Reuse of soil-like material solidified by a biomass fly ash-based binder as engineering backfill material and its performance evaluation

The reuse of soil-like material (SLM) obtained from landfill mining as engineering backfill materials contributes to sustainable waste management. In this paper, a new biomass fly ash-based binder (BB) containing biomass fly ash (BFA), carbide slag (CS), and phosphogypsum (PG) is designed to solidify the SLMs. The mechanical properties, permeability, microstructure, and physicochemical characteristics of the BB-solidified SLM are comprehensively characterized. The optimum proportion of ternary BBs consisting of 80% BFA, 15% CS, and 5% PG was determined through tests on paste samples. The different landfill depths of SLMs show significant variability in solidification/stabilization (S/S) effects due to their different physicochemical properties. The mechanical and permeability properties of BB-solidified SLM improve with the increasing BB content and the age of solidification. Microstructural and phase analyses indicated the formation of significant amounts of ettringite crystals and C-(A)-S-H gels were generated by the pozzolanic reaction, forming a stable and dense microstructure. The variations in pH and conductivity were correlated with the development of mechanical properties. Moreover, the organic matter content and leached heavy metal content of SLM2 and SLM3 after S/S treatment did not exceed the specified limits. This study can provide theoretical guidance for the resource utilization of the stabilized/solidified SLMs.