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Madani H.,K. N. Toosi University of Technology | Bagheri A.,K. N. Toosi University of Technology | Parhizkar T.,Building Research Institute, Egypt
Cement and Concrete Research | Year: 2012

This study reveals that the nanosilica hydrosols with higher specific surface areas had faster pozzolanic reactivity, especially at early ages; moreover, the results are indicative of the accelerating influence of nanosilicas and silica fume on the hydration of cement. Faster initial and final setting times observed for cement pastes containing nanosilicas are consequence of these mechanisms. However, less hydration degree of cement compared to the plain paste was observed at age of 7 days and after. This can be attributed to the entrapment of some of mix water in the aggregates of nanosilicas formed in cement paste environment, making less water available for the progress of cement hydration. The same mechanism is believed to be responsible for the reduction of flowability of cement pastes. © 2012 Elsevier Ltd. Source

Kaveh A.,Iran University of Science and Technology | Shakouri Mahmud Abadi A.,Building Research Institute, Egypt
Journal of Constructional Steel Research | Year: 2010

In this study, cost optimization of a composite floor system is performed utilizing the harmony search algorithm and an improved harmony search algorithm. These algorithms imitate the musical performance process that takes place when a musician searches for a better state of harmony, similar to the optimum design process which looks for the optimum solution. A composite floor system is designed by the LRFD-AISC method, using a unit consisting of a reinforced concrete slab and steel beams. The objective function is considered as the cost of the structure, which is minimized subjected to serviceability and strength requirements. Examples of composite floor systems are presented to illustrate the performance of the presented algorithms. © 2010 Elsevier Ltd. All rights reserved. Source

Kaveh A.,Iran University of Science and Technology | Shakouri Mahmud Abadi A.,Building Research Institute, Egypt
International Journal of Civil Engineering | Year: 2011

Cost optimization of the reinforced concrete cantilever soil retaining wall of a given height satisfying some structural and geotechnical design constraints is performed utilizing harmony search and improved harmony search algorithms. The objective function considered is the cost of the structure, and design is based on ACI 318-05. This function is minimized subjected to design constraints. A numerical example of the cost optimization of a reinforced concrete cantilever retaining wall is presented to illustrate the performance of the presented algorithms and the necessary sensitivity analysis is performed. Source

Karami M.,University of Tehran | Akhavan Bahabadi M.A.,University of Tehran | Delfani S.,Building Research Institute, Egypt | Ghozatloo A.,Research Institute of Petroleum Industry RIPI
Solar Energy Materials and Solar Cells | Year: 2014

Nanofluids are found to have good stability and useful optical and thermal properties as direct sunlight absorbers in solar collectors. The inherent hydrophobic nature of carbon nanotubes was overcome using a new dispersion procedure (treating carbon nanotubes with base media) to prepare nanofluids. To the authors' knowledge, this is the first application of aqueous suspension based on alkaline functionalized carbon nanotubes as an absorber fluid in a sunlight harvesting device. Dispersion stability and optical properties of the nanofluid were estimated. Spectral absorbance analysis confirms the relative stability of prepared nanofluids versus sediment time. The extinction coefficient of aqueous suspensions of functionalized carbon nanotubes shows remarkable improvement compared to the base fluid even at low particle loadings. We also demonstrate thermal conductivity improvements of up to 32% by adding only 150 ppm functionalized carbon nanotubes to water as the absorbing medium. Their promising optical and thermal properties, together with the appropriate stability of nanofluids, make them very interesting for increasing the overall efficiency of low-temperature direct absorption solar collectors. © 2013 Elsevier B.V. Source

Rashad A.M.,Building Research Institute, Egypt
Journal of Cleaner Production | Year: 2015

In this study, cement has been partially replaced with a Class F fly ash (FA) at a level of 70% to produce high-volume fly ash (HVFA) concrete (F70). F70 was modified by partially replacing FA with silica fume (SF) at levels of 10% and 20%, by weight. All HVFA concrete types were compared to the neat Portland cement (PC) concrete. After curing, the specimens were exposed to elevated temperatures ranging from 400 C to 1000 C with an interval of 200 C. Weight and compressive strength before and after firing have been thoroughly explored. The various decomposition phases formed were identified using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated higher relative strength of all HVFA concrete types. F70 exhibited the highest relative strength. The SF blends exhibited good fire performance up to 600 C, then severe degradation in the residual strength was observed at 800 and 1000 C. © 2014 Elsevier Ltd. All rights reserved. Source

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