Search Results (1,493)

Tunnels frequently experience issues such as lining spalling and water leakage, making the stability of tunnel support critical for engineering safety. Given that tunnels are subjected to various ground stress disturbances and groundwater influences, it is essential to investigate the mechanical properties and damage mechanisms of tunnel support materials under different loading paths and saturation levels. Fiber-reinforced concrete (FRC) is widely used for tunnel support; in this study, uniaxial compression tests were conducted on FRC with different fiber contents (0%, 0.5%, 1.0%) under varying loading paths (monotonic, pre-peak cyclic loading, full cyclic loading). The stress–strain behavior, volumetric strain, and elastic modulus were analyzed. The results indicate that increasing fiber content enhances strength and stiffness, while higher water content leads to a significant water-weakening effect, reducing both parameters. To classify crack types, the logistic regression (LR) algorithm is employed based on the AF-RA features, identifying tensile damage (which accounts for 60–80%) as more dominant than shear damage. Using this classification, AE event distributions reveal the spatial characteristics of internal damage in FRC. Gaussian process regression (GPR) is further applied to predict the AE parameters, enabling the assessment of the tensile and shear damage responses in FRC. The location and magnitude of the predicted wave crest indicate extreme damage levels, which become more pronounced under a higher saturation condition. A damage constitutive model is proposed to characterize the post-peak softening behavior of FRC. The numerical verification demonstrates good agreement with the experimental results, confirming the model’s capability to describe the softening behavior of FRC under various fiber and water contents. Full article

The limited mechanical properties of composite materials, including stiffness, strength, and biocompatibility, restrict their effectiveness in biomedical applications. This research enhanced the mechanical properties and biocompatibility of polylactic acid and carbon fiber-reinforced composites (PLA/CFRCs) by incorporating multi-walled carbon nanotube (MWCNT) fillers. The methodology involved synthesizing MWCNTs and integrating them into PLA/CFRC laminates using fusion-blending, dispersion, and interlaminar spray-coating. Raman spectroscopy confirmed the presence of MWCNTs, with characteristic D and G band peaks and an I_D/I_G of 1.44 ± 0.089. SEM revealed MWCNTs in the PLA/CFRC matrix and allowed size determination, with an outer diameter range of 125–150 nm and a length of 14,407 ± 2869 nm. FTIR identified interactions between the matrix and the MWCNTs, evidenced by band shifts. TGA/DSC analysis showed thermal stability above 338 °C for all composites. The tensile tests revealed that all composites had values greater than 19 GPa for the elastic modulus and 232 MPa for the ultimate strength. Cytotoxicity assays confirmed biocompatibility, and all samples maintained a cell growth rate greater than 80%. This study highlighted the potential of nanotechnology to optimize the mechanical behavior of polymer-based composites, expanding their applicability in biomedical fields. Full article

The environments found in space research pose numerous challenges to the materials used in aerospace structures, such as high incidence of ultraviolet radiation (UV) and micrometeorite impacts. Therefore, this work analyzes the combined effects of exposure to UV radiation and damage caused by sandblasting on the mechanical performance of a hybrid composite of epoxy matrix reinforced with carbon and glass fibers to simulate service conditions both in low Earth orbit (LEO) and in exoplanet environments. The blasting was carried out with silica particles with dimensions compatible with those found in the dust of the Martian atmosphere, and the damage produced by these particles has dimensions similar to those observed in several impact/wear events of structures exposed to LEO conditions. A qualitative analysis of the effect of UV radiation carried out by colorimetry showed a significant change in the color of the material, which became more greenish and yellowish. This color change is indicative of degradation processes in the polymer matrix. FT-IR analysis showed an increase in the carbonyl band with increasing aging time, which is consistent with the color change measured in the material. However, the interlaminar shear strength was not affected by UV radiation in the time used in this work. This behavior was attributed to the fact that UV radiation initially causes deterioration only on the surface of the material. From the results of the bending tests, both the three-point bending test and impulse excitation test, it was found that the effect of UV radiation on the elastic modulus of the composites was more important than the effect of blasting damage. It was also observed that initial UV exposure, prior to sandblasting, has a synergistic effect on the deterioration of flexural strength. Full article

