Civil Engineering Applications
The civil engineering market encompasses a wide range of uses for scrap tires. In almost all applications, scrap tire material replaces some other material currently used in construction such as lightweight fill materials like expanded shale or polystyrene insulation blocks, drainage aggregate, or even soil or clean fill.
A considerable amount of tire shreds for civil engineering applications come from stockpile abatement projects. Tires that are reclaimed from stockpiles are usually dirtier than other sources of scrap tires and are typically rough shredded. Rough tire shreds can be used as embankment fill and in landfill projects.
39 states approve tire shreds for civil engineering applications. (Source: Rubber Manufacturers Association, 2003. )
Civil Engineering Applications
- Subgrade Fill and Embankments
- Backfill for Wall and Bridge Abutments
- Subgrade Insulation for Roads
- Septic System Drain Fields
- Other Uses
- Environmental Studies on Using Scrap Tires for Civil Engineering Applications
Scrap Tire Promotional Video
Subgrade Fill and Embankments
Tire shreds can be used to construct embankments on weak, compressible foundation soils. Tire shreds are viable in this application due to their light weight. For most projects, using tire shreds as a lightweight fill material is significantly cheaper than alternatives.
Examples of projects using scrap tires as subgrade fill and/or embankments include:
- Two highway embankments on weak clay in Portland, Maine.
- An interstate ramp across a closed landfill in Colorado.
- Mine access roads across bogs in Minnesota.
- Stabilization of a highway embankment in Topsham, Maine.
- Reconstruction of a highway shoulder in a slide prone area in Oregon.
Other uses of tire shreds: subgrade fill and embankments include retaining forest roads, protecting coastal roads from erosion, enhancing the stability of steep slopes along highways, and reinforcing shoulder areas.
For additional information, see:
- US DOT Federal Highway Research Center, User Guidelines for Tires Shreds as Embankment or Fill
- Texas DOT Specifications for the Use of Recycled Materials
Backfill for Walls and Bridge Abutments
Tire shreds can be useful as backfill for walls and bridge abutments. The weight of the tire shreds reduces horizontal pressures and allows for construction of thinner, less expensive walls. Tire shreds can also reduce problems with water and frost build up behind walls because tire shreds are free draining and provide good thermal insulation.
Recent research has demonstrated the benefits of using tire shreds in backfill for walls and bridge abutments.
Subgrade Insulation for Roads
In northern climates, excess water is released when subgrade soils thaw in the spring. Placing a 6 to 12-inch thick tire shred layer under the road can prevent the subgrade soils from freezing in the first place. In addition, the high permeability of tire shreds allows water to drain from beneath the roads, preventing damage to road surfaces.
For more information on civil engineering applications, consult:
- ASTM specifications for use of tire shreds in civil engineering applications, specifically ASTM D6270-98 available on the ASTM Web site [Note: users must pay to download/view a copy of the ASTM specifications]
- State DOT engineering reports;
- Leachate data; and
- Training courses on highway and landfill applications.
Landfill construction and operation is a growing market application for tire shreds. Scrap tire shreds can replace other construction materials that would have to be purchased. Scrap tires may be used as a lightweight backfill in gas venting systems, in leachate collection systems, and in operational liners. They may also be used in landfill capping and closures, and as a material for daily cover.
Septic System Drain Fields
Some statesAlabama, Florida, Georgia, South Carolina, and Virginiaallow tire shreds to be used in construction of drain fields for septic systems. Tire-derived material replaces traditional stone backfill material, but reduces the expense and labor to build the drain fields. Tire chips can also hold more water than stone and can be transported more easily due to their light weight.
Challenges to using tire shreds in drain fields include tire chip quality (tire chips must be clean cut and be of uniform size) and economicsin some areas, stone is abundant and cheap; tire shreds must be cheaper than stone to be used readily.
- Playground surface material
- Gravel substitute
- Drainage around building foundations and building foundation insulation
- Erosion control/rainwater runoff barriers (whole tires)
- Wetlands/marsh establishment (whole tires)
- Crash barriers around race tracks (whole tires)
- Boat bumpers at marinas (whole tires)
Environmental Studies on Using Scrap Tires in Civil Engineering Applications
A literature review was done by the University of Maine on the water quality and environmental toxicology effects of tire-derived aggregate (TDA). The review found that: TDA has a limited effect on drinking water quality and fresh water aquatic toxicity for a range of applications including lightweight backfill for walls and bridge abutments, insulation and drainage layers beneath roads, free-draining and insulating backfill for residential foundations, vibration damping layers beneath rail lines, landfill leachate collections systems, drainage layers in landfill caps, landfill gas collection systems, and drainage aggregate for drain fields for on-site waste water treatment systems. TDA is unlikely to increase the concentration of substances with primary drinking water standards above those naturally occurring in the groundwater. It is likely that TDA will increase the concentration of iron and manganese, but the data indicates that these elements have limited ability to migrate away from the TDA installation. This literature review compiled by Dr. Dana Humphrey and Michael Swett of the University of Maine.
- Literature Review of the Water Quality Effects of Tire Derived Aggregate and Rubber Modified Asphalt Pavement (PDF) (58 pp, 332K, about PDF)
Several environmental studies have been performed to assess the potential for toxics to leach from tires when placed in wet soils. The impact of scrap tires on the environment varies according to the local water and soil conditions, especially pH value.
- Chelsea Centers Technical Report on Environmental Impacts of Rubber In Light Fill Applications (PDF) (20 pp, 153K, about PDF)
Two studies by the University of Maines Department of Civil Engineering on water quality of tire leachate below the ground water table showed that if the groundwater pH is near neutral (not too acidic or basic), tire shreds have only a small impact on groundwater quality.
- Field Study of Water Quality Effects of Tire Shreds Placed Below the Water Table (PDF) (10 pp, 183K, about PDF)
Minnesota began using shredded tires as a lightweight fill material in 1985 on logging roads through areas with weak soils. This report documents seven sites in Minnesota that used shredded waste tires as lightweight fill. Shredded tires were proven to be a viable form of lightweight fill because they are relatively lightweight, inexpensive and non-biodegradable. (Please note that this report mentions pyrolysis as a potential market for scrap tires, but after many attempts, pyrolysis has never been proven to be economically viable in the US.)