Tread on me.

Processed scrap tires can make a sensible aggregate material for many civil engineering applications, University of Maine professor Dana Humphrey told attendees of 2005 ConExpo-Con/Agg session.

Humphrey has been researching and publishing reports about tires as a drainage and fill material since the early 1990s. "TDA has properties the engineers need," he said.

The civil and environmental engineering professor listed several positive attributes of what he calls tire-derived aggregate (TDA), saying it is a light, compressible material that offers good drainage qualities and is also a good insulator for cold-weather climates and is "often the cheapest choice."

Civil engineering applications can consume an enormous amount of tires, according to Humphrey, who said 600 feet of highway embankment fill space can consume some 1.2 million passenger tire equivalents (PTEs). In 2004, some 60 million PTEs were used in civil engineering applications, according to Humphrey.

He provided details on three different projects in California and Oregon that used TDA in a cost-effective manner. In one California project, the California Department of Transportation saved $470,000 by using TDA rather than pumice as an embankment material.