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Credit: Photo: James R. Rosenmerkel

During construction on County Trunk Highway S in northwestern Racine County, Wis., construction crews travel on recycled base stabilized with fly ash.
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Credit: Photo: James R. Rosenmerkel

Road crews place hot-mix asphalt over the stabilized, recycled subgrade.
EVALUATION

During a field review, Katz indicated he was pleased with the condition of the subgrade. The lower course of HMA paving showed no evidence of surface stress, indicating the stabilizing was successful. Katz also pointed out that using FDR with fly ash allowed the county to save up to an additional 2 inches of HMA to achieve the desired strength, stretching tight budget dollars. At current prices, HMA pavement costs approximately $25,000 per mile. Engineering studies indicate that in designing HMApavements, the structural coefficient for pulverized, fly-ash stabilized base course, increases from 0.14 to 0.30 in the American Association of State Highway and Transportation Officials formula, accounting for the savings in HMA thickness.

Mehring offered an additional advantage to the stabilizing: “Construction equipment for an adjacent bridge project was able to traverse the recycling area with no delays and no damage,” he said. Katz indicated Racine County likely will tackle more projects using FDR methods with fly ash as the stabilizer.

VALUE OF REUSE

Stabilizing existing road materials with fly ash conserves resources and makes use of a product that might otherwise be discarded. In addition to stabilizing reclaimed asphalt pavement, fly ash also is used stabilize subgrade materials with predominantly clay soils. In this application, soft subgrades exhibit CBR increases from 4 to 6 to as much as 45 to 60 when treated with 10% to 12% Class “C” fly ash.

Recycling road materials is gaining attention across the country. The U.S. Environmental Protection Agency is promoting reuse of industrial products in a new initiative called Top 20—Construction Initiatives. The American Coal Ash Association—along with the EPA, Federal Highway Administration, and other groups—is developing a Green Highway Initiative to promote sustainable construction techniques in the national transportation system.

— Rosenmerkel is a consultant to Lafarge North America, Herndon, Va.