Characterization of a new silica alumina-based backfill material utilizing large quantities of coal combustion byproducts

In this paper, a new silica alumina-based backfill material utilizing large quantities of coal combustion byproducts (CCPs) was investigated. The experimental results show that this material had excellent workability as fresh backfill slurry because of its high flowability and low bleeding rate, and the data also demonstrate that the material had good mechanical properties in a compressive test, as the hardening body of the backfill material reached around 7 MPa in 360 days. The results indicate that milled fly ash with a large specific surface area (represented as the Blaine value) significantly enhanced the performance of the silica alumina-based backfill material. The optimal design for this backfill material in this experiment was a composition of 30% milled fly ash at a pulp density 75.2%. Although the backfill slurry contained a large amount of industrial solid waste, the TCLP results indicate that none of the tested hazardous elements exceeded EPA limits, indicating that this backfill material is able to stabilize and/or solidify the hazardous elements very well.