AASHTO PP 59-09 (2013)

This practice covers the use of coal combustion fly ash (typically but not limited to non-selfhardening ash) as a fill material for the construction of embankments.

When properly processed, hauled, spread, and compacted on a prepared grade to appropriate density standards, coal combustion fly ash used alone, or blended with traditional soil aggregate or other approved aggregate materials, can be expected to provide a lighter-than-normal weight fill material (85 to 100 pcf, 1360 to 1600 kg/m³) with adequate stability and load support for use as road or highway embankment.

The technique described in this practice uses containment berms, cover fill material, and sometimes a liner and leachate system to isolate the fly ash and any resulting effluent. This is a conservative approach to the environmental issues raised by the use of fly ash as fill, and may not be required for all fly ashes or for all regulatory requirements.

This practice recognizes that since fly ash is a by-product of the burning of coal in electricityand steam-generating facilities, various state, county, and local environmental laws and regulations apply if fly ash is used as an alternative embankment material. Aspects of fly ash that are of environmental concern are identified. Therefore, this standard discusses elements such as impermeable layers and leachate collection, as they may be required according to the environmental regulations affecting the proposed installation.