Search Results (575)

Steel–concrete composite beams are widely used in bridge infrastructure but are vulnerable to deterioration due to uniform and pitting corrosion, particularly at the lower flange. This study investigates the flexural behavior of corroded steel–normal strength concrete (NSC) composite beams and evaluates rehabilitation using ultra-high-performance concrete (UHPC) slab replacement, with and without additional steel plate strengthening. A comprehensive finite element analysis was conducted considering three beam spans (5, 7, and 9 m), two corrosion types, and three corrosion levels. The results indicate that both corrosion types significantly reduce flexural capacity due to cross-sectional loss, with pitting corrosion causing greater strength reduction than uniform corrosion at the same weight loss because of stress concentration effects. Replacing the NSC slab with a UHPC slab effectively restores and often enhances load-carrying capacity beyond that of intact beams while reducing dead load, demonstrating the superiority of the proposed rehabilitation approach. The combined use of UHPC slab replacement and welded steel plate strengthening provides the greatest improvement, revealing a strong synergistic effect. A case study of a corroded steel bridge in Pennsylvania confirms the practical applicability of the method, showing that UHPC-based rehabilitation increases the load rating from below unity to above unity. These findings highlight UHPC as an efficient and sustainable solution for extending the service life of aging steel bridges. Full article

Ultra-high-performance concrete (UHPC) has attracted extensive attention because of its superior mechanical performance and durability. However, many existing tensile constitutive models are still obtained mainly by fitting macroscopic stress–strain curves, and the coupling among tensile damage development, steel-fiber parameters, and structural-scale response has not been sufficiently clarified. In this work, an acoustic-emission-informed tensile damage model was established for UHPC. Direct tensile tests were carried out on UHPC specimens containing steel fibers with aspect ratios of 43, 65, and 100 and volume fractions ranging from 0.5% to 3.0%, while acoustic emission signals were collected during loading. The normalized cumulative AE count was adopted as a damage indicator, and its evolution with tensile strain was described using a Weibull-type function. A fiber factor combining fiber volume fraction and aspect ratio was further incorporated into the damage constitutive equation. The proposed relationship was checked against 14 independent tensile datasets reported in the literature. After correction, the mean relative error of the predicted model parameter was reduced to 2.6%, with a standard deviation of 4.1%, and the fitted stress–strain curves all achieved R² values above 0.85. The constitutive model was then implemented in ABAQUS for the simulation of reinforced UHPC beams. By introducing a member-level reduction coefficient of μ = 0.84, the numerical load–deflection curve showed improved agreement with the experimental beam response. The coefficient is empirical and is applicable only to the beam configuration investigated here unless further validation is performed. Overall, the proposed model provides a damage-based link among AE monitoring, steel-fiber reinforcement parameters, and member-scale numerical analysis. Full article

Using industrial by-product lithium slag (LS) as a raw material for ultra-high performance concrete (UHPC) is an important way to achieve low-carbon prefabricated structures. However, existing studies lack a constitutive model for LS-UHPC and its application in prefabricated beam connection nodes. To fill this gap, this paper first established a tensile-compressive constitutive model for LS-UHPC through mechanical tests; then it was embedded into the finite element model to simulate the bending performance of the connection nodes of the post-cast LS-UHPC prefabricated beams and verified by the test results. Finally, parameter analysis is carried out. The results show that moderately increasing the diameter of longitudinal reinforcement can significantly improve the flexural bearing capacity of the connection node, but when the diameter exceeds 18 mm and HRB500 high-strength steel bars are used, the node exhibits over-reinforced failure characteristics; increasing the strength grade of ordinary concrete has a limited effect on the improvement of flexural bearing capacity (<5%). This study clarified the mechanical constitutive relationship of LS-UHPC, revealed the failure mechanism and bearing capacity evolution law of its prefabricated connection nodes under parameter changes, and provided a theoretical basis and design suggestions for the application of low-carbon lithium slag UHPC in prefabricated assembly structures. Full article

