Search Results (3,510)

This work presents an innovative approach to enhancing the performance of concrete with reclaimed asphalt pavement (RAP) aggregates using titanium dioxide (TiO₂) nanoparticles. Traditional limestone coarse aggregates were partially replaced with 30% and 50% RAP aggregates; a subset of mixtures containing RAP aggregates was treated with TiO₂ nanoparticles. The rheological, mechanical, and long-term properties of concrete, along with changes in its chemical composition following the addition of RAP and TiO₂, were evaluated. Results revealed that using 30% and 50% RAP in concrete mixtures reduced their compressive strength by 18% and 27%, respectively. However, using TiO₂ in those mixtures enhanced their compressive strength by 8.7% and 6.3%. Moreover, concrete with 50% RAP exhibited an 85% increase in water absorption (the highest among all mixtures) compared to the control. TiO₂ treatment was most beneficial in the 30% RAP mixture, reducing its water absorption by 32.5% compared to its untreated counterpart. Additionally, the 30% RAP mixture treated with TiO₂ showed the highest resistance to sulfates among modified mixtures, as its compressive strength decreased by 10.4% compared to a decrease of 23% in the strength of the untreated 30% RAP mixture. Statistical analysis using single-factor ANOVA showed that integrating RAP aggregates with or without the presence of TiO₂ particles would significantly affect the concrete properties in terms of their population means. The t-test analysis, on the other hand, proved sufficient evidence that the mean values of the 30% RAP mixture treated with TiO₂ would not differ significantly from the control in terms of its slump and water absorption properties. The chemical structure analysis revealed an increase in the Si-O-Si and Si-O functional groups when using TiO₂ in RAP mixtures, suggesting improved hydration activity and accelerated C-S-H formation in the treated RAP mixtures. Moreover, distinct C-H peaks were witnessed in concrete with untreated RAP aggregates, resulting from the aged asphalt coating on the RAP, which weakened the bond between the RAP and the cementitious matrix. Full article

The integration of wood and concrete in building structures is a well-established practice typically realized through mechanical connectors. However, the thermomechanical behavior of wood–concrete composite façades assembled via adhesive bonding remains underexplored. This study introduces a novel concept—the adhesive-bonded wood–concrete façade, termed “Hybrimur”—and evaluates the response of these façade panels under thermal gradients, with a focus on thermal bowing phenomena. Four full-scale façade prototypes (3 m high × 6 m wide), consisting of 7 cm thick concrete and 16 cm thick laminated timber (GL24h), were fabricated and tested both with and without insulation. Two reinforcement types were considered: fiberglass-reinforced concrete and welded mesh reinforcement. The study combines thermal analysis of temperature gradients at the adhesive interface with analytical and numerical methods to investigate thermal expansion effects. The experimental and numerical results revealed thermal strains concentrated at the wood–concrete interface without inducing panel failure. Thermal bowing (out-of-plane deflection) exhibited a nonlinear behavior influenced by the adhesive bond and the anisotropic nature of the wood. These findings highlight the importance of accounting for both interface behavior and wood anisotropy in the design of hybrid façades subjected to thermal loading. A tentative finite element model is proposed that utilizes isotropic wood with properties that limit the accuracy of the results obtained by the model. Full article

Rail transport is widely regarded as a sustainable and environmentally friendly option for long-distance freight and passenger movement during its operation phase. However, its construction and maintenance phases often result in substantial environmental impacts, which must be addressed to improve the overall sustainability of railways. This study aims to identify solutions that improve the performance of railway tracks, reduce maintenance requirements, and minimize environmental impact. With this objective, the potential of artificial inclusions and innovative composite materials in enhancing the sustainability of railway tracks is investigated through a comprehensive methodology, combining experimental, analytical and numerical approaches. A novel composite material, comprising soil, scrap tire aggregates and an adhesive, demonstrated strong potential as a sustainable base layer for ballastless railway tracks, exhibiting minimal strain accumulation (0.29–0.98%) under 50,000 load cycles and adequate damping. Incorporation of cellular artificial inclusions in the substructure layers of ballasted tracks reduced cumulative settlement by up to 33% and slowed track geometry deterioration. Use of planar artificial inclusions beneath a pile-supported railway embankment enhanced the load transfer efficiency and curtailed settlement, while also lowering environmental impact by reducing concrete usage. The findings of this study highlight strong potential of these approaches in improving track performance and the overall sustainability of railways. Full article

