Graduate Thesis Or Dissertation
 

The role of alumina in the mitigation of alkali-silica reaction

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  • The use of fly ash as a supplementary cementitious material (SCM) has increased in the last century due to its various environmental benefits as a recycled product. Within the last 60 years, it has been found that it can be used to effectively control damage induced by Alkali-Silica Reaction. However, it is not completely understood how to properly assign a dosage of fly ash to control the reaction. This depends greatly on the fly ash characteristics (e.g. composition, particle size, and reactivity), the reactivity of the aggregate (e.g. high to low reactivity level) and the environmental exposure conditions. The characteristics of the fly ash depend on the coal source being burned and the burning conditions that result in the fly ash formation. A major concern when supplementing cement with fly ash for ASR mitigation is the effect of the alkali contribution of the fly ash to the concrete pore solution. Current test methods cannot accurately determine the alkali contribution of fly ashes and there is no standardized test method to doing so. When contributed by the implementation of a SCM, alumina has been found to play a role in the ability of an SCM to mitigate ASR-induced damage. It has been observed that fly ashes containing higher levels of alumina (18-25%) tend to improve concrete durabilty more effectively when compared to fly ashes with lower levels of alumina. Additionally, the use of metakaolin, which is composed of 45-50% alumina, has been found to lessen expansion with a lower percentage of cement replacement than would be required if fly ash is used. Furthermore, the use of fly ash with another SCM material, a high quality ultra-fine fly ash or alumino-siliceous metakaolin, in ternary blends may improve the performance of fly ash resulting in a broadening of the spectrum of SCMs usable for ASR mitigation. For successful use of SCMs, it is important to develop an understanding of the alkalisilica reaction and the ability of such SCMs to control expansion. This report provides an overview of alkali-silica reaction and the use of fly ash and metakaolin as SCMs to mitigate expansion due to the reaction, with an emphasis on the role of alumina when contributed from the two materials.
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file details Warner_FINAL_THESIS.pdf 2017-08-15 公开 下载