This paper presents the first stage of an experimental investigation of creep in two-layer reinforced concrete beams. It deals with the methodology of testing beams under long-term loading aimed at the investigation of the real linear creep effect. The investigated beams consisted of a normal-strength concrete (NSC) in the tensile zone and steel-fibered high-strength concrete (SFHSC) in the compression one. The specimens are subjected to four-point bending under loads that correspond to 70 and 85% of their load-bearing capacity. The loads are applied using special amplifying devices. The experiments at this stage lasted 90 days. Deflections are measured in the midspan of each specimen. During the first 24 h after applying the loads, the deflections were recorded every 10 s, and after 24 h, every hour. During the tests, no cracks have been observed near the supports as well as between the NSC and SFHSC layers. The cracks appeared within the limits of the pure bending zone only. Load-deflection curves were obtained and analyzed. The maximum midspan deflection in the tested beams was less than 1/250 of the beam span, which indicated that at linear creep, the two-layer beams are safe and remain in the elastic stage. The obtained results form a basis for the second stage of the experimental research that will be focused on the non-linear creep effect in such beams. Full article

Technological issues with the production of gluten-free rice crackers with spirulina powder were examined in this work through their rheological, textural, color, sensory, and nutritional aspects. A part of gluten-free whole-grain rice flour was replaced with 5, 10, and 15% spirulina powder in an appropriate recipe for crackers. The rheological analysis presented obtained dough samples as viscoelastic systems with dominant elastic components (G′ > G″ and Tan δ = G″/G′ is less than 0). The addition of spirulina contributed to a softer dough consistency according to a statistically significant (p < 0.5) decrease of Newtonian viscosity during the creep phase for a maximum of 43.37%, compared to the control dough. The 10 and 15% quantities of spirulina powder led to a statistically significant (p < 0.5) increase in the viscoelastic parameter J_max, which indicated a greater dough adaptability to stress. The textural determination of the dough pointed statistically significantly (p < 0.05) to decreased dough hardness and improved dough extensibility and confirmed all rheological measurements with high correlation coefficients, indicating good physical dough properties during processing. Spirulina certainly affected the change in the color of the dough from a yellow-white to intense green, which also had a significant impact on the sensory quality of the baked crackers. Many sensory properties of the crackers were improved by the addition of and increasing amounts of spirulina (appearance, brittleness, hardness, graininess, and stickiness). The results for the dough and for the final crackers pointed to very good technological aspects for the development of a gluten-free bakery product with high nutritional value, such as increased polyphenolic content (with the majority of catechins), protein, total dietary fibers, and mineral content compared to the control sample. Full article

This study evaluates the performance of lightweight aggregate deep beams strengthened with low-cost glass fiber-reinforced polymer composite (Lo-G) wraps as an alternative to expensive synthetic fiber-reinforced polymers (FRPs). The investigation includes side-bonded and fully wrapped configurations of Lo-G wraps, alongside carbon FRP (CFRP) strips for comparison. The experimental results show that epoxy-based anchors provided significantly better resistance against de-bonding than mechanical anchors, improving beam performance. Strengthening with Lo-G wraps resulted in a peak capacity increase of 17.0% to 46.9% for side-bonded beams in Group 2, 10.5% to 41.4% for fully wrapped beams in the strip configuration in Group 3, and 15.4% to 42.7% for CFRP strips in Group 4. The ultimate deflection and dissipated energy were also improved, with dissipated energy increases of up to 264.6%, 322.3%, and 222.7% for side-bonded and fully wrapped Lo-G wraps and CFRP strips, respectively. The side-bonded configuration with two or three Lo-G wraps, supplemented by epoxy wraps, outperformed fully wrapped 250 mm strips in peak capacity, with peak capacity improvements of up to 46.9%. However, beams with mechanical anchors showed poor performance due to premature debonding. They rely on friction and expansion within the concrete to resist pull-out forces. If the surrounding concrete is not strong enough or if the anchor is not properly installed, it can lead to failure. Additionally, reducing strip spacing negatively impacted performance. Lo-G wraps showed an 8.5% higher peak capacity and 32.8% greater dissipated energy compared to CFRP strips. Despite these improvements, while Lo-G wraps are a cost-effective alternative, their long-term performance remains to be investigated. None of the existing models accurately predicted the shear strength contribution of Lo-G wraps, as the lower elastic modulus and tensile strength led to high deviations in prediction-to-experimental ratios, underscoring the need for new models to assess shear strength. Full article

