In 1974, Houston, Texas, tried an unusual material for road construction: ash left behind after municipal waste was burned. Instead of sending the residue to landfill, engineers used it in an asphalt concrete base course on a city street. Three years later, the experimental section was reported to be performing almost like a conventional asphalt pavement. According to the US Department of Transportation’s ROSA P. collection , the project was an early example of turning a difficult waste stream into a construction material. The mix contained 89% incinerator ash, 9% asphalt and 2% lime by weight, meaning that most of the material in the experimental road base came from waste rather than newly quarried aggregate.
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