Thesis--Technical University of Denmark. / Bibliography: p. 157-[159].

Thesis (M.S.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on June 25, 2010). Bibliography: leaves 89-94.

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1949. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed July 8, 2010) Includes bibliographical references (p. 47) and index (p. 48-52).

Thesis (Ph.D.)--University of Pretoria, 2001. / Summaries in Afrikaans and English. Includes bibliographies. Available on the Internet via the World Wide Web.

The results of an extensive series of trials on a 100 tonnes per day cement kiln have provided a fundamental insight into the aerodynamics, burning mechanism and heat transfer in the sintering zone of such kilns. Accurate monitoring of the input and output variables has enabled mass and heat balances to be made on the system, and from these results it has been possible to isolate the areas where major fuel savings can be achieved. Slurry moisture, excess air and external heat losses are all variables where improvements and better control would reduce fuel consumption and increase the efficiency of rotary kilns. It has been shown that the external temperature profile of the kiln shell provides a useful indication of the various reaction regions that exist in the process cycle. From calculations of the heat lost from the shell, it has been shown that half the external heat losses occur from the sintering zone of the kiln. Specialized instrumentation has been developed to measure gas temperatures and extract combustion gas samples during the normal range of operation of the kiln. An analysis of these results has led to a formula to predict the length of the flame as influenced by the significant operating parameters. The measured gas concentrations have been used to predict the combustion rate within the flame, and a favourable comparison of this rate has been made with published data. The measurement of flame temperatures in the kiln has shown that the average flame temperature that may be encountered in a cement kiln is approximately 1800°C. Point temperatures of up to 2100°C were measured, and it was observed that increased excess air produced a shorter, hotter flame, but reduced the temperature of the combusted gases, resulting in a poorer quality product. A mathematical model has been developed to predict the gas and refractory temperature and heat flux profiles occurring in a rotary kiln sintering zone. The method is based on that of Hottel and Sarofim, but modified to account for the specialised firing conditions necessary for cement production. The model has been tested against the measured data obtained from the kiln trials, and the degree of agreement found to be encouraging. Use of this model should enable the cement, lime, and refractory industries to comprehend the effect of changes to operational variables, with a resulting improvement in heat utilisation, product quality and plant life.

The hydration reaction of tricalcium silicate and the various factors which influence it have been investigated using calorimetry, thermogravimetry, quantitative X-ray diffractometry, scanning and transmission electron microscopy and energy dispersive X-ray analysis. Various factors associated with the synthesis and subsequent storage of tricalcium silicate were found to alter its reactivity and it is thought that these may be responsible for much of the variability in the reported reactivity of tricalcium silicate preparations. The contribution of the individual factors (such as particle size distribution and impurity ion content) to such reactivity changes was investigated. Use of the Avrami equation to model the rate of heat output curves obtained by calorimetry was found to give good fits to the experimental data. Apparent activation energies of control and calcium chloride accelerated reactions were determined from the rate parameters derived from the fitting procedure. However, it is shown that the amount of mechanistic information which can be obtained from such a fitting procedure is limited. Observation of the detailed chemical and morphological changes occurring during the hydration of tricalcium silicate and the manner in which they are influenced by incorporation of calcium chloride (as a model accelerator) and sucrose (as a model retarder) show that during the later stages of hydration the chemistry of the reaction is not affected by the presence of the admixtures, but that their incorporation does cause some changes in the microstructure of the gel product.

A brief review is made of the rheology of suspensions in general and cement slurries in particular. The factors influencing the flow behaviour of these systems are discussed. It is pointed out that the rheological properties of cement slurries can not be determined by theory alone from the original constituents, and experimental tests combined with empirical formulae are needed. The co-axial cylinder viscometer was used to characterise the rheological behaviour of the cement slurry used in this investigation, the slurry being made highly thixotropic by the use of additives, It is shown that no single flow model, however complex, can correctly fully describe the flow behaviour of such materials. The cement slurry used in this research programme had a structure which changed continuously with time and, when pumped through a pipe, formed a high water content slip layer on the pipe surface. An accurate theoretical solution for this type of pipe flow is lacking in the literature. A new method to predict the pressure gradient of such suspensions flowing in pipes is proposed and the technique was tested using a small pumping line and also with data extracted from the literature. The shear vane test, commonly used to measure shear strength of soils, was developed to measure gel strength of the cement slurry used in this investigation. It is shown that the gel strength measured with this technique is of considerable benefit when assessing the real material behaviour.

