorporating 1.0% (by volume) steel fibers. A modified drop-weight impact test procedure was developed based on the ACI 544-2 R standard by introducing sand bedding and adjustable rubber belts to mitigate data scatter. Repeated impact tests were conducted on a total of 130 specimens, including 90 UHPFRC specimens and 40 steel fiber-reinforced concrete with the strength grade of 60 MPa (CF60) specimens. The results demonstrated that the modified test method significantly reduces data variability. Using Minitab statistical software, the parameters were estimated using the Maximum Likelihood Estimation (MLE) method, and the goodness-of-fit was evaluated with the Anderson-Darling (AD) test, which confirmed that both the impact count for initial cracking and ultimate failure conformed to the Normal and Weibull distributions. The impact resistance of UHPFRC decreases with increasing CG content, whereas its impact toughness increases. Compared to the CF60 steel fiber concrete, the UHPFRC mixture with coal gangue exhibited a 76.42% higher impact resistance at failure and a 157.92% greater post-cracking impact toughness, despite its earlier crack initiation. The progression of impact damage, quantified by the maximum crack width and crater dimensions, was best described by exponential and logarithmic models, respectively. A sample size of five specimens is recommended for practical impact assessment, providing a margin of error within 20% at a 90% confidence level. This study establishes a refined testing protocol and a probabilistic evaluation framework for assessing the impact resistance of sustainable UHPFRC in structural applications.

Fatigue cracks in steel elements repaired with traditional crack-stop holes are susceptible to perforation, enabling propagation and resulting in inadequate fatigue life improvement. The fatigue performance of cracked steel elements repaired by cold-expanded crack-stop holes was experimentally investigated, and the effects of cold expansion ratios and hole-to-crack tip distances on the fatigue life were examined. Finite element (FE) simulation tests were conducted to reveal the residual stress distributions around the crack-stop holes after cold expansion. The results show that higher cold expansion ratios significantly enhance fatigue life under an identical hole-tocrack tip distance. When the hole-to-crack tip distance was 0 mm, a cold expansion ratio of 2% yielded the greatest fatigue life improvement, with a 50.82% increase compared to specimens without cold expansion. Moreover, the residual stress was distributed nonlinearly along the thickness direction of the steel elements, with the peak residual stress occurring near the exit side of the cold expansion mandrel. Finally, based on the critical distance theory and residual stress weight allocation coefficient, a fatigue life prediction model for the crack initiation at the hole edges was developed. Simultaneously, based on linear elastic fracture mechanics, a fatigue life prediction model for the crack growth was proposed. The results indicated that the experimental and predicted values of the total fatigue life are in good agreement. This study offers a cold expansion technique for crack-stop holes, providing a novel technique for extending the fatigue life of cracked steel structures.

Variable-stiffness load transfer components (LTCs) mitigate stress concentration in bonded CFRP anchors, yet their wide-temperature behavior remains unclear. This study proposes a three-segment bonded anchorage system incorporating high-performance epoxy adhesive modified with 200-mesh quartz sand to tailor the stiffness distribution of the LTC. Monotonic tensile tests were conducted on 62 specimens, covering three stiffness-ratio distributions (LTC1-LTC3), three bond lengths (200-300 mm), and four temperatures (-20 degrees C, 0 degrees C, 20 degrees C, and 70 degrees C). A finite element model using connector elements and the LaRC05 failure criteria was validated against experimental data and subsequently employed for parametric investigations on sleeve outer diameter and segment length ratio. Experimental results indicate that at 20 degrees C, LTC3 achieved an average equivalent shear stiffness of 410.95 kN/mm, 1.84 and 1.68 times that of LTC1 and LTC2, respectively, and showed a clear bond-length enhancement effect. At 70 degrees C, stiffness deteriorated markedly; however, LTC3 with a 250 mm bond length maintained K = 60.00 kN/mm, produced a more uniform shear stress distribution, and delivered anchorage efficiency above 95% across the investigated temperatures. An optimized configuration (outer diameter 45 mm; segment ratio 1:2:3) reduced stress concentration and lowered the matrix damage index by 16.6% under room-temperature conditions.