Ultra-high-performance concrete (UHPC) formulated with alternative binders represents a promising pathway for reducing carbon emissions while enabling multifunctional material performance. This study investigates the mechanical and electrical evolution of two systems: a traditional Portland cement-based UHPC (REF) and a geopolymer counterpart (GEO) where cement is fully replaced by ground granulated blast furnace slag (GGBS) and silica fume. By evaluating both mixes with and without steel fibers, the research assesses how binder chemistry interacts with conductive pathways to influence strength, resistivity, and impedance. Mechanical testing revealed comparable 28-day compressive strengths for the reference and geopolymer mixes (123 MPa and 120 MPa, respectively), which increased to 139 MPa and 130 MPa upon fiber incorporation. Electrical characterization showed that the geopolymer binder significantly enhances conductivity; resistivity values dropped from 9645 Ω·m in the reference mix to 925 Ω·m in the geopolymer and further to 76 Ω·m with fiber reinforcement. Impedance spectroscopy supported these results, as the GEO mixes displayed smaller Nyquist arcs compared to the REF system, indicating greater ionic mobility associated with pore solution chemistry and the GGBS-rich gel structure. Ultimately, this study demonstrates that geopolymer UHPC matches the mechanical integrity of Portland-based systems while offering superior electrical conductivity, making it a strong candidate for low-carbon, self-sensing infrastructure. Full article

Ultra-high performance concrete (UHPC) is widely used for its excellent compactness and durability. However, steel fibers in UHPC may form conductive paths, affecting electrochemical testing of internal rebars. To assess the applicability of current testing standards in UHPC, specimens of UHPC, high-performance concrete (HPC), and normal concrete (NC) with different cover thicknesses are designed. Open circuit potential (OCP), linear polarization resistance (LPR), and Tafel polarization curves are adopted to compare the corrosion behavior during 180 days of chloride immersion. Results show that UHPC has the most negative OCP, followed by NC and HPC. According to ASTM C876, this would indicate the highest corrosion risk for UHPC, contradicting its well-known superior chloride resistance. Hence, ASTM C876 is not applicable to UHPC. Corrosion current density (I_corr) is smallest in UHPC, followed by HPC and NC, consistent with chloride resistance ranking, indicating good applicability of the linear polarization method to UHPC. The anodic Tafel slope is larger than the cathodic one for all specimens, showing anodic control, unaffected by steel fibers. Larger cover thickness leads to higher OCP, higher polarization resistance, and lower I_corr. At 30 mm cover, internal rebars in UHPC are essentially non-corroded. Full article

Four-point bending tests were conducted on precast ultra-high-performance concrete (UHPC) segmental beams reinforced with unbonded prestressing tendons. A nonlinear finite element model was established and rigorously validated against the experimental data to simulate their flexural behavior. The experimental results show that compared with monolithic beams, the segmental beams experience a slight reduction in flexural capacity of 9.22% and 12.44% for the double-joint and triple-joint configurations, respectively. Nevertheless, the segmental beams possess greater ductility reserves; specifically, their average peak displacements increased from 9.83 mm for the monolithic beams to 11.60 mm and 14.78 mm for the double-joint and triple-joint beams, respectively, demonstrating substantially improved ductility. Based on the validated finite element model, extensive parametric analyses were performed. The numerical results indicate that concrete strength and steel strand reinforcement ratio significantly enhance the load-carrying capacity. Furthermore, shifting the joint positions away from the loading points increases the beam’s bending capacity, though this enhancement aggressively flattens out beyond a critical distance threshold of 0.25 L (L is the effective span). Finally, segmental beams with shear-resistant keyed joints exhibit higher overall stiffness and ultimate load-carrying capacity compared to those with plain flat joints. Full article

