Search Results (8,564)

Microplastics (MPs) and nanoplastics (NPs) have emerged as pervasive pollutants across different aquatic systems on a global basis, yet integrated assessments linking wastewater, riverine, and marine environments remain scarce. The present study provides the first comprehensive evaluation of MPs in three interconnected aquatic matrices of Northern Greece, namely surface seawater from the Thermaic Gulf, surface freshwater from the Axios River, and influent and effluent wastewaters from the Thessaloniki WWTP (Sindos). During two sampling periods spanning late 2023 and spring 2024, suspected MPs were isolated, morphologically classified by stereomicroscopy, and chemically characterized through pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). MPs were ubiquitously detected in all substrates, exhibiting distinct spatial and compositional patterns. Seawater samples displayed moderate concentrations (1.5–4.8 items m⁻³) dominated by fibers and fragments, while riverine samples contained slightly higher levels (0.5–2.5 items m⁻³), enriched in fibrous forms and polyolefins (PE, PP). Wastewater influents showed the highest MP abundance (78–200 items L⁻¹; 155.6–392.3 µg L⁻¹), decreasing significantly in effluents (11–44 items L⁻¹; 27.8–74.3 µg L⁻¹), corresponding to a removal efficiency of 81–87.5%, being the first indicative removal efficiencies in a Greek WWTP. Among the different polymers detected, polyethylene, polypropylene, and poly(ethylene terephthalate) were identified as the most prevalent polymers across all matrices. Interestingly, a shift toward smaller size classes (125–500 µm) in effluents indicated in-plant fragmentation processes, while increased concentrations during December coincided with increased rainfall, highlighting the influence of hydrological conditions on MP fluxes. The combined morphological and polymer-specific approach provides a holistic zunderstanding of MP transport from inland to marine systems, establishing essential baseline data for Mediterranean environments and reinforcing the need for integrated monitoring and mitigation strategies. Full article

Fused Deposition Modeling (FDM) is a widely used additive manufacturing technique that enables the fabrication of components using polymeric and composite materials; however, the mechanical performance of printed parts is jointly influenced by multiple printing parameters, which complicates the control and prediction of their mechanical properties. In this study, an attention-enhanced multi-modal convolutional neural network (ATT-MM-CNN) is developed to predict the tensile performance of carbon fiber reinforced polylactic acid (PLA-CF) composites manufactured by FDM. Four key printing parameters, layer thickness, nozzle temperature, material flow rate, and printing speed, are systematically investigated, resulting in 256 parameter combinations and corresponding tensile test data for constructing a multi-modal dataset. By integrating multi-modal feature representations and incorporating an attention mechanism, the proposed model effectively learns the nonlinear relationships between printing parameters and mechanical performance under multi-parameter conditions. The results show that all evaluation metrics, including accuracy, precision, recall, and F1-score, exceed 0.95, and the prediction accuracy is improved by at least 17.3% compared with baseline models. These findings demonstrate that the proposed ATT-MM-CNN provides an effective and reliable framework for tensile property prediction and process-parameter optimization of FDM-printed composite structures. Full article

Agave lechuguilla fibers exhibit high tensile strength, low density and durability, but their use in natural rubber composites is underexplored. This study investigates alkaline-treated fibers (149–180 µm) as reinforcements for natural latex. Fibers were pretreated with a methanol–acetone mixture, followed by immersion in 10% NaOH at 70 °C for 1 h, removing lignin and hemicellulose as confirmed by FTIR and SEM. Thermogravimetric analysis showed three weight-loss stages: moisture/volatiles (9.4%), hemicellulose (peak at 341 °C), and cellulose/lignin (peak at 482 °C), with <3% residue above 500 °C. Treated composites exhibited enhanced tensile strength (4.68 ± 1.2 MPa vs. 1.3 ± 0.8 MPa for untreated) and elongation at break (530 ± 51% vs. 452 ± 32%). Hardness increased from 21.8 (neat latex) to 30.3, and compression resistance was improved. Optical microscopy revealed strong fiber–matrix adhesion with uniform dispersion. Alkaline treatment enhances interfacial bonding and mechanical performance, making A. lechuguilla fibers a sustainable reinforcement for eco-friendly composites in automotive, construction, and packaging sectors. Full article

