Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains vii, 53 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 48-53).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains viii, 152 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 87-91).

Pulverized samples of Utah bituminous, Beulah (North Dakota) low Na lignite, Beulah high Na lignite and Texas (San Miguel) lignite coals were burned at a rate of 2.5 kg/hr in a laboratory furnace under various (overall fuel lean) combustion conditions. Particle size distributions (PSD) and size segregated particle filter samples were taken at various positions within the convection section. Temperature and gas concentrations were measured throughout. The evolution of the submicron PSD within the convection section for the four coals was similar, although the location of the initial particle mode at the convection section inlet varied with coal type. While staged (.8/1.2) combustion of the Utah bituminous coal had a variable effect on the volume of submicron aerosol produced, staged combustion of two of the three lignites (Beulah low Na and Texas) caused a definite increase in the submicron aerosol volume. Vapor enhancement due to a localized reducing atmosphere, which would effect coals of higher ash volatility or higher inherent ash content, is thought to explain this behavior. Depressed combustion temperatures associated with the high moisture content of the Beulah high Na lignite are thought to offset the effects of staging. Increased combustion temperatures (through oxygen enrichment) caused staged volume increases for the Beulah high Na lignite. Combustion temperatures are a controlling factor even at more extreme staging conditions. Chemical analysis of the size segregated particle samples show the trace elements, As, Pb, Zn and the major elements, Na and K to be enriched in the submicron aerosol. Auger depth profiles show these small particles to be comprised of a core enriched in Fe, Si, Ca and Mg and surface layers enriched in Na and K. These results point to a mechanism of homogeneous nucleation of low vapor pressure species followed by successive layering of progressively more volatile species. Volatile species are enriched in the submicron aerosol due to the large surface areas provided. Modeling efforts show that while coagulation may be the dominant mechanism to describe the aerosol evolving within the convection section, it cannot be used solely to predict the PSD. Another mechanism, presumably surface area dependent growth (condensation) must be included.

No description available.

The discovery of geopolymers is a breakthrough which provides a cleaner and environmentally-friendlier alternative to Ordinary Portland Cement (OPC). Since the pioneering days, the understanding of the chemistry, synthesis, and practical application of geopolymers has improved to the extent that commercialisation of geopolymers on a large scale is possible in the near future. However, the fundamental breakthroughs and understanding to date are based on investigations of ‘pure’ raw materials, like metakaolinite. The utilisation of metakaolinite has been useful in a research setting, but will be impractical for widespread application. Therefore, the thesis attempts to do a more detailed study on geopolymers synthesised from waste materials, such as fly ash. The motivation for using fly ash as the main raw material is driven by various factors: (1) it is cheap and available in bulk quantities, (2) it is currently under-utilised, except for its use as an additive in OPC, (3) it has high workability, and (4) it requires less water (or solution) for activation.

Geopolymer cements offer an alternative to, and potential replacement for, ordinary Portland cement (OPC). Geopolymer technology also has the potential to reduce global greenhouse emissions caused by OPC production. There is already a considerable amount of work and research conducted on geopolymers in the past decades, and it is now possible to implement this technology commercially. However, to ensure that geopolymer becomes commercially available and able to be used in the world, further understanding of its ability to provide durable and long lasting materials is required. One main property which is still relatively unexplored compared to other properties is its shrinkage properties. The objective of this thesis is therefore to examine the shrinkage of geopolymers and factors which might influence it. / The factors which influence geopolymer strength were investigated as being the factors which may influence shrinkage. The selection of the activating solution is an important factor in forming the final product of a geopolymer. Activating solution SiO2/Na2O ratio is determined to be an important influence on the shrinkage of geopolymer. SEM images of the samples enable observation of the sample topology and microstructure. An important observation was the existence of a ‘knee point’ which also occurs in OPC shrinkage. The ‘knee point’ is the point where the shrinkage goes from rapid shrinkage to slow shrinkage. From SEMs it is noted that the samples past the knee point are shown to have a smoother topology which means it is more reacted. / Autogenous shrinkage is an important issue for OPC containing a high amount of silica, and is also a key factor in geopolymer shrinkage. Autogenous shrinkage is tested by keeping samples in a sealed environment where water lost to drying is kept to a minimum. It is noted that sealing and bagging the samples reduces the shrinkage considerably. The water to cement ratio, which is an important factor in OPC shrinkage, is also explored for the case of geopolymers. Water content plays an important role in determining early stage shrinkage, and has little to no effect on the later stage shrinkage. The water loss from the samples during drying on exposure to environment is noted and compared. The addition of more water did not necessary means that more water was lost. / Addition of slag is known to be beneficial to geopolymers by giving early structural strength and faster setting time. Commercial geopolymer concrete will also include the use of slag. However, the addition of slag up to a certain extent gives a deleterious affect on shrinkage. / A different type of Class F fly ash source with different composition data was used to see its effect on shrinkage, with only a slight influence observed between the two ashes tested. Fly ash was also ground for different lengths of time before use in geopolymerization, with grinding for less than 12 hours giving higher shrinkage than an unground sample, but shrinkage the decreasing with grinding for 18 or 24 hours. This initial higher shrinkage has been attributed to the mechanism of grinding which resulted in unevenly shaped fly ash particles taking up a larger initial volume resulting in higher shrinkage. The sample grinded for 24 hours showed higher shrinkage due to the particle size to be so fine that agglomerates may have form during mixing which would result in a lower reaction rate which increases the shrinkage. Elevated curing temperatures also reduce geopolymer shrinkage. / Thus, it is clear that the shrinkage of geopolymers is influenced by a wide range of variables, and more notably by a few important variables: activating solution ratio, addition of water, grinding and bagging. The shrinkage of geopolymers can be correlated to the strength to a certain extent. However, the understanding of the shrinkage of geopolymers is still at a very initial phase, and further research is required.

Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Bibliography: leaves 250-257.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [240]-247).

Thesis (Ph. D.)(Chemistry)--University of Pretoria, 2004. / Title from opening screen (viewed Oct. 8, 2004). Includes bibliographical references.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Mulalo Doyoyo; Committee Member: Dr. Arash Yavari; Committee Member: Dr. Kenneth M. Will. Part of the SMARTech Electronic Thesis and Dissertation Collection.