Search Results (253)

To address the susceptibility of traditional concrete to explosive spalling and the lack of in situ damage-monitoring methods at high temperatures, in this study, a novel self-sensing, high-temperature-resistant Engineered Cementitious Composite (ECC) was developed. The matrix contains eco-friendly glass sand reinforced with a hybrid system of polypropylene fibers (PPFs) and carbon fibers (CFs). The evolution of mechanical properties and the multimodal self-sensing characteristics of the ECC were systematically investigated following thermal treatment from 20 °C to 800 °C. The results indicate that the hybrid system exhibits a significant synergistic effect: through PFFs’ pore-forming mechanism, internal vapor pressure is effectively released to mitigate spalling, while CFs provide residual strength compensation. Mechanically, the compressive strength increased by 51.32% (0.9% CF + 1.0% PPF) at 400 °C compared to ambient temperature, attributed to high-temperature-activated secondary hydration. Regarding self-sensing, the composite containing 1.1% CF and 1.5% PPF displayed superior thermosensitivity during heating (resistivity reduction of 49.1%), indicating potential for early fire warnings. Notably, pressure sensitivity was enhanced after high-temperature exposure, with the 0.7% CF + 0.5% PPF group achieving a Fractional Change in Resistivity of 31.1% at 600 °C. Conversely, flexural sensitivity presented a “thermally induced attenuation effect” primarily attributed to high-temperature-induced interfacial weakening. This study confirms that the “pore-formation” mechanism, combined with the reconstruction of the conductive network, governs the material’s macroscopic properties, providing a theoretical basis for green, intelligent, and fire-safe infrastructure. Full article

To enhance the damage resistance of protective engineering materials under extreme loads such as explosions and impacts, this study, building upon the improvement in impact resistance of concrete achieved by rubber modification, further incorporates steel fibers and glass fibers to synergistically enhance impact resistance and to investigate the underlying mechanisms. Using split Hopkinson pressure bar (SHPB) testing, a comparative investigation was conducted on the dynamic mechanical responses of four specimen groups, namely plain rubberized concrete, single steel fiber-reinforced, single glass fiber-reinforced, and hybrid steel–glass fiber-reinforced rubberized concrete, over a strain-rate range of 30–185 s⁻¹. The results demonstrate that the incorporation of hybrid fibers significantly enhances the dynamic compressive performance of plain rubber concrete. Specifically, the dynamic compressive strength increases from 40.73–61.29 MPa to 60.25–101.86 MPa, accompanied by a 59.5% increase in strain-rate sensitivity. Meanwhile, the fragment fineness modulus after failure rises from 3.20–3.33 to 3.73–4.20, indicating improved post-impact integrity. In addition, the hybrid fiber-reinforced specimens exhibit the highest energy dissipation capacity at identical strain rates. Their dynamic stress–strain responses are characterized by higher stiffness, improved ductility, and more pronounced progressive failure behavior. These findings provide experimental evidence for the design of high-impact-resistant protective engineering materials. Full article

Sustainability concerns over the management and handling of the growing volume of waste tires have necessitated the exploration of potential applications for the reuse and recycling of this resource, as they are categorized as hazardous wastes and are typically incinerated through thermal processing or dumped in landfills, resulting in significant environmental issues. The recycled steel and textile fibers from tires can be incorporated in concrete to assist in mitigating this impending environmental calamity, primarily by enhancing the efficacy of concrete. The present study aims to investigate the effect of using recycled tire steel fibers (RTSF) and recycled tire textile fibers (RTTF) in concrete, as economically viable and environmentally friendly alternatives to commercially available fibers. Although literature on the use of recycled fibers in concrete is available, the research is very limited in terms of their hybrid use and with minimal environmental analysis. Consequently, to address the gaps, this research concentrates on the use of RTSF and RTTF as a hybrid mix in concrete with life cycle assessment (LCA) to balance the mechanical performance and environmental sustainability. The experimental work is formulated to suggest an optimum dose of RTSF and RTTF, as a hybrid mix form, to be incorporated in concrete that imparts sufficient strength and workability. The fibers were integrated with dosages of 0.75%, 1%, and 1.25% for RTSF and 0.25%, 0.5%, and 0.75% for RTTF, respectively, by volume in non-hybrid form, while in hybrid form, they were reinforced as four different combinations (1%:0.5%, 0.75%, 0.75%, 0.5%, 0.5%:0.5%, and 0.75%:0.25%) by volume of RTSF and RTTF, respectively. Fresh and hardened properties of concrete were tested according to the ASTM standards. The results showed that concrete with hybrid fibers outperformed the concrete with normal individual fibers in both fresh and hardened states tests. The mechanical strength results showed that the synergistic use of RTSF and RTTF can enhance the strength, toughness, ductility, and crack resistance of the concrete. The hybrid mix H1 comprising 1% RTSF and 0.5% RTTF was ascertained as the optimal mix showing the highest mechanical performance with embodied CO₂ and energy values only slightly higher than the control mix, while offering the significant sustainability benefit of utilizing recycled fibers. 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

