Performance of olive waste ash concrete exposed to elevated temperatures

This study explores the influence of olive waste ash (OWA) on the performance of concrete exposed to elevated temperatures in the range from 400 to 600 °C. The performance of concrete to elevated temperature was evaluated using compressive strength and electrical charge of concrete. Three OWA levels were used in the study: 7%, 15%, and 22% by weight of cement. The other experimental parameters investigated in the study were elevated temperature (400 and 600 °C), aggregate type (crushed basalt and volcanic tuff), w/c ratio (0.5 and 0.7), and air content (non-air and air entrained). After the initial moist curing period of 90 days, concrete specimens were exposed to elevated temperatures for a period of 2 h using an electric furnace.     

Properties of Portland cement-modified asphalt binder using Superpave tests

This study investigates the effect of cement additive on some properties of asphalt binder using Superpave testing methods. Six cement-to-asphalt (C/A) ratios were considered in the study: 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 by volume of asphalt binder. The experimental tests that were conducted in the study included the Superpave rotational viscosity (RV) test and the dynamic shear rheometer (DSR) test. The RV test was conducted at the Superpave-specified high temperature of 135 °C that represents the average mixing and laydown temperature, and at seven different rotational speeds of 5, 10, 20, 30, 50, 60, and 100 rpm. On the other hand, the DSR test was conducted at four test temperatures of 58, 64, 70, and 76 °C; one lower and two higher than the Superpave high performance grade (PG) temperature of the asphalt binder used in the study (PG 64). The loading frequency used in the DSR test was 10 rad/s (1.59 Hz) as specified by the Superpave system. Results of the study showed that the addition of Portland cement to asphalt binders increased the rotational viscosity (RV) of asphalt binders at 135 °C and different rotational speeds. The C/A ratio of 0.15 was found to be the optimum ratio that achieved a balanced increase in the rotational viscosity and the value of the DSR G^*/sin δ rutting parameter of asphalt binders. The C/A ratio had insignificant effects on the Newtonian behavior, the phase angle (δ), and the elastic behavior of asphalt binders. The increase in C/A ratio increased the stiffness of asphalt binders represented by the complex shear modulus (G^*) value. The increase in the C/A ratio improved the rutting parameter, G^*/sin δ value, at all temperatures. The increase in C/A ratio improved the Superpave high PG temperature (the high temperature at which the asphalt binder passed the Superpave criteria for G^*/sin δ value). It was also shown that the best function that described the relationship between each of RV, G^*, and G^*/sin δ and the C/A ratio was the exponential function with high coefficient of determination (R²).     

Studies of composite films of polyethylene oxide doped with potassium hexachloroplatinate

The permittivity and conductivity relaxation processes of polyethylene oxide (PEO) composite along with potassium hexachloroplatinate (K₂PtCl₆) electrolytes additive forming PEO/K₂PtCl₆ complex composite have been investigated. The complex composite has been used as a model for dry-polymer electrolytes (PEs) due to the fact that, the anion is large enough for mimicking the immobilized anion in real dry-polymer electrolytes. Stand-free composite films with 0%, 1%, 3%, and 5% concentrations of K₂PtCl₆ have been studied using broadband dielectric spectroscopy in the temperatures range from 150 K until 345 K. The microstructural dynamics revealed the α-, β-, and σ-relaxations and their salient spectral characteristics at various concentrations of K₂PtCl₆ in PEO. The experimental ε” master curves were fitted to HN function for one and/or two relaxation peaks with and without the electrical conductivity contribution in order to investigate the relaxation time (τ), dielectric strengths (Δε), modulus formalism (M”) and the electrical conductivitie (σ). The translational and reorientational degrees of freedom of PEO/K₂PtCl₆ complex composites are responsible for the relaxation behavior which is predicted to be correlated to the relaxation behavior of the polymer electrolyte below and above the glass transition temperature (T_g). The relaxation time (τ) deduced from β-relaxation follows Arrhenius-like behavior while that deduced from α-relaxation process follows Vogel–Tamman–Fulcher (VTF) behavior.     

Effect of elevated temperature on bond between steel reinforcement and fiber reinforced concrete

The bond behavior between fiber reinforced concrete and 20-mm reinforcing steel rebars was evaluated under elevated temperatures. Fifty modified pullout specimens (100×100×400 mm) were prepared using high strength concrete with basalt aggregate and different volumetric mixtures of three types of fibers, namely brass-coated steel fibers, hooked steel fibers, and high modulus polypropylene fibers, before being cured for 28 days at 40 °C. Specimens, designated for heat-treatment, were then subjected to elevated temperatures, ranging from 350 to 700 °C, whereas unheated (control) ones were left in laboratory air. The overall response of control and heat-damaged specimens, pulled out up to failure, and cracking extent and continuity were described. Standard cubes (100 mm³) were cast, cured, and heat treated under similar conditions, then tested to evaluate compressive and splitting strengths. The results showed marked reductions in residual compressive, splitting and steel–concrete bond under high temperatures with dramatic changes in bond stress–free-end slip trend behavior. Use of fibers minimized the damage in steel–concrete bond under elevated temperatures and hence the reduction in bond strength. Specimens which incorporated hooked steel fibers attained the highest bond resistance against elevated temperatures followed, in sequence, by those prepared with the mixture of hooked and brass-coated steel, the mixture of hooked steel and polypropylene, and brass-coated steel fibers. Statistical models for bond stress versus free-end slip and bond strength versus exposure temperature were developed. These showed excellent agreement with the trend behavior of present experimental data.     

Hybrid Zinc Oxide Nanorods/Carbon Nanotubes Composite for Nitrogen Dioxide Gas Sensing

This study reports on the synthesis and fabrication of hybrid nanocomposite based on single-walled carbon nanotubes–ZnO nanorods (SWCNT-ZnONR) as resistive gas sensors for NO₂ detection. The sensor was prepared using the standard simple and cost-effective hydrothermal process. The sensor was characterized by x-ray diffraction (XRD) and scanning electron microscopy. The findings revealed enhanced porous SWCNT-ZnONR nanocomposites due to the high porosity of the SWCNT. It was also found that the sensor exhibited average response and recovery times of about 70 s and 100 s, respectively. The XRD peak at 26° indicated that the SWCNT pattern was not disturbed, while sensitivity increased with temperature up to 150°C, at which the sensitivity was maximum. Similarly, the sensor sensitivity increased with NO₂ concentration at all levels examined. Moreover, the results indicate that the sensor shows significant promise for NO₂ gas sensing applications.     

Optimizing the tilt angle of solar collectors

Solar collectors need to be tilted at the correct angle to maximize the performance of the system. In this paper, the annual solar fraction of the system (the fraction of energy that is supplied by solar energy) is used as an indicator to find the optimum inclination angles for a thermosyphon solar water heater installed in northern and southern parts of Jordan. Calculations are carried out using the powerful computer program TRNSYS (Transient System Simulation). The system is assumed to operate with a daily hot water load of 150 l at 55°C flowing during the day according to the widely used Rand consumption profile. The results show that the optimum inclination angle for the maximum solar fraction is about φ+(0→10°) for the northern region (represented by Amman) and about φ+(0→20°) for the southern region (represented by the town of Aqaba). These values are greater than those for maximum solar radiation (which is commonly used as an indicator) at the top of the collector by about 5 to 8°.