, Former Professor, Soil, Water & Climate
Recycling part or all of the pavement materials in an existing road during reconstruction is an attractive construction alternative, as it both cost-effective and environmentally friendly. However, recycled base materials may contain asphalt binder, fines, and/or other deleterious materials that can adversely affect strength and stiffness. This project assessed the gravel equivalency, life expectancy, and potential environmental impacts of fly-ash stabilized recycled pavement materials through large-scale laboratory experiments, small-scale laboratory tests typically used for design and analysis, and continued monitoring of two existing roads where fly ash stabilization has been conducted and extensively documented. Researchers also evaluated the leaching of potentially hazardous elements from the stabilized materials using laboratory column tests and continuous monitoring of lysimeters at the two road sites. Researchers compared data obtained from the laboratory tests and the lysimeters with predictions from the models SESOIL and WiscLEACH, which were specifically designed to assess potential groundwater impacts of potentially hazardous elements added to soil. Results of the study had a direct impact on the ability to design and evaluate bituminous roads and streets in Minnesota where fly ash is used for in-situ base stabilization. The design method was developed in the context of the "gravel equivalency" (GE) design methodology employed for local roads in Minnesota.