The use of scrap tires in construction projects is not just a way of getting rid of scrap tire stockpiles. It also is a cost-effective construction material providing properties that engineers need in certain projects, according to Dana Humphrey, professor of civil engineering at the University of Maine.
``There are way too many materials in the recycled product market where somebody wants you to take it, but it doesn't do anything for end users,'' Mr. Humphrey said at the 20th annual Clemson Tire Industry Conference, held March 10-12 in Hilton Head. ``This product does do something.''
In general, tire chips and pieces of two to 12 inches in size are used in construction and civil engineering projects, according to Mr. Humphrey. In use, they are known as tire-derived aggregate (TDA). In 1990, some 2 million scrap tires were used for TDA; by 2003, he said, that number had burgeoned by 52 million.
TDA's light weight, low earth pressure, thermal insulation, drainage and compressibility make it ideal for projects in low-lying coastal areas or anywhere the soil is weak, he added.
``If you put it as a filler against a wall, it doesn't push the wall very hard,'' he said. ``Its drainage properties are so high that they're difficult to measure in a laboratory.''
The low cost of TDA also increases its desirability. ``TDA is often the cheapest alternative if you need its unique properties,'' Mr. Humphrey said.
Among the projects made-to-order for TDA are lightweight fill for highway embankments, retaining wall backfill, vibration damping layers for rail lines, insulation to limit frost penetration and drainage layers for landfills and septic tank leach fields, he explained.
Civil engineering projects also are sure-fire ways to achieve scrap tire abatement, he said. The average TDA-using construction project utilizes 75 tires per square yard, meaning that a single project can use more than 1 million tires. One highway embankment in Portland, Maine, used 1.2 million scrap tires.
``They used all the scrap tires in Wyoming for one project,'' Mr. Humphrey said. ``There are plenty of states that would love to have that problem.''
Most people outside the industry don't realize it, but TDA is an engineered product made to exact specifications, Mr. Humphrey noted. ``The size of the pieces is 12 inches maximum because if you use big, long chunks, it's hard for a contractor to work with,'' he said.