Optimization and evaluation of ultra high-performance concrete

P. N. Ojha,P. N. Ojha,Abhishek Singh,Brijesh Singh,V. V. Arora 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.1

Ultra-High Performance Concrete (UHPC) has been defined as a cementitious based compo-site material with compressive strength above 150 MPa and enhanced durability via its discontinuous pore structure. The microstructure of UHPC is denser and more homogeneous in comparison to conventional concrete. UHPC has several advantages over conventional concrete but the use of it is limited due to the high cost and limited design codes. Methodology for production and development of UHPC needs to be established. The paper covers both optimization and evaluation of Ultra-High-Performance Concrete along with highlighting the importance of packing density, mixing procedure and curing regimes containing a high volume of mineral admixture and ultrafine materials. Cementitious content of all the mixes in the study was kept in the range of 1000 kg/m3 and water to binder ratio was kept as 0.17. This study focuses on the methodology to be adopted for optimizing the packing density of UHPC, the challenges associated with it and their influence on compressive strength.

Synthesis and characterization of reduced graphene oxide decorated with CeO₂-doped MnO₂ nanorods for supercapacitor applications

Ojha, Gunendra Prasad,Pant, Bishweshwar,Park, Soo-Jin,Park, Mira,Kim, Hak-Yong Elsevier 2017 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.494 No.-

<P><B>Abstract</B></P> <P>A novel and efficient CeO<SUB>2</SUB>-doped MnO<SUB>2</SUB> nanorods decorated reduced graphene oxide (CeO<SUB>2</SUB>-MnO<SUB>2</SUB>/RGO) nanocomposite was successfully synthesized via hydrothermal method. The growth of the CeO<SUB>2</SUB> doped MnO<SUB>2</SUB> nanorods over GO sheets and reduction of GO were simultaneously carried out under hydrothermal treatment. The morphology and structure of as-synthesized nanocomposite were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, which revealed the formation of CeO<SUB>2</SUB>-MnO<SUB>2</SUB> decorated RGO nanocomposites. The electrochemical performance of as-prepared CeO<SUB>2</SUB>-MnO<SUB>2</SUB>/RGO nanocomposites as an active electrode material for supercapacitor was evaluated by cyclic voltammetry, charge-discharge, and electrochemical impedance spectroscopy (EIS) methods in 2M alkaline medium. The obtained results revealed that as-synthesized CeO<SUB>2</SUB>-MnO<SUB>2</SUB>/RGO nanocomposite exhibited higher specific capacitance (648F/g) as compared to other formulations (MnO<SUB>2</SUB>/RGO nanocomposites: 315.13 F/g and MnO<SUB>2</SUB> nanorods: 228.5 F/g) at the scan rate of 5mV/s. After 1000 cycles, it retained ∼90.4%, exhibiting a good stability. The high surface area, enhanced electrical conductivity, and good stability possess by the nanocomposite make this material a promising candidate to be applied as a supercapacitor electrode.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Evaluation of Polymer Modified Mortar and Bonding Agent for Structural Repair

Ojha P N,Kaura Puneet,Singh Brijesh,Daniel Y N,Kumar Nitesh 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.2

Polymer modified mortar is found to be suitable for structural repair and strengthening of damage structural elements. Conventional mortar is not preferred in repair of concrete since it has inferior mechanical property and durability performance. Polymer based mortar is an alternative to conventional mortar with enhanced mechanical properties. However, there are limited specifications and guidelines available for specifying PMM mixes for structural repair work. The research work aims to evaluate the mechanical performance of polymer based mortar with varying concentration of styrene butadiene rubber latex at laboratory scale. Another aspect in repair of corrosion damage structures is the bond between the substrate concrete and repair mortar. In order to study the effectiveness of bonding agents, the performance evaluation of bonding agents has been evaluated using slant shear test and pull-off test as per ASTM C 882 and EN 1542 respectively. Findings of study indicates that at 8-10 percent concentration of dry polymer solid by cement mass in polymer based mortar is the optimum dosage. Styrene-butadiene rubber based polymer mortar showed improvement in flow in comparison to normal mortar however, mixes with crushed sand shows decrease in flow which is due to presence of more fines. Slant shear and pull-off test method shows epoxy bonding agent give better bond strength as compared to SBR latex.

