Performance of concrete coating under varying exposure conditions

This paper reports the results of a study conducted to evaluate the performance of ten concrete coatings, representative of five generic types, under varying exposure conditions. The performance of selected coatings was assessed on laboratory specimens by testing their adhesion to concrete, crack-bridging ability, chloride permeability and resistance to moisture and thermal variations. The data indicate that the overall performance of epoxy resin and polyurethane coatings was better than that of other generic types of coatings depending on chemical formulations. Further, a variation in the performance of coatings of similar generic type was noted. The selected coating needs to be tested under conditions similar to the exposure environment. Guidelines for the selection of concrete coatings appropriate for the service conditions are presented along with the performance criteria.

---

Résumé Ce papier rapporte les résultats d'une étude qui a été conduite afin d'évaluer la performance d'une dizaine de revêtements en béton représentant cinq types génériques sous des conditions d'exposition variables. La performance des revêtements sélectionnés a été évaluée sur des échantillons de laboratoire en testant leur adhérence au béton, leur aptitude à émousser les fissures, la perméabilité des chlorures et la résistance à l'humidité et aux variations thermiques. Les données indiquent que la performance globale de la résine époxyde et des revêtements de polyuréthanne était meilleure que celle des autres types de revêtements en fonction de leurs formulations chimiques. De plus, une variation de la performance des revêtements de type générique similaire a été notée. Les revêtements sélectionnés doivent être testés sous des conditions similaires à celles de l'environnement d'exposition. Les règles de sélection des revêtements de béton approriés pour les conditions de service sont présentées ainsi que les critères de performance.

     

Performance evaluation of repair systems under varying exposure conditions

This paper reports results of a study conducted to assess the performance of commonly utilized repair systems when exposed to some selected exposure conditions, such as marine, belowground, fire, acid, and sulfur fumes. The performance of the selected repair systems was assessed by exposing large-sized repaired concrete specimens to the selected exposure conditions in addition to thermal variations. After the completion of the exposure, the repaired specimens were visually examined for damage to the surface coating and presence of rust stains, salt scaling, etc. The bond of the coating with the substrate was evaluated and then the specimens were crushed to retrieve reinforcing steel bars that were examined for the extent of corrosion, if any. The data developed in this study were utilized to recommend repair systems suitable for the selected exposure conditions.     

Modeling the performance of direct-detection Doppler lidar systems including cloud and solar background variability

Previous modeling of the performance of spaceborne direct-detection Doppler lidar systems assumed extremely idealized atmospheric models. Here we develop a technique for modeling the performance of these systems in a more realistic atmosphere, based on actual airborne lidar observations. The resulting atmospheric model contains cloud and aerosol variability that is absent in other simulations of spaceborne Doppler lidar instruments. To produce a realistic simulation of daytime performance, we include solar radiance values that are based on actual measurements and are allowed to vary as the viewing scene changes. Simulations are performed for two types of direct-detection Doppler lidar system: the double-edge and the multichannel techniques. Both systems were optimized to measure winds from Rayleigh backscatter at 355 nm. Simulations show that the measurement uncertainty during daytime is degraded by only approximately 10-20% compared with nighttime performance, provided that a proper solar filter is included in the instrument design.     

Adhesion force approximation at varying consolidation stresses for fine powder under humid conditions

Interparticle adhesion forces in fine powders are greatly influenced by varying relative humidity (RH) conditions. The present study estimated the interparticle adhesion forces developed in corn starch powder under humid conditions at varying applied consolidation stresses using tensile strength determination approach. Shear test was used to determine tensile strength of powder at 1–9 kPa consolidation pressures and extrapolated values of tensile strength at zero stress were used for force estimation in non-consolidated powders. A strong dependence of interparticle adhesion force on consolidation and RH conditions was observed, mainly due to alteration in the number of adhesive contacts and contact area. The results indicated that, at low consolidation and high RH, capillary force is the prevailing force contributing to the total interparticle adhesion in contrast to higher consolidation conditions where load induced contact force plays a dominant role. Furthermore, for nonconsolidated samples, the adhesion forces registered a steep jump above 60% RH which was primarily attributed to dominance of the liquid bridge forces. Also, forces determined from tensile strength approach and those predicted theoretically, as a summation of individual forces, yielded a similar trend. Overall, a simple and effective approach for interparticle force estimation of consolidated as well as loosely packed powders under varying humidity conditions is presented here.     

