Solidified lake sediment with industrial waste and construction waste used as barrier cover material: mechanical strength, water resistance performance, and microscopic analysis

This study introduces a novel landfill cover material, employing lake sediment as a substrate, stabilised with fly ash, slag, desulfurisation gypsum and construction waste. The mechanical properties, including shear strength parameters, unconfined compressive strength, hydraulic conductivity, volumetric shrinkage, and water content, of the solidified sludge were evaluated. The microscopic mechanism of the solidified sludge were investigated through XRD, FTIR, and SEM-EDS techniques. A novel three-layer composite capping cover system for landfills is proposed, comprising an upper capillary barrier layer, a middle drainage layer and a bottom impermeable layer . Indoor rainfall simulation tests were conducted to assess the water retention performance of this capping cover system under repeated moderate, heavy, and torrential rainfall events. The early strength of the solidified sludge exhibited rapid development, with cohesion and internal friction angle reaching 382.56 kPa and 57.67°, respectively, after 3 days. After 28d, the unconfined compressive strength ranged from 6.93 to 14.29 MPa, with hydraulic conductivity between 3.98-23.1 × 10^-8cm/s. The hydration reactions of the industrial waste residues resulted in the formation of Ettringite, Gypsum, and hydrous calcium (aluminum) silicates. The Ettringite and Gypsum crystals formed an internal support framework, while the generation of gel-like substances such as C-S-H and C-A-S-H facilitated product aggregation. The RSM was employed to optimise the material ratio of the solidified sludge, while the Pearson coefficient facilitated correlation analysis. This study provides valuable data for designing landfill solidified sludge cover systems and offers a new approach for the co-disposal of sludge and industrial waste.