As research on fiber-reinforced concrete progresses, investigating the enhancement effect of hybrid fiber-reinforced concrete becomes increasingly crucial. In the present research, the contents of steel fiber (SF) and polypropylene fiber (PP) were set as variable parameters to study the mechanical performance of steel-polypropylene hybrid fiber-reinforced concrete (SPFRC). Mechanical performance tests were undertaken on 16 groups of standard specimens. The failure modes were observed, the strength variation patterns were analyzed, and both a strength prediction equation and a complete stress–strain curve equation were established. Research results indicated that the specimen containing 1.5% SF and 0.25% PP exhibited the maximum strength enhancement compared with plain concrete: cube compressive strength improved by 27.78%, and splitting tensile strength surged by 41.18%. When the SF content was 1.5% and that of PP was 0.5%, the specimen’s elastic modulus experienced the greatest enhancement, reaching 58.59%. Hybrid fibers significantly enhanced the mechanical performance of SPFRC, simultaneously exerting strengthening, crack-resistance, and toughening effects. The research findings offer both experimental evidence and theoretical support for promoting research and engineering applications of SPFRC. Full article

With the continuous growth of the demand for concrete in infrastructure construction, natural aggregate resources have become increasingly scarce. The preparation of concrete using desert sand and recycled aggregates has emerged as an effective approach to achieving the sustainable development of building materials. However, desert sand recycled concrete still confronts critical durability-related challenges when exposed to freeze–thaw conditions. We examined how hybrid fibers (steel fibers and hybrid PP fibers) affect the mechanical performance and freeze–thaw durability of desert sand recycled aggregate concrete, along with the underlying mechanisms. Mechanical properties (compressive, splitting tensile, flexural strength) and freeze–thaw damage indicators (mass loss, dynamic elastic modulus) were tested. The findings indicated that at a 30% desert sand replacement ratio, the concrete achieved optimal initial mechanical properties. For the hybrid fibers group (F0.15-S0.5) with 0.15% hybrid PP fibers and 0.5% steel fibers incorporated, relative to the control group, its compressive strength rose by 31.6%, while mechanical property loss was notably mitigated after 125 freeze–thaw cycles. Freeze–thaw damage models based on the exponential function and the Aas-Jakobsen function were established. Microscopic analysis indicated that the fibers effectively suppressed crack propagation and interfacial transition zone (ITZ) damage. This research offers critical experimental evidence and theoretical frameworks for the application of fiber-reinforced desert sand recycled concrete in cold-climate regions. Full article

This study introduces a hybrid framework combining an Artificial Neural Network (ANN) with the Jaya optimization algorithm to predict the minimum Carbon Fiber Reinforced Polymer (CFRP) area required for flexural strengthening of reinforced concrete (RC) cantilever walls. A multilayer perceptron (MLP) network was trained on 500 Jaya-optimized design scenarios incorporating twelve design variables, including geometry, loads, and material properties. The ANN achieved high predictive accuracy, with R-values near 1.0 across training, validation, and testing phases. Five independent test cases yielded an average error of 3.69%, and 10-fold cross-validation confirmed model robustness (R = 0.9996). A global perturbation-based sensitivity analysis was also conducted to quantify the influence of each input parameter, highlighting wall length, moment demand, and concrete strength as the most significant features. This integrated ANN–Jaya model enables rapid, code-compliant CFRP design in accordance with ACI 318 and ACI 440.2R-17, minimizing material usage and ensuring economic and sustainable retrofitting. The proposed approach offers a practical, data-driven alternative to traditional iterative methods, suitable for application in modern performance-based structural engineering. Full article

