Digitized by Kansas Correctional Industries

No description available.

It is generally very difficult to produce high-performance concrete having concurrently high strength, high durability, high workability and high dimensional stability. This is because low water content is required to achieve high strength and high durability, high water content and large paste volume are required to achieve high workability, and low cement content and small cement paste volume are required to achieve high dimensional stability. One way of overcoming such conflicts is to add fillers to increase the packing density of concrete so that the amounts of water and paste needed to fill voids could be reduced. In this study, the use of fillers to improve the packing density and performance of concrete is investigated by measuring the packing density and overall performance of cement paste and concrete mix samples with different types and amounts of fillers added. The packing density results revealed that finer fillers are more effective in improving the packing density for releasing more excess water (water in excess of that needed to fill voids) to lubricate the solid particles. Moreover, triple blending of two fillers of different fineness with cement can better increase the packing density than double blending of just one filler with cement. On the other hand, the workability, strength and dimensional stability results showed that the addition of condensed silica fume, fly ash microsphere or superfine cement could improve the overall workability-strength performance of cement paste through increasing the packing density of the cementitious materials, while the addition of condensed silica fume, fly ash or limestone fine coeuld improve the overall dimensional stability-strength performance of concrete through decreasing the cement content or cement paste volume. Hence, the incorporation of fillers to improve the packing density opens up the possibility of using ultra-low W/CM ratio and ultralow paste volume to produce an ultrahigh-performance concrete. However, despite increases in packing density and excess water, the addition of fillers does not always improve the workability. Generally, the addition of fillers would more significantly increase the workability at low W/CM ratio and less significantly increase or even decrease the workability at high W/CM ratio. In-depth analysis indicated that both the excess water and solid surface area have great effects on the rheology. In this regard, a parameter called water film thickness (WFT), which is defined as the average thickness of water films coating the solid particles and may be determined as the excess water to solid surface area ratio, is proven to be the key factor governing the rheology. Therefore, it should be the WFT rather than the packing density that should be maximized in the mix design of high-performance concrete. The addition of fillers would increase both the excess water and solid surface area. If the proportional increase in excess water is larger than the proportional increase in solid surface area, the WFT would increase, but if otherwise, the WFT would decrease. To increase the WFT, a filler that can significantly increase the packing density without excessively increasing the solid surface area is the best choice. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

D. Tech. Chemistry / The cement industry plays a major role in the world economy. Analytical techniques are central to its success. Many of the techniques currently in use, mainly wet classical methods, could be improved and optimized to increase economic benefits. The aim of this study was to identify and optimized selected analytical techniques. Four analytical methods were selected: the determination of available lime in lime, Cr(VI) in cement and cement-related materials, chloride in various cementitious materials as well as minor and trace elements in cement clinker and gypsum.

No description available.

The aim of this thesis is to develop a better understanding about the degradation mechanisms occurring within lithium-ion cells which eventually lead to their failure. An introduction to the components and operation of Li-ion cells is followed by proposed degradation mechanisms which limit the lifetime of cells. These mechanisms and how they can be identified from electrochemical testing are discussed. Electrolyte additives can be used to improve the safety of Li-ion cells or decrease the rate of cell degradation. Different types of additives and testing methods are discussed followed by an introduction to high precision coulometry which can be used to detect the impact of additives on cycling performance. The High Precision Charger that was constructed for this project is described and shown to meet the desired precision. The use of additives and different materials to extend lifetime of cells is shown to be detectable through the use of high precision coulometry. High precision coulometry proves to be a more efficient way of estimating the lifetime of cells under realistic conditions in a reasonably short amount of time. / MSc. Thesis

No description available.

No description available.

Graduation date: 1961

Thesis (M. Med. Sc.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 30-33).