Epoxy bonded joints are widely used in carbon fiber-reinforced polymer (CFRP)-steel composite structures and CFRP strengthened steel structures; however, the bond shear performance may be significantly degraded under elevated ambient temperatures. To effectively improve the bond strength and toughness at elevated temperatures, the bonded interface modification technique using electrospun nanofiber veils were carefully studied in this research. CFRP-steel double-lap joints were fabricated using different nanofiber veils (with three different areal densities, i.e., 0 g/m2, 1.5 g/m2, and 4.5 g/m2). The bond-slip behaviors were tested at four temperature levels of 25℃, 40℃, 55℃ and 70℃. The results indicate that the most effective areal density of nanofiber veil for interfacial modification is 4.5 g/m2. Unmodified bonded interfaces failed mainly subjected to steel-adhesive interface debonding. The occurrence of this failure mode was effectively mitigated by the incorporation of nanofiber veils. For bonded interfaces modified with 4.5 g/m² nanofiber veils, the bond strength and ultimate displacement were increased by 129.4% and 65.8% respectively at 70 °C, relative to the unmodified counterparts. This study provides innovative technology for improving the interfacial strength and ductility of CFRP reinforced steel structures in elevated-temperature environments.

Ultra-high performance concrete (UHPC) typically relies on high cement/clinker content, leading to elevated cost and environmental burdens. This study develops a lower-carbon UHPC by (i) reducing cement demand through partial cement replacement with gold tailings (GT, 10

The direct shear behavior and governing mechanisms of ultra-high performance concrete (UHPC) members under the coupled effects of shear reinforcement and confining stress remain poorly characterized. To address this gap, direct shear push-off tests were conducted on 32 UHPC specimens to evaluate the influence of joint type, reinforcement ratio, and confining stress. Results indicate that confining stress effectively mitigates interface debonding by enhancing interfacial friction. Notably, shear capacity increases exceeded 20% for both flat and keyed wet-joint specimens, compared to approximately 15% for monolithic cast specimens. The most significant enhancement was observed within the 2-5 MPa confining stress range, with increases of 142.8% and 34.6% for flat and keyed wet-joint specimens, respectively. Conversely, an excessively high reinforcement ratio (2.1%) reduces the effective shear area, restricting the strength gain to less than 10% and impeding the full synergistic interaction between reinforcement and the UHPC matrix. In contrast, the combination of an optimal reinforcement ratio and moderate confining stress effectively alleviates brittle failure in keyed joints, leading to substantial improvements in both ductility and shear capacity. Furthermore, shear reinforcement effectively sustains and transfers shear forces after cracking in wet-joint specimens, significantly enhancing the post-failure residual shear capacity. Residual shear stress is increased by over 69% and 11% for flat and keyed wet-joint specimens, respectively. Finally, based on the experimental results, a predictive formula for the direct shear capacity of UHPC wet-joints was developed, incorporating the combined effects of confining stress and shear reinforcement.

This study examines the impact of a self-developed high-performance adhesive (G3) and commercial adhesive (Sikadur 30) on the static and fatigue performance of steel plates with edge defects, reinforced by bonded carbon fiber reinforced polymer (CFRP). Specimens included base plates with edge defects, crack-stop holes, and CFRP plates or fabrics bonded on both sides. Static tensile and fatigue tests were conducted to evaluate the effects of adhesive type, CFRP type, layer count, and crack-stop holes on load characteristics, crack propagation, and fatigue life. Results revealed that while CFRP reinforcement did not alter ultimate tensile strength, it converted the load-displacement curve into a serrated shape due to debonding events. CFRP significantly reduced crack propagation rates and enhanced fatigue life by 3.3-5.3 times, with double-sided bonding of 4 CFRP fabric layers matching the performance of 1.4 mm thick CFRP plates. G3 adhesive outperformed Sikadur 30. crack-stop holes improved crack initiation life but reduced section stiffness, potentially limiting crack propagation length. Comprehensive consideration of load, hole size, and crack propagation length is essential when designing crackstop holes.

To investigate the group studs effect in steel-Ultra High Performance Concrete (UHPC) joints sections, 12 pushout specimens with 1, 3, 5, and 7 stud rows were tested. The study examined failure modes, load-slip behavior, and the reduction factor in single-stud capacity. The results show that: 1) All specimens failed by unilateral stud shear with wedge-shaped UHPC crushing at stud roots; 2) Load-slip curves exhibited elastic, plastic, and failure stages, with ultimate slip under 6 mm; 3) The average shear capacity per stud decreased by 6 %, 11 %, and 13 % for 3, 5, and 7 rows, respectively, compared to 1-row; 4) Finite element analysis revealed significant coupling between stud spacing and row number, showing up to 15 % capacity reduction with small spacings (<= 2.3d) and multiple rows, while larger spacings (>= 4.5d) minimized this effect; 5) A proposed formula for the group studs reduction factor, considering spacing and rows, shows good agreement with tests, providing a reference for design.

