Search Results (26,079)

Hybrid fiber-reinforced concrete (HFRC), renowned for its significantly enhanced mechanical properties and structural integrity, is widely used in infrastructure construction and has become a key avenue of modern high-performance concrete development. The hybrid application of basalt fiber (BF) and polypropylene fiber (PPF) at optimized ratios generates synergistic effects, improving both mechanical performance and material service reliability. To explore and evaluate the synergistic mechanism of BF-PPF hybrid fibers on concrete’s mechanical properties and performance, this study employs an orthogonal experimental design and mechanical testing methods, measuring the materials’ static compressive strength (loading rate: 0.6 mm/min), splitting tensile strength (loading rate: 0.12-0.14 MPa/s), dynamic elastic modulus (measured by the ultrasonic method), and dynamic compressive strength (loading rates: 0.6 mm/min, 6 mm/min, and 60 mm/min). For these tests, we prepared 100 mm × 100 mm × 100 mm cubic specimens (for static compressive, dynamic compressive, and splitting tensile tests) and 400 mm × 100 mm × 100 mm prismatic specimens (for dynamic elastic modulus tests), with three parallel specimens in each test group. In addition, the microstructure was characterized by scanning electron microscopy (SEM) to observe the fiber-matrix interaction. The results show that when the BF/PPF volume ratio is 1:2 (BF0.05PPF0.1), the concrete’s compressive strength, splitting tensile strength, and elastic modulus increase by 13.7%, 76.3%, and 116.0%, respectively, with corresponding synergistic effect indices (Q) of 0.057, 0.213, and 0.241, indicating obvious positive synergy. Under dynamic loading, hybrid combinations with higher PPF content (e.g., BF0.05PPF0.1) exhibit strain-rate-dependent enhancements in compressive strength and better impact resistance. SEM analysis reveals that fibers inhibit microcrack propagation through fiber bridging, network distribution, and pull-out resistance, while also improving the interfacial transition zone’s structure. These findings provide theoretical support for the engineering application of composite fiber-reinforced concrete materials. Full article

This study provides an in-depth structural analysis of UNESCO World Heritage Apulian trulli, considering the three-layer dry-stone structure of their characteristic conical roofs. An integrated approach involving laser scanning, ground-penetrating radar, endoscopic investigation, and laboratory materials testing is used to identify and characterize the multi-wythe masonry system. A detailed finite element model is created in ANSYS to analyze seismic performance on Italian building codes. The model is validated through ambient vibration testing using accelerometric measurements. The diagnostic survey identified a three-layer system including exterior stone wythe, interior wythe, and rubble core, with compressive strength of stone averaging 2.5 MPa and mortar strength of 0.8 MPa. The seismic assessment will allow the examination of displacement patterns and stress distribution under design load conditions (ag = 0.15 g). The structural analysis demonstrates adequate performance under design loading conditions, with maximum stress levels remaining within acceptable limits for historic masonry construction. The experimental validation confirmed the finite element model predictions, with good correlation between numerical and experimental frequencies. The improvement of the overall seismic performance with the multi-wythe configuration and the role of wall thickness and geometric proportions will be taken into account. The methodology aims to provide technical evidence supporting the continued use of vernacular buildings while contributing to scientifically informed conservation practices throughout the region. Full article

To elucidate the mechanism by which soil disturbance affects tillage performance during subsoiling remediation of northeastern primary sodic saline–alkali soil, this study established a mathematical prediction model linking subsoiler configuration parameters with draft force and soil porosity based on the soil dynamic equation and the fourth strength theory. Discrete element simulation and field experiments demonstrated the model’s accuracy in predicting draft force and soil looseness (error < 5%). Among three configuration patterns evaluated, the “W”-type arrangement was selected for further simulation testing and predictive analysis through parameter adjustment. The simulation results aligned with the prediction results. Particle flow analysis revealed a quadratic relationship between subsoiler spacing variation, draft force, and soil looseness. At the particle scale, soil particle movement patterns were found to govern macroscopic effects, where soil clogging and repeated disturbances emerged as primary drivers of nonlinear variations in draft force and soil porosity. Finally, field experiments and simulations were performed using the parameter combinations predicted by the mathematical model, confirming the accuracy of these parameters. Through a tripartite validation approach combining mathematical modeling, DEM simulation, and field trials, this study systematically elucidates the complete mechanism whereby subsoiler arrangement parameters influence the tillage performance of sodic saline–alkali soil via soil–tool interactions, providing theoretical foundations for optimizing subsoiling equipment design and reducing energy consumption in saline–alkali land cultivation. Full article