Conjugate problems of unsteady heat and mass conduction under varying external conditions

A closed system of algebraic and ordinary differential equations that enables one to simply and with a high degree of accuracy solve unsteady problems of heat conduction and diffusion extraction of a substance from solids of standard shapes - a plate, a cylinder, and a sphere - under varying external conditions is proposed. The method of solution is based on a unified universal dependence that describes with a high degree of accuracy the distribution of temperatures or concentrations of the substance in the above solids and on equations that determine variations in characteristics involved in this dependence with time and space as the solids move.     

Noise, clutter, and determinism in infrared spectral signatures under varying meteorological conditions

Infrared remote detection of chemical and biological agents in a complex environment depends on the ability to recognize threat signatures and differentiate them from the signatures of innocuous materials. In this paper, we addressed the methods of producing the constraint spectra needed to ensure reliable operation in a meteorologically changing environment. We collected arrays of background spectra of ground, woods, and low-angle sky on an irregular basis over a period of a year. Based on the hypothesis that the concentration fluctuations of species in the sensor's field of view can be exploited to form signatures, the standard deviations of the array (the result is characteristic of all fluctuations) and the difference array (the result is characteristic of sensor fluctuations) were computed. Subtracting these two spectra and filtering the result produced a spectrum, which is a measure of the IR fluctuations in the scene. The resulting set of scene spectra were processed into aberrant noise, and deterministic groups by numerical filtering and statistical methods.     

Deformation and tearing of circular plates with varying support conditions under uniform impulsive loads

Transient dynamic finite element analysis of circular plates with varying support configurations under uniform single square wave form impulsive load has been carried out in FEA package ANSYS. Experimental results of Teeling-Smith and Nurick [The deformation and tearing of thin circular plates subjected to impulsive loads. Int J Impact Eng 1991;11(1):77–91] and Nurick et al. [Tearing of blast loaded plates with clamped boundary conditions. Int J Impact Eng 1996;18(7–8):803–27] for the onset of thinning and tearing at the boundary of clamped circular plates subjected to uniformly loaded air blasts have been used to compare and validate the numerical simulation and procedure. The Mode II failure with respect to clamped circular plates has been simulated using a rupture strain criteria. Mode III failure or plastic shear sliding, has been considered using a shear strain failure criteria as proposed by Wen and Jones for plates. A stiffness reduction scheme has been proposed to decide on the initiation and progression of tearing in conjunction with suitable failure model under Modes II and III. The evolution of deflections, plastic zones, rupture zones and failure modes under the blast loading conditions are found to match well with the experimental results. The validated numerical model has further been used to study the effect of plate thickness on the deformation and tearing response of the circular plates subjected to impulsive loads. The deformation, tearing and shock absorption response of clamped circular plates under uniform impulsive loads with ring support of varying edge configurations at the boundary have also been numerically studied. Further, the response of circular plate–tube combination with varying boundary support configurations has been studied. The plate has been considered at the mid-span of the tube of length equal to the plate diameter with the ends of the tube modelled as clamped. The numerical model has been used to study the effect of tube thickness variations on the deformation and tearing response of the circular plate under shock loads. The response of tube–plate combinations under uniform impulsive loads with ring support at the plate–tube junction have also been numerically studied.     

Doses under automatic exposure control (AEC) for direct digital radiographic (DDR) X-ray systems

Current guidelines quote tolerances for automatic exposure control (AEC) device performance for X-ray systems as 'Baseline ± X %'. However, in the situation where a baseline figure has not yet been achieved, as in the case of commissioning assessments, this tolerance is not relevant. The purpose of this work is to provide mean doses for direct digital radiography (DDR) X-ray system, operating in AEC, against which comparisons can be made. Dose measurements have been recorded under AEC operation on 29 DDR detectors from three different manufacturers. Two different testing protocols were examined: (1) water equivalent phantoms in front of the DDR detector and (2) aluminium block at the tube head. The average patient exit dose, using the aluminium block was 4.6 μGy with the antiscatter grid in place and 4.0 μGy with the grid removed. Using the water phantoms, the average dose was measured at 17.1 μGy with the antiscatter grid in place and 5.4 μGy with grid removed. Based on these results, it is clear that different testing configurations significantly impact on the measured dose.     

Stress intensity factors for curvilinear cracks loaded under anti-plane strain (mode III) conditions

A general solution to the elastic and thermoelastic problems with a rigid circular-arc inclusion is presented. The proposed analysis is based upon the complex variable theory dealing with sectionally holomorphic functions which is reduced to the solution of the Hilbert problem. It is indicated that both the stress and thermal stress fields near the inclusion tip possess a square-root singularity similar to that for the corresponding crack problem. In analogy to the stress intensity factors defined for crack problem, stress singularity coefficients are introduced in this paper to characterize the near tip fields. Complete stress fields and the corresponding stress singularity coefficients as the circular-arc inclusion are under uniform remote load, concentrated force and uniform heat flux are given. Failure initiation of an infinite plate embedded with a rigid arc inclusion under different loading conditions is also discussed.     

