Thermo-mechanical properties of concrete containing high-volume mineral admixtures

This paper reports the results of a study conducted to evaluate the influence of high-volume class C fly ash (FA), blast furnace slag (BFS) and both FA+BFS on the thermal conductivity (TC), compressive strength, water absorption and density of concrete. TC decreased with the increase of FA, BFS and FA+BFS as replacement for Portland cement. The reductions in TC due to FA, BFS and FA+BFS were, respectively, up to 39%, 18% and 31%. The addition of FA, BFS and FA+BFS in the concrete had a decreasing effect on TC. Their addition also decreased compressive strength as a function of replacement percent. However, this reduction in compressive strength decreased with increasing curing period.     

Development of a New Methodology for Indirect Determination of Nitrite,Nitrate, and Total Nitrite in the Selected Two Groups of Foods by Spectrophotometry

A new indirect preconcentration procedure was developed for micellar sensitive detection of trace nitrite as analyte by spectrophotometry. The method is based on ion association of triiodide ion, I₃ ^? or I₂, produced by the reaction of nitrite at low concentrations with excess iodide in presence of ion-pairing agent, Coomassie brilliant blue R 250 (CBB), and electrophilic attack of nitrosyl cation produced by disproportionation of nitrite depending on concentration to ion-pairing agent at higher concentrations than 5 μg L^?1 in acidic medium, and then extraction of the ion-pairing complex formed from aqueous solution into the micelles of Triton X-114 at sodium acetate medium. The calibration graphs were rectilinear in the range of 0.5–5 and 5–200 μg L^?1 with increasing and decreasing slopes in micellar phase, respectively. The detection and quantification limits of the method were 0.15 and 0.50 μg L^?1, and the precision (as RSD) for five replicate measurements of different concentrations of nitrite was in the range of 2.3–4.8%. The average recoveries of spiked nitrite residues ranged from 97 to 104%. The method is free of matrix interferences and successfully applied to the indirect determination of nitrite, nitrate, and total nitrite in selected two groups of foods. Also, the accuracy was validated by analysis of a certified reference material as well as recoveries of spiked samples. The objective of the study is to provide an alternate economical method to determine the contents of nitrite, nitrate, and total nitrite after homogenization, extraction, reduction, and preconcentration from sample matrix.

Open image in new window

Graphical Abstract

     

Carbonized electrospun polyacrylonitrile nanofibers as highly sensitive sensors in structural health monitoring of composite structures

Electrospun polyacrylonitrile (PAN) nanofibers were stabilized at 280°C for 1 h in an ambient condition, and then carbonized at 850°C in inert argon gas for additional 1 h in order to fabricate highly pure carbonous nanofibers for the development of highly sensitive sensors in structural health monitoring (SHM) of composite aircraft and wind turbines. This study manifests the real‐time strain response of the carbonized PAN nanofibers under various tensile loadings. The prepared carbon nanofibers were placed on top of the carbon fiber pre‐preg composite as a single layer. Using a hand lay‐up method, and then co‐cured with the pre‐preg composites in a vacuum oven following the curing cycle of the composite. The electric wires were connected to the top surface of the composite panels where the cohesively bonded conductive nanofibers were placed prior to the tensile and compression loadings in the grips of the tensile unit. The test results clearly showed that the carbonized electrospun PAN nanofibers on the carbon fiber composites were remarkably performed well. Even the small strain rates (e.g., 0.020% strain) on the composite panels were easily detected through voltage and resistance changes of the panels. The change in voltage can be mainly attributed to the breakage/deformation of the conductive network of the carbonized PAN nanofibers under the loadings. The primary goal of the present study is to develop a cost‐effective, lightweight, and flexible strain sensor for the SHM of composite aircraft and wind turbines. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43235.     

Spatio-temporal querying recurrent multimedia databases using a semantic sequence state graph

We present an indexing method for spatiotemporal data: semantic sequence state graph (S³G). S³G maintains objects with their locations as states and events as transitions. The spatial information is maintained in states while the semantic events result in temporal ordering between the states. If the objects visit the same locations repeatedly, we call such databases as recurrent databases. Our querying interface supports queries based on spatio-temporal logic that includes operators such as ??next?? and ??eventually??. The interactive querying interface enables the user to build the query interactively and see the intermediate results of the query.     

Effect of glass fiber‐reinforced polymer and epoxy injection on compressive strength of elevated temperature damaged concrete

Glass fiber‐reinforced polymer (GFRP) materials have received a great deal of interest among civil engineers during the past decade. This paper presents an overview of experimental studies carried out on GFRP‐wrapped and epoxy‐injected concrete samples exposed to elevated temperatures. For this purpose, 0.30, 0.35 and 0.40 water to binder (w/b) ratios were used. For each w/b ratio, normal aggregates were replaced by lightweight aggregates with a size fraction of 0–2 mm at three different volume fractions such as 10%, 20% and 30% of total aggregate volume. At the same time, a group of air‐entrained samples was also cast for each w/b ratios. Prepared samples were exposed to 600 °C for 3 h. The damaged samples were separately repaired by GFRP and epoxy injection. Before and after elevated temperature exposure, water absorption and compressive strength were tested. After repairing with GFRP and epoxy injection, only the compressive strength test was carried out. GFRP improved the compressive strength between 1–22% and 348–1403% for samples before and after being exposed to elevated temperatures, respectively. Epoxy injection increased the compressive strength of the samples, exposed to elevated temperature, between 1% and 123%. However, the epoxy injection process failed to recover the compressive strength of the samples before elevated temperature exposure. Copyright © 2012 John Wiley & Sons, Ltd.     