Amine-assisted synthesis of FeWO₄ nanorodg-C₃N₄ for enhanced visible light-driven Z-scheme photocatalysis

Ojha, Devi Prashad,Karki, Hem Prakash,Song, Jun Hee,Kim, Han Joo Elsevier 2019 Composites Part B, Engineering Vol.160 No.-

<P><B>Abstract</B></P> <P>Highly crystalline FeWO<SUB>4</SUB> nanorods (FWO NRs) were prepared using an amine in a hydrothermal reaction. A photocatalyst active to visible light was designed by preparing 5FWO/g-CN heterostructures via in-situ hydrothermal methods. Fabricated heterostructures were analyzed using X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), BET measurements, transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), and Fourier transform spectroscopy (FTIR). The photocatalytic activity toward the degradation of salicylic acid (SA) was investigated under visible light irradiation. The active species trapping experiments showed that the holes, as well as the electrons, exhibited an obvious influence on the photocatalytic degradation process. Examinations of the mechanism showed that the enhanced photocatalytic activity was mainly ascribed to reduced recombination rate and band gap broadening in a Z-scheme mechanism, which enhance the efficient transfer and the oxidation potential of the holes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Wolframite-type FeWO<SUB>4</SUB> nanorod was synthesized hydrothermally using triethanolamine. </LI> <LI> Photodegradation of salicylic acid was enhanced by FeWO<SUB>4</SUB>/g-C<SUB>3</SUB>N<SUB>4</SUB> heterostructure. </LI> <LI> Predominant active species were identified by using scavengers. </LI> <LI> Z-scheme photodegradation mechanism was suggested. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Decoration of g-C₃N₄ with hydrothermally synthesized FeWO₄ nanorods as the high-performance supercapacitors

Ojha, Devi Prashad,Karki, Hem Prakash,Song, Jun hee,Kim, Han Joo Elsevier 2018 Chemical physics letters Vol.712 No.-

<P><B>Abstract</B></P> <P>Highly crystalline FeWO<SUB>4</SUB> nanorods (FWO NRs) prepared by a hydrothermal reaction is combined with g-C<SUB>3</SUB>N<SUB>4</SUB> (gCN) nanosheet as an electrode material for the supercapacitor. Fabricated nanocomposites were analysed using X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), and Raman Spectroscopy. Pseudocapacitive performance of the FWO/gCN nanocomposite was evaluated by cyclic voltammetry (CV), electrochemical impedance and galvanometric experiments in an alkaline medium. Thus FWO/gCN nanocomposite exhibited a high specific capacitance of 357 F g<SUP>−1</SUP> at 5 mV s<SUP>−1</SUP> and demonstrated a superior long-term cyclic stability, with the specific capacitance retention of about 80% after 1000 cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The g-C<SUB>3</SUB>N<SUB>4</SUB> decorated FeWO<SUB>4</SUB> nanorod was synthesized by in-situ hydrothermal method. </LI> <LI> High surface area and low aggregation enabled fast diffusion of ion and electrons. </LI> <LI> The electrical conductivity of low cost, abundant FeWO<SUB>4</SUB> is improved with g-C<SUB>3</SUB>N<SUB>4</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Design of ternary hybrid ATO/g-C₃N₄/TiO₂ nanocomposite for visible-light-driven photocatalysis

Ojha, Devi Prashad,Karki, Hem Prakash,Kim, Han Joo THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 Journal of Industrial and Engineering Chemistry Vol.61 No.-

<P><B>Abstract</B></P> <P>Antimony-doped tin oxide (ATO) nanoparticles with an average size of ∼8nm were prepared by co-precipitation and subsequent heat-treatment. A series of ATO/g-CN/TiO<SUB>2</SUB> composites with various ATO contents were successfully prepared by sol–gel method. The composites were characterized using N<SUB>2</SUB> adsorption/desorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The results indicated that the highest photocatalytic performance is obtained with the incorporation of ATO and g-CN nanoparticles with TiO<SUB>2</SUB>. BET surface area, PL spectra, and CV measurements were presented to further study the mechanism of the photoactivity. The superior performance of the ATO/g-CN/TiO<SUB>2</SUB> nanocomposite photocatalyst may be attributed to the high surface area charge-carrier transport medium, a higher carrier transfer rate and lower recombination rate.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Three-dimensionally assembled manganese oxide ultrathin nanowires: Prospective electrode material for asymmetric supercapacitors

Ojha, Gunendra Prasad,Pant, Bishweshwar,Muthurasu, Alagan,Chae, Su-Hyeong,Park, Soo-Jin,Kim, Taewoo,Kim, Hak-Yong Pergamon Press 2019 Energy Vol.188 No.-

