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Use of Florida Phosphogypsum in Synthetic Construction Aggregate

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In its role to provide technology to promote the efficient use of minerals and mineral process waste, the U.S. Bureau of Mines has conducted research to identify and develop high volume uses for phosphogypsum. An asphalt-concrete containing 20 percent phosphogypsum met the Florida Department of Transportation specifications for Type II, SAHM and ABC-1 asphalt concretes. Mixtures containing up to 50 percent phosphogypsum and the remainder clays, produced aggregate when fired at 1,000°C with strengths that exceeded 1,000 psi. Mixtures containing a maximum of 50 percent phosphogypsum, 6 to 10 percent lime and the remainder fly ash had compressive strengths as high as 4,800 psi. Mixtures of phosphogypsum with cement, cement kiln dust, silica powders and calcium chloride were also investigated, but were not considered useful for road construction.