A reclaimer train combined previously milled roadway materials, fly ash, and engineered asphalt emulsion with the existing surface by remixing the materials with 2% fly ash and 3.5% asphalt emulsion. Photo: Richard Kronick

A study prepared by CTC & Associates LLC and released in 2008 by the Wisconsin DOT revealed that although several states have performed full-depth reclamation (FDR) projects with fly ash, few — if any — had used it in conjunction with engineered asphalt emulsions like the project in Le Sueur County, Minn.

The report includes the results of a North American survey of state and provincial transportation departments. The five-question survey answered by 23 states and three provinces indicated that just three states — Iowa, Nebraska, and Texas — routinely use fly ash as part of full-depth asphalt reclamation projects.

For example, the Nebraska Department of Roads uses fly ash or emulsion in all FDR projects, but emulsions are used only when the roadway sits on sandy soils, not in combination with the fly ash. Fly ash is currently used on a limited basis in Wisconsin DOT full-depth asphalt reclamation projects.

A byproduct of coal-fired plants, fly ash is often added to soils to stabilize weak bases and subgrades. Less than 5% of the 22 million tons recycled annually is used to strengthen bases and subbases, according to the Federal Highway Administration. About 60% of recycled fly ash is directed toward concrete production.