“In recent years many environmental concerns have been raised concerning the disposal of solid waste material. Landfills that have accumulated sold waste are running out of space. Many landfills have been shown to be the source or site of toxic waste that has spread to the surrounding communities, or have been suspected or feared of harboring and spreading toxins. Moreover, natural resources have been used up and discarded in solid waste facilities, raising concerns that these natural resources are becoming scarce or are in short supply.”

“As a result, there is growing interest in efforts to recycle solid waste materials. Building and road construction and building demolition produce a considerable amount of waste, known in the trade as construction and demolition (C&D) debris. C&D debris includes a wide variety of materials, including concrete, bricks, mortar, masonry, asphalt, metals, plastics, glass, ceramics, fiberglass and batt insulation, soil, dust, drywall, wood, plaster, paper, cardboard, dirt, and other materials.”

“In some areas, concrete is being successfully recycled. The larger pieces of concrete are sorted out from the debris and crushed to form recycled concrete aggregate (RCA), which is recycled to form recycled aggregate concrete (RAC). Japanese Patent No. 2002-053362, published Feb. 19, 2002, is representative of this approach (see the Abstract, "reutilization of concrete debris", "steps of: recycling concrete debris", etc.). The smaller RCA fines are sometimes recycled to form mortar or other masonry products. Similarly, larger pieces of glass, metal, paper, and drywall may be sorted from the debris and recycled. However, inevitably there is a residue of finer particles resulting from the crushing, shredding, or grinding of the C&D debris that has a mixed composition, referred to as C&D debris fines, that heretofore could not be economically recycled and is therefore simply dumped at the landfill for disposal.”

“The only current uses for C&D debris fines are limited to alternative daily cover (ADC) for landfills, soil beds or road beds, earth engineering uses, and the like. Even use for these purposes is sometimes problematical. For example, it has been estimate that C&D debris fines contain about 20% drywall by weight. Drywall contains gypsum (calcium sulfate), which is often converted to hydrogen sulfate when used as ADC in landfills. The resulting odor, similar to rotten eggs, is noxious, and in high enough concentrations, may leach into the soil and underground water, potentially posing a health hazard or damaging nearby crops or vegetation.”

(Cummings and Chuckran, US Patent 7,815,729; 10/19/2010)

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