Collaborative Research: Investigation of the Effect of Fly Ash Variability on Cement Paste Microstructure and Mechanical Properties Using Simulated Fly Ash

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This research will improve our understanding of the fundamental factors controlling the reactivity of fly ash in Portland cement concrete, leading to more accurate predictive models of performance that will enable the calculation of optimum cement replacement factors for fly ash/cement mix design,. The major innovation is the use of a simulated whole fly ash, which matches all the major properties of a real fly ash, as a model system for investigating systemically the individual factors that control its reactivity. These major properties include the glassy phase composition, the inert mass fraction and composition, and the particle size distribution (PSD). Each simulated fly ash will be a mixture of several types of synthetic glassy particles made with characteristic chemical compositions that match those of real fly ashes. These compositions will be based on analyses of individual fly ash particles using Computer Controlled SEM. The PSD, glass chemical composition and inert fraction will be independently varied among the simulated fly ashes. The mixing of the solid particles will be done using the novel Resonance Acoustic Mixing method to ensure homogenization. This research uses a combination of three measurement techniques to measure the reactivity at different length scales: wet chemistry, thermogravimetry, and standard tests of engineering properties such as compressive strength and durability. Also, the molecular structure of the gel hydration products will be characterized with solid state NMR. This multiscale approach provides a bridge from individual particle data to macroscopic engineering properties. The results of this research will lead to a model of the reactivity as a function of the glass composition, PSD and inerts fraction. It will accelerate the usage of fly ash as a replacement for Portland cement by the concrete industry. In terms of economic benefits, the increased use of fly ash will lower the cost of concrete structures. The environmental benefits include the reduction in the number of landfills otherwise needed for fly ash disposal, as well as reduced energy consumption and lower CO2 emissions from Portland cement manufacture. This collaborative project will enhance the research and education for undergraduate and graduate students between two institutions.