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Liners for waste containment constructed with class F and C fly ashes
B G Palmer1, T B Edil, C H Benson
1Malcolm Pirnie, Inc., Columbus, OH 43240, USA. bpalmer@pirnie.com
Journal of Hazardous Materials
|August 11, 2000
Summary
Class F fly ash mixtures can create low hydraulic conductivity landfill liners when compacted properly. Field construction proved challenging, highlighting the need to manage cracks and metal leaching for effective fly ash liners.
Area of Science:
- Geotechnical Engineering
- Environmental Engineering
- Materials Science
Background:
- Class F fly ash is a byproduct of coal combustion with potential for use in civil engineering applications.
- Residual organic carbon in fly ash can affect its engineering properties, including hydraulic conductivity.
- Low hydraulic conductivity liners are crucial for landfill containment to prevent leachate migration.
Purpose of the Study:
- To evaluate the hydraulic conductivity of Class F fly ash mixtures for landfill liner applications.
- To compare laboratory findings with field performance of a constructed fly ash liner.
- To identify challenges and considerations for using fly ash in low hydraulic conductivity liners.
Main Methods:
- Laboratory preparation and testing of compacted fly ash specimens (Class F, Class C, sand, bottom ash) using flexible-wall permeameters.
- Field construction of a test pad using fly ash mixtures.
- Field measurement of hydraulic conductivity using sealed double-ring infiltrometers and two-stage borehole permeameters.
- Laboratory testing of specimens retrieved from the field test pad.
Main Results:
- Mixtures of Class F and Class C fly ashes with coarse aggregate achieved low hydraulic conductivity when compacted wet of optimum water content.
- Field construction of the fly ash liner presented challenges in achieving laboratory-determined low hydraulic conductivity values.
- Field tests indicated higher hydraulic conductivity due to cracks and permeable interlift regions.
- Leachate analysis revealed potential for metal leaching, requiring design considerations.
Conclusions:
- Class F fly ash mixtures, particularly with Class C fly ash and aggregate, can be suitable for landfill liners if compacted appropriately (wet of optimum).
- Field implementation requires careful control to mitigate issues like cracking and interlift permeability, which significantly increase hydraulic conductivity.
- Metal leaching from fly ash liners is a critical factor that must be addressed during the design phase.