Modeling of cyclic stress–strain behavior and damage mechanisms under thermomechanical fatigue conditions

A multi-component model was applied to predict the cyclic stress–strain response of different alloys under thermomechanical fatigue conditions based upon isothermal hysteresis loops. A ductile AISI 304 L-type stainless steel and two high strength alloys, the near-α titanium alloy IMI 834 and the nickel-base superalloy IN 100, were chosen as test materials. These represent alloys with rather different dislocation slip modes, stress–strain characteristics and damage mechanisms. Model predictions are compared with experiments and the differences in cyclic stress–strain response and damage mechanisms under isothermal and thermomechanical fatigue conditions, respectively, are discussed based upon microstructural observations.     

Efficient photodegradation of methylene blue (MB) under solar radiation by ZrC nanoparticles

Due to increase in water pollution, there is a need to dwindle this problem for a clean and green future. Photocatalysts like ZnO, CaO and TiO₂ have proved to be triumphant in removal of environmental contaminants. In this present work, ZrC nanopowder has been synthesized using a single-step reduction technique by heating zirconium oxide (ZrO₂) and hexane (C₆H₁₄) in metallic Mg powder and is used as a photocatalyst for the degradation of methylene blue (MB) dye under solar radiation. Optimization of synthesis parameters (temperature, holding time and carbon content) has been done to obtain single phase ZrC. Various characterization techniques like X-ray diffraction (XRD), transmission electron microscope (TEM), differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA) and X-ray photoelectron spectroscopy (XPS) were studied for various structural, thermal and surface characteristics of as-synthesized samples. The effect of synthesis parameters on crystal distortion of ZrC particles was studied with the help of Double Voigt analysis. Further, the comparative catalytic activity as photodegradation of MB dye with the help of optimized sample was studied under UV and solar radiations. As an effect of illumination source with the same concentration of catalyst and dye, 80% degradation was observed under solar radiations which is quite higher than that observed under UV in 5?h.     

Aggregation of self-assembled Ni(OH)2 nanosheets under hydrothermal conditions

We investigate aggregation process of the Ni(OH)₂ under hydrothermal condition. The samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the self-assembled Ni(OH)₂ nanosheets with the hexagonal structure is about 30 nm in thickness. We investigate the effect of reaction temperature on the morphology of the product. The nanosheets can aggregate together when the temperature and reaction time are suitable. And a possible mechanism is also proposed to explain the growth and aggregation process of Ni(OH)₂ nanosheets.     

Modeling quantum transport under AC conditions: application to intrinsic high-frequency limits for nanoscale double-gate Si MOSFETs

An approach for studying the performance of phase-coherent devices under high-frequency conditions is presented. Quantum predictions on cutoff frequencies are obtained by directly solving the time-dependent Schrodinger equation under oscillating potential profiles at frequencies comparable with the inverse of the electron transit time. As an example, the small-signal admittance parameters for a simple double-gate Si transistor are computed, showing that its intrinsic amplifying properties are degraded at terahertz frequencies. Classical results, obtained by solving the classical Boltzmann equation through the standard Monte Carlo technique, are comparable to quantum predictions. The approach opens a new path for the understanding of the electron phenomenology in phase-coherent devices under ac conditions.     

In-flight experiment for combined planar antennas and solar cells (SOLANT)

An in-flight experiment to validate advanced solar antenna structures (SOLANT) in space is presented. Two different antennas have been designed and manufactured, one for global positioning system (GPS) reception and one for S-band beacon transmission. Both units use slot aperture radiators embedded in identical mechanical structures. The GPS antenna has been designed to generate an omni-directional radiation pattern with righthanded circular polarisation thus fulfilling NavStar specifications. The S-band beacon antenna is based on a four-element circularly polarised array providing 6 dBic of gain. These antennas are integrated within two solar panels, which form the upper layer of the antenna structure. The two panels are identical, make use of gallium arsenide (GaAs) solar cells arranged in two strings and provide a peak power of 10 W each. The SOLANTs were launched, fixed to a Cosmos payload adapter and remained operative for 2 years, well beyond their expected lifetime. This study summarises the design and performance tests performed prior the launch and during the orbital operation.     

