Tire chips (scrap tires cut into 1- to 12-inch pieces) have a number of qualities that make them well-suited for use in road and bridge construction. Tire chips are:
Tire chips can help reduce fill weight and address slope stability, landslide, and embankment settlement problems. Tire chip unit weights (compacted in place) range from 40 pcf for a thin fill with no soil cover to 60 pcf for a thick fill covered with a thick soil cover. Gravel compares at 125 pcf. For retaining wall and bridge abutments, tire chips reduce wall pressure, which can save money. For example, using tire chips as backfill can lower pressure at the base of a 5-foot wall by 50 percent.
Tire chips are more permeable than most granular aggregates and can be used in roadside French drains or drainage layers. Tire chip permeability is greater than 10 cm/s. Tire chips have also been shown to be a great thermal insulator, eight times better than gravel, in fact. Moreover, tire chips are durable and cheap.
Tires chips are generally uniformly graded with specific gravities ranging from 1.02 to 1.27 depending on whether steel belted, glass belted, or a mixture were measured. Specific gravities for soils are typically 2.60 to 2.80, more than double that of tire chips. Water absorption capacities generally range from 2 to 4.3 percent. Unlike most soils, water content does not affect tire chip compaction. Compacted dry unit weights of tires range from 38 - 43 pcf, approximately 1/3 the unit weight of soils. However, the unit weights of tire chips does increase under the weight of overlying soils and tire chips.
Large volumes of tires can be used in civil engineering construction applications. As a guideline, 75 tires yield about 1 cubic yard of compacted tire chip fill, and 1,000 tires will fill a 14-cubic-yard dump truck.