Steel plates with open holes are common in engineering structures such as bridges and towers for pipeline penetrations and connections. These openings, however, induce significant stress concentration under alternating tension–compression loading (stress ratio R = −1), drastically accelerating fatigue crack initiation and threatening structural integrity. Effective identification and mitigation of such stress concentrations is crucial for enhancing the fatigue resistance of perforated components. This study proposes a closed-loop methodology integrating theoretical weak zone identification, targeted CFRP reinforcement, and experimental validation to improve the fatigue performance of open-hole steel plates. Analytical solutions for dynamic stresses around the hole were derived using complex function theory and conformal mapping, identifying critical stress concentration angles. Experimental tests compared unreinforced and CFRP-reinforced specimens in terms of circumferential strain distribution, dynamic stress concentration behavior, and fatigue life. Results indicate that Carbon fiber-reinforced polymer (CFRP) reinforcement significantly reduces stress concentration near 90°, smooths polar strain distributions, and slows strain decay. The S–N curves shift upward, indicating extended fatigue life under identical stress amplitude and increased allowable stress at identical life cycles. Comparison with standardized design curves confirms that reinforced specimens meet higher fatigue categories, providing practical design guidance for perforated plates under alternating loads. This work establishes a systematic framework from theoretical prediction to experimental verification, offering a reliable reference for engineering applications. Full article

On-orbit cutting is a critical process for the on-orbit manufacturing of carbon fiber reinforced polyetheretherketone composites (CF/PEEK) truss structures, with pulsed laser cutting serving as one of the feasible methods. Achieving high-quality cutting of CF/PEEK remains a major challenge for on-orbit manufacturing. Therefore, the cutting process of CF/PEEK prepreg tape was studied by an ultraviolet (UV) nanosecond laser. A three-factor, five-level orthogonal experiment was carried out to analyze the influence of laser repetition rate (LRR), laser cutting speed (LCS), and laser scanning times (LCTs) on cutting quality. The ablation mechanism dominated by the photothermal effect between the UV nanosecond laser and CF/PEEK was analyzed, and the by-products in the cutting process were explored. Finally, the optimal cutting quality (the width of slit (W_s) = 41.69 ± 3.54 μm, the heat-affected zone (HAZ) = 87.27 ± 7.30 μm) was obtained under the process conditions of LRR 50 kHz-LCS 50 mm/s-LCT 16 times. The findings show that the W_S and HAZ increase with the increase in LRR and LCT and the decrease in LCS, and the carbon fiber decomposes and escapes due to the photothermal effect. Full article

Although bamboo holds great promise as a sustainable construction material in industry, its susceptibility to cracking during drying compromises its mechanical performance and limits its structural applications. This study aims to develop a predictive model for bamboo cracking and investigate effective mitigation strategies. A crack evaluation model for round bamboo was established based on an analysis of tangential stress and validated experimentally in a climate chamber. The model demonstrated a prediction accuracy of 75–80% with a built-in safety margin, while analysis revealed that outer surface strain, inner surface strain, radial elastic modulus, and culm outer diameter all positively correlated with tangential stress, highlighting the importance of controlling these factors to prevent cracking. Moreover, a surface-bonded palm fiber wrapping method was proposed and tested, which significantly enhanced the crack resistance and delayed crack initiation. The effect was most pronounced in 1-year-old bamboo, while culms aged 3, 5, and 7 years remained crack-free until moisture content fell below 5%. The proposed model accurately predicts cracking behavior in bamboo, offering theoretical support for its structural use and practical insights for crack prevention. Full article

