Durability study of MSWI fly ash solidified sediment as intermediate cover material in landfills under drying-wetting cycles.

Municipal solid waste incineration (MSWI) fly ash partially replaces the cement-solidified sediment as intermediate cover materials in landfills, which can realize the resource utilization of MSWI fly ash and sediment. In this study, durability of MSWI fly ash solidified sediment as intermediate cover materials in landfills under drying-wetting cycles was investigated through various laboratory tests including unconfined compressive strength (UCS), direct shear (DS), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). Results revealed that the UCS, internal friction angle (φ), and cohesion (c) increased with the number of drying-wetting cycles and the decreased of MSWI fly ash replacement ratio. The increase of φ and c improved the stability of landfill, and the durability index (Δ) of the samples after 5th drying-wetting cycles were greater than 1. The dry-wet cycle will cause the pores of the sample to increase. Additionally, calcium carbonate precipitation was also generated during the treatment, indicating that the solidified sediment not only underwent hydration reaction and carbonation reaction but also dry matrix contraction reaction in the process. Both reactions facilitated growth of strength and increase in resistance of MSWI fly ash solidified sediment to drying and wetting cycles. These findings suggest that MSWI fly ash solidified sediment can serve as a green and sustainable intermediate cover material in landfills.