Despite the increasing application of segmented cast UHPFRC (SC-UHPFRC), systematic research on how keyedjoint geometry affects the inclined-section shear performance remains lacking. To address this gap, this study investigates the shear behavior of SC-UHPFRC beams with a moderate shear span-to-depth ratio of 2.4 under combined flexural-shear loading, focusing on wet-joint geometry. Experimental results demonstrate that cracking typically initiated as vertical cracks at the wet keyed joint, followed by the propagation of diagonal shear cracks along its shear-weakened surface. SC-UHPFRC beams with flat, single-keyed, and corbel-keyed joints failed in a brittle manner. Compared to monolithic cast UHPFRC (MC-UHPFRC) beams, the load-bearing capacities of SCUHPFRC beams decreased by 14.35% (corbel-keyed), 11.23% (single-keyed), and 2.41% (double-keyed), whereas the flat-joint specimen exhibited nearly identical capacity. Furthermore, a finite element analysis validated by experimental data demonstrates that failure modes and ultimate loads are fundamentally governed by interfacial mechanical behavior, principal compressive stress continuity, and joint geometry. In corbel-keyedjoint beams, the stress distribution follows an arch-truss model, where diagonal shear cracks initiate at the weak bond interface along specific load paths. Ultimately, the failure mechanism is dictated by an inclined compressive field defined by the principal compressive stress trajectories. Therefore, engineering design must rationally plan joint locations and select configurations that harmonize with the principal stress flow.

Clarifying the shear resistance performance and establishing a suitable calculation method for reinforced ultrahigh-performance concrete (R-UHPC) members are crucial prerequisites for ensuring the widespread application and safe design of slender UHPC structures. This study investigates the direct shear performance of monolithic cast R-UHPC components through experimental analyses of 28 Z-shaped specimens. The test results reveal that crack propagation in precracked R-UHPC specimens bascially follows the preseted V-shaped groove interface, where shear strength was lower than those of intact and slotted specimens. The incorporation of steel fibers and shear reinforcement enhances specimen ductility failure characteristic, where their synergistic interaction with shear reinforcement significantly enhances shear stress transfer efficiency and crack propagation control. However, increasing the steel reinforcement ratio reduces the possibility of simultaneously achieving the maximum shear contributions from both the UHPC matrix and the steel reinforcement. Besides, our findings demonstrate that raising the fiber volume fraction is significantly more effective in improving shear strength than increasing the shear reinforcement ratio. The fiber reinforcement plays a more dominant role in enhancing the shear resistance of R-UHPC members. The height of the shear plane significantly influences the mechanical behavior of R-UHPC specimens, particularly in terms of shear strength, shear stiffness, and slip development. Building upon these insights, a predictive model for the direct shear capacity of monolithic cast R-UHPC components was proposed, incorporating factors such as UHPC matrix strength, fiber volume fraction, shear reinforcement ratio, shear plane height, and V-shaped grooves.

This study investigates the Huangdong Daning River Bridge project in Guangxi, where the innovative side-span and mid-span synchronous closure technology for continuous rigid-frame bridges (CRFB) was systematically implemented for the first time in this region of China. A comparative finite element model developed in MIDAS Civil 2024 was employed to analyze the mechanical behavior mechanisms of main girders under span-by-span closure and synchronous closure processes. The numerical simulation results demonstrate that the stress distribution in main girders shows no significant sensitivity (<3%) to closure method differences during both the bridge completion phase and 10-year shrinkage-creep cycle. However, distinct closure sequences (asynchronous vs. synchronous) exhibited notable impacts on the girder alignment at the completion stage. The cumulative deviation induced by differential installation elevations of formwork segments necessitates precise dynamic control during construction monitoring. Furthermore, shrinkage and creep effects manifested differential influences on pier top horizontal displacements and bending moments when employing different closure methods, though all variations remained within 5%. The synchronous multi-span closure technology effectively mitigates structural mutation risks during construction while achieving superior alignment accuracy, rational stress distribution, and accelerated construction progress as verified by field implementation.

