Coal bottom ash as a geomaterial: Influence of particle morphology on the behavior of granular materials

Previous studies of mechanical properties of solid residue byproducts such as coal bottom ash have been restricted to small and intermediate shear strains of approximately 0.1-20%, due to the limitations of the standard equipment used (e.g. triaxial and direct shear tests) and to confining pressures up to around 1.5 MPa. The objective of the present research was to study the behavior of coal bottom ash sampled in southern Brazil, ranging from very small to very large shear strains, as well as to high isotropic pressures, to determine its complete behavior. Comparisons are made with results from a granular soil with a similar grading and also with those of uniform sand with similar average particle size. High pressure isotropic compression and bender element tests, as well as standard triaxial tests and ring shear tests were carried out on compacted specimens of coal bottom ash, a sandy residual soil with a similar grain size distribution, as well as on a uniform sand. In order to explain the effect of the particle morphology of the coal bottom ash on its mechanical behavior, an investigation was also undertaken based on thin section and scanning electron micrographs, which revealed intra-particle voids in the coal ash. The results indicate that the general behavior of the bottom ash compares favorably with conventional granular materials, providing a promising solution to the disposal problem, and also an economic alternative to the use of conventional soils as construction materials.