Investigation on the Mechanical, Microstructural, and Electrical Properties of Graphene Oxide-Cement Composite

Nanotechnology refers to the use of the materials or particles ranging from a few nanometers (nm) to 100 nanometers (nm) in a wide range of applications. Use of nanomaterials in cement composite to enhance the mechanical properties, fracture toughness and other functionalities has been studied for decades. In this regard, one of the carbon-based nanomaterials, Graphene Oxide (GO), has received attentions from researchers for its superior mechanical properties (e.g. tensile strength, yield strength, and Young\u27s modulus). Although GO is not lucrative in increasing electrical conductivity (EC) of cement paste compared to that of graphene- another derivative of GO, reduced graphene oxide (rGO), might be a solution to increase EC. Another derivative of GO is the solution to the problem. In this research, the compressive strength and flexural strength of GO-cement composite (GOCC) and rGO-cement composite (rGOCC) have been investigated with 0.01% and 0.05% GO and rGO content. GOCC-0.05% showed 27% increase in compressive strength compared to the control cement paste after 28 days (d) of hydration. GOCC-0.01% showed only 3.4% increase in compressive strength compared to the control. rGOCC-0.05% showed 21% increase in compressive strength and 15.5% increase in Modulus of Rupture (MOR) compared to the control cement paste after 28 d of hydration. On the other hand, rGOCC-0.01% showed 7% increase in compressive strength and 0.35% increase in MOR after 28 d. GOCC-0.05% showed increasing trends in compressive strength after 28 d indicating continuation of hydration. Similarly, rGOCC-0.05% also showed increasing trends in compressive and flexural strength after 28 d, possibly due to the reason described earlier. Microstructural investigation on GOCC-0.05% and GOCC-0.01% by X-ray Diffraction (XRD) illustrated that the crystallite sizes of tobermorite-Å and jennite, which are mineralogical counterpart of disordered Calcium-Silicate-Hydrate (C-S-H), increases from 3 d to 28 d, representing the crystallite growth due to continued hydration. However, the crystallite size of GOCC-0.05% was smaller than that of GOCC-0.01% at both 3 d and 28 d, indicating finer nucleated grains. According to Hall-Petch equation, mechanical strength increases with decreasing particle size. Finer particles or grains can increase the strength in cement composites in several other ways: (1) GO acted as heterogeneous nucleation sites because of reactive functional groups. Activation energy was decreased by these defects in the cement paste, and consequently, numerous nuclei of C-S-H. with high surface area were formed, (2) because of finer grains, cracks are forced to move along a tortuous path, which makes the structure difficult to fail, and strength increased consequently (3) Finer grains of GOCC-0.05% created compacted hydration products decreasing porosity which can indirectly increase the strength. The above reasons, separately or in conjunction, might increase the strength of GOCC-0.05% and proved that GO is responsible for increasing heterogeneous nucleation sites during cement hydration. Early age hydration (EAH) characteristics were investigated for rGOCC specimens with 0.1% and 0.5% rGO content. Scanning Electron Microscope (SEM), Energy Dispersive X-ray analysis (EDX), and X-ray Diffraction (XRD) were employed to study the EAH characteristics. SEM/EDX, and XRD analysis were performed after 15 min, 1 h, 3 h and 24 h of hydration. (EAH) study on rGOCC-0.1% showed that at 15 min hydration, numerous precipitates of, possibly, C-S-H formed along the grain boundary (GB) of unhydrated cement grains. This served as visual confirmation of Thomas and Scherer\u27s Boundary Nucleation and Growth (BNG) model that hydration of cement grains was initiated by the short burst of nucleation of C-S-H embryos along GB. EDX on rGOCC-0.1% and rGOCC-0.5% showed that Ca/Si ratio in C-S-H was ~2.0. This finding indicated that C-S-H structure in this study was concurrent with that of impure jennite. XRD analysis also evidently showed that jennite was present, possibly possessing a short range ordered (SRO) structure, referring to local crystalline structure in a very short area. After consulting Chen\u27s work, it would be appropriate to say that C-S-H found in this study resembled more as C-S-H (II), which is disordered jennite. It was also observed that as expected with cement with nanomaterials, with continuing hydration, pore spaces were filled with hydration products such as C-S-H, ettringite, CH, sulfoaluminates etc,. Lastly, Electrical resistivity (ER) testing on 9 sets of rGOCC specimens was conducted. The specimen includes 0.5%, 1%, 5% rGO content, and the control conditioned in both oven dry (OD) and saturated surface dry (SSD). ER increased with the increase of rGO content from 0.5% and 1% compared to that of the control. However, the ER of rGOCC-5% was significantly decreased, showing 93% reduction compared to the control, which can be interpreted as a threshold value for sensing applications to be explored. As expected, large reduction of ER value occurred on the specimens with the SSD condition. This reduction can be attributed to the ionic conduction though the pore solution of the composites. As the rGO content increased, so did the potential nucleation sites for hydration (as can be seen in SEM images), which might block the number of contact points among the rGO, resulting in low conduction and high resistivity. However, as rGO content increased to 5%, the contact areas/points increased to a degree that could trump the nucleation seeding sites, resulting in decreased ER. The ER measured with the rGOCC specimens was comparable to that of cement composites incorporating carbon fibers (CF), and steel fibers, but higher content of rGO are required to have a similar ER range of those fiber cement composites. This might be due to smaller sizes of rGO sheets and lower aspect ratio compared to other nanofibers causing drastic reduction of electron tunneling mechanism compared to other fibers