This research investigates the influence of potassium hydroxide (KOH) treatment on the mechanical, flexural, and impact properties of flax/glass and jute/glass hybrid composites. Hybrid composite materials have been developed, incorporating natural fibers that are both treated and untreated by KOH, with glass fiber within an epoxy matrix. Natural fibers, such as flax and jute, were chemically treated using different KOH concentrations and immersion times specific to each fiber type. Following the treatment, both fibers were rinsed with distilled water and subsequently dried. The natural fiber’s chemical interaction was analysed using FTIR. Hybrid composites were fabricated via the integration of intercalated layers of natural fibers and glass fiber using hand layup followed by compression molding. Mechanical properties, including impact resistance, flexural strength, elastic modulus, and tensile strength, were evaluated in accordance with ASTM guidelines. KOH-treated flax/glass composites (T-F2G2) demonstrated enhanced fiber–matrix bonding, indicated by elevated tensile strength (118.16 MPa) and flexural strength (168.94 MPa) relative to untreated samples. The impact strength of T-F2G2 composites increased to 39.33 KJ/m² due to the removal of impurities and exposure of hydroxyl groups, which interact with K⁺ ions in KOH, thereby improving their mechanical properties. SEM analysis of cracked surfaces confirmed enhanced bonding and reduced fiber pull-out, indicating improved interfacial compatibility. The findings demonstrate that KOH treatment effectively preserves cellulose integrity and enhances fiber–matrix interactions, positioning it as a viable alternative to NaOH for hybrid composites suitable for lightweight and environmentally sustainable industrial applications. Full article

The incorporation of waterborne polyurethane (WPU) into bacterial cellulose (BC) fibers significantly improved the tensile strength of the resulting WPU/BC composite film, achieving an enhancement of 19.4 times. The formation of hydrogen bonds between WPU and BC effectively eliminates cavities within the BC matrix, achieving significant plasticization and toughening. Compared with the pure BC film (WPU/BC-0), the elastic modulus of the WPU/BC-5 composite film is reduced by 97.5%, and surface hardness is decreased by 96.9%. When integrated with a flexible EGaIn electrode, the wearable composite film demonstrated exceptional potential in flexible electronics, reliably enabling point-of-care detection of human electrocardiograph (ECG) signals. This WPU-regulated BC approach provides a promising alternative for fabricating flexible and durable substrates suitable for wearable device applications. Full article

Thalassemia, once associated with limited survival, now sees extended life expectancy due to treatment advancements, but new complications such as pseudoxanthoma elasticum (PXE)-like syndrome are emerging. In fact, thalassemia patients develop PXE-like features more frequently than the general population. These features include skin lesions, ocular changes, and vascular issues like arterial calcifications, all linked to oxidative damage from iron overload. PXE-like syndrome in thalassemia mimics inherited PXE but is acquired. The underlying cause is thought to be oxidative stress due to iron overload, which induces free radicals and damages elastic tissues. Unlike inherited PXE, this form does not involve mutations in the ABCC6 gene, suggesting different pathogenic mechanisms, including abnormal fibroblast metabolism and oxidative processes. The vascular calcification seen in this syndrome often follows elastic fiber degeneration, with proteoglycans and glycoproteins acting as nucleation sites for mineralization. The condition can lead to severe cardiovascular and gastrointestinal complications. Studies have shown a significant incidence of PXE-like skin lesions in thalassemia patients, with some dying from cardiovascular complications. Research on ABCC6, a transporter protein involved in ectopic mineralization, has highlighted its role in various conditions, including PXE, beta-thalassemia, and generalized arterial calcification of infancy. ABCC6 mutations or reduced expression led to ectopic mineralization, affecting cardiovascular, ocular, and dermal tissues. The exact molecular mechanisms linking ABCC6 deficiency to ectopic mineralization remain unclear, though it is known to influence calcification-modulating proteins. This review focuses on the role of ABCC6 in the pathogenesis of calcifications, especially intracranial vascular calcifications in PXE and beta-thalassemia. Full article