Early-age cracking limits the structural use of steel fiber-reinforced lightweight aggregate concrete (SFLWAC), and robust experimental evaluation methods are still needed. This study examines the influence of steel fiber volume fractions (i.e., 0%, 0.5%, 1.0%, and 2.0%) on the cracking performance of SFLWAC through mechanical testing, autogenous shrinkage measurements, and two types of partially restrained ring tests, with and without a clapboard. The performance of three crack resistance indices is compared: the strain-based ASTM C1581 index, a stress-based area index, and a newly proposed energy-based index defined as the strain energy accumulation degree (SEAD), i.e., the ratio between the accumulated and critical strain energy density. The 28-day splitting tensile strength was improved by 77.9% and autogenous shrinkage was diminished by 30.7% as steel fiber volume content increased from 0 to 2.0%, thereby improving the resistance to shrinkage-induced cracking. In the partially restrained ring tests, SEAD decreased with increasing fiber content, and crack initiation occurred when SEAD reached an approximately constant threshold, whereas ASTM C1581 and the area index could not consistently rank mixtures when some rings cracked and others remained intact. These results demonstrate that SEAD provides a physically meaningful and unified measure of cracking risk for SFLWAC under partially restrained shrinkage and has the potential to be extended to other fiber-reinforced concretes and shrinkage-related cracking problems. Full article

This paper presents an experimental and numerical investigation of continuous reinforced concrete (RC) beams made of self-compacting concrete (SCC) strengthened with fiber-reinforced polymer (FRP) bars using the Near-Surface Mounted (NSM) method. While the majority of previous studies have focused on simply supported beams, this work examines two-span continuous beams, which are more representative of real structural behavior. Four SCC beams were tested under static loading to evaluate the influence of the FRP reinforcement position on flexural capacity and deformational characteristics. The beams were strengthened using glass FRP (GFRP) bars embedded in epoxy adhesive within pre-cut grooves in the concrete cover. Experimental results showed that FRP reinforcement significantly increased the ultimate load capacity, while excessive reinforcement reduced ductility, leading to a more brittle failure mode. A three-dimensional finite element model was developed in Abaqus/Standard using the Concrete Damage Plasticity (CDP) model to simulate the nonlinear behavior of concrete and the bond–slip interaction at the epoxy–concrete interface. The numerical predictions closely matched the experimental load–deflection responses, with a maximum deviation of less than 3%. The validated model provides a reliable tool for parametric analysis and can serve as a reference for optimizing the design of continuous SCC beams strengthened by the NSM FRP method. Full article

Polymer composites have opened a novel innovation phase in additive manufacturing (AM), and now lightweight, high-strength, and geometrical advanced components with tailored functionalities can be produced. The present study introduces advances in polymer composite materials and their integration into AM processes, particularly in rapidly growing industries such as aerospace, automotive, biomedical, and electronics. The embedding of cutting-edge reinforcement materials, such as nanoparticles, carbon fibers, and natural fibers, into polymer matrices enhances mechanical, thermal, electrical, and multifunctional properties. These material developments are combined with advanced fabrication techniques, including multi-material printing, in situ curing, and functionally graded manufacturing, which achieves accurate regulation of microstructures and properties. Furthermore, high-impact innovations such as smart polymer composites with self-healing or stimuli-responsive behaviors, the growing shift toward sustainable, bio-based composite alternatives, are driving progress. Despite significant advances, challenges remain in interfacial bonding, printability, process repeatability, and long-term durability. This review offers a comprehensive overview of current advancements and outlines future directions in polymer composite–based AM. Full article

