Search Results (488)

This study investigates the differences in flexural behavior of ultra-high-performance concrete (UHPC) arising from variations in test methods and key experimental parameters. Flexural tensile tests were conducted on 51 specimens representing 17 combinations of test variables, including steel fiber length (13 mm and 19.5 mm), specimen cross-sectional dimensions (75 × 75 mm, 100 × 100 mm, and 150 × 150 mm), presence or absence of a notch, and loading configuration (three-point and four-point loading). The tests were performed in accordance with ASTM C1609 and EN 14651, and both deflection and crack mouth opening displacement (CMOD) were normalized by the span length to compare the influence of each parameter. The notched specimens demonstrated significantly improved reliability, exhibiting up to an 8.4-fold reduction in standard deviation due to the consistent initiation of cracking. Regarding size effects, the 75 × 75 mm specimens showed an overestimation of flexural performance due to the wall effect of fiber distribution, whereas the 100 × 100 mm and 150 × 150 mm specimens exhibited similar flexural responses. The comparison of loading configurations revealed that three-point loading produced up to 11.7% higher flexural tensile strength than four-point loading, attributable to concentrated moment–shear interaction and the combined effects of fiber bridging and shear resistance mechanisms. In addition, specimens with longer steel fibers (19.5 mm) exhibited 5.2–9.7% higher flexural performance than those with shorter fibers (13 mm), which is attributed to enhanced interfacial bonding and improved crack dispersion capacity. Full article

Existing studies have demonstrated that insufficient horizontal deformation capacity of columns under high axial compression ratios constitutes a key factor leading to seismic damage in ordinary concrete frame structures. This paper proposes a novel framed structure incorporating composite columns by combining ultra-high performance concrete (UHPC), which exhibits excellent mechanical properties, with normal concrete (NC). The design concept maintains the overall mechanical performance of the composite column frame structure while significantly reducing the lateral stiffness when the composite columns are configured in a “split-column form.” For instance, the lateral stiffness of ZH-5 in the “split-column form” is only one-tenth of that of ZT-1 in its initial state, leading to a substantial enhancement in horizontal deformation capacity. This design approach maintains the overall mechanical performance of the composite column frame structure while significantly enhancing its horizontal deformation capacity by reducing lateral stiffness through the “split-column” configuration. Using the ABAQUS finite element software 2021, a finite element model of a multi-story frame column structure was developed. Research findings indicate that the frame structure utilizing UHPC-NC composite columns exhibits reduced tensile damage, lower peak and plastic displacements, and a relatively smaller inter-story drift angle. Specifically, the plastic drift angle of the UHPC-NC composite column frame structure from the first to the fourth story is 5% to 31% smaller than that of the conventional reinforced concrete column frame structure. The novel UHPC-NC composite column frame structure demonstrates superior seismic performance. Full article

Ultra-high-performance concrete (UHPC) has been increasingly adopted in applications requiring superior mechanical performance and high durability under aggressive environments. However, its large-scale use is still limited by the high binder content and the lack of a standardized mix design methodology. Among the existing approaches, particle packing-based mix design methods have shown the most promising results, optimizing the composite structure and enabling efficient material proportioning. This study aimed to evaluate the influence of the particle distribution coefficient (q = 0.20 and 0.25) and the cement consumption ratio (15%, 20%, and 25%) on achieving the lowest packing deviation index (PDI) values using a rational UHPC mix design method. The results indicated that increasing q allowed a reduction of up to 15% in cement content, corresponding to 106 kg/m³ less binder. In contrast, changes in cement consumption, which led to different PDI values for the same q, had a significant effect on compressive strength. Mixtures with 20% cement and consumption of 598 kg/m³ exhibited the lowest PDI values (180 and 190) and the highest 91-day compressive strengths (147.0 and 151.1 MPa). Fiber reinforcement improved toughness and post-elastic energy absorption capacity. Overall, UHPC with reduced cement content and high mechanical performance can be achieved using a rational mix design method when an appropriate q value is selected. Full article