The growing demand for sustainable pavement materials has increased interest in using recycled concrete aggregate (RCA) as a substitute for natural aggregates. However, the mechanical, durability, and environmental performance of roller-compacted concrete pavement (RCCP) incorporating very high RCA contents (≥75%) remains poorly understood, particularly when combined with hybrid steel fiber reinforcement. This knowledge gap limits the practical adoption of high-RCA RCCP in infrastructure applications. To address this gap, this study investigates the eco-efficiency of RCCP produced with 75% RCA and different steel fiber systems, including industrial (ISF), recycled (RSF), and hybrid (HSF) combinations. Mechanical performance was evaluated through compressive, tensile, and flexural testing, while freeze–thaw durability was assessed under extended cyclic exposure. Environmental impacts were quantified through a cradle-to-gate life cycle assessment (LCA), and a multi-criteria decision analysis (MCDA) was applied to integrate mechanical, durability, and environmental indicators. The findings show that although high-RCA mixtures exhibit reduced mechanical performance due to weaker interfacial bonding, HSF reinforcement effectively mitigates these drawbacks, enhancing toughness and improving freeze–thaw resistance. The LCA results indicate that replacing natural aggregates and industrial fibers with RCA and RSF substantially reduces environmental burdens. MCDA rankings further identify HSF-reinforced high-RCA mixtures as the most balanced and eco-efficient configurations. Overall, the study demonstrates that hybrid steel fibers enable the development of durable, low-carbon, and high-RCA RCCP, providing a viable pathway toward circular and sustainable pavement construction. Full article

Concrete remains the most widely used construction material globally; however, its intrinsic limitations—low tensile strength, brittle behavior, and susceptibility to microcracking—necessitate performance enhancement for demanding structural applications. Hybrid fiber-reinforced concrete (HFRC) offers a promising solution, yet the optimal balance of steel fibers (SF) and polypropylene fibers (PF) for structural elements such as slabs remains insufficiently understood. This study experimentally investigates the flexural behavior of 42 reinforced concrete slabs (21 one-way and 21 two-way) incorporating systematically varied SF–PF volumetric ratios, advancing current knowledge by identifying performance-optimal hybrid configurations for each slab type. One-way slabs were tested under four-point bending and two-way slabs under three-point bending, with structural responses evaluated in terms of load capacity, cracking behavior, deflection characteristics, and failure modes. The results demonstrate that fiber dosage does not proportionally enhance strength, as excessive content leads to fiber balling and reduced workability—highlighting the need for optimized hybrid proportions rather than indiscriminate addition. Quantitative findings confirm significant performance gains with properly tuned hybrid mixes. For one-way slabs, the optimal combination of 0.7% SF + 0.9% PF achieved 115% of the ultimate load of the control specimen, demonstrating a substantial improvement in flexural resistance. Two-way slabs exhibited even greater enhancements: first-crack load increased by up to 213%, and ultimate load improved by 40.36%, while deflection capacity rose by 44.81% at first crack and 39.80% at ultimate load with the optimal 0.9% SF + 0.1% PF mix. Comparatively, two-way slabs outperformed one-way slabs across all metrics, benefiting from multidirectional stress distribution that enabled more effective fiber engagement. Overall, this study provides new insight into hybrid fiber synergy in RC slabs and establishes quantified optimal SF–PF combinations that significantly enhance load capacity, ductility, and crack resistance for both one-way and two-way systems. Full article

