With the escalating costs of materials and construction for highways and streets, many agencies charged with the responsibility of designing and constructing highways are utilizing byproduct stabilized (pozzolanic) materials. Low-strength (pozzolanic) materials have been used fairly extensively in some areas of the United States as well as abroad. In general, pozzolanic materials have been used to stabilize an aggregate base or subbase by addition of fly ash and a source of lime to develop a cementitious reaction. Additionally, portland cement or cement kiln dust have been used to stabilize aggregate subbase and (or) base materials.

Until recently, the use of stabilized materials in highway and street construction in Kentucky was not often economically competitive with abundant supplies of high-quality aggregates. However, as costs of production and processing aggregate materials have increased, so has the feasibility of stabilized bases, and particularly pozzolanic base materials.

Mixtures that have been considered recently and evaluated to some degree include the following:

Lime kiln dust, fly ash, and dense-graded aggregate;

Byproduct lime and dense-graded aggregate;

Lime kiln dust, fly ash, dense-graded aggregate, and sand;

Lime kiln dust, fly ash, and limestone mine screenings (waste material from limestone quarrying operations); and

"Scrubber sludge," quicklime, and dense-graded aggregate or pond ash.

Pozzolanic base or subbase materials have been utilized on an experimental basis for a number of Lexington, Kentucky, street projects. Two projects for the Kentucky Transportation Cabinet also are being evaluated. Thus, performance experience currently is limited, but at the same time evolutionary.

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Prepared for a seminar on Fly Ash Utilization in Highway Construction Atlanta, Georgia. Sponsored by the Federal Highway Administration March 12-13, 1985.