<P><B>Abstract</B></P> <P>In this report, we have forwarded a noble synthesis route for the fabrication of self-supported three-dimensional networks of manganese oxide ultrathin nanowires (3D MnO<SUB>2</SUB>-UTNWs) via a simple and cost-effective process for the first time. The formation of ultrathin nanowires (5 nm in diameter with several micrometer lengths) and their 3D assembly was achieved via a slow-reduction of potassium permanganate by oleylamine under constant stirring at 80 °C for 50 h. The resultant material was characterized using FE-SEM, TEM, XRD, FTIR, BET, XPS and Raman techniques. As-fabricated 3D MnO<SUB>2</SUB>-UTNWs network was used as the electrode material for supercapacitor. The electrochemical studies of the material revealed an excellent electrochemical performance with a high specific capacitance of 544.7 Fg<SUP>-1</SUP> at 1 Ag<SUP>-1</SUP> and excellent life span of 86.3% after 5000 cycles. An asymmetric supercapacitor was assembled using 3D-MnO<SUB>2</SUB> UTNWs and nitrogen-doped graphene hydrogels (NGHs) as the positive and negative electrodes; respectively. The 3D-MnO<SUB>2</SUB> UTNWs//NGHs device delivered an admirable specific capacitance of 56.5 Fg<SUP>-1</SUP> at 1 Ag<SUP>-1</SUP>, energy density of 21 Whkg<SUP>−1</SUP> at 840 Wkg<SUP>-1</SUP>, and extraordinary cyclic stability of 81.3% after 5000 cycles. This method provides a novel green synthetic route to prepare 3D MnO<SUB>2</SUB>-UTNWs without utilizing non-ambient reaction parameters.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3D-networks of MnO<SUB>2</SUB> ultrathin nanowires were prepared. </LI> <LI> The mechanism of 3D-network formation is discussed. </LI> <LI> It showed high specific capacitance of 544.7 F/g at 1 A/g. </LI> <LI> The nanowires were used as electrode material for asymmetric supercapacitor. </LI> <LI> The synthesis process is simple, effective, and can be scaled up. </LI> </UL> </P>

Photo-Fenton degradation of organic pollutants using a zinc oxide decorated iron oxide/reduced graphene oxide nanocomposite

Ojha, Devi Prashad,Joshi, Mahesh Kumar,Kim, Han Joo Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.1

<P><B>Abstract</B></P> <P>Herein, we report a magnetically-separable tertiary composite, zinc oxide-decorated iron oxide deposited reduced graphene oxide (ZnO-Fe<SUB>3</SUB>O<SUB>4</SUB>/rGO), as a heterogeneous catalyst for photo-Fenton degradation of organic pollutants in aqueous media under ambient conditions. In this study, zinc oxide nanoparticles were hydrothermally deposited on the surface of Fe<SUB>3</SUB>O<SUB>4</SUB>/GO composite that was synthesized by a solvothermal process. The physicochemical properties of the as–synthesized composite were explored using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) studies. The as-prepared catalyst showed superior stability and, due to the presence of the magnetic Fe<SUB>3</SUB>O<SUB>4</SUB> nanospheres, could be conveniently separated from the reaction system with an external magnet for reuse. The as-synthesized, ZnO-Fe<SUB>3</SUB>O<SUB>4</SUB>/rGO composite exhibited superior catalytic activity for the degradation of azo-dye compared to pristine ZnO, ZnO/Fe<SUB>3</SUB>O<SUB>4</SUB>, Fe<SUB>3</SUB>O<SUB>4</SUB>, and Fe<SUB>3</SUB>O<SUB>4</SUB>/GO. These results revealed the synergistic effects between the different components of the catalyst and confirmed the rapid redox reaction between Fe<SUP>2+</SUP> and Fe<SUP>3+</SUP>. It was also observed that this catalytic behavior could be reproduced in consecutive experiments without a considerable decrease in efficiency. All of these merits indicate that the composite catalyst is a promising candidate for the degradation of organic compounds under visible light in environmental remediation applications.</P>

Relevance of Multivariate Analysis in Management Research

Ojha, Sateesh Kumar Korea Data Strategy Society 2016 Journal of information technology applications & m Vol.23 No.3

Often we receive misled conclusion in the research if properly variables are not analyzed. In different functional issues of management it is very essential that all the latent and observed variable are properly understood so management decisions will be relevant and effective. The objective of this paper is to investigate the use of different multivariate tools for analyzing in the management research : applied or basic. The sources of data is primary as well as secondary. The primary includes the observation of different research articles of the proceedings of different conferences. And the secondary includes different publications related to multivariate analysis. The study has revealed the reasons of not using such tools of research. The preliminary finding reveals that most of the researches do not use such analytical tools in a comprehensive manner. Carelessness in design while fixing the design aspect is the main reasons of not using appropriate design.

Carrier Based Common Mode Voltage Reduction Techniques in Neutral Point Clamped Inverter Based AC-DC-AC Drive System

Ojha, Amit,Chaturvedi, Pradyumn,Mittal, Arvind,Jain, Shailendra The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.1

Common mode voltage (CMV) generation is a major problem in switching power converter fed induction motor drive systems. CMV is the zero sequence voltage generated due to the switching action of power converters. Even a small magnitude of CMV with a high rate of change may circulate large bearing currents which may damage a machine's bearings and shorten its life. There are several methods of controlling CMV. This paper presents 3-level sinusoidal pulse width modulation based techniques to control the magnitude and rate of change of CMV in multilevel AC-DC-AC drive systems. Simulation and experimental investigations have been presented to validate the performance of proposed technique to control CMV in 3-level neutral point clamped inverter based AC-DC-AC system.