Building structures are inherently susceptible to damage from extreme dynamic loads, while conventional concrete exhibits inadequate tensile resistance. While hybrid fibers systems can surpass the limitations of single-fiber reinforcement through their synergistic action, their internal damage mechanisms under impact loading remain inadequately understood. This study investigates the dynamic splitting behavior of hybrid fibers-reinforced cementitious composites combining polyvinyl alcohol (PVA) with either steel (SF) or polyethylene (PE) fibers, using Split Hopkinson Pressure Bar (SHPB) tests at strain rates of 5–31 s⁻¹, along with industrial CT scanning for meso-scale damage analysis. Results indicate that the SF–PVA hybrid improved strength by up to 15.6% compared to mono-PVA, while the PE–PVA hybrid achieved an 11.1% increase. All hybrid systems exhibited improved energy dissipation (which rose 25–45% with strain rate) and displayed secondary stress peaks. Quantitative CT analysis revealed distinct damage patterns: the mono-PVA specimen developed extensive damage networks (porosity: 7.20%; crack ratio: 4.48%), the SF-PVA hybrid system displayed the lowest damage indices (porosity: 3.29%; crack ratio: 1.76%), whereas the PE-PVA hybrid system exhibited the most significant dispersed damage pattern (crack-to-pore ratio: 39.32%). The hybrid systems function via distinct mechanisms: SF–PVA offers multi-scale reinforcement and superior damage suppression, whereas PE–PVA enables sequential energy dissipation, effectively dispersing concentrated damage. These insights support tailored fiber hybridization for impact-resistant structural design. Full article

This study examines the synergistic influence of recycled concrete aggregates (RCAs), industrial steel fibers (ISFs), recycled steel fibers (RSFs), and hybrid ISF/RSF (HSF) on the structural, durability, and environmental performance of roller-compacted concrete pavement (RCCP). Twenty mixtures were prepared with 0 and 50% RCA and fiber dosages of 0–0.9%, including plain, single-fiber, and HSF systems. Compressive, splitting tensile, and flexural strengths, as well as freeze–thaw resistance up to 300 cycles, were experimentally evaluated. Environmental performance was quantified through a cradle-to-gate life cycle assessment (LCA) covering nine impact categories and integrated with a multi-criteria decision analysis (MCDA) using the weighted sum method (WSM) and technique for order of preference by similarity to ideal solution (TOPSIS). Results indicate that 50% RCA replacement reduced compressive strength by ~21% but decreased global warming potential (GWP) by 15%. Hybrid fiber reinforcement significantly improved mechanical and durability properties, achieving up to 51% higher tensile strength and >85% strength retention after 300 freeze–thaw cycles compared with the control mix. The LCA showed notable reductions in GWP, acidification potential, and non-renewable energy demand when ISF and natural aggregates were partially substituted with RSF and RCA. The MCDA identified N50_R50_ISF0.3_RSF0.3 (50% RCA with 0.6% HSF) as the optimal mixture, achieving the highest eco-efficiency index (WSM = 0.80; TOPSIS = 0.73). These findings confirm that integrating RCA with hybrid steel fibers enhances the mechanical and durability performance of RCCP while substantially reducing environmental burdens, providing a viable strategy for low-carbon and circular pavement construction. Full article

To address the poor resistance of recycled aggregate concrete (RAC) to chloride ion penetration and freeze–thaw deterioration in cold coastal regions, this study introduces basalt fibers (BFs) as a reinforcement to improve its durability and structural integrity. Rapid freeze–thaw and electric flux tests, combined with scanning electron microscopy (SEM), were employed to systematically evaluate the effects of fiber volume fraction and length configuration on the frost resistance and chloride impermeability of basalt fiber-reinforced RAC (BFRAC). The experimental results demonstrated that the incorporation of basalt fibers markedly enhanced the coupled durability of RAC, with the mixture containing 0.15% fiber volume and a balanced hybrid of short (12 mm) and long (18 mm) fibers achieving the most favorable performance. This mixture effectively reduced mass loss and strength degradation under repeated freeze–thaw cycles while substantially lowering chloride ion penetration compared with plain RAC. Microstructural observations revealed that the hybrid fiber system formed a multi-scale three-dimensional network, in which short fibers restrained microcrack initiation and long fibers bridged macrocracks, jointly refining the pore structure and improving the interfacial bonding between recycled aggregates and the cement matrix. This synergistic mechanism enhanced matrix compactness and obstructed chloride transport, leading to a more stable and durable composite. The findings not only establish an optimal basalt fiber design for improving RAC durability but also elucidate the fundamental mechanism underlying hybrid fiber synergy. These insights provide valuable theoretical guidance and practical strategies for developing sustainable, high-performance concrete suitable for long-term service in cold-region coastal infrastructures. Full article

