Code provisions for high strength concrete strength-temperature relationship at elevated temperatures

This paper presents results of experiments, conducted at NIST and elsewhere, to measure compressive strength of concrete at elevated temperature. The paper compares the test data with existing design rules and recommendations to assess their applicability to HSC. Based on the compiled data, the paper proposes new strength-temperature relationship for HSC and discusses the need for standardizing the test procedure for testing concrete at high temperature and for a revision of the current design guides to include new data for properties of concrete at high temperature.

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Résumé Cet article présente les résultats expérimentaux, recueillis au NIST et ailleurs, pour mesurer la résistance à la compression du béton soumis à des températures élevées. Cet exposé compare les données disponibles avec les règles et recommandations existantes pour la conception d’un béton afin de déterminer leur applicabilité pour le béton à haute résistance (HSC). Basé sur les données compilées, cet article propose une nouvelle relation entre la résistance et la température pour le béton à haute résistance, On discute de la nécessité de standardiser la procédure de mesure de la résistance du béton à haute température. On discute aussi de la nécessité de revoir les guides actuels pour y inclure les données récemment disponibles concemant les propriétés du béton à haute tempèrature.

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Editorial Note Dr. Long T. Phan is a RILEM Senior Member. He participates in the work of RILEM TC HTC ‘Mechanical concrete properties at high temperature-Modelling and applications’. Dr. Nicholas J. Carino is also a RILEM Senior Member. Both of them work at NIST, a RILEM Titular Member.     

Fatigue of 7075-T651 aluminum alloy under constant and variable amplitude loadings

The fatigue crack growth (FCG) behavior of 7075-T651 aluminum alloy was studied under constant and variable amplitude loadings in vacuum, air and 1% NaCl solution. In the study of constant amplitude loading fatigue, the stress ratios were 0.1 and 0.85 and the loading frequency was 10 Hz. In the study of variable amplitude loading fatigue, the load spectrums were tension type and tension–compression type, and the average loading frequency was about 5 Hz. The results of FCG tests, under constant and variable amplitude loadings, validated the unified two parameter driving force model, accounting for the residual stress and stress ratio effects on fatigue crack growth.     

A review on amorphous noble-metal-based electrocatalysts for fuel cells: Synthesis,characterization, performance,and future perspective

An urgent need for cleaner energy alternatives has driven the research of fuel cells, and consequently, electrocatalysts. Noble metals such as Pt and Pd are well known as the most suitable catalysts for fuel cell reactions. However, because of their high costs, much effort has been invested to improve their efficiency. Amorphous noble metal nanoparticles are promising electrocatalysts because of their abundant uncoordinated active sites that result from their long-range disordered lattice. Researches on amorphous Pt- and Pd-based catalysts have progressed well with several different synthesis routes. This review aims to systematically study the differences, advantages, and disadvantages of these methods and the resulting characteristics, performance in fuel cell applications, and future prospects of the amorphous Pt- and Pd-based catalysts.     

The effect of maturity and season on health-related bioactive compounds in wild harvested fruit of Terminalia ferdinandiana (Exell)

This study reports changes in the concentrations of important health-related bioactive compounds (vitamin C and ellagic acid) and morphology of wild harvested Kakadu plum fruits that were collected during three harvest seasons and four maturities. The results showed that fruit weight increased, whereas fruit length and width changed slightly with the advance in maturity. Vitamin C increased up to 20 folds (from 1.2 to 21.2% dry weight [DW]) from immature to mature stage, whereas ellagic acid decreased approximately three times (from 6.5 to 2.1% DW). Similar trends were observed over the three harvest seasons studied. A positive correlation between fruit weight and vitamin C, whereas a negative correlation with ellagic acid was observed, indicating that maturity plays an important role in contributing to the variation of ellagic acid and vitamin C. Season also had an effect and showed the influences of rainfall, temperature and solar exposure on the biosynthesis of vitamin C and ellagic acid.     

Enhanced microwave absorption properties of Y-Co2Z/PANI hexaferrites composites in the frequency range of 0.1–18 GHz

We prepared Ba_3−xY_xCo₂Fe₂₄O₄₁ (Y-Co₂Z, x = 0, 0.2, and 0.4) by the solid-state reaction method. Y-Co₂Z and polyaniline (PANI) composites (named as Y-P0, Y-P2, and Y-P4) were prepared by using the in-situ polymerization method. The Y-doping played an important role in the variation of lattice parameters, a and c. The combination of Y-doping and PANI modified the magnetic properties of the composites, which could be observed by the changing of the saturation magnetization and coercivity. This combination had also affected the electromagnetic properties of composites through the measurements of complex permittivity and permeability. Using the transmission line theory, we calculated refection loss (RL) of composites with the variation thickness of 1.00–2.50 mm. Our composites tuned the minimum RL from the X band (RL = −29.6 dB at 11.4 GHz for Y-P2) to Ku band (RL = −16.3 dB at 15.7 GHz for Y-P4 and RL = −26.4 dB at 16.6 GHz for Y-P4). For maximum effective bandwidth, our composites covered a huge range from the S and C bands (Y-P0 with 3.9 GHz in the range of 3.4–7.3 GHz) through the X band (Y-P2 with 3.9 GHz in the range of 9.0–12.9 GHz) to the Ku band (Y-P4 with 4.0 GHz in the range of 13.8–17.8 GHz). Those properties proved that the composites could act as promising absorbers in the S, C, X, and Ku bands.     

Porous NiO via pulsed electrodeposition towards enhanced electrochromic properties

Journal of Applied Electrochemistry - Herein, a facile pulse electrodeposition procedure with a 1 s off-time between pulses is reported for a successful fabrication of porous nickel oxide...     

Enhanced photocatalytic activities of vandium and molybdenum co-doped strontium titanate under visible light

In this report, undoped, mono and co-doped perovskite strontium titanate (SrTi_1−(x+y)Mo_xV_yO₃) were synthesized by the sol-gel method, and their physical and optical properties were investigated. Furthermore, the photocatalytic degradation activities of the synthesized powders were conducted in 10 ppm methylene blue solution under visible-light irradiation. A maximum degradation efficiency of 91.5% was achieved in SrTi_0.9Mo_0.05V_0.05O₃ powder whereas only 59.9% of degradation was found in undoped SrTiO₃. The improved efficiency in co-doped SrTiO₃ was due to the doping of metal cations, Mo⁺⁶ and V⁺⁵ in the host lattice, which created impurity defect states thereby effectively reducing the bandgap energy of the semiconductor.