Due to the limitations of concrete mixing, transportation and maintenance, large span ultra-high-performance fibre-reinforced concrete (UHPFRC) bridges inevitably need to be cast in segments, resulting in weakly stressed longitudinal joints between adjacent segments. However, current research on the structural performance of segmented cast UHPFRC (SC-UHPFRC) bridges is insufficient to support the application of large span UHPFRC bridges. Therefore, to investigate the shear performance of SC-UHPFRC beams, 6 SC-UHPFRC beams and 3 monolithic cast UHPFRC (MC-UHPFRC) control beams under bending and shear loads were carried out. The study variables cast methods, shear span-to-depth ratios (0.8, 1.6 and 2.4), with/without stirrups and fibre volume fractions (2.0 % and 3.0 %). The experimental results indicated that the failure modes of SC-UHPFRC beams mainly included direct shear failure, diagonal shear failure, flexural-shear failure, and flexural failure, depending on the shear span-to-depth ratio and stirrups. As the shear span-to-depth ratio decreased from 2.4 to 0.8, the cracking at the cold joints in the SC-UHPFRC beam became progressively more severe. When the shear span-to-depth ratio of the SC-UHPFRC beams without stirrups increased from 0.8 to 1.6 and 2.4, the ultimate load decreased by 49.5 % and 64.1 %, respectively. The cold joint interface became a critical factor influencing the failure mode and shear strength of SC-UHPFRC beams when the shear span-to-depth ratio was lower than 1.6. The addition of stirrups and an increase in fibre volume fraction could improve the shear performance of SCUHPFRC beams, potentially resulting in more flexural damage. Additionally, a modified shear capacity model for SC-UHPFRC beams was developed based on the shear capacity model for MC-UHPFRC beams and taking into account the reduction in shear strength at cold joints in UHPFRC beams. The calculated results of this model were in excellent agreement with the experimental results.

The bonding interface serves as a vulnerable point in steel structures strengthened with carbon fiber-reinforced polymer (CFRP), significantly influenced by the mechanical properties of adhesives and temperature. To understand the mechanisms through which temperature changes affect the properties of adhesive materials and the CFRP-steel interface, 70 adhesive tensile specimens and 28 CFRP-steel double-lap joint specimens were prepared based on the self-developed high-performance adhesive G3 and the typical commercial adhesive Sika30. Tests were conducted at seven different temperatures (-20 degrees C, -5 degrees C, 10 degrees C, 25 degrees C, 40 degrees C, 55 degrees C, and 70 degrees C). The results indicate that compared with 25 degrees C, an increase in temperature leads to a decrease in adhesive strength, whereas the ultimate bearing capacity of CFRP-steel double-lap joints increases when the temperature is below a certain value but still lower than the glass transition temperature (Tg) of the adhesive. However, a rapid decline in both adhesive and CFRP-steel joint performance occurs when the temperature approaches or exceeds the Tg of the adhesive. Decreasing the temperature results in a reduction in the ultimate bearing capacity of CFRP-steel double-lap joints. Therefore, when reinforcing with adhesive-bonded CFRP, it is essential to consider the adverse effects not only of adhesive softening at high temperatures but also of embrittlement in low-temperature strengthening systems.

The mechanical properties of ultra-high-performance concrete (UHPC) are significantly influenced by the interfacial bond performance between the steel fibers and UHPC matrix, which can be effectively enhanced by surface-modification of steel fibers. Nevertheless, there is still a lack of comprehensive research on the interfacial bond performance of surface-modified steel fibers, especially corrosion-modified steel fibers, under varying parameters such as loading rates and inclination angles. This study systematically investigated the interfacial bond performance of three types of corrosion-modified steel fibers (dezincification, chelation, and dezincificationchelation) under various pullout parameters through the single-fiber pullout tests. The microstructure and element distribution of modified steel fiber surface were revealed using scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and atomic force microscopy (AFM), and the corresponding modification mechanism was analyzed. The modification degree of three modification methods was evaluated by surface roughness. Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) analysis and atomic force microscopy (AFM) analyses were also conducted to elucidate the underlying mechanisms and patterns. The effects of loading rates (0.018, 0.18, and 1.8 mm/s) and inclination angles (0 degrees, 30 degrees, and 45 degrees) were also studied. Test results indicated that the average bond strength and pullout energy of modified steel fibers increased by 64.3 % and 96.6 %, respectively. The bond performance of S steel fibers with a diameter of 0.2 mm with minor roughness (Rq <= 27.1 nm) demonstrated a noticeable range of loading rate sensitivity, specifically between 0.018 and 0.18 mm/s. Conversely, the bond performance of L steel fibers with a diameter of 0.3 mm exhibited complete rate sensitivity within the range of 0.018-1.8 mm/s. The bond performance of inclined steel fibers also increased compared to aligned steel fibers; however, attenuated tensile strength and severe stress concentration led to the fracture of some surface-modified steel fibers. The average bond strength of S and L steel fibers increased with increasing inclination angle, and their maximum pullout energy occurred at 45 degrees and 30 degrees, respectively. Theoretical studies were also conducted, revealing that the spalling coefficients of inclined unmodified steel fibers were 1.5, and the predicted fracture angles of the inclined modified fibers were concentrated between 42.7 degrees and 44.5 degrees.