Cement is an essential material in today’s society because, as a major constituent of concrete, it forms a fundamental element of any housing or infrastructure development. The chemical process of making cement clinker produces CO2, a major greenhouse gas contributing to climate change. This makes it imperative for us to find ways of using this resource more efficiently. Using waste from other industries, as a raw material is a huge opportunity for the cement industry to reduce its environmental impact. Cement extenders are used as a substitute for some of the Portland cement in concrete. The reasons for the use of extenders, is a growing awareness of the engineering, economical and ecological benefits and the variety of useful enhancements, which they give to the concrete properties. The aim of the research is to determine whether a gasification ash can be used as a cement extender in concrete. In this study the properties of cement and concrete containing gasification ash was compared to the properties of cement and concrete containing fly ash. The physical, chemical and mineralogical composition of a gasification ash sample was investigated, and it was found that gasification ash has an angular shape and a similar chemical composition as fly ash. The chemical requirements of the gasification ash meet the majority of the requirements specified for cement extenders. Where limits are exceeded it is by a very narrow margin. The effect of a gasification ash on the short and long term properties of concrete of both interblending and intergrinding was investigated. The experimental work revealed that gasification ash improves the compressive and tensile strength of concrete in both interblending and intergrinding. Gasification ash does not have a detrimental effect on stiffness of concrete, and did not creep significantly more than concrete containing fly ash. The porosity and permeability does not increase when gasification ash is used as a cement extender. Gasification ash should therefore not decrease the durability of concrete. The use of gasification ash as a cement extender has advantages to both the cement industry and the environment. / Dissertation (MEng(Structural))--University of Pretoria, 2007. / Civil Engineering / unrestricted

The problem of the investigation of the mechanism of failure in compression of neat cement and mortar specimens is considered in this thesis. The study was made on two hundred specimens of cement paste and mortar, of which approximately one half were tension briquets and the other half compression cylinders. The underlying theory which led to this study was that failure in compression in specimens with aggregate (mortar and concrete) is due to the wedging action of the particles of aggregate within the matrix of cement paste. Steam-curing was used to avoid delay in the hardening of cement. It was found that the cement used was of the type which continues hardening after being steam-cured. The importance of having the specimens at a constant temperature throughout their mass and at room temperature when the tests were performed was realized. An investigation of the effect of end conditions on test cylinders in compression was conducted. It is considered that the confined rubber end conditions used were an improvement on testing with lubricated ends only. Observations were made on the effect of the bursting action of water in compression tests of moist specimens. A study of the effect of stress concentration around voids was made on tension specimens. Compression specimens made of neat cement, mortar and cement with inclusions in the form of balls were studied. Inclusions were placed in cement cylinders to imitate the action of the aggregate in mortar and concrete specimens. Tests on compression specimens with inclusions were useful in the interpretation of results of tests on neat cement and mortar cylinders and in the study of the stress-strain curves. Transverse bending tests of cylinders were made with the purpose of investigating the presence of transverse cracks formed in the cylinders as a consequence of the application of compressive loads. They did not provide a good method of investigation but were very useful in that they were an aid to realizing the effect of the horizontal cracks in the stress-strain curves. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Alkali-silica reaction (ASR) in cement is a major contributor to failure of cement structures around the world, causing increased repair costs and possible rebuild expenses. Alkali levels are indicative of the potential for ASR and are therefore measured and quantified. A linear correlation relating cement alkali concentration measured by X-ray fluorescence spectroscopy (XRF) and peak ratio measured by Fourier transform infrared spectroscopy (FTIR) is developed. Regression analysis of plots correlating alkali content measured by FTIR absorption band (750 cm-1/923 cm-1) ratio versus equivalent alkali (Na2O)e (%Na2O + 0.658 % K2O) quantified by XRF show linear correlation coefficient, R2, of 0.97. Results of this investigation are discussed in terms of microstructural disorder coefficient Cd which is a reactivity criterion for ASR-susceptible aggregates proposed by Bachiorrini [31]. XRF is a popular technique for alkali quantification but FTIR is faster, safer, and less expensive technique compared to XRF. Portable instrumentation is available for both techniques but FTIR systems are less expensive.