Characterization of crystalline and amorphous phases and respective reactivities in a Class F fly ash

A comprehensive approach to qualitative and quantitative characterization of crystalline and amorphous constituent phases of a largely heterogeneous Class F fly ash is presented. Traditionally, fly ash composition is expressed as bulk elemental oxide contents as determined by x-ray fluorescence spectroscopy. However, such analysis does not discern between relatively inert crystalline phases and highly reactive amorphous phases of similar elemental composition. Analytical techniques commonly used in the fields of chemistry and materials science have been modified and applied to effectively characterize the discrete crystalline and amorphous phases in a Class F fly ash.;X-ray diffraction has been used to identify the crystalline phases present in the fly ash, and the Rietveld quantitative phase analysis method has been applied to determine the relative proportion of each of these phases. A synergistic method of scanning electron microscopy, energy dispersive spectroscopy, and multispectral image analysis has been developed to identify and quantify the amorphous phases present in the fly ash. High-resolution spatial element maps are generated through intensive energy dispersive spectroscopy. The maps are statistically combined, phase boundaries are delineated, and relative phase fractions are determined through multispectral image analysis.;Controlled leaching experiments have been performed to quantify the reactivity of the constituent phases in alkaline environments. Fly ash samples were subjected to various alkaline solutions for periods ranging from 1 day to 365 days. The fly ash was physically separated from the solution, the crystalline phase fractions were determined through Rietveld quantitative x-ray diffraction, and the amorphous phase fractions were determined through multispectral image analysis. The phase distributions of the leached fly ash were compared to those of the raw, unleached ash. The composition of the leachate solution was also analyzed using inductively coupled plasma - optical emission spectroscopy.;The application of x-ray diffraction, Rietveld quantitative phase analysis, scanning electron microscopy, energy dispersive spectroscopy, multispectral image analysis, and inductively coupled plasma---optical emission spectroscopy techniques to the characterization of fly ash has facilitated a more comprehensive understanding of the widely-used engineering material.