Physical and morphological studies of size-classified coal fly ash

A study of the physical and morphological properties of four fractions of size-classified coal fly ash is reported. Volume median diameters of the four size fractions are 2.2, 3.2, 6.3, and 20 microns, respectively. The size distributions of the four fractions are compared to isokinetically collected samples. Density variations and results of three standard particle sizing techniques are discussed in terms of particle size and morphological properties. Eleven morphological particle types are quantified by light microscopy. Relative abundances of the 11 morphological particle types within each size cut appear to be particle size dependent. The finest fraction is composed of 87% nonopaque solid spheres and 7.9% cenospheres in contrast to the coarsest fraction composed of 26% nonopaque solid spheres and 41% cenospheres. The density variation with particle size is explained in terms of the relative abundances of predominant particle types. On the basis of morphological appearance, a coal fly ash morphogenesis scheme is developed.