Search Results (218)

Fatigue cracking and stiffness degradation remain critical challenges for concrete flexural members used in bridge decks, crane beams, pavements, and other structures subjected to repeated loading. Layered beams that combine normal concrete in the compression zone with steel-fiber concrete in the tension zone offer a promising route to reduce self-weight while retaining crack resistance and ductility. However, the coupled influence of layer depth and fiber dosage on the flexural fatigue response of such members is still insufficiently quantified for reliable engineering design. Unlike previous studies that mainly focused on homogeneous SFRC members, UHPC-based members, or layered beams under static loading, the present study addresses a more practice-oriented but less explored problem, namely the flexural-fatigue behavior of cast-in-place layered beams composed of normal concrete in compression and steel-fiber concrete in tension. More importantly, the study does not examine fiber effect or layer geometry separately, but quantifies within one unified framework how lower-layer height ratio and fiber dosage jointly govern fatigue life, stiffness retention, crack development, and failure transition. A calibrated nonlinear finite-element model with damage-plasticity constitutive laws and cycle-block degradation was further established to reproduce the experiments and to conduct a broader parametric study. The results show that no horizontal crack formed at the cast interface and that the strain-deflection response preserved the typical three-stage fatigue evolution. Increasing either the steel-fiber volume fraction from 0.8% to 1.6% or the lower-layer height ratio from 0.5 to 0.7 markedly prolonged fatigue life and improved crack control. A practical fatigue-life relation, a stiffness-degradation law, and a numerical response surface are proposed, indicating that a height ratio of 0.6–0.7 combined with a fiber dosage of 1.2%–1.6% provides the best balance between fatigue durability, stiffness retention, and failure ductility. Full article

This study addresses the limited availability of unified experimental datasets comparing ribbed steel and smooth FRP bars embedded in the same hybrid-fiber high-performance concrete (HPC) matrix under identical conditions. It investigates the mechanical and bond behavior of a triple-fiber HPC combining hooked-end steel (ST), basalt (BA), and polypropylene (PP) fibers and reinforced with steel, GFRP, and CFRP bars of identical diameter and embedment. Under a uniform curing regime, the HFRC reached a compressive strength of approximately 82 MPa and exhibited a high fracture energy G_f approximately 3.7 kJ/m² with a stable post-peak response in a notched-beam test, demonstrating effective multi-scale crack bridging within a dense hybrid fiber network. Pull-out tests on 200 mm embedment revealed distinct interfacial mechanisms: ribbed steel developed a pronounced peak bond stress (τ_max = 13.05 MPa) and the largest bond energy (G_b = 146 N/mm) due to mechanical interlock, whereas smooth GFRP and CFRP showed low τ_max (=1.46 and 0.78 MPa) and smoothly decaying τ–s governed by adhesion–friction with G_b = 3–4 N/mm. A consistent experimental framework enabled direct mechanistic comparison of bond–slip behavior across reinforcement types without confounding matrix or curing variables. Simple constitutive laws calibrated to the experimental τ–s curves (ramp–softening for steel and ramp–plateau or exponential for FRP) captured the stiffness, strength, and energy hierarchy with low error. The main contribution of this study lies in providing a configuration-consistent reference dataset and calibrated bond–slip descriptions for hybrid-fiber HPC members reinforced with both steel and FRP bars. The results highlight the role of the hybrid fiber network in improving crack stability and provide design-oriented parameters for anchorage assessment and nonlinear bond–slip modeling. Although the results are based on a limited experimental program, they establish a mechanistically coherent basis for further optimization of hybrid HPC matrices and development of performance-based anchorage formulations in high-performance structural applications. Full article