The use of sisal fibers to reinforce concrete and mortar enables the development of sustainable cement-based materials suitable for various construction elements. However, the high-water absorption of natural fibers can cause dimensional instability and poor fiber–matrix bonding, which reduces strength over time. Physical and chemical treatments can decrease water absorption and enhance the dimensional stability and bonding properties of fibers, but their effects on composite performance require further clarification. This study produced composites with 2%, 3%, and 4% by mass of sisal fibers subjected to different treatments, including hornification, washed alkaline treatment, and unwashed alkaline treatment. Fibers were characterized through water absorption, dimensional variation, scanning electron microscopy (SEM), X-ray diffraction, thermogravimetric analysis and direct tensile testing. Composites were evaluated by water absorption, capillarity, drying shrinkage, direct tensile and four-point bending tests to assess the influence of fiber treatment and content. Results showed that alkaline treatment significantly improved the physical and mechanical properties of sisal fibers. Consequently, composites reinforced with alkaline-treated fibers achieved superior performance compared to those reinforced with hornified fibers, with the best results observed at the highest fiber mass fraction (4%). These findings demonstrate the potential of treated sisal fibers to enhance the durability and mechanical behavior of natural fiber-reinforced cementitious composites. Full article

Tires are composed of various rubber polymers and reinforcing carcasses, and their wet skid resistance is influenced by the coupled effects of multiple factors. The braking force coefficient (BFC) is the primary performance indicator for evaluating tire wet skid resistance. This study proposes a novel method for evaluating the BFC of tires by integrating laboratory-simulated wet road tests with finite element simulations. A 295/60R22.5 all-steel radial tire was selected as the test object, and the simulation results showed good agreement with the experimental data, with a BFC error of 7.14%. This consistency confirms the reliability and accuracy of the proposed model in predicting tire wet grip performance. This study also investigated the effects of different working conditions of the tested tire on the BFC. The results showed that the wet grip performance of the tire on wet concrete surfaces was significantly lower than that on wet asphalt surfaces. Specifically, the BFC increased with the increase in braking slip ratio, decreased slightly with the rise in tire inflation pressure, and exhibited relatively low sensitivity to vertical load variations. All these results demonstrate that this integrated evaluation method provides targeted guidance for the mechanical performance optimization of tire tread rubber composites. Full article

Reinforced composite prestressed concrete hollow square (RCPHS) piles, installed through pre-drilling, grouting, and static jacking, integrate the large lateral contact area of cement–soil casings with the high strength and stiffness of prestressed concrete cores. This study combines full-scale vertical static load tests and finite-element (FE) simulations to explore the interaction among the core pile, plain-concrete casing, and surrounding soil. Results show that, at 3600 kN, RCPHS piles exhibit 76% less pile-head settlement compared to PHS piles, and a 36.5% reduction in pile-material expenditure is achieved using the RCPHS scheme. At the same settlement of 23 mm, RCPHS piles carry 87% more load than PHS piles. A 3D FE model developed in ABAQUS reveals that the core pile carries approximately 94% of the applied load. When the load exceeds 4180 kN, the axial force in the casing sharply increases at depths of 7–10 m. The simulated P–s curves align well with field measurements, confirming model accuracy. The superior performance of RCPHS piles is attributed to the graded elastic modulus and coordinated stress distribution of the core–casing–soil system, which enhances interface friction and overall load capacity. These findings provide a foundation for the design optimization of RCPHS piles in dense sandy foundations. Full article

Concrete materials undergo a series of physical and chemical changes under high temperature, leading to the degradation of mechanical properties. This study investigates basalt fiber-reinforced concrete (BFRC) through high-temperature testing using the split Hopkinson pressure bar (SHPB) apparatus. Impact compression tests were conducted on specimens after exposure to elevated temperatures to analyze the effects of varying fiber content, temperature levels, and impact rates on the mechanical behaviors of BFRC. Based on fractional calculus theory, a dynamic constitutive equation was established to characterize the viscoelastic properties and high-temperature damage of BFRC. The results indicate that the dynamic compressive strength of BFRC decreases significantly with increasing temperature but increases gradually with higher impact rates, demonstrating fiber-toughening effects, thermal degradation effects, and strain rate strengthening effects. The proposed constitutive model aligns well with the experimental data, effectively capturing the dynamic mechanical behaviors of BFRC after high-temperature exposure, including its transitional mechanical characteristics across elastic, viscoelastic, and viscous states. The viscoelastic behaviors of BFRC are fundamentally attributed to the synergistic response of its multi-phase composite system across different scales. Basalt fibers enhance the material’s elastic properties by improving the stress transfer mechanism, while high-temperature exposure amplifies its viscous characteristics through microstructural deterioration, chemical transformations, and associated thermal damage. Full article

