No description available.

The purpose of this study was to implement a new, rapid field method to effectively and accurately detect harmful clay minerals in aggregate fines by using the modified methylene blue (MMB) test. The focus of this study was based on existing knowledge that expansive, or swelling, clays can cause performance problems in pavements whose coarse aggregate fraction contains an appreciable amount of clay. It has been shown through various research projects along with pavement sections in the field that have failed due to distresses caused by the presence of a considerable amount of deleterious clay minerals. As part of this study, nearly thirty aggregate sources, mainly throughout Texas, have been collected and tested using the MMB test. These samples also underwent chemical separation in order to determine the amount of clay contained within each sample. A strong correlation between the MMB test and the clay content detected by chemical separation results has been established. In other words, clay-rich samples have been reflected by the results of the MMB test, thus providing evidence of the test’s accuracy in detecting expansive clay minerals. In addition to the quantification of aggregate fines by mineralogy, performance testing using hot mix asphalt (HMA) and Portland cement concrete (PCC) mixes was also conducted. In one phase of the study, known amounts of standard clay minerals were introduced to the mixes, and performance testing was carried out. This was done in hopes of establishing a limit of tolerable amounts of clay in coarse aggregate fines that would not sacrifice concrete performance. In another phase of this study, natural stockpiled aggregates from select quarries throughout Texas known to contain clay minerals in the aggregate fines were used to make Portland cement concrete to see how they performed as the coarse aggregate fraction of the mixes. Through extensive methylene blue and concrete performance testing, the aim was to establish a threshold methylene blue value (MBV) that corresponds with the maximum permissible clay content within the aggregate fines.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Self-consolidating concrete (SCC) is an advanced type of concrete that can flow under its own mass without vibration, pass through intricate geometrical configurations, and resist segregation. SCC constituent materials and mixture proportions must be properly selected to achieve these flow properties. The effects of any changes in materials or mixture proportions on hardened concrete performance must be considered in evaluating SCC. A research project was conducted to investigate the role of aggregates in SCC. The objectives of this research were to evaluate the effects of aggregate characteristics and mixture proportions on the workability and hardened properties of SCC, to identify favorable aggregate characteristics for SCC, and to develop guidelines for proportioning SCC with any set of aggregates. The research indicated that although SCC can be proportioned with a wide range of aggregates, the selection of favorable aggregates can significantly enhance the economy and performance of SCC. The effects of aggregate grading; maximum size; shape, angularity, and texture; apparent clay content; and packing density were evaluated. The main effect of aggregates larger than approximately 75 [mu]m was found to be on the minimum required paste volume for achieving SCC workability. It was found that dust-of fracture microfines, defined as mineral material finer than approximately 75 [mu]m produced during the crushing of aggregates, could be an economical choice to comprise part of the paste volume. Based on the results of this research, a mixture proportioning procedure for SCC was developed. The procedure is based on a consistent, rheology-based framework and was designed and written to be accessible and comprehensible for routine use. In the procedure, SCC is represented as a suspension of aggregates in paste. Aggregates are selected on the basis of grading, maximum size, and shape and angularity. The paste volume is set based on the aggregate characteristics in order to achieve workability requirements. The paste composition is established to achieve workability and hardened property requirements. / text

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The purpose of this paper is two fold. Firstly, to introduce and study the Silov Boundary of a Banach algebra of continuous complex valued functions defined on a compact Hausdorff space X. Secondly, to apply the definition of Silov Boundary to more general families of functions, namely, to linear spaces and semi-groups of functions. It will be seen that in these latter cases, existence of the Silov Boundary depends on certain restricting assumptions about the linear space or semi-group. [...]

Asphaltenes correspond to the fraction of oil that is insoluble in heptane but is soluble in toluene. The aggregates of asphaltene are of interest because they cause serious problems in the production of oil. Asphaltenes contain fluorescent moieties, and as such they can be studied by fluorescence techniques. The first objective of this work was to develop methodologies to study the fluorescence of asphaltenes, and to investigate the fluorescence of asphaltenes at various concentrations. Time-resolved fluorescence studies indicate that asphaltenes have different chromophores with different lifetimes. The average lifetime of the asphaltene emission decreased when the asphaltene concentration was increased because of quenching processes occurring within the aggregates. The measurement of lifetimes at different excitation and emission wavelengths demonstrated that different components of asphaltene aggregate at different concentrations. The second objective of this work was to investigate how accessible the asphaltene aggregate is to small molecules by fluorescence quenching experiments. Nitromethane was the quencher used in the fluorescence of asphaltenes. The quenching efficiencies were found to be independent of the concentration of asphaltenes. However, the quenching efficiencies differed for different chromophores, suggesting a selective quenching for nitromethane of the excited states for the different chromophores of asphaltenes. The third objective of this thesis was to investigate the fluorescence of externally added probes that might be incorporated in asphaltene aggregates through π−π stacking. Pyrene was chosen as the probe because its fluorescence properties are strongly affected by its surroundings. The pyrene emission was quenched by nitromethane. The quenching efficiencies determined for pyrene in the absence or the presence of asphaltene aggregates were the same. This suggests that pyrene is located in an open environment, where the asphaltene aggregates do not offer any protection for pyrene from nitromethane. / Graduate

Thesis (doctoral)--Technische Universiteit Delft, 2000. / Includes bibliographical references (p. [139]-145).

Thesis (doctoral)--Technische Universiteit Delft, 2000. / Includes bibliographical references (p. [139]-145).