This study investigates the shear behavior of glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) beams to address challenges associated with their low elastic modulus, absence of yielding, and reduced stirrup efficiency in bending regions. GFRP bars are increasingly adopted as an alternative to steel due to their superior corrosion resistance, durability, and cost-effectiveness. This study focuses on the effects of stirrup type, stirrup spacing, and shear span-to-effective depth ratio on the structural performance of GFRP RC beams. Twelve full-scale beams were tested under four-point bending, incorporating three GFRP shear reinforcement configurations: fabricated closed stirrups, integrated straight bar systems, and discrete vertical bars. Experimental observations were analyzed in terms of failure modes, load-carrying capacity, energy absorption, and deformation characteristics. Results indicate that fabricated F-type stirrups provide the highest shear performance, though their effectiveness is limited by premature rupture at bending points. Site-integrated S- and T-type configurations offer practical alternatives, maintaining structural integrity while mitigating bend-related stress concentrations, but with slightly lower energy absorption and load capacity. Increasing stirrup spacing significantly reduces shear resistance and shifts failure from flexural to shear-dominated modes. Comparisons with widely used design codes and analytical models show that CSA S806-12 provisions offer the most reliable predictions, while other guidelines tend to over- or underestimate shear capacity depending on configuration and a/d ratio. The study highlights the importance of optimizing stirrup type and spacing to enhance the shear performance of GFRP RC beams. Findings provide valuable insights for improving current design methodologies, offering guidance for engineers seeking durable, corrosion-resistant alternatives to steel reinforcement in aggressive environments. This research demonstrates that innovative site-integrated stirrup configurations can bridge practical fabrication constraints without compromising overall shear performance, promoting more efficient and resilient GFRP RC structures. Full article

Dredged reservoir sediments (DRS), generated in large volumes during dam desilting operations, pose significant stockpiling and land-use challenges in Mediterranean regions. Owing to their high fines content and moderate plasticity, these sediments present potential for reuse as compacted hydraulic barrier materials. This study evaluates the feasibility of using DRS as a liner material and, for the first time, provides a direct comparative assessment of natural (wheat straw fibers, WSF) and synthetic (polypropylene fibers, PPF) reinforcement within the same sediment matrix under liner-relevant conditions. Fiber contents of 0–0.9% (by dry mass) were investigated. Mechanical and consolidation behaviors were assessed using direct shear and oedometer tests. Fiber inclusion significantly improved shear strength, with an optimal response at 0.6%. At this dosage, PPF reduced the compression index by ~50%, while WSF provided moderate but consistent improvement. Estimated hydraulic conductivity increased slightly with fiber addition but remained within the range typically reported for compacted barrier materials. FTIR analysis indicated distinct reinforcement mechanisms, with lignocellulosic interactions for WSF and mechanical bridging for PPF. These results demonstrate that DRS can be effectively valorized as liner materials, while highlighting the contrasting performance of biodegradable and synthetic fibers, with 0.6% identified as a balance between mechanical efficiency and material sustainability. Full article

To address the limitation of insufficient mechanical strength and short service life in biodegradable bamboo fiber mulch film (BFM) replacing plastic film in agriculture, this study applied a biochemical method to make bamboo fiber and used bacterial cellulose (BC) as a natural nanoscale reinforcing agent to fabricate high-performance bacterial cellulose bamboo fiber mulch film (BC-BFM). The physical and mechanical properties, chemical structure, seed germination and degradation behavior performance of BC-BFM were characterized. Results demonstrated the structural compactness and homogeneity of the BC-BFM were improved markedly with the increase in BC addition and BC formed a 3D nanofibrillar network that effectively bridged inter-fiber voids. The tensile, burst and tear indexes of BC-BFM all significantly rose with BC addition. Notably, compared to plastic film and BFM, BC-BFM exhibited a good effect on mung bean seed germination and the best growth speed was at 5% BC addition. Furthermore, the degradation test showed that the degradation rate of BC-BFM within 90 d was three times less than that of BFM and service life was similar to plastic film. This showed that it was a promising method to prepare biodegradable high-quality BFM through biochemical preparation of bamboo fiber and BC nanocellulose reinforcement. This method markedly enhanced the mechanical performance and durability of BC-BFM, providing a feasible technical path for the development of biodegradable high-performance green agricultural covering materials with long service life. Full article

The integration of real-time monitoring capabilities into concrete materials offers significant potential for improving the safety and durability of building infrastructure. This study investigates the real-time electromechanical behavior of steel fiber-reinforced self-sensing concrete under compressive and splitting tensile loading. Eighteen cubes (150 × 150 × 150 mm) and eighteen cylinders (150 × 300 mm) containing 0.5%, 1.5%, and 3% steel fiber volume fractions were tested. Electrical resistance was continuously recorded at one-second intervals using an Arduino–ESP32-based system, enabling in situ tracking of damage evolution. The conductive steel fiber network functioned as an intrinsic sensing phase, where load-induced microstructural changes altered electrical pathways. Resistance variations consistently preceded visible cracking, with pronounced nonlinear increases observed at 65–80% of peak load, indicating micro-crack initiation. Distinct electromechanical stages were identified, including elastic stability, compaction-induced resistance reduction near yield, and rapid resistance growth during crack propagation. Higher fiber contents improved both mechanical performance and sensing sensitivity through enhanced crack-bridging and conductive network stability. Although curing age influenced baseline resistance, reliable real-time damage detection was achieved across all specimens. The findings demonstrate the feasibility of steel fiber-reinforced concrete as a cost-effective, distributed monitoring material for early damage detection in building structures. Full article

