Most of the highways in the United States were built in 1950s and 1960s and have deteriorated significantly to date. More than 96% of the current highways and most surface streets are paved with asphalt. Asphaltic pavement that is removed during road reconstruction or rehabilitation is often landfilled with significant costs and environmental issues. Quarrying virgin aggregate for road reconstruction also results in environmental problems and energy consumption. There is an increased trend to recycle existing asphalt pavement in situ as base course for the new pavement surface. However, the load carrying capacity of such a base course is of concern due to the inclusion of asphalt and possibly fine-grained materials. Reuse of existing material in place would reduce material, transportation, and disposal costs and save energy. Much CKD is reintroduced to the Portland cement manufacturing process as kiln feed, but amounts are limited by alkalinity requirements for Portland cement and kiln operation issues. Too much CKD can clog parts of the system. Other options for reuse include soil stabilization, soil amendment for agriculture, and wastewater treatment. Cement kiln dust stabilization for rehabilitation of roads would provide another option to DOTs and municipalities depending on location and availability of suitable material.
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