Local variations in mechanical properties are commonly observed in engineering structures, driven by complex manufacturing histories and harsh service environments. The evaluation of mechanical properties accurately constitutes a fundamental requirement for structural integrity assessment. The Instrumented Indentation Technique (IIT) can play a critical role in the in-site testing of local properties. However, it could be often a challenge to correlate indentation characteristics with uniaxial stress–strain relationships. In this study, we investigated quantitatively the connection between the indentation responses of commonly used metals and their plastic properties using the finite element inversion method. Materials typically exhibit plastic deformation mechanisms characterized by either linear or power-law hardening behaviors. Consequently, conventional prediction methods based on a single constitutive model may no longer be universally applicable. Hence, this study developed methods for acquiring mechanical properties suitable for either the power-law and linear hardening model, or combined, respectively, based on analyses of microstructures of materials exhibiting different hardening behaviors. We proposed a novel integrated IIT incorporating microstructures and material-specific constitutive models. Moreover, the inter-dependency between microstructural evolution and hardening behaviors was systematically investigated. The proposed method was validated on representative engineering steels, including austenitic stainless steel, structural steel, and low-alloy steel. The predicted deviations in yield strength and strain hardening exponent are broadly within 10%, with the maximum error at 12%. This study is expected to provide a fundamental framework for the advancement of IIT and structural integrity assessment. Full article

Aeolian sand is the primary geological material for construction in desert regions, and its stabilization with industrial solid wastes-based geopolymer (ISWG) provides an eco-friendly treatment replacing cement. This study comparatively investigated the enhancement effects of chemical activators and expansive agents on compressive strength of aeolian sand stabilized by ISWG (ASIG). Three chemical activators—NaOH, Ca(OH)₂, and CaCl₂—along with two expansive agents—desulfurized gypsum and bentonite—were considered. Through X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, mercury intrusion porosimetry and pH values tests, the enhancement mechanisms of the additives on ASIG were elucidated. Results demonstrate that the expansive agent exhibits significantly superior strengthening effects on ASIG compared to the widely applied chemical activators. Chemical activators promoted ISWs dissolution and hydration product synthesis, thereby densifying the hydration product matrix but concurrently enlarged interparticle pores. Desulfurized gypsum incorporation induced morphological changes in ettringite, and excessive desulfurized gypsum generated substantial ettringite that disrupted gel matrix. In contrast, bentonite demonstrated superior pore-filling efficacy while densifying gel matrix through a compaction effect. These findings highlight bentonite superior compatibility with the unique microstructure of aeolian sand compared to conventional alkaline activators or expansive agents, and better effectiveness in enhancing the strength of ASIG. Full article

This study examines the effects of three polymer binders—polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyacrylic acid (PAA) on the mechanical properties and dry–wet cycle corrosion resistance of cement mortar at different dosages (1–4%). Mechanical testing combined with scanning electron microscopy (SEM) and molecular dynamics (MD) simulations was conducted to validate the experimental findings and reveal the underlying mechanisms. Results show that polymers reduce early-age strength but improve flexural performance, and at low dosage, enhance compressive strength. PVA and PAA exhibited a pronounced improvement in mechanical strength while PVA and PEG showed a significant improvement in wet cycle corrosion resistance. SEM observations indicated that polymers encapsulate cement particles, enhancing interfacial bonding while partially inhibiting hydration. MD simulations revealed that PVA and PAA interact with Ca²⁺ via Ca-O coordination, while PEG primarily forms hydrogen bonds, resulting in distinct water-binding capacities (PEG > PVA > PAA). These interactions explain the enhanced mechanism of mechanical and dry–wet cycle resistance properties. This work combined experimental and molecular-level validation to clarify how polymer–matrix and polymer–water interactions govern mechanical and durability, respectively. The findings provide theoretical and practical guidance for designing advanced polymer binders with tailored interfacial adhesion and water absorption properties to improve cementitious materials. Full article

Lightweight aggregate concrete is known for its potential to decrease overall building load and cost. Aero Aggregates’ Aerolite is a foamed glass aggregate (FGA) available in seven different sizes which has the potential to replace normal weight aggregates to create lightweight concrete. This research analyzes the feasibility of using FGAs in optimized concrete mix designs and employing those designs in a full-scale building. Nine different mix designs were created using optimization methods, including the Tarantula Curve and 0.45 power chart, to determine the ideal aggregate proportions. All mixes were cast in 0.1 m diameter, 0.2 m tall cylinders and tested after 7 and 28 days to determine unit weight (density), compressive strength, and modulus of elasticity. After testing, the optimal design was identified as 65% coarse and 15% fine aggregates to be replaced with FGAs because it gave the best unit weight and compressive strength for structural lightweight concrete. The optimal concrete mix design was used to create an example building model in RAM Structural Systems to prove that FGA concrete can reduce cost, materials required, and carbon emissions on a larger scale. Full article