Concrete-encased steel (CES) bridge piers can be considered as a robust alternative to traditional reinforced concrete sections, especially in regions prone to seismic activity. CES piers combine the ductility of steel with the compressive strength of concrete, offering improved energy dissipation and resilience during earthquakes. Given the lack of CES design specifications in the Canadian design code, it is crucial to compile a body of knowledge describing the behavior of the CES bridge pier in order to facilitate the codification of the design guide. This study assesses the seismic performance of CES rectangular bridge piers with a focus on how variations in the steel section configuration affect the pier’s overall behavior under seismic loads. To conduct this assessment, a fiber element model was employed to model CES bridge piers subjected to seismic loading. The thickness and height of the web and the width and the thickness of the flanges of the I-shape steel section were varied to understand their impact on the bridge’s seismic performance. In addition to the I-shape sections, a crossed two-I-shape section was also studied. Spectral analysis, nonlinear pushover analysis and nonlinear time-history analysis was performed on the bridge models in order to better understand the seismic performance of the studied bridge piers. Simulation results indicate that larger flanges increase the pier’s bending moment capacity, allowing it to absorb greater seismic energy and undergo larger deformations without failing. This increases the overall ductility of the pier and enhances its ability to dissipate seismic energy. However, excessively large flanges or web can reduce the concrete cover and reduce the durability of the pier in the context of Canadian extreme-winter conditions. The study concludes that a balance between web thickness and flange width must be achieved to ensure the bridge can resist seismic forces while maintaining sufficient ductility and energy dissipation. Therefore, an optimized design, according to seismic demands, enhances the overall resistance of CES bridge piers. Full article

The long-term behavior of reinforced concrete (RC) structures under sustained loading is strongly affected by creep and cracking, particularly under service conditions where tension stiffening and curvature changes are significant. This study investigates the flexural response of cracked RC beams through combined numerical and experimental analyses. A new 1D finite element model is proposed, integrating nonlinear material behavior, damage mechanics, and time-dependent effects, including creep in both compression and tension. The model relies on a layered fiber section approach and uses a Newton–Raphson iterative procedure to solve equilibrium, allowing accurate prediction of strain, curvature, and internal force evolution over time. The model shows excellent agreement with experimental observations and ABAQUS simulations, accurately capturing deflection trends and crack development. Its performance is further validated using a database of 55 RC beams, including specimens with recycled aggregates and fiber reinforcement. Across this dataset, 84.5% of predicted deflections fall within ±1 mm of measured values, with an R² of 0.960, demonstrating strong reliability. A Sobol-based sensitivity analysis identifies load ratio as the most influential parameter on long-term deflection, followed by concrete strength and humidity. Overall, the model offers an efficient and robust tool for long-term deflection prediction, bridging simplified design rules and complex 3D simulations. Full article

This study evaluates bamboo–coir hybrid composite panels developed for formwork applications using an 80:20 fiber–matrix ratio and a 50:50 bamboo-to-coir distribution. The novelty of this study lies in the combined assessment of formwork-relevant mechanical performance, Mode I and Mode II fracture behavior, finite element validation and post-fracture microstructural correlation for a high fiber volume fraction natural fiber hybrid panel. Mechanical, durability, fracture, numerical and microstructural investigations were performed and benchmarked against 10 mm thick construction-grade plywood. The hybrid panels exhibited a density of 805 ± 10.84 kg/m³, which is within 0.7% of plywood, a tensile strength of 50.20 ± 2.85 MPa, representing an increase of 41.8% over plywood, and a flexural strength of 38.60 ± 2.10 MPa, corresponding to an increase of 12.9% as compared to plywood. The impact energy absorption of hybrid panels was 7.85 ± 0.62 J, which is 26.6% greater than plywood. Mode I fracture testing yielded a fracture toughness of 456.65 ± 15.42 J/m², corresponding to an increase of 9.3% over plywood, while Mode II fracture toughness yielded a value of 792.42 ± 30.18 J/m², representing an increase of 13.7% over plywood. Finite element predictions deviated from experimental load–displacement responses by 5–13%. SEM observations identified fiber bridging, fiber pullout and interfacial sliding in the hybrid panels, consistent with the measured fracture energy values. The results indicate that bamboo–coir hybrid panels satisfy the mechanical and fracture performance requirements for reusable formwork systems. Full article