In accelerated bridge construction, precast concrete girders are connected to cast-in-place concrete slab using shear transfer reinforcement across the interface plane to ensure the composite action. The steel transverse reinforcement is prone to severe corrosion due to the extensive use of de-icing salts and severe environmental conditions. As glass fiber-reinforced polymer (GFRP) reinforcement has shown to be an effective alternative to conventional steel rebars as flexural and shear reinforcement, the present research work is exploring the performance of GFRP reinforcements as shear transfer reinforcement between precast and cast-in-place concretes. Experimental testing was carried out on forty large-scale push-off specimens. Each specimen consists of two L-shaped concrete blocks cast at different times, cold joints, where GFRP reinforcement was used as shear friction reinforcement across the interface with no special treatment applied to the concrete surface at the interface. The investigated parameters included the GFRP reinforcement shape (stirrups and headed bars), reinforcement ratio, axial stiffness, and the concrete compressive strength. The relative slip, reinforcement strain, ultimate strength, and failure modes were reported. The test results showed the effectiveness and competitive shear transfer performance of GFRP compared to steel rebars. A shear friction model for predicting the shear capacity of as-cast, cold concrete joints reinforced by GFRP reinforcement is introduced. Full article

To address the dual challenges of improving precast cable trench joint performance and promoting solid waste recycling for carbon neutrality, this study developed a jute fiber-reinforced recycled aggregate concrete (JFRAC) and established a complete technical chain via experiments and numerical simulations. Compressive strength tests were conducted on JFRAC with varying jute fiber volume content and recycled coarse aggregate (RCA) replacement ratio to obtain their influence on the stress–strain relationship. A modified Concrete Damaged Plasticity (CDP) model was proposed by introducing correction coefficients for compressive strength and elastic modulus, achieving over 95% agreement with experimental data. Finite element simulations of cable trench joints showed that JFRAC outperforms C30 concrete, with the same compressive strength, in ultimate bearing capacity (↑4.17%), peak displacement (↑18.78%), and ductility (↑14.66%). JFRAC provides substantial environmental and economic advantages by reducing carbon emissions by 2.29% and saving costs of CNY 62.43 per meter of precast cable trench. Parametric studies indicated bolt grade and number are the primary performance influencers. Bolt grade’s impact diminishes as it increases from 8.8 to 10.9, while bolt number linearly enhances load-bearing capacity. This study provides a feasible path for JFRAC to replace conventional concrete in cable trenches, realizing both economic and environmental benefits. Full article

This study experimentally evaluates the mechanical and microstructural performance of single- and double-layer intraply hybrid composite (IRC) laminates produced using the hand lay-up method, focusing on Glass–Aramid (GA), Aramid–Carbon (AC), and Carbon–Glass (CG) configurations. Tensile, flexural, compressive, and density tests were conducted in accordance with relevant ASTM standards to assess the influence of hybrid type and layer number under field-representative manufacturing conditions. Microstructural investigations were performed using optical microscopy and scanning electron microscopy (SEM) to identify fabrication-induced imperfections and their relationship to mechanical behavior. The results demonstrate that increasing the laminate configuration from single to double layer significantly enhances mechanical performance across all hybrid types. Double-layer AC laminates exhibited the highest tensile strength (330.4 MPa) and Young’s modulus (11.93 GPa), corresponding to improvements of approximately 85% and 59%, respectively, compared to single-layer counterparts. In flexural loading, the highest strength was observed in double-layer CG laminates (97.14 MPa), while compressive strength was maximized in double-layer AC laminates (34.01 MPa), indicating improved stability and resistance to compression-driven failure. Statistical analysis confirmed that layer number is the dominant parameter governing mechanical response, exceeding the influence of hybrid configuration alone. Microstructural observations revealed fiber misorientation, incomplete resin impregnation, and localized voids inherent to manual fabrication. However, these imperfections were consistently distributed across all specimens and did not obscure comparative mechanical trends. Coefficients of variation generally remained below 10%, indicating acceptable repeatability despite non-ideal manufacturing conditions. Full article