Implementing formative assessment strategies represents a challenge for higher education institutions. As they are frequently adopted only to support summative assessment and final grading, this study aims to investigate the most effective formative assessment strategies for higher education. It emphasizes the features of peer- and group-assessment, underlining strengths and weaknesses of both formative assessment strategies. Additionally, this study investigates the relationship between metacognitive and evaluative formative assessment aspects to support students’ learning processes and highlights the connection between formative and summative approaches. In the academic year 2023–2024, 240 higher education students were involved in a four-stage mixed-method study, alternating peer- and group-assessment strategies split in two steps focused on, respectively, metacognitive and evaluative aspects. Qualitative and quantitative data were collected after each stage. The findings revealed that students preferred the group-assessment and that the metacognitive formative assessment helped them improve their learning and prepare for the final test with summative assessment. Regarding policy implications, on the basis of this study, higher education institutions should improve instructor capacity to integrate formative assessment activities in their courses. Full article

Dissolved Gas Analysis (DGA) of power system transformers has emerged as one of the most effective transformer health diagnosing tools by analyzing the gases dissolved in the insulating oil. There are various traditional DGA techniques like Key Gas Method, Roger’s Ratio, IEC ratio, Dornenburg’s Ratio, and Duval Triangle method. However, these techniques have limitations such as inconsistent results, the inability to detect low-energy faults, and reliance on expert knowledge due to complex interpretation. To overcome these limitations, this paper introduces an integrated fuzzy logic system that enhances DGA interpretation by combining the diagnostic strengths of Key Gas Method, Roger’s Ratio, IEC ratio, and Duval Triangle methods. To obtain a final, human-readable diagnosis, the output of each technique is incorporated into a higher-level fuzzy inference system once each is modeled separately with fuzzy logic, having known membership functions and rule bases. To test this model, oil samples of known results of different transformers are used and compared to the results given by the proposed fuzzy inference system. The proposed method is easier and more feasible for practical use since it not only improves fault detection accuracy and reliability but also allows for easier interpretation by non-specialists. This study makes an additional contribution to a higher-level, more effective, and more accurate method for transformer fault detection by overcoming the interpretational difficulties and weaknesses of conventional DGA approaches. Full article

This study analyzes the compressive behavior and reliability of Al-Mg-Si (6061) metal matrix composites reinforced with different weight fractions of Al₂O₃ and SiC ceramics and cast with graphite and steel molds. Compression tests were carried out according to ASTM E9 with 0–8 wt.% reinforcement. The mold material significantly influenced the strength due to the cooling rate and interfacial adhesion. A two-parameter Weibull model assessed statistical reliability and extracted the shape (β) and scale (η) parameters using linear regression. Advanced models—lifelines (frequentist) and Bayesian models—were also applied. Graphite molds yielded composites with higher shape parameters (β = 6.27 for Al₂O₃; 5.49 for SiC) than steel molds (β = 4.66 for Al₂O₃; 4.79 for SiC). The scale values ranged from 490–523 MPa. The lifelines showed similar trends, with the graphite molds exhibiting higher consistency and scale (ρ = 7.45–9.36, λ = 479.71–517.49 MPa). Bayesian modeling using PyMC provided posterior distributions that better captured the uncertainty. Graphite mold samples had higher shape parameters (α = 6.98 for Al₂O₃; 8.46 for SiC) and scale values of 489.07–530.64 MPa. Bayesian models provided wider reliability limits, especially for SiC steel. Both methods confirmed the Weibull behavior. Lifelines proved to be computationally efficient, while Bayesian analysis provided deeper insight into reliability and variability. Full article

This study explores the mechanical characteristics of 3D-printed specimens fabricated using TPU-95A filament, with a focus on the influence of key printing variables—temperature, speed, and layer height—on tensile strength, toughness, and surface hardness. Through systematic testing, the tensile evaluation revealed a peak tensile strength of 329.02 kgf/cm² and toughness of 1.56 under conditions of elevated temperatures and optimized layer configurations. Similarly, the hardness assessment indicated a maximum average value of 74.9 Shore A, emphasizing the substantial effect of process parameters on material integrity and resilience. A detailed variance analysis confirmed the pivotal roles of temperature and layer height in enhancing mechanical properties. Using a statistical optimization approach, optimal printing conditions were identified, demonstrating that higher temperatures, moderate speeds, and reduced layer heights significantly improve the balance between strength, flexibility, and durability. These findings contribute to the development of tailored fabrication strategies, offering practical insights for applications where precision and mechanical reliability are critical. Full article