Ultra-High-Performance Concrete (UHPC) is being increasingly utilized in major engineering projects due to its excellent mechanical properties, strong durability, and superior overall performance. Nevertheless, the widespread use of premium cementitious materials leads to high expenses and a substantial environmental impact. In this work, crushed recycled paste was calcined at 600 °C for two hours to produce calcined recycled fine powder (RFP) with varying hydration reactivity. UHPC was produced using the RFP in place of some of the cement. Chemical activation was accomplished by adding a composite activator system made up of Ca(OH)₂, Na₂SO₄, Na₂SiO₃·9H₂O, and K₂SO₄ in order to further improve the performance of UHPC. Particle size, viscosity, fluidity, mechanical properties, and hydration products were analyzed to establish the best activator type and dosage, as well as the ideal activation procedure for recycled fine powder. By mass replacement of cementitious materials, when 15.0% of the calcined recycled fine powder was added, the compressive strength of UHPC reached 149.1 MPa, a 23.2% increase over reference UHPC without calcined recycled fine powder. The results show that the calcined recycled fine powder ground for 60 min exhibits the highest activity. More hydrated products were formed in UHPC as a result of the addition of Ca(OH)₂. The compressive strength peaked at 162.2 MPa at an incorporation rate of 1.5%, which is 8.8% higher than UHPC without an activator. Full article

Incorporating coarse aggregates into ultra-high-performance concrete (UHPC-CA) can reduce material costs, yet reliably predicting its strength-related behavior and overall performance remains challenging. This study examines UHPC-CA through a two-stage orthogonal experimental program comprising 18 mixtures with coarse aggregate, fly ash, and hybrid fiber reinforcements (steel, polypropylene, and composite fibers). Microstructural characterization using scanning electron microscope (SEM) and X-ray computed tomography (X-CT) was conducted to assess interfacial features and crack evolution and to link these observations to the measured mechanical response. Experimentally, fiber reinforcement markedly enhanced post-cracking performance. Compared with the fiber-free control mixture, the optimal hybrid configuration increased flexural strength from 6.9 to 23.5 MPa and compressive strength from 60.1 to 90.5 MPa. The steel–composite fiber system outperformed the steel–polypropylene system, which is consistent with the tighter composite-fiber interfacial bonding observed by SEM/X-CT and supports the feasibility of partially substituting steel fibers. An artificial neural network (ANN) model trained on 50 mixtures and evaluated on 10 unseen mixtures achieved an R² of 0.9703, an MAE of 1.22 MPa, and an RMSE of 2.11 MPa for compressive strength prediction, enabling sensitivity assessment under multi-factor coupling. Overall, the proposed experiment–characterization–modeling framework provides a data-driven basis for performance-oriented mix design and rapid screening of UHPC-CA. Full article

Ultra-high-performance concrete (UHPC) is an advanced cementitious composite material with high durability and the strength properties exceeding those of conventional concrete. This paper presents the results of experimental testing assessing the freeze–thaw durability of UHPC specimens with varying fiber types (13 mm straight microfibers and 30 mm hooked-end fibers) and fiber percentages, as well as pre-existing cracks. The performance of all specimens was evaluated by measuring resonant frequency at intervals during testing and residual flexural strength after the completion of 350 freeze–thaw cycles. All specimens showed no degradation of resonant frequency over time. However, the pre-cracked specimens showed an increase in resonant frequency over the course of testing. The uncracked straight fibers specimens exposed to freeze–thaw cycles had the highest flexural strength, but the flexural resistance of the pre-cracked straight fibers specimens increased compared to the control specimens after 350 freeze–thaw cycles. The pre-cracked hooked fiber specimens showed higher first cracking strength and similar ultimate strength to the uncracked specimens after freeze–thaw exposure. Full article

