Recycled agricultural waste has potential for use in many applications not related to highways. Uses of agricultural wastes (with a few notable exceptions) in highways are usually restricted to landscaping applications. It is estimated that more than 2 billion tons (1.8 X 1012 kg) of agricultural waste is produced each year in the United States. This represents about 46 percent of the total waste produced in the United States each year.
Animal Manure. Animal manure is produced at a rate of 1.6 billion tons (1.5 X 1012 kg) annually in the United States. Other than its use as fertilizer or as composting material for landscaping rights-of-way, it has little recycling value for highways.
Crop (Green) Waste. Of the 400 million tons (363 X 109 kg) of crop waste produced annually from harvesting operations and grain processing, the potential to use rice husk ash to increase compressive strength in concrete is the most promising highway use. Research has also been conducted into converting cellulose waste to an oil appropriate as an asphalt extender.
Logging and Wood Waste. It is estimated that about 70 million tons (64 X 109 kg) of lumber waste from logging and milling operations is produced each year. Only about one — third of the wood from logged trees is used as lumber. Much of the remainder is used in other industry applications. Uses in highways include mulching and lightweight fill material for embankments or to repair slides. Application as lightweight fill material has been well documented and proven to be successful. Life expectancy of such embankments is estimated at 50 years.