This study investigates the mechanical behavior of a new type of link slab through experimental testing and numerical simulation. A full-scale segmental specimen of an I-shaped steel–concrete composite beam was designed, and a vertical active plus horizontal follow-up loading system was employed to realistically simulate the stress state of the link slab. In parallel, a nonlinear finite element model was established in ABAQUS to validate and extend the experimental findings. Test results indicate that the link slab exhibits favorable static performance with a ductile flexural tensile failure mode. At ultimate load, tensile reinforcement yielded while compressive concrete remained uncrushed, demonstrating high safety reserves. Cracks propagated primarily in the transverse direction, showing a typical flexural tensile cracking pattern. The maximum crack width was limited to 0.4 mm and remained confined within the link slab region, which is beneficial for long-term durability, maintenance, and repair. The FE model successfully reproduced the experimental process, accurately capturing both the crack development and the ultimate bending capacity of the slab. The findings highlight the reliability of the proposed structural system, demonstrate that maximum crack width can be evaluated as an eccentric tension member, and confirm that bending capacity may be assessed using existing design specifications. Full article

Stable adhesion on non-magnetic, steep, and irregular underwater surfaces (e.g., concrete dams with cracks or biofilms) remains a challenge for inspection robots. This study develops a novel adsorption mechanism based on the synergistic operation of a Venturi-ejector and a composite suction cup. The mechanism utilizes the Venturi effect to generate stable negative pressure via hydrodynamic entrainment and innovatively adopts a composite suction cup—comprising a rigid base and a dual-layer EPDM sponge (closed-cell + open-cell)—to achieve adaptive sealing, thereby reliably applying the efficient negative-pressure generation capability to rough underwater surfaces. Theoretical modeling established the quantitative relationship between adsorption force (F) and key parameters (nozzle/throat diameters, suction cup radius). CFD simulations revealed optimal adsorption at a nozzle diameter of 4.4 mm and throat diameter of 5.8 mm, achieving a peak simulated F of 520 N. Experiments demonstrated a maximum F of 417.9 N at 88.9 W power. The composite seal significantly reduced leakage on high-roughness surfaces (Ra ≥ 6 mm) compared to single-layer designs. Integrated into an inspection robot, the system provided stable adhesion (>600 N per single adsorption device) on vertical walls and reliable operation under real-world conditions at Balnetan Dam, enabling mechanical-arm-assisted maintenance. Full article

The durability of asphalt concrete is highly dependent on the geometry and mineralogy of coarse aggregates, yet their combined influence on mechanical and moisture resistance properties is still not fully understood. This study evaluates the effects of coarse aggregate geometry, specifically flat and elongated particle ratios and angularity, as well as mineral composition (quartz versus calcite), on asphalt mixture durability. The durability of mixtures was evaluated through Marshall properties as well as moisture susceptibility indicators, including the tensile strength ratio (TSR) and index of retained strength (IRS). Statistical analyses (ANOVA and t-tests) were also conducted to confirm the significance of the observed effects. Results showed that mixtures containing higher proportions of flat and elongated particles exhibited greater void content, reduced stability, and weaker moisture resistance, with the 1:5 flat-to-elongated ratio showing the most adverse impact (TSR 73.9%, IRS 69.2%). Conversely, increasing coarse aggregate angularity (CAA) enhanced mixture performance, with TSR values rising from 63.5% at 0% angularity to 81.2% at 100% angularity, accompanied by corresponding improvements in IRS. Mineral composition analysis further demonstrated that calcite-based aggregates achieved stronger bonding with asphalt binder and superior resistance to stripping compared to quartz-based ones. These findings confirm that aggregate geometry and mineralogy exert a decisive influence on asphalt mixture durability. They also highlight the need to revise current specifications that permit the use of uncrushed coarse aggregate in asphalt base courses, particularly when such layers may serve as surface courses in suburban or low-volume roads, where long-term resistance to moisture damage is critical. Full article

This research explores the phenomenon of plate-end (PE) debonding in reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) composites. This type of failure represents a key mechanism that undermines the structural performance and efficiency of FRP reinforcement systems. Despite the widespread use of FRP in structural repair due to its high strength and corrosion resistance, PE debonding—often triggered by shear or inclined cracks—remains a major challenge. Traditional computational models for predicting PE debonding suffer from low accuracy due to the nonlinear relationship between influencing parameters. To address this, the research employs machine learning techniques and SHapley Additive exPlanations (SHAP), to develop more accurate and explainable predictive models. A comprehensive database is constructed using key parameters affecting PE debonding. Machine learning algorithms are trained and evaluated, and their performance is compared with existing normative models. The study also includes parameter importance and sensitivity analyses to enhance model interpretability and guide future design practices in FRP-based structural reinforcement. Full article