The addition of sulfoaluminate cement (SAC) to ultra-high-performance concrete (UHPC) enables sustainable high-speed construction due to the high 7-day strength without thermal curing. The fast hydration of SAC, however, endangers the admixture efficacy, which may compromise the structural integrity of the infrastructure components. This study investigates the effect of the physical form of polycarboxylate ether (PCE) superplasticizers on the performance of UHPC with the incorporation of SAC in ambient conditions. A paired experimental design of 32 mixtures compared liquid superplasticizers (LSPs) and powder superplasticizers (PSPs) in various binder compositions (OPC/SAC of 1/4–4/1) and water-to-binder ratios (0.18–0.21) at a constant dosage of admixtures of 1% except where w/b 0.18 (1.5% superplasticizers and 1% retarders were used). Findings indicate that LSPs enhance workability and compressive strength by 45% and 10.03%, respectively. The underlying mechanism is explained by comprehensive microstructural characterization through the use of Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. SEM study showed a 23% decrease in porosity, and XRD patterns showed the increased formation of amorphous C-S-H gel for LSPs. The higher levels of Al³⁺ incorporated into the gel structure (C-A-S-H) of the liquid forms was also verified by FTIR spectra. Mechanically, the research reveals one of the kinetic mismatches, where the rate of SAC hydration is greater than the rate of powder dissolution, which leads to a failure to fully disperse and shear-controlled failures. LSPs, in contrast, make it possible to disperse particles immediately, so the matrices become more dense and shift to axial failure. These results provide practical guidelines to infrastructure engineers to use liquid superplasticizer in SAC-based systems in order to achieve sustainability and reliability in terms of performance in precast and fast-track construction projects. Full article

Ultra-high-performance concrete incorporating coarse aggregates (UHPC-CA) exhibits pronounced multi-scale heterogeneity and staged damage evolution. However, existing single-scale reinforcement strategies often fail to address the complete micro-to-macro fracture process, leaving a critical research gap in achieving full-stage crack control. To address this, this study introduces a novel cross-scale toughening strategy using hybrid steel fibers (SF) and calcium carbonate whiskers (CCW), and decouples the coupled influences of water-to-binder (W/B) ratio, coarse aggregate (CA), and multi-scale fibers via an orthogonal design. Mechanical properties, fiber dispersion, and pore structure are jointly characterized to establish structure–property relationships. An optimal composition (W/B = 0.32, CA = 18%, SF = 2%, CCW = 1%) is identified, achieving a balanced enhancement of strength and ductility. Results indicate that matrix densification is primarily controlled by W/B via pore refinement, while mechanical performance is governed by the interplay between fiber spatial uniformity and interfacial integrity; the roles of CA and CCW are clearly stress-state dependent. Furthermore, a novel cross-scale synergistic mechanism is revealed, in which micro-scale CCW regulates microcrack initiation and stabilizes the pre-peak response, whereas macro-scale SF dominates post-peak behavior through crack bridging and pull-out energy dissipation. This sequential activation enables a full-stage enhancement of tensile performance, shifting failure from brittle localization to pseudo-ductile multiple cracking. The findings provide a correlative framework for tailoring UHPC-CA through multi-scale hybrid reinforcement. Full article

Designing ultra-high-performance concrete (UHPC) mixtures requires balancing multiple, often conflicting, performance criteria, particularly mechanical strength and rheological behavior. However, the limited availability of publicly accessible datasets containing synchronized multi-property measurements, together with cross-source heterogeneity, poses a major challenge for robust data-driven modeling under small-sample conditions. To address this issue, this study proposes an integrated framework combining cross-source data harmonization, Variational Autoencoder (VAE)-based latent-space augmentation, multi-output deep learning, interpretability analysis, and Genetic Algorithm (GA)-driven inverse design. A dataset comprising 139 valid UHPC records was curated from 22 peer-reviewed studies and expanded to 2780 samples through VAE-based augmentation. Using the augmented dataset, a multi-output deep neural network was developed to jointly predict compressive strength, flexural strength, yield stress, and plastic viscosity. On the independent test set, the model achieved R² values of 0.8601, 0.9212, 0.8464, and 0.6603, respectively. Comparative benchmarks and augmentation ablation analyses further showed that VAE-based augmentation consistently improved predictive performance and generalization, especially under small-sample conditions. SHAP and partial dependence analyses identified curing age, steel fiber content, water-to-binder ratio, and superplasticizer dosage as the dominant factors governing UHPC performance. Finally, the trained surrogate model was coupled with a GA for multi-objective inverse optimization, and experimental validation of three candidate mixtures confirmed good agreement between predicted and measured values. This study provides a transparent and engineering-oriented methodology for the integrated prediction, interpretation, and optimization of UHPC mixtures. Full article