Psychometric validation of the Bangla fear of COVID-19 Scale: confirmatory factor analysis and Rasch analysis

The recently developed Fear of COVID-19 Scale (FCV-19S) is a seven-item uni-dimensional scale that assesses the severity of fears of COVID-19. Given the rapid increase of COVID-19 cases in Bangladesh, we aimed to translate and validate the FCV-19S in Bangla. The forward-backward translation method was used to translate the English version of the questionnaire into Bangla. The reliability and validity properties of the Bangla FCV-19S were rigorously psychometrically evaluated (utilizing both confirmatory factor analysis and Rasch analysis) in relation to socio-demographic variables, national lockdown variables, and response to the Bangla Health Patient Questionnaire. The sample comprised 8550 Bangladeshi participants. The Cronbach α value for the Bangla FCV-19S was 0.871 indicating very good internal reliability. The results of the confirmatory factor analysis showed that the uni-dimensional factor structure of the FCV-19S fitted well with the data. The FCV-19S was significantly correlated with the nine-item Bangla Patient Health Questionnaire (PHQ-90) (r = 0.406,

Error-Resilient Techniques For Digital Image Transmission Over Wireless Channels

This dissertation studies issues related to image communication and proposes several improved joint source-channel coding methods for efficient image data transmission over noisy channel. However, the applicability of these techniques vary to certain extent and hence, these are encapsulated in the form of three independent chapters

ARTICLE IN PRESS YDSPR:775 JID:YDSPR AID:775 /FLA [m3SC+; v 1.78; Prn:12/10/2007; 11:15] P.1 (1-10) Digital Signal Processing •• • (••••) •••–•••

www.elsevier.com/locate/dsp Error-resilient transmission of quality-scalable images over wireless channel

Error-resilient transmission of resolution-scalable image and video over wireless channels

A new robust transmission strategy for scalable image and video is proposed. To protect the coded bit-stream according to the channel conditions, the proposed scheme exploits the progressive by resolution' structure of the scalable code-stream and takes into account the unequal importance as well as the effect of channel errors at different resolution levels towards reconstructing the source. A salient feature of the algorithm is its compatibility for multimedia applications requiring multi-resolution transmission to single or multiple clients. Results show that the proposed algorithm enables considerable gains in terms of subjective and objective image qualities over existing approaches.(1

Recycling of Municipal Solid Waste Incineration (MSWI) Ash as Aggregate Replacement in Concrete

