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 prop-erties, permeability, microstructure, and physicochemical characteristics of the BB-solidified SLM are compre-hensively 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 solidifica-tion. 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 var-iations 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.

Automated summary

The study focuses on the solidification of soil-like material obtained from landfill mining using a biomass fly ash-based binder (BB). The mechanical properties, permeability, microstructure, and physicochemical characteristics of the BB-solidified material are comprehensively characterized. The results indicate that the BB-solidified material improves in terms of mechanical properties and permeability with increasing BB content and solidification age.