Discovery Magazine

Photo Credit: Global Tire Recycling Wildwood FL

Ground Tire Rubber (GTR) as a Stabilizer for Subgrade Soils

Ground tire rubber (GTR) is often included in asphalt pavements as a way to minimize tire deposition in landfills. With large ground tire rubber stockpiles available for various uses, finding new uses for this waste material is imperative.  Recent developments in the asphalt paving and binder industries are limiting the amount of ground tire rubber that will be used in new hot mix asphalt pavements. Therefore, methods to stabilize subgrade soils with GTR should be investigated to further reduce tire volume at landfills. The feasibility of this alternative as well as performance implications will be measured. The final goal of this research is to increase the use of a waste product without affecting the long-term performance of pavements. 

The research team is evaluating the use of ground tire rubber as a component in FDOT stabilized subgrade soils.  Three different subgrades are being evaluated along with three GTR sizes (1" 3/8" and No 40 mesh).  The subgrade soils range from relatively strong (i.e. LBR of about 60) to relatively weak (i.e., LBR near 20) materials.  Volumetric blends of up to 16% GTR are being tested with the three subgrades.  The geotechincal testing program includes:

  • Limerock Bearing Ratio (LBR, which is FDOT's version of the California Bearing Ratio CBR test),
  • Consolidation testing,
  • Resilient Modulus Testing,
  • Permeability Testing,
  • Moisture-Density testing,
  • Grain Size testing
  • Organic Content testing
  • Creep Testing

The test data will be summarized and presented to FDOT in a final report by June 2014. The research team includes both graduate and undergraduate students, who have renovated 2000 sf of lab space, begun to obtain ground tire rubber and Subgrade soils and assemble the testing equipment.  Early results indicate that very low percentages of GTR can be added to the relatively strong LBR or 60 material without adversely affecting the LBR.