In the unregulated co-landfill disposal of stabilized fly ash and municipal solid waste (MSW), the organic acid in MSW leachate poses a significant threat to the environmental safety of stabilized fly ash. Bulk bags (FIBCs)used for packaging stabilized fly ash may experience varying degrees of damage in landfill environments, which directly influence the percolation pathways of the invading liquid, subsequently affecting the leaching behavior of heavy metals in fly ash. A column leaching experiment was conducted to simulate the impact of organic acid on the leaching behavior and environmental risk associated with six heavy metals (Pb, Zn, Cu, Cd, Cr, Ni) in fly ash under multiple percolation paths. The findings suggest that the complex percolation paths can more effectively prevent heavy metals leaching from fly ash. Furthermore, the leaching of heavy metals is the lowest when the percolation path does not go through the bottom, with Pb, Zn, Cu, Cd, Cr and Ni being only 4.85 %, 27.36 %, 0.11 %, 2.22 %, 13.04 % and 0.42 % of the highest leaching amount under other paths (except Zn, the highest leaching of heavy metals is under the top in and bottom out path). Indicate that the integrity of FIBCs bottom significantly reduces the leaching of heavy metals, and favors environmental risk control of heavy metal, with the RI value did not reach the high-risk level (>= 600) in all stages. The percolation path has the most significant influence on the cumulative leaching amount of Cu, while it has the least influence on Zn. This influence is due to factors such as the contact degree of fly ash and organic acid, the transfer rate of heavy metals in liquid phase, and the properties of heavy metals. Heavy metal leaching was typically higher towards the end of the experiment, especially under the top in and bottom out path.

Expansive clays feature high compressibility and large swelling-shrinkage potential, which may cause significant damage to the infrastructures, including pavements. This study investigates the potential use of industrial waste ash generated from municipal solid waste incineration (MSWI) as a more sustainable treatment method to treat expansive soils compared to the use of conventional coal fly ash. A series of tests was conducted to study the mechanical, durability, and environmental performance of the MSWI fly ash in comparison with the coal fly ash. The study reveals that the compressive strength and resilient modulus of 20% MSWI fly ash treated sample increased to 0.86 MPa and 213 MPa respectively, depicting an increase of 150% and 240% of the control clay specimen. Results also indicate that MSWI treated expansive clay shows better performance during the soaked California bearing ratio (CBR) testings, moisture susceptibility and cyclic wetting-drying tests compared to coal fly ash treated samples. Microlevel investigations reveal that the influence of cation exchange is more decisive in the MSWI-treated clays due to the presence of higher Ca2+ ions, during the early stages, and the influence of hydration is stronger at the later stage of stabilisation. X-ray diffraction (XRD) results show that gismondine, albite, calcite, portlandite, andradite, and ettringite are the main crystalline phases formed during the stabilization. Heavy metal concentrations after the stabilisation are within the allowable limit defined by state regulations. Applying MSWI fly ash as a ground treatment for expansive clays can reduce the consumption of natural resources, promoting a zero landfill policy.