A new type of steel-UHPC composite slab (SUCS) with PerfoBond Leiste shear connectors (PBL) is designed to address the issues of fatigue cracking and pavement damage in orthotropic steel deck (OSD). To further promote the widespread application of the SUCS in practical engineering, a method combining a BP neural network model, and a multi-objective particle swarm optimization (MOPSO) algorithm was proposed to optimize the SUCS. To validate the feasibility of the optimal solution of the SUCS, finite element (FE) analyses and experimental tests were performed under the most unfavourable stress state. The results showed that the BP neural network model, as a surrogate model, can be effectively employed to supplement FE analysis. Compared to the traditional SUCS design, the optimal SUCS featured a significant reduction in cost and self-weight. In addition, it not only possesses adequate stiffness, good ductility, cracking resistance and flexural performance, but also demonstrates significant advantages in both economic and environmental performance. The relative slip between the steel plate and the UHPC was extremely small before approaching ultimate load, demonstrating prefect bonding between steel and UHPC at the interface. The nominal cracking strengths of the optimal SUCS were above 12 MPa, more than 1.7 times the maximum tensile stress of the UHPC layer (7.16 MPa) from the FE analyses. Preliminary FE analysis results and experimental data indicate that the optimization method proposed in this study is feasible for SUCS design.

To investigate the effects of solar radiation temperature on steel-concrete composite beams in long-span bridges, a temperature analysis method based on meteorological parameters is proposed. First, an accurate thermal analysis model was established based on the principles of heat conduction and finite element computation theory. The model's accuracy was validated using measured data. Subsequently, the representative values of temperature differences for the composite beam were calculated based on the analysis of historical meteorological data. The calculation method integrated the finite element temperature field model with the generalized extreme value distribution function. Finally, the simulated solar radiation temperature field was applied to the overall finite element model of the long-span bridge. The comprehensive influence of solar radiation temperature effects on long-span bridges was then evaluated. The results indicate that the finite element analysis results are in good agreement with the measured values. The 50-year return period representative value (Td) for the maximum vertical positive temperature difference in the composite beam is 17.613 C-degrees. The compressive stress induced in the concrete bridge deck of the composite beam by temperature loads during the operational phase exceeds twice that caused by lane loads. By analyzing seven different load effect combinations, the impact of the most unfavorable load effect combination on the bridge structure was determined. This provides an important reference for bridge design and assessment. This research offers a novel method for understanding and predicting the temperature response of long-span bridges. Additionally, it provides theoretical foundations and technical support for achieving the lightweight goals of bridge health monitoring.

The carbon emissions associated with concrete production remain a significant unresolved issue. One effective approach to mitigate this problem is to partially substitute cement with supplementary cementitious materials. The aim of the present study was to develop low-carbon, high-strength Engineered Cementitious Composites (HSECC) by incorporating low-hydration active solid waste in the form of coal gangue powder. To investigate the mechanical properties and underlying microscopic mechanisms of these composites, comprehensive testing was conducted, including assessments of compressive strength, tensile strength, single-crack tensile behaviour, three-point flexural performance, and scanning electron microscopy. The test results reveal that the integrity of the damaged compressive specimen was high. Compared with the test group without coal gangue powder, the incorporation of coal gangue powder significantly reduced the compressive strength, decreasing by 27.2% and 32.5%, respectively. The tensile strain hardening phenomenon appeared in all experimental groups. The inclusion of an optimal amount of coal gangue powder enhanced the tensile strain capacity, with the maximum tensile strain capacity reaching 4.15%. Increasing fibre length substantially reduced crack width; for instance, the crack width in the 18mm fibre test group was 31μm, which is only 33.6% of the crack width observed in the 12mm fibre group. Additionally, the incorporation of coal gangue powder significantly contributed to the reduction of crack width. In the context of embodied energy and embodied carbon in HSECC, PVA fibres and cement were found to be the primary contributors. Substituting a portion of the cement with coal gangue powder and silica powder significantly reduced both embodied energy and embodied carbon. The present study provides a novel utilisation method for coal gangue, a solid waste byproduct, which significantly mitigates its environmental impact. Additionally, the high-strength ECC produced using exclusively local materials demonstrates potential for broader implementation, particularly in applications such as concrete for bridge expansion joint anchorage zones and seismic retrofitting of external masonry walls.