This study investigates the interlayer properties and sustainability of 3D-printed ultra-high-performance concrete (UHPC) modified with antimony tailings (ATs). The different AT ratios considered were 2.7, 5.4, 8.1, 10.8, and 13.5 wt% additions. The mechanical experiments show the optimal concentration resulting in compressive and flexural strength of 11.2% and 17.2% enhancement at 28 days, respectively. SEM analysis revealed that AT enhances the interlayer strength of 3D-printed UHPC and influences the anisotropic behavior of the matrix around steel fibers. X-CT demonstrated that increasing the AT from the compared group to 13.5% reduced the pore volume from 2.02% to 0.30%. Furthermore, an environmental impact assessment of the 10.8 wt% AT exhibited a 32.5% reduction in key indicators including abiotic depletion (ADP), acidification potential (AP), global warming potential (GWP), and ozone depletion potential (ODP). Consequently, UHPC incorporating AT offers superior environmental sustainability in the practical construction of 3D-printed concrete. This research provides practical guidance in optimizing 3D-printed UHPC engineering, further facilitating the integrated design and manufacturing of multi-layer structures. Full article

This review surveys the recent literature on the fire resistance of reinforced concrete (RC) columns based on a bibliometric analysis of publications to reveal research trends and focus areas. The collected studies are synthesized from the perspectives of materials, structural behaviors, parameter influences, and predictive modeling. From the material aspect, the review summarizes the degradation mechanisms of conventional concrete at elevated temperatures and highlights the improved performance of ultra-high-performance concrete (UHPC) and reactive powder concrete (RPC), where dense microstructures and fiber bridging effectively suppress spalling and help maintain residual capacity. In terms of structural behavior, experimental and numerical studies on RC columns under fire are reviewed to clarify the deformation, failure modes, and effects of axial load ratio, slenderness, cover thickness, reinforcement ratio, boundary restraint, and load eccentricity on fire endurance. Parametric analyses addressing the influence of these factors, as well as the heating–cooling history, on overall stability and post-fire performance is discussed. Recent advances in thermomechanical finite element analysis and the integration of data-driven approaches such as machine learning have been summarized for evaluating and predicting fire performance. Future directions are outlined, emphasizing the need for standardized parameters for fiber-reinforced systems, a combination of multi-scale numerical and machine-learning models, and further exploration of multi-hazard coupling, durability, and digital-twin-based monitoring to support next-generation performance-based fire design. Full article

The joint represents a critical component in precast concrete segmental bridges (PCSBs), playing an essential role in transferring shear stress. The efficacy of steel shear keys in comparison to conventional concrete tooth keys has been proven in terms of their shear transfer capability. In this study, a novel design using ultra-high-performance concrete (UHPC) to replace conventional concrete around the steel shear keys was proposed. A 30 m span precast concrete segmental T-girder with epoxy steel shear-keyed joints was fabricated to evaluate the effectiveness of the joint system. Experimental measurements included crack development, load–deflection response, and strain distribution. Furthermore, a finite element (FE) model was developed and validated with the experimental results. The results indicate that the epoxy steel shear-keyed joints effectively transmitted shear stress between segments, with the girder achieving an ultimate load of 1750 kN and a ductile flexural failure mode. The validated FE model accurately captured the critical characteristics of the structure. Finally, an effective calculation method was introduced to predict the ultimate load. Full article

