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2. PHD Thesis / Tesis PHD
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Title:	The strength and micro structures of sustainable high strength high-volume fly ash concrete with nano materials exposed to high temperature
Authors:	Rahel Khalid Ibrahim (P49143)
Supervisor:	Roszilah Hamid, Assoc. Professor Dr.
Keywords:	Fly ash Nano materials
Issue Date:	18-Nov-2013
Description:	High-volume fly ash has been widely used in concrete to reduce the cost and environmental impact of producing cements. However, using high volumes of fly ash decreases the early and later strength for concrete significantly. On the other hand, concrete losses a big amount of its strength among exposure to fire. In this research, high strength concretes containing nanomaterials; sustainable high strength concretes containing high volumes of fly ash; and concretes having higher resistance to fire were produced by using nanosilica. The research was conducted in four stages. In the first stage, three different percentages of nanosilica, nanoalumina and nanoclay were used to study their performances in producing high strength mortars. The experimental results have shown that, among the utilized nanomaterials, nanosilica has had the best performance. In the second stage, cement has been replaced by different percentages of high volumes of fly ash and different percentages of nanosilica were used to compensate the strength loss by the fly ash. The third stage was carried out by subjecting the specimens to high temperatures of 400°C and 700°C to produce high strength mortars that have more residual strength after exposure to high temperature. The last stage was conducted on samples which had the optimum performances in the previous three stages. Moreover, for explaining the obtained results and making a link between nano, micro and macro scale properties, SEM, BET pore size distribution, XRD and TGA tests were performed. Based on the results obtained, it is possible to produce sustainable high strength mortars having the compressive strength of more than 90 MPa and a residual compressive strength, after exposure to high temperature, of 57 MPa by replacing cement with the combination of 45% of fly ash plus nanosilica. Results has also shown that, as for concrete, sustainable high strength concrete with compressive strengths ranging from 65 to 80 MPa and a residual compressive strength, after exposure to high temperature, ranging from 35 to 52 MPa can be produced by replacing cement with 17.5 to 52.5% of fly ash and 2.5 to 7.5% of nanosilica. The scanning electron microscope (SEM) images showed the beneficial effect of nanosilica in making the paste structure denser. Pore size distribution (following method from Brunauer, Emment, and Teller - BET) results showed the performance of nanosilica in pore refinement and reducing the pore volumes after exposure to high temperature. The X-Ray diffraction (XRD) diagrams showed high pozzolanic reactivity for nanosilica. The thermogravimetric analysis (TGA) results emphasized that exposure to temperatures greater than 400°C causes the hydration products to decompose considerably. This study has met its objectives via the aims of producing high strength concrete by using nanomaterials, producing sustainable high strength concretes containing large volumes of fly ash and producing sustainable high strength concrete with higher residual compressive strength after exposure to high temperatures.,Ph.D
Pages:	169
Call Number:	TA455.F55.I257 2013 3
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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