Distance to the pith is a parameter that is known to be correlated with the mechanical properties of wood, but it is not utilized in strength grading machines. This study aimed to investigate how different the mechanical properties and grading yields are for Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) boards with small and large distances to the pith, respectively, and whether the distance to the pith could be an interesting parameter to use for strength grading in combination with other predictor variables. For this purpose, 221 boards were scanned to obtain fiber orientation and local density. Their dynamic modulus of elasticity and distance to the pith were measured, and they were finally tested in bending. The boards were classified into two categories: corewood if a board’s cross-section was entirely located within a radius of 200 mm from the pith, and outerwood otherwise. The results show that corewood presents lower mechanical properties than outerwood, explained especially by the higher knottiness of corewood. Distance to the pith improves the grading yields of a machine based on fiber orientation measurements, but using the dynamic modulus of elasticity rather than the distance to the pith leads to better results. Distance to the pith can be used as a single or secondary parameter to predict timber strength if the dynamic modulus of elasticity is not used. Full article

This study explores the microwave (MW) drying of Melia dubia wood, with a comprehensive approach that addresses various facets. The primary objectives were to examine drying behavior and the evaluation of drying defects. The drying rates for various treatments were calculated both above and below the Fiber Saturation Point (FSP). The most optimal treatment, characterized by minimal defects, exhibited a drying rate of 0.4 g/min above FSP, 0.29 g/min below FSP, and an overall drying rate of 0.35 g/min. There were no observable drying-induced defects in the dried wood, suggesting a promising aspect of MW drying. Static bending and compression tests parallel to the grain were carried out to analyze the impact of MW drying on the mechanical properties. MW-dried wood exhibited reductions of 7 ± 3%, 10 ± 2%, and 9 ± 2% in the modulus of elasticity (MOE), modulus of rupture (MOR), and maximum compressive strength (MCS), respectively. The decline in mechanical properties may be attributed to the micro-cracks or damage in its microstructures. These findings emphasize the need for a balanced approach in optimizing MW drying methods to mitigate the reduction in mechanical properties while capitalizing on the advantages of reduced drying time and uniform drying. Full article

The synergistic application of ultra-high-performance concrete (UHPC) and bamboo scrimber provides innovative solutions for sustainable structural engineering. In this study, the structural response mechanism of the combined beams under the steel plate–screw composite connection system was systematically investigated by designing three shear connection gradient specimens (TS200/300/400) to address the key scientific issues of the mechanical behavior of the bamboo–UHPC interface. Based on the unidirectional compression tests of bamboo–UHPC composite shear connections and four-point bending tests of composite beams, the damage modes, load-mid-span deflection relationship, bending stiffness, bamboo–UHPC slip and normal lift were evaluated for all the composite beams with the shear connection gradient as a parameter. The results showed that the flexural performance of the composite beams went through three stages: elastic behavior, damage development and final damage. The interfacial slip and interfacial lift-off have more obvious asymmetric spatial distribution characteristics, and increasing the shear joint degree can delay the separation between the UHPC and the bamboo layer, thus enhancing the structural integrity. Typical features of the final damage are the bending damage of ultra-high-performance concrete and bamboo fiber damage. This study highlights the potential of UHPC–bamboo composite beams for sustainable construction and emphasizes the importance of optimizing shear connection for improved performance. Full article

