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- 저자 : Elrahman, M.A. (검색결과 7 건)
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정상엽,Mohamed Abd Elrahman,Dietmar Stephan 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.4
Insulating concrete is a material designed to reduce heat conduction with pores/insulations, and these pores strongly affect the material characteristics. In general, the insulation effect is directly proportion to the pore volume, while the material strength decreases as the porosity increases. To overcome this contrary, anisotropic insulations with different spatial distributions are proposed and investigated in this study. A set of mortar specimens with different arrangements of coin-shaped insulations are produced to examine the anisotropic insulation effect on the material characteristics. In addition, different types of insulation materials and their effect on the materials are also investigated here. X-ray computed tomography images and probabilistic description methods are used to confirm the arrangement of the insulations. The thermal and mechanical responses for different directions are investigated using both experimental and numerical methods. From the results, it is demonstrated that the use of anisotropic insulations for a specific direction can enhance the insulation efficiently as well as minimizing the loss of compressive strength.
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Nondestructive tests for defections detection of nanoparticles in cement-based materials: A review
Kaloop, Mosbeh R.,Elrahman, Mohamed Abd,Hu, Jong Wan Techno-Press 2022 Advances in nano research Vol.12 No.1
To date, nondestructive tests (NDT) applications and advances in detecting the dispersion and defections of the nano concrete (NC) materials fields are very limited. The current paper provides a review of the dispersion efficiency of nanomaterials in cement-based materials and how NDT can be efficiently used in detecting and visualizing the defections and dispersions of NC. The review identifies the characteristics of different types of nanoparticles used in NC. Nanomaterials influences on concrete characteristics and their dispersion degree are presented and discussed. The main aim of this article is to present and compare the common NDT that can be used for detecting and visualizing the defections and dispersions of different kinds of nanomaterials utilized in NC. The different microscopy and X-ray methods are explicitly reviewed and compared. Based on the collected data, it can be concluded that the fully detecting and visualizing of NC defections and dispersions have not been fully discovered and that needs further investigations. So, the distinction of this paper lies in defining NDT that can be employed for detecting and/or visualizing NC defections and dispersions.
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Chung, S.Y.,Stephan, D.,Elrahman, M.A.,Han, T.S. Butterworth Scientific ; Elsevier Science Ltd 2016 Construction and Building Materials Vol.111 No.-
An insulating medium is a material designed for reducing heat conduction through entrained voids in the material. A specimen of insulating media contains numerous voids, the spatial distribution of which strongly affects the physical properties of the material, such as thermal conductivity and strength. The thermal performance of the material improves as the void ratio increases while the strength of the material decreases. Therefore, an appropriate method for examining the void distribution in the materials is necessary for better understanding of the material behavior. In this study, the effect of anisotropic voids on the material properties of insulating media is investigated. A 3D printer is utilized to generate a series of insulating media with different anisotropic voids. The void distributions of the specimens are characterized using probabilistic functions, and the thermal and mechanical properties of the specimens are also evaluated by means of real and numerical experiments. The results demonstrate an effect of anisotropic voids on the material properties that appropriately arranged anisotropic voids strongly affect the reduction of thermal conductivity for a specific direction, and that anisotropic voids can be utilized as a promising approach to develop high-performance insulating materials.
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Kaloop, Mosbeh R.,Bardhan, Abidhan,Hu, Jong Wan,Abd-Elrahman, Mohamed Techno-Press 2022 Advances in nano research Vol.13 No.5
This study investigates the efficiency of ensemble machine learning for predicting the lightweight-aggregate concrete (LWC) characteristics. A stacking ensemble (STEN) approach was proposed to estimate the dry density (DD) and 28 days compressive strength (Fc-28) of LWC using two meta-models called random forest regressor (RFR) and extra tree regressor (ETR), and two novel ensemble models called STEN-RFR and STEN-ETR, were constructed. Four standalone machine learning models including artificial neural network, gradient boosting regression, K neighbor regression, and support vector regression were used to compare the performance of the proposed models. For this purpose, a sum of 140 LWC mixtures with 21 influencing parameters for producing LWC with a density less than 1000 kg/m<sup>3</sup>, were used. Based on the experimental results with multiple performance criteria, it can be concluded that the proposed STEN-ETR model can be used to estimate the DD and Fc-28 of LWC. Moreover, the STEN-ETR approach was found to be a significant technique in prediction DD and Fc-28 of LWC with minimal prediction error. In the validation phase, the accuracy of the proposed STEN-ETR model in predicting DD and Fc-28 was found to be 96.79% and 81.50%, respectively. In addition, the significance of cement, water-cement ratio, silica fume, and aggregate with expanded glass variables is efficient in modeling DD and Fc-28 of LWC.
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Ismail Ali Mohamed Ali,Saad Ahmad Elsayed,Abd-Elrahman Noha Ahmed Fouad,Elfahl Ahmed Mohamed Abdelhalim 사단법인약침학회 2023 Journal of Acupuncture & Meridian Studies Vol.16 No.4
Background: Obesity-induced dyslipidemia is one of the main factors contributing to morbidity and mortality associated with metabolic syndrome, atherosclerosis, and coronary artery disease among patients with systemic lupus erythematosus (SLE). Objectives: This research aimed to assess the effect of adding laser acupuncture therapy (LAT) to a Pilates exercise program (PEP) and low-calorie diet protocol (LCDP) on blood lipids among 60 obese women with SLE. Methods: Study participants were women aged between 23 and 49 years, randomly assigned to one of two groups, A or B, each comprising 30 women. In addition to adherence to the LCDP, both groups were supervised five times weekly during 50-minute PEP sessions. Group A also received LAT three times weekly, with each session lasting 2 minutes on selected acupoints. After the 12-week intervention, plasma total cholesterol, high-density lipoprotein, triglycerides, and low-density lipoprotein were assessed. Results: Both groups demonstrated significant improvement in the aforementioned lipids after the 12-week intervention. A comparison between the post-intervention values of the lipids in the groups revealed a significant improvement favoring group A (the group that received LAT). Conclusion: Adding a 12-week LAT regimen to PEP and LCDP significantly improved lipid profiles among 60 obese women with SLE.
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Pawel Sikora,Levent Afsar,Sundar Rathnarajan,Morteza Nikravan,정상엽,Dietmar Stephan,Mohamed Abd Elrahman 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.6
The use of alternative and locally available materials is encouraged in the construction industry to improve its sustainability. Desert regions with shortages in freshwater and river sand as fine aggregates in concrete have to search for alternative materials such as seawater, dune sand, and waste glass powder to produce lightweight concretes. The potential negative effects of adding these alternative materials can be reduced by adding nanosilica to the cementitious system at very low quantities. This study evaluates the feasibility of using these alternative materials and nanosilica (NS) in producing lightweight aggregate concretes (LWACs). A systematic study was carried out to understand the synergistic effect of nanosilica and seawater in improving the hydration characteristics of the developed cementitious systems. Also, the effect of these alternative materials on the fresh properties of the cementitious system was assessed by slump flow tests. The evolution of compressive strength at early ages was investigated after 2, 7, and 28 days of moist curing and an improvement in the strength development in concretes with seawater was observed. Furthermore, the integrity of the developed LWACs was analyzed using oven-dry density, thermal conductivity, water porosity and shrinkage measurements. Moreover, the capillary porosity and sorptivity measurements revealed the denser microstructure in the nano-modified seawater lightweight concretes. In the end, the life-cycle assessment study calculated the benefit of alternative materials in terms of carbon footprint and water consumption. As an outcome, a sustainable solution for producing LWACs containing seawater, dune sand or glass powder was proposed.
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