Ultra-high-performance concrete (UHPC) delivers outstanding durability and strength but typically relies on high Portland cement content. This study evaluates a 20% cement replacement with limestone powder (LP) in UHPC and benchmarks performance under two curing regimes: moist curing (MC) and warm bath curing at 90 °C (WB). Metrics include workability, compressive and flexural behavior, shrinkage, freeze–thaw resistance, chloride transport (surface resistivity, RCPT), material cost, and embodied CO₂. LP improved fresh behavior: flow increased by 14.3% in plain UHPC and 33% in fiber-reinforced UHPC (FR-UHPC). Compressive strengths remained in the UHPC range at 28–56 days (approximately 142–152 MPa with LP), with modest penalties versus 0%-LP controls (about 2–5% depending on age and curing). Under WB at 56 days, controls reached 154 MPa (plain) and 161 MPa (FR-UHPC), while LP mixes achieved 145.2 MPa (plain) and 152.0 MPa (FR-UHPC). Flexural performance was reduced with LP: for FR-UHPC, 28-day MOR under MC was reduced from 15.5 MPa to 12.7 MPa and under WB from 14.3 MPa to 10.3 MPa; toughness under MC was reduced from 74.4 J to 51.1 J. Durability indicators were maintained or improved despite these moderate strength reductions. After 300 rapid freeze–thaw cycles, all mixtures retained relative dynamic modulus near 100–103%, with negligible MOR losses in LP mixes (plain UHPC: −1.1% with LP versus −4.7% without; FR-UHPC: −3.7% versus −8.1%). Chloride transport resistance improved: at 56 days under MC, surface resistivity increased from 558 to 707 kΩ·cm in plain UHPC and from 252 to 444 kΩ·cm in FR-UHPC; RCPT for LP mixes was 139 C (MC) and 408 C (WB), about 14–23% lower than respective controls. Drying shrinkage was reduced by roughly 23% (plain) and 28% (FR-UHPC). Sustainability and cost outcomes were favorable: embodied CO₂ was reduced by 18.8% (plain) and 15.5% (FR-UHPC), and material cost was reduced by about 4.5% and 2.0%, respectively. The main shortcomings are moderate reductions in compressive and flexural strength and toughness, particularly under WB curing, which should guide application-specific limits and design factors. Full article

Corrugated metal pipe (CMP) culverts are key pieces of infrastructure in drainage and waterway management, but many are reaching their end of life and require rehabilitation. While existing repair methods have a long track record of success, they can be cost prohibitive and may significantly affect the hydraulic properties of culverts. Ultra-high performance concrete is internally reinforced, stronger, and more durable than conventional concrete, offering a modern solution to culvert deterioration. The seven mockups described include trials with top-formed UHPC, thixotropic UHPC, and a UHPC shotcrete placement. Shotcrete UHPC was not found to be viable at this time due to challenges with maintaining mix consistency and adhesion to the substrate. Top forming and thixotropic UHPC were found to be the best options for building a consistent invert lining for culvert rehabilitation but posed unique challenges in design, construction, and material consistency. This paper describes the methods of construction, challenges during construction, and the results of each test. It is the author’s intent to give owners a new tool for culvert rehabilitation, provide designers with each of the variables in implementation, and help contractors mitigate risks by discussing the challenges encountered for UHPC invert linings. Full article

Based on the design concept of double-skin composite columns, this study proposes an enhanced configuration in which the inner steel tube is reinforced with fiber-reinforced polymer (FRP) stirrup-confined ultra-high-performance concrete (UHPC), leading to the development of FRP stirrup-confined UHPC–steel tube (FSCUS) hollow composite columns. Twelve glass FRP stirrup-confined UHPC–steel tube (GFSCUS) hollow composite column specimens were tested under axial compression. Analysis of load–displacement curves, and of load–strain curves of individual components, was performed. The effects of various parameters, including thickness and outer diameter of the steel tube, configuration and spacing of the GFRP stirrup, and steel fiber content of the UHPC, on the compressive behavior of the GFSCUS hollow composite columns were systematically investigated. The test results indicate that the influence of the thickness and outer diameter of the steel tube on the axial compression behavior is primarily governed by the effectiveness of the composite action between the steel tube and the confined concrete under axial compression load. The spacing and configuration of the FRP stirrup, conversely, determine the efficacy of the confinement provided to the concrete. The incorporation of steel fibers enhances both the peak load and the ductility due to their bridging effect. However, an excessive fiber content can restrict the lateral expansion of the concrete, thereby diminish the confining effect of the hoops and leading to a reduction in load-carrying capacity. Full article

