Experimental study of the influence of friction at the supports on longitudinal shear resistance of composite slabs

Abstract The aim of this work is to evaluate the behavior and strength of composite slabs considering the influence of the friction at the sheeting-concrete interface in the region of the support. Results from tests conducted in the Structural Engineering Department of Federal University of Minas Gerais (UFMG) were used. A Steel Deck 60 system was considered, which consists of a trapezoidal profile with “V” shaped embossments. Deflections, end slips and strains of the steel decks were measured, allowing for the analysis of the behavior of the composite slab system and for the determination of its failure mode. The influence of friction of the region of support in the longitudinal shear resistance was evaluated through the partial shear connection method, which also allowed for establishing criteria and determination of analytical expressions for calculating the ultimate load. Comparative analyses reveal that the influence of the friction of the region of support in the shear-bond resistance is more significant in composite slabs with short shear spans. Design expressions which incorporate friction will also be presented. Their application have demonstrated the efficiency of the method for evaluating the longitudinal shear resistance

Experimental study of the influence of friction at the supports on longitudinal shear resistance of composite slabs

<div><p>Abstract The aim of this work is to evaluate the behavior and strength of composite slabs considering the influence of the friction at the sheeting-concrete interface in the region of the support. Results from tests conducted in the Structural Engineering Department of Federal University of Minas Gerais (UFMG) were used. A Steel Deck 60 system was considered, which consists of a trapezoidal profile with “V” shaped embossments. Deflections, end slips and strains of the steel decks were measured, allowing for the analysis of the behavior of the composite slab system and for the determination of its failure mode. The influence of friction of the region of support in the longitudinal shear resistance was evaluated through the partial shear connection method, which also allowed for establishing criteria and determination of analytical expressions for calculating the ultimate load. Comparative analyses reveal that the influence of the friction of the region of support in the shear-bond resistance is more significant in composite slabs with short shear spans. Design expressions which incorporate friction will also be presented. Their application have demonstrated the efficiency of the method for evaluating the longitudinal shear resistance.</p></div

A highly adhesive PIL/IL gel polymer electrolyte for use in flexible solid state supercapacitors

In this work we have demonstrated how to prepare a novel gel polymer electrolyte (GPE) with remarkable adhesive characteristics by combining a synthesized poly(ionic liquid) consisting of poly(1-vinyl-3-propylimidazolium bis(fluorosulfonyl)imide) (poly(VPIFSI)) and a commercial ionic liquid: 1-ethyl-3-methyl imidazolium bis(fluorosulfonyl)imide (EMIFSI). For this purpose several PIL/IL-GPEs systems (considering the amount of IL) were subjected to electrochemical characterization. The influence of the PIL/IL-GPE (50 wt% of IL) on the properties of a flexible solid state supercapacitor was evaluated using electrochemical impedance spectroscopy, cyclic voltammetry and the galvanostatic charge/discharge technique that allows synchronous measurements of the cell voltage and the potential of the positive and negative electrodes. The influence of the ions on the formation of the electric double layer in the device during cycling employing different conditions and folding angles is discussed. The properties of the adhesive PIL/IL-GPE, such as high conductivity, good interaction between the PIL matrix and the IL liquid phase that prevents any leakage (thereby contributing to greater safety) together with the good adherability and wettability of the gel electrolyte on the electrode surface have produced a device with an improved rate capability and cyclability that undergoes hardly any changes in C,, E, and P of the cell when folded.The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil, for the financial support received (Universal 2014, Process No. 458487/2014-7). The authors are also grateful to the Instituto Nacional de Ciência e Tecnologia em Nanomateriais de Carbono – INCT Nanocarbono and to profs. Dorila Piló Veloso and José Dias de Souza Filho (Department of Chemistry/UFMG/Brazil) for performing the NMR analysis. S.A.Alexandre also acknowledges the scholarship received from CNPq. R.L. Lavall is recipient of fellowship from CNPq (grant number 313304/2017-3). R. Santamaría would like to thank financial support from Ministerio de Economía, Industria y Competitividad (project MAT2016-77114-R)

Insights on the Behavior of Imidazolium Ionic Liquids as Electrolytes in Carbon-Based Supercapacitors: An Applied Electrochemical Approach