The growing demand for radiation-shielded infrastructure highlights the need for materials that balance shielding performance with environmental and economic sustainability. Heavyweight self-compacting concretes (HWSCC), commonly produced with barite (BaSO₄) or magnetite (Fe₃O₄) aggregates, lack systematic life cycle comparisons. The aim of this study is to systematically compare barite- and magnetite-based HWSCC in terms of life cycle environmental impacts, life cycle cost, functional performance (strength and shielding), and end-of-life circularity, in order to identify the more sustainable and cost-effective material for radiation shielding infrastructure. This study applies cradle-to-grave life cycle assessment (LCA) and life cycle cost analysis (LCC), in accordance with ISO 14040/14044 and ISO 15686-5, to evaluate barite- and magnetite-based HWSCC. Results show that magnetite concrete reduces global warming potential by 19% eutrophication by 24%, and fossil resource depletion by 23%, while lowering life cycle costs by ~23%. Both concretes achieve comparable compressive strength (~48 MPa) and shielding efficiency (µ ≈ 0.28–0.30 cm⁻¹), meeting NCRP 147 and IAEA SRS-47 standards. These findings demonstrate that magnetite-based HWSCC offers a more sustainable, cost-effective, and ethically sourced alternative for radiation shielding in healthcare, nuclear, and industrial applications. In addition, the scientific significance of this work lies in establishing a transferable methodological framework that combines LCA, LCC, and performance-normalized indicators. This enables scientists and practitioners worldwide to benchmark heavyweight concretes consistently and to adapt sustainability-informed material choices to their own regional contexts. Full article

Normal concrete exhibits poor resistance to chloride penetration, often leading to reinforcement corrosion and premature structural failure. In contrast, ultra-high-performance concrete (UHPC) demonstrates superior resistance to corrosion caused by chloride salts. The chloride diffusion behaviour of UHPC was investigated via long-term immersion (LTI) and rapid chloride migration (RCM) tests. Additionally, this study presents the first development of a time-dependent diffusion model for UHPC under chloride corrosion, as well as the proposal of a performance-based design method for calculating the protective layer thickness. Results show that the incorporation of steel fibers reduced the chloride diffusion coefficient ($D$) by 37.9%. The free chloride content (FCC) in UHPC increased by 92.0% at 2 mm after 300 d of the action of LTI. $D$ decreased by up to 91.0%, whereas the surface chloride concentration ($C_{\mathrm{s}}$) increased by up to 92.5% under the action of LTI. The time-dependent models of $D$ and $C_{\mathrm{s}}$ followed power and logarithmic functions, respectively. An increase in UHPC surface temperature, relative humidity, and tensile stress ratio significantly diminishes the chloride resistance of UHPC. The minimum UHPC protective layer thicknesses required for UHPC-HPC composite beams with design service lives of 100 years, 150 years, and 200 years are 30 mm, 37 mm, and 43 mm, respectively. Full article

This study investigates the structural behavior of composite double-web steel beams filled with different types of concrete made from a combination of recycled concrete aggregates and normal aggregates. The research includes both experimental and numerical analyses. Seven specimens were tested under symmetrical two-point loading, all having identical geometric properties: a span length of 1100 mm, flange plates 120 mm wide and 6 mm thick, and web plates 3 mm thick and 188 mm deep. The specimens were divided into two groups, with a control beam without concrete infill. Group one included beams filled with normal concrete in different locations (middle region, two sides, and fully filled), while group two mirrored the same fill locations but used recycled concrete instead. The experimental results showed that using normal concrete improved the ultimate load by 10.19% to 55.30%, with the fully filled beam achieving a maximum increase in ductility of about 568% and a stiffness improvement ranging from 2.6% to 39% compared to the control beam. Beams filled with recycled concrete showed increases in ultimate load from 9.52% to 42.03%, ductility improvements of up to 380%, and stiffness enhancements between 4.5% and 8.03%. Numerical modeling using ABAQUS (2021) showed excellent agreement with the experimental results, with differences in ultimate load and maximum deflection averaging 5.5% and 7.9%, respectively. Full article

In recent years, a growing number of studies have focused on improving shear distribution and mitigating stress concentration in PBL shear connectors through the incorporation of composite materials. However, research on Twin-PBL shear connectors remains limited. Therefore, this study employed the finite element method to develop 23 finite element models to evaluate the shear performance of the Twin-PBL rubber-ring shear connector. The results indicate that the Twin-PBL rubber-ring shear connector with a 4 mm thick rubber ring exhibits a 7.5% decrease in shear force and a 71.1% reduction in shear stiffness compared to the conventional Twin-PBL shear connector. Furthermore, parametric analysis reveals that increasing the thickness of the rubber ring reduces both shear capacity and shear stiffness, while higher concrete strength, greater perforated rebar strength, and larger perforated rebar diameter enhance both shear capacity and stiffness. In contrast, the strength of the perfobond steel plate has minimal influence. Based on these findings, a predictive formula is proposed to estimate the shear capacity of the Twin-PBL rubber-ring shear connector. Full article