The structural application of Fiber-Reinforced Polymers (FRP) is significantly hindered by their inherent thermal sensitivity. This paper presents a comprehensive review of the fire performance of FRP materials and FRP-concrete systems, spanning from material-scale degradation to structural-scale response. Distinct from previous studies, this review explicitly distinguishes between the fire behavior of internally reinforced FRP-reinforced concrete members and externally applied systems, including Externally Bonded Reinforcement (EBR) and Near-Surface Mounted (NSM) techniques. The thermal and mechanical degradation mechanisms of FRP constituents—specifically reinforcing fibers and polymer matrices—are first analyzed, with a focused discussion on the critical role of the glass transition temperature T_g. A detailed comparative analysis of the pros and cons of organic (epoxy-based) and inorganic (cementitious) binders is provided, elaborating on their respective bonding mechanisms and thermal stability under fire conditions. Furthermore, the effectiveness of various fire-protection strategies, such as external insulation systems, is evaluated. Synthesis of existing research indicates that while insulation thickness remains the dominant factor governing the fire survival time of EBR/NSM systems, the irreversible thermal degradation of polymer matrices poses a primary challenge for the post-fire recovery of FRP-reinforced structures. This review identifies critical research gaps and provides practical insights for the fire-safe design of FRP-concrete composite structures. Full article

Toughening modification of epoxy resin (EP) matrices is important for advancing high-performance fiber-reinforced composites. A promising strategy involves the use of multi-component additive systems. However, synergistic effects in such additive systems are difficult to achieve for multidimensional performance optimization due to insufficient interfacial interactions and competing toughening mechanisms. Herein, a “hard–soft” biphasic synergistic toughening system was engineered for epoxy resin, composed of furan-ring-grafted polyhedral oligomeric silsesquioxane (FPOSS) and liquid polysulfide rubber. The hybrid toughening agent significantly enhanced the integrated performance of the epoxy system: Young’s modulus, tensile strength, and elongation at break increased by 13%, 56%, and 101%, respectively. These improvements are attributed to the formation of enriched molecular chain entanglement sites and optimized dispersion, facilitated by nucleophilic addition reactions between flexible rubber segments and rigid FPOSS units with the epoxy matrix. The marked enhancement in toughness primarily stems from the synergistic toughening mechanism involving “crazing pinning” and “crazing-shear band”. Concurrently, FPOSS incorporation effectively modulated the curing reaction kinetics, rendering the process more gradual while substantially elevating the glass transition temperature (T_g) of the cured system by 16.82 °C and endowing it with superior thermal degradation stability. This work provides a simple and unique strategy to leverage multi-scale mechanisms for the construction of epoxy-based composites with good toughness and strength, and enhanced heat resistance. Full article

Façades account for approximately 15–20% of a building’s embodied carbon, making them a key target for material decarbonization. While bio-composites are increasingly explored for façade insulation, cladding systems remain dominated by carbon-intensive materials such as aluminum and fiber-reinforced polymers (FRPs). This paper presents findings from a study investigating the use of food-waste-derived bulk fillers in bio-composite materials for façade cladding applications. Several food-waste streams, including hazelnut and pistachio shells, date seeds, avocado and mango pits, tea leaves, and brewing waste, were processed into fine powders (<0.125 μm) and combined with a furan-based biobased thermoset resin to produce flat composite sheets. The samples were evaluated through mechanical testing (flexural strength, stiffness, and impact resistance), water absorption, freeze–thaw durability, and optical microscopy to assess microstructural characteristics before and after testing. The results reveal substantial performance differences between waste streams. In particular, hazelnut and pistachio shell fillers produced bio-composites suitable for façade cladding, achieving flexural strengths of 62.6 MPa and 53.6 MPa and impact strengths of 3.42 kJ/m² and 1.39 kJ/m², respectively. These findings demonstrate the potential of food-waste-based bio-composites as low-carbon façade cladding materials and highlight future opportunities for optimization of processing, supply chains, and material design. Full article