Fabrication and characterization of NiCoZn-M (M: Ag, Pd and Pt) electrocatalysts as cathode materials for electrochemical hydrogen production

Ag, Pd and Pt-modified alkaline leached NiCoZn composite coatings were prepared on a copper specimen by electrochemical technique. The chemical composition of layers before and after leaching as well as after noble metal modification was determined by energy dispersive X-ray spectroscopy (EDX). The surface morphologies of the composite coatings were examined with the help of scanning electron microscopy (SEM). The hydrogen evolution activity of the electrodes was studied in 1 M KOH solution. For this purpose, cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques were used. Furthermore, the change of hydrogen evolution activity of the electrodes as a function of operation time in alkaline solution was also investigated. Surface morphologies showed that the composite coatings prepared to have compact and porous surface. EDX analysis confirmed the presence of Ag, Pd and Pt metals over the NiCoZn layer. The co-deposition of nickel, cobalt and zinc on copper surface and subsequently alkaline leaching of zinc rendered cathode material very active in hydrogen evolution. The modification of alkaline leached NiCoZn ternary coating by deposition of small amounts of Ag, Pd and Pt can further enhance the hydrogen evolution performance of this Raney-type electrode when compared to NiCoZn individually. The order of hydrogen evolution activity of catalysts studied is Ni < NiCoZn < NiCoZn-Pd < NiCoZn-Ag < NiCoZn-Pt. The long-term electrolysis tests showed that the Pt-modified electrode has the better time stability than the others. The superiority of Pt-modified catalyst explained by well known intrinsic catalytic activity of Pt.     

Adsorption of copper(II), cobalt(II), and iron(III) ions from aqueous solutions on poly(ethylene terephthalate) fibers

The adsorption behavior of poly(ethylene terephthalate) (PET) fibers towards copper(II), cobalt(II), and iron(III) ions in aqueous solutions was studied by a batch equilibriation technique. Influence of treatment time, temperature, pH of the solution, and metal ion concentration on the adsorption were investigated. Adsorption values for metal ion intake followed the following order: Co(II) > Cu(II) > Fe(III). One hour of adsorption time was found sufficient to reach adsorption equilibrium for all the ions. The rate of adsorption was found to decrease with the increase in the temperature. Langmuir adsorption isoterm curves were found to be significant for all the ions studied. The heat of adsorption values were calculated as −5, −2.8, and −3.6 kcal/mol for Cu(II), Co(II), and Fe(III) ions, respectively. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1935–1939, 1998     

Microstructure and Property Relationships in Resistance Spot Weld between 7114 Interstitial Free Steel and 304 Austenitic Stainless Steel

Due to the differences in physical, chemical and mechanical properties of the base metals, the resistance spot welding of dissimilar materials is generally more challenging than that of similar materials. The influence of the primary welding parameters affecting the heat input such as peak current on the morphology, microhardness, and tensile shear load bearing capacity of dissimilar welds between 304 grades austenitic and 7114 grade interstitial free steel has been investigated in this study. The optimum welding parameters producing maximum joint strength were established at a peak current of 9 kA, where the electrode force is kept 6×10-5 Pa and weld time is kept constant 17 cycles, respectively. The primary cause of weakening the weldment is identified as the excessive grain growing region of heat affected zone (HAZ) in case of 7114 grade interstitial free steel.     

Supercritical-gas extraction of Turkish coking coal

Treatment of Zonguldak coal with toluene at 360 °C gave yields of extract which increased from 19–32% as the pressure of the extraction was increased from 11.6 to 29 M Pa. These yields were similar to those previously obtained by supercritical-gas extraction of lignites but the composition of the extracts differed. The lignite extracts contained a much higher proportion of petroleum ether-soluble material and only half the proportion of material insoluble in both petroleum ether and benzene than the Zonguldak coal extract. Benzene, biphenyl, naphthalene, phenanthrene, pyrene, benzoanthracene and be-nzophenanthrene nuclei were identified in the coal extract. Comparison of the yields of substituted benzenes with those obtained by low-temperature carbonization suggests that the proportions of different substitution pattern is determined by the structure of the fuel. Less naphthalene nuclei were found than expected but relatively large yields of biphenyls were obtained which were attributed to their formation from toluene in the presence of phenols.     

Electrochemical synthesis and characterization of poly-2-aminothiazole

2-Aminothiazole (2AT) was electrochemically polymerized on a Pt electrode using cyclic voltammetry (CV) technique from 0.01 M monomer containing 0.3 M ammonium oxalate solution. The high quality poly-2-aminothiazole (pAT) films with a light-brownish color were obtained on the Pt surface. The electrochemical behavior of the pAT-coated Pt electrode (Pt/pAT) was investigated in monomer-free 0.3 M ammonium oxalate solution by CV technique. The chemical structure characterization was investigated by UV–vis spectroscopy (UV–vis) and Fourier transform infrared spectroscopy (FTIR) techniques. The surface morphology of the polymer film was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface morphology studies showed that, a homogeneous and compact film was formed on the Pt surface. Further, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) techniques were used to investigate the thermal properties of the polymer film. It was found that the thermal stability of the pAT film is relatively high. The solubility of the pAT was tested in common organic solvents as well as in acidic and basic solutions.