This study presents a reliable methodology for analyzing reinforced ultra-high-performance fiber-reinforced concrete (UHPFRC) elements by linking material behavior to structural performance. A non-linear finite element model (NLFEM) is proposed to simulate the tensile response of reinforced UHPFRC elements, with particular emphasis on shrinkage effects. The model operates in two phases: the first simulates shrinkage during specimen storage and the second simulates the mechanical tensile test, using the internal stresses from the first phase as initial conditions. The model was validated through an experimental program involving reinforced UHPFRC ties. The NLFEM accurately reproduced the load–displacement response using average UHPFRC tensile parameters obtained from a simplified Four-Point bending test Inverse Analysis method (4P-IA). It reliably predicted the shrinkage strain range and its impact on stiffness loss during microcrack initiation and stabilization, where tension-stiffening behavior is critical. Additionally, the simulation from the model captured the transition from microcracking to macrocrack formation and the role of fiber bridging in maintaining stiffness. The predicted shrinkage strain aligns with values reported in the literature and represents a conservative upper bound, neglecting the potential effects of creep and relaxation. Overall, the NLFEM effectively simulates the full tension-stiffening behavior of reinforced UHPFRC, including three-dimensional effects, and provides a reliable tool for structural analysis and design. Full article

To clarify the shear lag effect and flexural performance of glass fiber-reinforced polymer (GFRP) composite truss web girder bridges and verify the feasibility of substituting steel truss webs with GFRP members, a refined finite element (FE) model was established via ABAQUS. Transverse and longitudinal stress distributions in concrete slabs were systematically analyzed under mid-span concentrated, full-span distributed, and two-point symmetric loads, with a parallel performance comparison against steel truss web girder bridges. The transverse shear lag effect exhibited distinct interlayer differences, with the top slab effective width ratio 15–20% lower than that of the bottom slab; stress peaks at truss-slab joints stemmed from concentrated shear transfer, while bottom slab stress troughs were induced by boundary constraints. Longitudinally, the effective width ratio averaged 0.65 at beam ends, dropped to the minimum at loading points, and recovered to over 0.98 in non-loaded zones. Performance comparisons showed that under the applied load patterns, the GFRP system exhibited a flexural performance similar to that of the steel system, with mid-span deflection differences of 0.29–0.30 mm and normal stress deviations below 0.1 MPa. This study quantifies the multi-case shear-lag response characteristics, verifies that GFRP truss webs can achieve flexural behavior comparable to steel webs under the investigated conditions, and provides theoretical support for the refined design and engineering applications of this novel bridge structure. Full article

The shear behavior of basalt fiber-reinforced polymer (BFRP) bars is crucial for their applications in geotechnical reinforcement and composite structures. In this study, double-side direct shear tests were conducted to investigate the progressive failure mechanism of BFRP bars. The results reveal a three-stage process: initial matrix-dominated vertical shear, followed by fiber-bridging dominated oblique tension-shear, and finally formation of a “brush-like” fracture surface with significant residual strength. The average peak shear strength of the ten specimens was 204.04 MPa with a coefficient of variation of 7.25%, while the initial shear modulus averaged 3.37 GPa with a coefficient of variation of 11.82%. Based on statistical damage theory, a shear constitutive model incorporating fiber bridging and residual strength is established. Parameter analysis indicates that the shape parameter m governs the post-peak softening rate, while the residual strength τ_res essentially determines the height of the residual plateau. The model achieves a goodness-of-fit (R²) exceeding 0.98 for most specimens, accurately describing the mechanical behavior from linear elasticity, damage-induced hardening, peak softening, to the residual stage. This study provides theoretical and experimental support for the engineering application of BFRP bars under complex stress states. Full article