This study aims to increase the knowledge on the interactions that occur at the electrode/electrolyte interface in carbon-based electric double-layer capacitors (EDLCs) when solvent-free ionic liquids are used as electrolytes. Many previous studies found in the literature are conducted using theoretical approaches, and they are unable to model all the variables and the complexity of an actual device with a complex carbon surface and an ionic liquid (IL). Here, the compatibility between imidazolium ionic liquids and different carbon materials-an activated carbon (AC), a mesoporous carbon (MES), multiwalled carbon nanotubes (MWCNTs), and reduced graphene oxide (RGO)-is empirically investigated applying synchronous chronopotentiometric tests to various symmetrical EDLCs. The study of the simultaneous evolution of the cell and electrode potentials of the various carbon/ILs cells, monitoring the evolution of specific capacitances and electrical resistances for each independent electrode, allows inferring about the ion-electrode compatibility, the limiting factors for charge accumulation, and its impacts on the performance of the global cell. The results indicate that the sp2 structures of MWCNTs and RGO favor interactions with the EMI+ cation on the negative electrode. In the positive electrodes, MES and AC favor interactions with the BF4- and TFSI- anions, respectively, yielding a higher specific capacitance and lower resistance.The authors thank the Conselho Nacional de Desenvolvimento Cienti ico e Tecnoló gico (CNPq)−Brazil for the financial support (PVE 2014, process number 400714/2014- 0), the Spanish Government and European Union (AEI/ FEDER, EU; project MAT2016-77114-R), N.Q.’s predoctoral contract (BES2017-082038), and Principado de Asturias (FEDER: IDI/2018/000121). The work was partially supported by the Brazilian Institute of Science and Technology (INCT) in Carbon Nanomaterials. P.F.R.O. acknowledges the Fundaca̧ o de Amparo a ̃ ̀Pesquisa do Estado de Minas Gerais (FAPEMIG)−Brazil (DOF no. 2720262/2018). P.F.R.O. and G. A.d.S. also acknowledge the scholarships received from CNPq. R.L.L. is a recipient of a fellowship from CNPq (grant number 313304/2017-3). P.F.R.O, G.G.S., and R.L.L. are members of the Rede Mineira de Quimica (RQ-MG) ́ −Brazil

Nanocompósitos de poliuretana termoplástica e nanotubos de carbono de paredes múltiplas para dissipação eletrostática Thermoplastic polyurethane and multi-walled carbon nanotubes nanocomposites for electrostatic dissipation

<abstract language="eng">Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 &#956;m length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT

Thermodynamic Study of Methylene Blue Adsorption on Carbon Nanotubes Using Isothermal Titration Calorimetry: A Simple and Rigorous Approach

In this article, a thermodynamic study of the methylene blue (MB) adsorption on carbon nanotubes (CNT), a known model system, was carried out by using a simple and rigorous experimental approach based on adsorption and isothermal titration calorimetry (ITC) experiments. Considering the thermodynamics of the process, the classical approach using the van’t Hoff approximation provided endothermic values for Δ_ads<i>H</i>⁰ while the ITC measurements revealed that the adsorption of MB on both unmodified and acid-modified CNTs is an exothermic process. The thermodynamic parameters for the systems were obtained using the infinite dilution regime and ITC data: Δ_ads<i>H</i>⁰ = −9.13 ± 0.02 kJ mol^–1, Δ_ads<i>G</i>⁰ = −21.18 ± 0.61 kJ mol^–1, and Δ_ads<i>S</i>⁰ = 40.42 ± 0.61 J K^–1 mol^–1 for u-CNT and Δ_ads<i>H</i>⁰ = −11.49 ± 0.34 kJ mol^–1, Δ_ads<i>G</i>⁰ = −27.88 ± 0.18 kJ mol^–1, and Δ_ads<i>S</i>⁰ = 54.97 ± 0.38 J K^–1 mol^–1 for f-CNT. The process is both enthalpically and entropically driven, having a more negative Δ_ads<i>G</i>⁰ for the system based on a modified nanotube. With this work, we expect to increase the interest of researchers in the study of other solid–liquid adsorption systems using calorimetric techniques and also contribute to a more accurate characterization of the thermodynamic properties without the use of an excessive number of approximations