The application of ultra-high performance concrete (UHPC) in the hogging moment region significantly enhances the crack resistance of concrete slabs of composite girders with integrated piers, while also providing economic benefits. To investigate the crack resistance performance and develop a calculation method for crack width in hogging moment region of steel–UHPC–normal concrete (NC) composite girders, a full-scale bending test was conducted. Based on the test results, the post-cracking residual tensile strength of UHPC was determined according to the energy equivalence principle. A calculation method for reinforcement stress incorporating the tensile contribution of UHPC at a cracked section was proposed and then the applicability for current design codes for crack width calculation was evaluated. For the UHPC–NC interface, a corresponding crack width calculation method was developed. The results indicate that cracks initiated on the surface of the NC layer beneath the UHPC overlay at the cantilever root. Then cracks developed in sequence at the top surface of the UHPC layer cantilever root, the UHPC–NC interface, and the mid-plane of the girder-to-pier joint. Ultimately, UHPC cracks exhibited a “numerous and closely spaced” distribution, whereas NC cracks were “few and widely spaced.” When the residual tensile strength of UHPC at cracked section was considered, the mean value and average coefficient of variation in the ratios of calculated to measured reinforcement stresses for different sections were 1.07 and 0.10, respectively, which can be further used for crack width calculation. The mean ratios of code-predicted to measured UHPC crack widths for different sections using the Chinese code, French code, and European code were 1.10, 0.98, and 1.13, respectively, with corresponding average coefficients of variation of 0.25, 0.33, and 0.28; the Chinese code is recommended for UHPC crack width prediction. For the UHPC–NC interface, an expression for crack width calculation was derived using the comprehensive theory, and the mean ratio of calculated to measured values and the coefficient of variation were 1.08 and 0.18, respectively, demonstrating good predictive accuracy. Full article

In recent years, Ultra High-Performance Fiber-Reinforced Concretes (UHPFRCs) have gained significant attention for their applications in structural components, particularly for improving impact resistance and post-cracking behavior. This study explores the behavior of thin Ultra High-Performance Concrete (UHPC) panels reinforced with synthetic fibers, focusing on the potential use of these materials for building façades. Three different synthetic fiber-reinforced mixes were developed, utilizing polyvinyl alcohol (PVA) microfibers, polypropylene (PP) macrofibers, and a hybrid combination of both. These thin, unreinforced panels were subjected to impact testing using a free-falling steel ball to evaluate their mechanical response. The results were analyzed in terms of crack patterns, crack openings, and overall impact resistance. Additionally, numerical analysis was implemented by using the ABAQUS^TM finite element code, in order to predict the panels’ performance under impact, providing a comparison between experimental results and numerical simulations. This investigation highlights the significant contribution of synthetic fibers in enhancing the toughness and impact resistance of UHPC panels, demonstrating their viability for structural applications requiring enhanced durability. Full article

The sustainable application of ultra-high-performance concrete (UHPC) is often constrained by high material costs and environmental footprints. While the individual effects of various industrial wastes have been extensively studied, the synergistic mechanism of multi-source waste in UHPC remains poorly understood. To fill the research gap, an eco-UHPC was developed wherein river sand (RS) was partially replaced by spontaneous combustion gangue sand (SCGS), and Portland cement (PC) was partially replaced by spontaneous combustion gangue (SCG) powder and phosphorous slag (PS). A systematic investigation was conducted to assess the packing density, flowability, mechanical properties, chloride ion penetration resistance, and micromorphology. The results indicate that 40% SCGS substitution (by mass) optimizes particle packing density and aggregate gradation, while PS incorporation significantly improves flowability by up to 16.83%. Notably, persistent pozzolanic reactions and the consumption of Ca(OH)₂ facilitate the generation of dense C-S-H gel, which creates a uniform microstructure and enhances late-stage compressive strength. Furthermore, superior chloride penetration resistance is achieved when the PS content is maintained below 20%. These findings support the synergistic utilization of SCGS, SCG, and PS in UHPC production, while facilitating broader application of UHPC through reduced costs and lower carbon emissions. Full article