Ultra-high-performance concrete (UHPC) mixtures exhibit tightly coupled ingredient–property relations and heterogeneous reporting, which complicate the data-driven prediction of compressive and flexural strength. We present an end-to-end framework that (i) harmonizes mixture records, (ii) completes numeric features using a dependence-preserving Gaussian copula routine, and (iii) standardizes/encodes predictors with training-only fits. The feature space focuses on domain ratios and concise interactions (water–binder, superplasticizer–binder, total fiber, water–binder, superplasticizer–binder, and fiber normalized by water–binder). A physics-informed multi-task neural network (PINN) is trained in log space with Smooth-L1 supervision and learned per-task noise scales for uncertainty-weighted balancing, while soft monotonicity penalties are applied to input gradients so that predicted strength is non-increasing in water–binder (both targets) and, when available, non-decreasing in fiber content for flexural response. In parallel, histogram-based gradient boosting is fitted per target; a convex combination is then selected on the validation slice and fixed for testing. On the held-out sets, the blended model attains an MAE/RMSE/R² of 10.86 MPa/14.68 MPa/0.848 MPa for compressive strength and 2.78 MPa/3.67 MPa/0.841 MPa for flexural peak, improving over the best single family by 0.5 RMSE (compressive) and 0.16 RMSE (flexural), with corresponding R² gains of 0.01–0.02. Residual-versus-prediction diagnostics and predicted–actual overlays indicate aligned trends and reduced heteroscedastic tail errors. Full article

The deployment of ultra-high-performance concrete (UHPC) is a strategic response to the urgent need for advanced building materials, particularly for the repair and enhancement of aging infrastructure. Highway bridges, which are constantly subjected to high stress, heavy usage, and corrosive environments, can be ideal candidates for UHPC application. The material’s exceptional abrasion resistance and ability to withstand severe weather conditions make it a compelling choice for projects where frequent renovation or maintenance is impractical. This study presents a risk-based cost–benefit analysis (RCBA) comparing UHPC reinforced bridge columns to conventional concrete reinforced bridge columns, focusing on seismic and corrosion hazards. While UHPC has a significantly higher initial material cost than traditional concrete, a simple comparison of initial costs alone is misleading. The RCBA methodology generally evaluates life-cycle cost, including initial construction, long-term agency costs, and user costs. The central question—whether UHPC’s superior performance justifies its higher initial investment—is addressed through RCBA. The presented RCBA is formulated as the ratio of the total life-cycle cost of conventional concrete to that of UHPC. The benefit is estimated as the difference in cumulative risks between bridges with conventional concrete and UHPC bridge columns, with fragility analysis conducted under seismic and corrosion hazards. The proposed approach is illustrated using an existing bridge located in Republic of Korea. Full article

Numerous studies have been published on various rheological aspects of conventional and high-performance concrete, some of which encompass multi-scale investigations. However, there is no published article that studies the rheology of ultra-high-performance concrete (UHPC) with a multi-scale approach. In this paper, a comprehensive investigation into the rheological properties of UHPC at three cementitious material scales was undertaken: the paste scale, the high-strength mortar scale, and the fiber-reinforced composite scale. The effect of cement type, supplementary cementitious materials (SCMs), and the water-to-binder ratio (w/b) on the rheology of UHPC at various material scales was evaluated using the appropriate rheometric apparatus. The results indicated that all of the UHPC mixtures in this study exhibited shear thickening behavior, and the degree of shear thickening increased as the w/b decreased. This phenomenon was systematically quantified at the paste, high-strength mortar, and fiber-reinforced composite scales, enabling direct comparison across material levels. Notably, the incorporation of silica fume suppressed the shear thickening behavior, as evidenced by the disappearance of the second-order term in the modified Bingham model, whereas slag had no such effect. The 28-day compressive strength of the investigated UHPC mixtures ranged between 100 and 150 MPa, and the mixture prepared with a combination of cement and silica fume (90C10SF) exhibited 35% higher compressive strength compared to the mixture prepared with cement and slag (90C10SL). Additionally, the UHPC mixture prepared with 90C10SF binder combination showed a 20% higher load-carrying capacity compared to the UHPC mixture made with 90C10SL and 80C10SL10SF binder combination. Full article