This study investigates the combined use of recycled concrete aggregate (RCA) and steel fibers—industrial (ISF), recycled (RSF), and hybrid ISF/RSF (HSF)—to enhance the mechanical performance, freeze–thaw durability, and environmental efficiency of roller-compacted concrete pavement (RCCP). Twenty mixtures incorporating two RCA levels (0% and 25%) and different fiber systems were tested. The results showed that, although RCA slightly reduced strength, hybrid fibers effectively compensated for this loss, improving toughness, tensile capacity, and resistance to freeze–thaw degradation. A life-cycle assessment demonstrated that substituting natural aggregates and industrial fibers with RCA and RSF lowers the embodied carbon and energy demand. A multi-criteria decision analysis identified mixtures with 25% RCA and hybrid fibers (0.9% HSF) as the most balanced solutions, combining an improved performance with a reduced environmental burden. The findings highlight hybrid fiber-reinforced, RCA-based RCCP as a practical and eco-efficient option for sustainable pavement infrastructure. Full article

In recent years, the demand for high-strength concrete (HSC) for buildings has been steadily increasing. Continuous HSC deep beams are frequently employed in various structural applications, including high-rise buildings, bridges, and parking garages, due to their superior load capacity. Some cases require the addition of openings after the construction for passing utilities such as drainage and electricity. This study experimentally examines four two-span HSC deep beams: one control solid beam, one beam with circular openings, and two beams that utilized different strengthening schemes. The openings were asymmetrical circular openings, with one positioned in each span. This study sought to regain the full capacity of beams with openings by employing two types of strengthening schemes. The first one used bolted steel plates, while the second was a hybrid scheme that combined bolted steel plates with externally bonded fiber-reinforced polymer (FRP) sheets. Test findings demonstrated that both methods effectively restored the load capacity of the strengthened beams. The strengthened beam with steel plates achieved a load capacity of 125% compared to the solid beam. Likewise, the beam retrofitted with hybrid steel/FRP composites reached 117%. Additionally, the energy dissipation and ductility index of the strengthened beam with steel plates were 32% and 77%, respectively, compared to the strengthened beam with hybrid steel/FRP composites. The findings emphasize the effectiveness of the applied retrofitting techniques in restoring the lost capacity due to the cutting of post-construction openings in deep beams. Full article

The current study aims to investigate the effect of using hybrid bars on the bending characteristics of hybrid fiber-reinforced concrete (FRC) beams. For this purpose, a series of flexural tests on FRC beams were conducted. Four FRC beams were fabricated, each with a section of 120 mm × 185 mm and an overall length of 1.5 m. The FRC beams’ tension reinforcement consisted of a hybrid configuration of steel and glass fiber-reinforced polymer (GFRP) rebars. The concrete mix included a hybrid fiber content of 1% by volume, with 0.75% for hooked-end steel fibers (SF) and 0.25% polypropylene fibers (PP). The simply supported FRC beams were tested under the action of two-point loads. The results demonstrated that the inclusion of hybrid fibers substantially improved the crack widening and propagation in FRC beams compared to normal concrete (NC) beams. The maximum load capabilities of the FRC beams surpassed those of the NC beams up to 13.2%. The GFRP bars further enhanced the beams’ load-carrying capacity with an observed increase of up to 42.5%, when compared to the steel-reinforced FRC beam (BFRC-3S). Additionally, hybrid reinforcement improved ductility, with increases of 39.1% and 167.1% when one or two GFRP bars were replaced by steel, respectively. Full article