This study proposes and investigates a modular assembled steel–ultra-high-performance concrete (UHPC) composite cable support bridge consisting of upper prefabricated UHPC ducts and a steel truss underneath. Finite element (FE) analysis is conducted to investigate the mechanical performance of the medium-span (L = 36 m) cable support bridge under service-loading conditions. The FE results indicate that under combined action of vertical and horizontal loads, the tensile damage in the UHPC ducts reaches approximately 10%, mainly concentrated near the end-support sections. The peak stress in the steel truss is far below its yield strength. The peak vertical displacement of the bridge is approximately L/225, below the allowable limit of L/150, and the peak horizontal displacement is negligible. A parametric analysis is performed for web sections in the midspan and end of the cable support bridge. Results show that the peak stress located at the lower chord increases with larger midspan web section. The increase in the midspan web section triggered a stress redistribution in the end webs and, consequently, a rise in the peak stress under the same load case; the peak vertical displacement decreases while the horizontal displacement exhibits marginal change. Appropriately scaling down the end diagonal web sections optimizes the material distribution, achieving a reduction in self-weight with negligible impact on the overall structural performance. Full article

Ultra-high-performance concrete (UHPC) matrix faces critical challenges of high carbon footprint and significant autogenous shrinkage. Supersulfated cement (SSC), a potentially lower-carbon binder comprising ground granulated blast-furnace slag and gypsum, offers a promising alternative. This study systematically investigated the effect of gypsum type—phosphogypsum (PG), dihydrate gypsum (DH), and anhydrite (AH)—on the early hydration and shrinkage behavior of UHPC matrix incorporating 30% SSC as Portland cement replacement. A multi-technique approach, including mechanical testing, isothermal calorimetry, XRD, TG-DSC, SEM, LF-NMR, and autogenous shrinkage measurements, was employed. Results demonstrate that gypsum type critically governs sulfate dissolution kinetics, thereby dictating phase assemblage and microstructural evolution. DH provides relatively rapid sulfate dissolution, promoting earlier AFt and gel formation, which is associated with the highest early strengths and a marked reduction in autogenous shrinkage. AH shows a slower but sustained sulfate supply, resulting in comparable 28-day strength with moderate shrinkage reduction. PG yielded the lowest autogenous shrinkage (374 μm/m at 7 d), but it also suffered from severe early-age retardation due to soluble phosphate impurities, as evidenced by the delayed hydration peak and lowest 3 d strength. This behavior is mainly related to strong early-age retardation, delayed hydration, delayed setting, and a prolonged low-stiffness state. These findings suggest that appropriate gypsum selection in SSC enables tailored early-age performance and improved volume stability in the UHPC matrix, offering guidance for utilizing industrial by-products such as phosphogypsum in sustainable high-performance concrete design. Full article

This study examines the flexural behavior of slender ultra-high-performance fiber-reinforced concrete (UHPC) beams with cross-sections intended for scalable precast production. The members are prestressed only, with no passive reinforcement. An experimental program on eighteen beams combined three cross-sectional typologies (rectangular as a reference, I-shaped, and H-shaped), three UHPC mixes with fiber contents of 130, 160, and hybrid 130 + 60 kg/m³, and two prestressing layouts (bottom-only and symmetric top-and-bottom). Prestress was indirectly controlled by evaluating effective tendon stress, with time-dependent prestress losses quantified using vibrating-wire strain gauges. Four-point bending tests provided material characterization and structural response, enabling assessment of stiffness and ultimate capacity. The results highlight the coupled influence of cross-section, fiber dosage, and prestress configuration on global response. Post-cracking residual strength in UHPC promoted stable multiple cracking, while prestressing governed deflection control. Residual equivalent flexural tensile stresses above 35 MPa at deflections over 50 mm, span/70, were achieved in I- and H-shaped sections, exceeding those of rectangular sections. Overall, the study substantiates the feasibility of lightweight, durable, prestressed UHPC members that deliver significant self-weight reductions without compromising reliability. Full article