In the U.S., about 250 million tons of municipal solid waste (MSW) is being generated annually, but only 34% of it is recycled or composted. The rest is combusted and / or disposed of in landfills. Combusting MSW is one of promising options to convert waste into energy and also it significantly reduces the volume of waste by nearly 90%. As byproduct, municipal solid waste incineration (MSWI) bottom and fly ashes are produced. Unlike European and Asian countries, the beneficial use of MSWI ash has not received an attention in the U.S. The use of MSWI ashes in civil construction sector can be one of promising options. The objective of this paper is to evaluate the feasibility of MSWI bottom ash (BA) as partial replacement of fine aggregate in concrete. Laboratory experimental studies were conducted to evaluate physical, mechanical, and durability performance of concrete containing the BA. The mechanical performance was investigated by measuring compressive strength at 28 days of age and absorption capacity. Analysis on measured data has shown that the addition of MSWI ash into concrete does not increase strength and durability properties but has comparable results with control samples

Recycling Of Municipal Solid Waste Incineration (Mswi) Ash As Aggregate Replacement In Concrete

In the U.S., about 250 million tons of municipal solid waste (MSW) is being generated annually, but only 34% of it is recycled or composted. The rest is combusted and / or disposed of in landfills. Combusting MSW is one of promising options to convert waste into energy and also it significantly reduces the volume of waste by nearly 90%. As byproduct, municipal solid waste incineration (MSWI) bottom and fly ashes are produced. Unlike European and Asian countries, the beneficial use of MSWI ash has not received an attention in the U.S. The use of MSWI ashes in civil construction sector can be one of promising options. The objective of this paper is to evaluate the feasibility of MSWI bottom ash (BA) as partial replacement of fine aggregate in concrete. Laboratory experimental studies were conducted to evaluate physical, mechanical, and durability performance of concrete containing the BA. The mechanical performance was investigated by measuring compressive strength at 28 days of age and absorption capacity. Analysis on measured data has shown that the addition of MSWI ash into concrete does not increase strength and durability properties but has comparable results with control samples

Image Registration for Video Coding and Medical Image Analysis

This dissertation explores innovative applications of diverse image registration techniques in the context of video coding and medical image analysis. Motion-compensated prediction is the key to video coding. Sophisticated motion-compensation technologies need to be integrated into future codecs to ensure its continual improvement. Previous works have explored alternatives to classical motion models that can only estimate translational movements in videos. But the cumulative rate-distortion performance has not been significant enough to see such approaches adopted in mainstream standards. In this thesis, an advanced motion compensation technique is presented that effectively predicts non-translational motion. A novel elastic motion model is derived for this purpose based on elastic image registration with 2-D cosine basis functions. To achieve superior performance, the proposed scheme takes advantage of larger macro-blocks with multi-level partitioning. Next, a novel block-partitioning scheme is introduced that attempts to slice the blocks based on motion-field discontinuity or geometry of edges rather than traditional predefined squares or rectangles. Both geometry-adaptive partitioning and higher-order elastic motion models are advanced coding techniques and can be considered as good candidates for future coders. However, it is vital that they are additive in performance, non-interfering and maintain justifiable complexity. Therefore, the elastic motion compensation platform has been extended by incorporating geometry-adaptive partitioning to attain even better compression.Finally, a new form of image registration, also known as 3D/2D registration is studied for analyzing relative movements in human joints from fluoroscopy images. This technology has many promising applications e.g. image-guided surgery, interventions and radiotherapy etc. However, precise measurement of out-of-plane movements remains a challenge for this to become a reality. In this study, a fast and accurate 3D/2D registration technique is put forward for kinematic analysis. The new algorithm takes advantage of a new multi-modal similarity measure called ‘sum of conditional variances’, a coarse-to-fine Laplacian of Gaussian filtering approach for robust gradient descent optimization and a novel technique for the analytic calculation of the required gradients for out-of-plane rotations. The accuracy and speed of the proposed method has been verified using clinical ‘gold-standard’ Roentgen Stereo Analysis (RSA)

Real-Time Optimized Error Protection Assignment for Scalable Image and Video over Wireless Channels

A new error protection assignment scheme with applications to real-time wireless multimedia transmission is presented. The proposed scheme exploits the structure of scalable sources to ensure optimal assignment. This novel approach recasts the nonlinear optimization problem into a linear one, and then further remodels it into a discrete programming problem, thereby reducing the computational complexity dramatically. Furthermore, the proposed algorithm does not impose any requirement on the convexity of the source; i.e., it can equally be applied on a convex or nonconvex source. Results show that the described method facilitates a significant complexity reduction with respect to existing schemes, while exhibiting almost equivalent performance