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has the characteristics of high strength, toughness, and excellent crack resistance. In order to fully utilize the high-strength properties of UHPFRC and reduce the structural weight and construction cost, solid slabs can be fabricated into hollow-core slabs or composite sandwich slabs. In order to further analyze the mechanical properties and mechanism of action of UHPFRC hollow-core slabs, one solid slab and two hollow-core slabs with the same geometric dimensions, reinforcement, and steel fiber volume content are designed in this paper, and their stress performance under a static load was investigated using a four-point bending test. The research results show that the UHPFRC hollow-core slab is anisotropic, and the bending stiffness of the section with parallel, distributed tubes is slightly smaller than that of the solid slab. The addition of steel fibers can greatly limit the development of cracks on a slab surface, so the elastic limit of a UHPFRC hollow slab is higher than that of a conventional concrete hollow slab. The whole bending process is roughly divided into the elastic stage, the elastic–plastic stage, and the plastic stage; the crack development process on the bottom of the slab can be classified into the cracking stage, the stable crack development stage, and the rapid propagation stage. In the elastic stage, the cross-sectional deformation of the UHPFRC hollow-core slab in the bending process still satisfies the assumption of a flat section. A row of parallel, round tubes on the neutral axis has a little effect on the cracking load, bearing capacity, and deformation capacity of the UHPFRC slab. By conducting the comparative analysis of the hollow rate and bearing capacity, when the hollow rate reaches 13.57%, the comprehensive weight of the solid slab is reduced by 13.16%, the cracking moment is slightly reduced, and the ultimate load is only reduced by 8.78%. Under the premise of meeting the bearing capacity, the hollow rate of the UHPFRC hollow-core slab can be appropriately increased to save money and energy. Full article

In the current era of heightened awareness regarding the impact of food choices, there has been a noticeable shift towards revisiting traditional ingredients. Following the growing interest in ancient grains, this study evaluated their potential use for enriching modern wheat dough and bread. The effects of substituting 20% of wheat flour with the bran of seven ancient grains on dough’s rheological properties and bread quality were assessed. The bran-enriched doughs maintained high stability (ST) values and showed an enhanced elastic behavior compared to the control. Nonetheless, a reduction in dough extensibility (E) was also noted. In terms of bread measurements, all bran-enriched breads exhibited a lower specific volume and a darker crust and crumb compared to the control bread. However, not all of the bran breads showed a harder and chewier loaf texture. The composite breads also exhibited enhanced total dietary fiber (TDF) and polyphenol content. A sensory evaluation revealed that Garfagnana (GAR) and Norberto (NOR) bran-breads received the highest overall liking scores. In conclusion, the incorporation of ancient grain brans presents a promising approach to enhancing modern wheat doughs and breads, offering nutritional benefits without significantly compromising their sensory and textural properties. Full article

Background/Objectives: Vascular aging is associated with increased arterial stiffness and changes in the wall structure, leading to a loss of elasticity. Silicon is abundant in arteries and plays a key role in the synthesis and stabilization of elastin fibers. In animal models of accelerated cardiovascular aging, a specific nutritional supplement based on silicon-enriched spirulina (SpSi) has been shown to have beneficial effects on vascular function. The present study, designed as a randomized, double-blind, placebo-controlled trial, aimed to evaluate the effectiveness of this SpSi supplement on aging-related changes in vascular function among healthy older adults. Methods: Here, 120 healthy volunteers aged 60–75 years were enrolled and randomly assigned to either the SpSi group (n = 60) or placebo group (n = 60). Over 6 months, the participants received either 3.5 g of specific 1% silicon-enriched spirulina (SpSi group) or placebo tablets daily. The primary outcome was the assessment of arterial wall pressure waveforms, which included blood pressure (BP) readings and the determination of the aortic pulse wave velocity (aPWV). Secondary outcomes included the vasomotor endothelial function through post-ischemic vasorelaxation, measured using the reactive hyperemia index (RHI), and carotid intima–media thickness. Results: When considering the entire sample, none of the studied parameters differed between the placebo and SpSi groups. However, when focusing on individuals with high–normal blood pressure (i.e., systolic BP between 130 and 150 mmHg) and aPWV levels above cutoff values (>10 m/s), the BP decreased by 8% (p < 0.001) and aPWV decreased by 13.5% (p < 0.0001) in subjects receiving SpSi. In individuals with BP and aPWV levels below the cutoff values, no effect was observed. Conclusions: In healthy elderly individuals, SpSi supplementation improved high–normal blood pressure and aortic pulse wave velocity, suggesting an enhanced vascular function. Full article