Core safety of Indian nuclear power plants (NPPs) under extreme conditions

Nuclear power is currently the fourth largest source of electricity production in India after thermal, hydro and renewable sources of electricity. Currently, India has 20 nuclear reactors in operation and seven other reactors are under construction. Most of these reactors are indigenously designed and built Heavy Water Reactors. In addition, a 300 MWe Advanced Heavy Water Reactor has already been designed and in the process of deployment in near future for demonstration of power production from Thorium apart from enhanced safety features by passive means. India has ambitious plans to enhance the share of electricity production from nuclear. The recent Fukushima accident has raised concerns of safety of Nuclear Power Plants worldwide. The Fukushima accident was caused by extreme events, i.e., large earthquake followed by gigantic Tsunami which are not expected to hit India’s coast considering the geography of India and historical records. Nevertheless, systematic investigations have been conducted by nuclear scientists in India to evaluate the safety of the current Nuclear Power Plants in case of occurrence of such extreme events in any nuclear site. This paper gives a brief outline of the safety features of Indian Heavy Water Reactors for prevention and mitigation of such extreme events. The probabilistic safety analysis revealed that the risk from Indian Heavy Water Reactors are negligibly small.     

Obvious enhancement in electrochemical capacitive properties for poly(3,4-ethylenedioxythiophene) electrodes prepared under optimized conditions

This work investigates the effect of preparation conditions on the supercapacitive performances of the poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes electrodeposited detailedly. These preparation conditions include electrode substrates, electrodeposition modes, parameters, and counter anions. Electrochemical characterizations indicate an evident impact of electrode substrates on the electrochemical behaviors of the PEDOT electrodes prepared. Graphite foils (GF) as the electrode substrate show better electrochemical capacitive properties relative to conductive glasses (CG). This can be ascribed to lower sheet resistance and better adhesion to the PEDOT films for the former. Moreover, SEM and AFM tests indicate that different electrodeposition modes, parameters, and counter anions would result in different morphologies and roughness for the PEDOT electrodes obtained, consequently affecting their supercapacitive performances. Among numerous preparation conditions, the polystyrene sulfonic acid salt-doped PEDOT deposited on GF substrates prepared with potentiostatic mode at 0.9 V shows the best supercapacitive behaviors, delivering the specific capacitance of 108.2 mF cm^?2 at 0.2 mA cm^?2, also exhibiting good rate capability and superior cycle performance (keeping 93.4% of initial capacitance after 10,000 cycles). This work indicates that the supercapacitive properties of PEDOT electrodes can be substantially enhanced by changing their preparation conditions.

     

Airborne CO(2) coherent lidar for measurements of atmospheric aerosol and cloud backscatter

An airborne CO(2) coherent lidar has been developed and flown on over 30 flights of the NASA DC-8 research aircraft to obtain aerosol and cloud backscatter and extinction data at a wavelength near 9μm. Designed to operate in either zenith- or nadir-directed modes, the lidar can be used to measure vertical profiles of backscatter throughout the vertical extent of the troposphere and the lower stratosphere. Backscatter measurements in absolute units are obtained through a hard-target calibration methodology. The use of coherent detection results in high sensitivity and narrow field of view, the latter property greatly reducing multiple-scattering effects. Aerosol backscatter profile intercomparisons with other airborne and ground-based CO(2) lidars were conducted during instrument checkout flights over the NASA Ames Research Center before extended depolyment over the Pacific Ocean. Selected results from data taken during the flights over the Pacific Ocean are presented, emphasizing intercom arisons with backscatter profile data obtained at 1.06 μm with a NASA Goddard Space Flight Center Nd:YAG lidar on the same flights.     

Dechlorination of atrazine using zero-valent iron (Fe0) under neutral pH conditions

Zero-valent iron (Fe0) is frequently used for the dechlorination of pesticides, because it is economical, easily acquired and stable. The kinetics of dechlorination by Fe0 are improved at low pH, but this requires additional acid addition, while dechlorination hardly occurs under basic conditions. Due to the buffer capacity of geological materials such as clay and sediment, however, the addition of acid to obtain a low pH may not be effective. In this research, the dechlorination constants of atrazine by Fe0 were measured with the addition of buffer solution to simulate the buffer capacity of sediment. In the presence of the buffer solution, the pH values remained neutral, while dechlorination occurred more slowly than that observed under acid additions but faster than that without any buffer. When the initial concentrations of atrazine were 10mg/L, 30 mg/L, and 50mg/L, its dechlorination was explained using pseudo-first order reaction kinetics. The pseudo-first order constants were 3.01 x 10(-2)d(-1) at 10 mg/L, 3.23 x 10(-2)d(-1) at 30 mg/L and 3.38 x 10(-2)d(-1) at 50mg/L. In addition, the half-lives of atrazine were 8.91 d at 10mg/L, 9.32 d at 30 mg/L, and 10.00 d at 50mg/L. Acid addition may not be omitted to obtain acidic pH conditions when dechlorination is necessary in geologic materials.