The punching shear capacity of reinforced ultra-high-performance concrete (UHPC) two-way slabs in applications such as floor slabs and bridge decks has attracted increasing attention. However, due to the insufficient consideration of the internal force transmission path and failure mechanism, existing empirical formulas exhibit limited accuracy for predicting the punching shear capacity of reinforced UHPC slabs. Therefore, based on the critical shear crack theory (CSCT), this study proposes a specific theoretical model where the tensile strain-hardening behavior and tensile strength of UHPC, the punching shear-span ratio, and the reinforcement ratio are comprehensively considered. In the proposed model, the steel fiber bridging contribution is derived via the variable engagement method (VEM), for which an equation describing the bond strength between steel fibers and UHPC matrix was developed. The feasibility of the proposed model was validated through an established experimental database. Furthermore, the effects of several key parameters on the punching shear behavior of reinforced UHPC slabs were analyzed. The results show that the proposed models can accurately predict the punching shear capacity and ultimate rotation angle of reinforced UHPC slabs. With increasing slab thickness, UHPC strength, and reinforcement ratio, the punching shear capacity increases, whereas the corresponding ultimate rotation angle and steel fiber contribution ratio decrease. Increasing the fiber volume fraction enhances both the fiber contribution and the punching shear capacity. For slabs with higher UHPC strength, the reinforcing effect of a higher reinforcement ratio is more pronounced. Full article

The rising environmental concerns over cement-based construction materials have led to the development of sustainable alternatives. Among these, geopolymers represent a promising class of low-carbon binders offering environmental benefits and competitive mechanical properties; however, their intrinsic brittleness limits their tensile and post-cracking performance. This study investigates the adoption of flax fibers as natural reinforcement to enhance ductility and post-peak behavior of metakaolin-based geopolymers. The performance of metakaolin-based geopolymers with flax fibers (MKFLAX) was experimentally evaluated in terms of strength, stiffness, toughness, and failure behavior. The addition of flax fibers enhanced ductility, toughness, and post-peak load-carrying capacity while slightly improving stiffness due to the bridging of cracks and the fiber pull-out mechanism. In comparison with the available literature on sisal, flax, and jute fibers, flax fibers showed improved performance due to the better dispersion within the matrix and higher tensile modulus. These findings highlight that flax fiber-reinforced metakaolin geopolymers show enhanced post-cracking behavior at the laboratory scale and could be of interest for sustainable cementitious materials, subject to further validation at the structural scale. Furthermore, a nonlinear finite element model was adopted based on damage mechanics to simulate the damage localization, stress–strain response and post-peak behavior of geopolymer composites. The numerical results showed a reasonable agreement with the experimental trends, particularly in the elastic and early softening phases. The findings are limited to the studied material system, fiber content, and small-scale samples and should be viewed as trend-level observations rather than generalized performance claims. Full article

Polymer modification is a well-established strategy for improving the performance and extending the service life of cementitious and other construction materials, with direct implications for environmental sustainability and infrastructure resilience. Among these polymers, polyvinylpyrrolidone (PVP), a non-ionic, water-soluble, and highly compatible polymer, has emerged as a uniquely versatile additive for mitigating degradation in aggressive environments. This review provides a critical and comprehensive synthesis of the state-of-the-art research on PVP’s roles in cement, mortar, concrete, and asphalt systems. The novelty of this work lies in its mechanistic integration and system-level interpretation, which consolidate fragmented knowledge across multiple domains—ranging from rheology and durability to nanotechnology and interfacial engineering—into a unified and coherent framework. Through cross-study comparison, this approach establishes a comprehensive understanding of PVP’s role in cementitious systems while outlining clear pathways for future research and practical implementation. This review provides the first integrated framework that connects PVP’s molecular structure, adsorption behavior, and ion-coordination mechanisms to its macroscopic influence on rheology, hydration, microstructure, and long-term durability. The review critically analyzes the underlying mechanisms, including physical pore-filling and crack-bridging, as well as chemical ion-coordination, which collectively govern PVP’s performance. Key quantitative findings are consolidated, showing that optimal PVP addition can reduce water absorption by over 35%, increase fracture toughness by ~47%, and, when used as an interfacial modifier, enhance the strain capacity of fiber-reinforced composites by over 100%. Reported benefits include improved workability, enhanced mechanical performance and toughness, superior durability under chemical and frost exposure, and the development of functional materials such as self-sensing concretes and photocatalytic coatings that support structural health monitoring and pollution mitigation. Overall, this review synthesizes current knowledge, consolidates experimental evidence in tabular form, and identifies future opportunities for leveraging PVP in the design of sustainable, low-impact, and environmentally resilient construction materials and infrastructures. Full article