Geotechnical Properties of Aged Municipal Solid Waste Incineration Fly Ash

Beneficial use of municipal solid waste incineration (MSWI) fly ash in road construction depends on the geotechnical properties required for performance. Geotechnical properties of aged MSWI fly ash samples were investigated through a series of laboratory tests. Physical properties of the aged MSWI ash closely resemble those of silty sand, with particle sizes ranging from 0.002 mm to 15 mm, specific gravity of 2.68-2.74 and maximum dry unit weight of 10.0-10.5 kN/m³. Hydraulic conductivity ranges from 10^-4 cm/s to 10^-6cm/s, which is similar to fine sands, silts and silty clays, and can be rated as “poor” drainage capacity. California bearing ratio (CBR) tests demonstrate that the CBR of aged ash samples is around 10 or higher, which can be rated as “fair-good” for fill and subgrade/subbase. Unconfined compressive strength is around 300 kN/m² and reduces by less than 2% after 10 freeze-thaw cycles, indicating that the aged MSWI fly ash is durable with respect to freeze-thaw. Based on the tested geotechnical properties, the aged MSWI fly ash is recommended as an alternative lightweight material for fill and subgrade/subbase.