Despite extensive research on alkali-activated materials, the comparative performance of sodium- and potassium-based hydroxide–silicate activator systems under low-alkali conditions remains insufficiently understood, particularly across different precursor compositions and engineering properties. This study comparatively evaluated practically workable sodium- and potassium-based activator systems in alkali-activated binders incorporating ground granulated blast-furnace slag, Class F fly ash, and silica fume. Eleven binary and ternary paste formulations were investigated at hydroxide molarities of 0.5–3 M and silicate-to-hydroxide ratios of 0.25–0.67 using NaOH–Na2SiO3 and KOH–K2SiO3 activator systems. Flowability, setting time, temperature evolution, 28- and 90-day compressive strength, 32-week drying shrinkage, water absorption, permeable void content, rapid chloride permeability test (RCPT), and Fourier transform infrared (FTIR) spectroscopy were evaluated. Increasing hydroxide molarity and silicate dosage generally accelerated reaction development and enhanced strength while reducing flowability. Potassium-activated binders exhibited 3–23% higher measured flow, shorter setting times, earlier temperature evolution, and 11–46% lower drying shrinkage. Conversely, sodium-activated binders generally achieved higher 28- and 90-day compressive strengths, together with 4–16% lower water absorption and permeable void contents and lower electrical charge passed during RCPT. FTIR spectroscopy revealed differences in the Si–O–T band positions between the activator systems, indicating differences in aluminosilicate network development. Overall, the findings establish important performance trade-offs between low-alkali sodium- and potassium-based formulations and provide a comparative basis for activator selection in the development of high-performance alkali-activated cementitious materials.
This study experimentally and numerically investigates how skew angle affects the structural behavior of reinforced concrete slabs under monotonic and repeated loading. Eight simply supported slab specimens were divided into four groups corresponding to skew angles of 0°, 15°, 30°, and 45°, with one specimen in each group tested under monotonic loading and the other under repeated loading. All specimens had plan dimensions of 1400 × 1400 mm and a thickness of 100 mm and were subjected to a concentrated load at mid-span. The repeated-loading protocol consisted of stepwise quasi-static loading–unloading cycles with the peak load increased by 5 kN in each successive cycle until failure. All specimens exhibited predominantly flexural failure, with major cracking concentrated within the middle region of the slabs. The first-cracking loads under repeated loading were approximately 9.1–12.0% lower than those of the corresponding monotonic specimens. The effect of repeated loading on yield and ultimate response depended on skew angle and did not exhibit a uniform trend. However, increasing skew angle generally reduced load resistance and increased deformation. Under repeated loading, the ultimate load decreased by approximately 13.2%, 27.6%, and 33.1% for skew angles of 15°, 30°, and 45°, respectively, relative to the zero-skew specimen. Under monotonic loading, the 45° specimen exhibited approximately 24.9% lower ultimate resistance than the zero-skew specimen. The displacement ductility response was non-monotonic; under monotonic loading, maximum ductility occurred at 30°, and under repeated loading, at 15°. A simplified equivalent-strip analytical model was used as a preliminary reference, while three-dimensional nonlinear finite-element models were developed using ANSYS. The finite-element predictions of ultimate load differed from the experimental results by approximately 5.6–15.2%, although larger differences were observed in the load–deflection response and crack distribution. Overall, the experimental findings suggest that skew angle and loading history may influence deformation, stiffness, and ultimate resistance. However, since only one specimen was tested for each configuration, the reported differences should be considered descriptive observations rather than statistically validated relationships. Further experimental investigations with replicate specimens are required to confirm these trends.
In this study, machine learning (ML) algorithms viz., Random Forest, eXtreme Gradient Boosting (XGBoost), and Least Absolute Shrinkage and Selection Operator (LASSO) were employed to predict the hardness, tensile, flexural, and impact strengths of nano fly ash-reinforced natural fibre composites. Three types of natural fibres (abaca, hemp, and kenaf) and varying nano fly ash content (1, 3, 5 vol.%) were attempted. The ML models, developed in Python environment, are trained using 80% of the data and the remaining were used for validation. Among the attempted models, Random Forest model achieved the highest prediction accuracy (99%) along with the lowest RMSE and SMAPE values. The XGBoost model followed closely with a 97% accuracy. In contrary, the accuracy of the LASSO varies between 45% and 75% for various mechanical properties along with higher RMSE and SMAPE values. Furthermore, a graphical user interface (GUI) was developed to facilitate data input, model selection, and visualization of predicted results.
The development of efficient, low-cost electrocatalysts to replace platinum-based materials remains a major challenge for direct methanol fuel cells (DMFCs). In this study, a trimetallic NiCoCu catalyst was prepared on electrospun carbon nanofibers (NiCoCu/CNF) by electrospinning followed by stabilization and carbonization. X-ray diffraction (XRD) analysis revealed an fcc metallic NiCoCu-type crystalline phase, with an average crystallite size of approximately 13.13 nm. Scanning electron microscopy (SEM) showed a continuous, bead-free fibrous morphology with an average fiber diameter of approximately 271 nm, while transmission electron microscopy (TEM) revealed well-dispersed nanoparticles with diameters of approximately 33–98 nm. The electrochemical behavior was evaluated by cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in an alkaline methanol electrolyte. The current density at 0.8 V increased from 21 mA cm−2 for NiCo/CNF to 111 mA cm−2 for NiCoCu/CNF, while the Tafel slope decreased from 248 to 125 mV dec−1. The NiCoCu/CNF electrode also exhibited a charge-transfer resistance of 14.63 Ω at 2 M methanol, the lowest value among the investigated methanol concentrations. The enhanced electrochemical response is associated with the combined effects of the Ni–Co–Cu composition, nanoscale structure, nanoparticle dispersion, and conductive CNF architecture. Overall, NiCoCu/CNF demonstrates promising platinum-free electrocatalytic performance for methanol oxidation under the investigated alkaline three-electrode conditions and merits further evaluation for alkaline DMFC applications.
The aviation industry faces increasing pressure to reduce carbon emissions and adopt sustainable materials, driving interest in natural fiber composites (NFCs) as lightweight alternatives to conventional synthetic composites; however, their applicability in aviation remains fragmented across material development, performance validation, and manufacturing integration. This systematic review, conducted per PRISMA 2020 guidelines, searched Scopus and Web of Science (2014–2026) using terms explicitly incorporating aviation, aerospace, and UAV relevance. From 412 identified records, 64 studies were retained after deduplication, screening, full-text eligibility assessment, and post-hoc verification by four independent co-authors. Findings were organized into three themes: (1) development of sustainable NFC materials, emphasizing hybrid composites and fiber treatments; (2) mechanical, thermal, and functional performance evaluation under aerospace-relevant conditions; and (3) advanced manufacturing, design optimization, and real-world aviation applications. The review finds that NFCs demonstrate substantial potential for lightweight aviation structures, including several certification-anchored component demonstrations, but that certification-relevant fire, smoke, and toxicity testing, structural-scale validation, and manufacturing repeatability data remain underrepresented in the current literature, representing priority directions for future research.