Background: Niacinamide exhibits a wide range of beneficial properties that support its use in skincare and the treatment of various dermatological conditions. This study aimed to evaluate skin hydration and to assess participants’ subjective perceptions of skin tone and overall skin condition following the use of a commercial niacinamide-containing preparation compared to usual skin care and a ceramide-containing preparation. Methods: Young adult women were enrolled and assigned to one of three groups: continued use of their usual skincare, application of a ceramide-containing cream, or application of a niacinamide-containing cream. The study period lasted three weeks. Skin hydration was measured using corneometry, and changes in skin appearance were documented through standardized photography and participant self-assessments. Results: Of the 50 participants enrolled, 46 completed the study. The niacinamide-containing cream significantly improved skin hydration (32.15 ± 12.61 vs. 39.09 ± 14.12; p = 0.0365) and reduced skin discoloration, with 81.2% of participants reporting improvement (p = 0.0407). The ceramide-containing cream was most effective in reducing redness, with 68.8% of participants noting visible improvement (p = 0.0017). No significant changes were observed in skin texture or the appearance of skin lesions across the tested groups. Conclusions: Use of a niacinamide-containing commercial cream resulted in measurable improvements in skin hydration and tone. A key strength of this study is its focus on real-life product application, offering practical insights into the performance of commercial skincare products under typical user conditions. Future studies should include additional objective measurements and larger, more diverse populations to enhance the reliability and generalizability of the results. Full article

While size effects in composite structures have been widely studied under quasi-static uniaxial loading, their influence under fatigue conditions, particularly in the presence of multiaxial stress states and elevated temperatures, remains insufficiently understood. This study investigates the fatigue behaviour of thick-walled $\pm {45}^{\circ }$ braided glass fibre-reinforced polyurethane composite box structures under varying temperature and loading conditions. A combined experimental approach is adopted, coupling quasi-static and fatigue tests on large-scale structures with reference data from standardised coupon specimens. The influence of temperature (23–80 °C) and multiaxial shear–compression loading is systematically evaluated. The results demonstrate a significant temperature-dependent decrease in compressive strength and fatigue life, with a linear degradation trend that aligns closely between the box structure and coupon data. Under moderate multiaxial conditions, the fatigue life of box structures is not significantly impaired compared to uniaxial test coupon specimens. Complementary non-destructive testing using air-coupled ultrasound confirms these trends, demonstrating that guided-wave phase-velocity measurements capture the evolution of anisotropic damage and are therefore suitable for in situ structural health monitoring applications. Furthermore, these findings highlight that (i) the temperature-dependent fatigue behaviour of thick-walled composites can be predicted using small-scale coupon data and (ii) small shear components have a limited impact on fatigue life within the studied loading regime. Full article

This study presents a rigorous experimental and numerical investigation of the synergistic effect of metakaolin (MK) and waste glass (WG) on the structural performance of reinforced concrete (RC) beams without stirrups. A two-phase methodology was adopted: (i) optimization of MK and WG replacement levels through concrete-equivalent mortar mixtures and (ii) evaluation of the fresh and hardened properties of concrete, including compressive and tensile strengths, elastic modulus, sorptivity, and beam shear capacity. Five beam groups incorporating up to 30% MK, 15% WG, and 1% steel fiber were tested under four-point bending. The results demonstrated that MK enhanced compressive strength (up to 22%), WG improved workability but reduced ductility, and the combined system achieved a 13% increase in shear strength relative to the control. Steel fibers further restored ductility, increasing the ductility index from 1.338 for WG-only beams to 2.489. Finite Element Modeling (FEM) using ABAQUS with the Concrete Damage Plasticity (CDP) model reproduced experimental (EXP) load–deflection responses, peak loads, and crack evolution with high fidelity. This confirmed the predictive capability of the numerical framework. By integrating material-level optimization, structural-scale testing, and validated FEM simulations, this study provides robust evidence that MK–WG concrete, especially when fiber-reinforced, delivers mechanical, durability, and structural performance improvements. These findings establish a reliable pathway for incorporating sustainable cementitious blends into design-oriented applications, with direct implications for the advancement of performance-based structural codes. Full article

This study prepared alkali-activated cementitious composites using high-whiteness kaolin, sodium water glass, and NaOH as the main raw materials. Multiple methods, including FE-SEM, XRD, whiteness/light transmittance tests, shrinkage rate measurements, DSC-TG, flexural strength testing, and hydrolysis resistance testing, were used to investigate the effects of curing temperature and time on material properties. The optimal parameters were determined as kaolin calcined at 1100 °C, activator modulus 1.25, calcined kaolin-to-activator ratio 1:1, and 2.5% deionized water added for molding. The optimal sample achieved a flexural strength of 23.81 MPa, with the bonding strength to porcelain 60.17 times that of gypsum and 1.90 times that of kaolin-bonded materials. Curing below 100 °C slowed polymerization, while temperatures exceeding 100 °C accelerated it, with violent reaction at 120 °C. Curing beyond 10 h reduced flexural strength. A large number of cage-like, ‘zeolite-like’ structures formed, closely relating to material properties. This study provides references for ceramic restoration materials. Full article