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Elemix concrete additive, an engineered lightweight synthetic particle (LSP) that uniformly reduces the weight of concrete, was used in a backfill mix for a 1,700-ft.-long, 26-ft.-wide mine slope built by Arch Coal, Inc. in Grafton, W.Va. The new Leer Mine will be a world-class underground facility, with projected annual output of 3.5 million tons of premium metallurgical coal.

The lightweight concrete mix fills the annular space between the excavated rock and a steel tunnel lining, which slopes at a 12 percent grade. The slope will provide a means of removing the coal, access for materials and equipment, and a secondary means of access/egress for mining personnel. Approximately 75,000 lbs. of Elemix LSP was used as part of a total volume of 8,000 cu. yd. of concrete.

“The lightweight concrete provided a strong backfill material at about one-third the density of normal concrete. The lower density allowed for rapid and continuous placement of the backfill without overloading the forms, saving substantial labor and overhead cost,” says Frank Stevens, construction manager for Cowin & Company, Inc., a mining construction specialist based in Birmingham, Ala. “The concrete flowed long distances without segregation or bridging, insuring complete backfill of the tunnel lining and consistent compressive strength.”

“[Our product] has been engineered to perform in exactly these types of applications,” notes Elemix Business Development Manager Kevin Foody, P.E. “The particle size and density provides the material properties to contribute to the plastic and hardened performance of the concrete.”

Elemix leverages its dynamic structure and dispersion characteristics to become an integral part of the concrete matrix, he adds, resulting in reliable consistency and improved performance for lightweight structural concrete. Used in combination with or as a replacement for normal-weight and lightweight aggregates, it achieves ICC-ES AC-408 code compliance while enabling builders to produce concrete that reduces construction costs, resists cracking, and pumps, places and finishes easily. — 412-225-1110;