Investigations on the fluidized solidified soil prepared by sand-washing sludge: Engineering properties, solidification mechanism, and environmental impact.

Abstract

Sand-washing sludge (SWS), a by-product of sand production processes, poses environmental challenges due to its massive accumulation. To improve resource utilization of waste SWS, this study stabilized SWS to prepare fluidized solidified soil (FSS) using ordinary Portland cement (OPC) and industrial solid waste (ISW). A systematic evaluation framework for FSS was developed by integrating key engineering properties (flowability, mechanical strength, and durability), microstructure, and environmental impact assessment. The results showed that the synergistic effect of SWS with OPC and ISW effectively improved the mechanical strength of FSS. The optimum performance was achieved with a mass ratio of SWS: OPC: ISW of 20:2:1, where the ISW composition comprised tailings: coal fly ash: ground granulated blast furnace slag: calcium carbide residue at a ratio of 20:43:129:8. The unconfined compressive strength, splitting strength, and resilient modulus of the resulting FSS reached 0.82, 0.64, and 242 MPa, respectively. These results confirmed that FSS met the strength requirements for structural backfill materials of the Chinese standard T/CMEA 32-2023. The incorporation of ISW contributed to the development of strength and the immobilization of heavy metals in FSS. Comprehensive environmental assessment confirmed the safety of FSS, with heavy metal leaching concentrations below regulatory thresholds and at low ecological risk levels. This study provides an efficient and environmentally friendly solution for resource utilization of SWS and establishes a theoretical foundation for further research and application of solidified soil materials.