Open Graded Terminally Blended Tire Rubber Asphalt
Terminally Blended Tire Rubber Asphalt (TBTRA) is composed of highly-modified liquid asphalt combined with melted tire crumb rubber. This mixture is then blended with an open graded friction course aggregate (i.e. gravel or slag). Based on decades of successful use in other parts of the country, the City is applying test sections to see how the product will perform in a Colorado environment. Potential advantages of using tire rubber asphalt (beyond the environmental sustainability considerations) include a smoother ride, reduced noise inside and outside the vehicle, filtering of storm water for reduced levels of road contaminates in the runoff, and better safety during rain storms from increased drainage with less standing water and splash back. However, in an era of reduced budgets and shrinking resources, the most compelling potential benefit of TBTRA is its durability; an extension of the life of Colorado Springs roads equates to a reduction in street resurfacing expenses, as well as increased safety and reduced driver delays.
Manufacturing method being tried by Colorado Springs:
Terminally Blended Process - Tire rubber and modified liquid asphalt are processed and combined in a closed-system plant, for better quality control and reduced air pollution, and then shipped to the contractor's asphalt plant to be combined with aggregate. (Figure 2) Local contractors do not require specialized equipment to use this product. (Figure 3) Unlike most traditional dense graded asphalt mixes, which have three to four percent voids (air pockets), the TBTRA mix that the City is using has voids ranging from 18 to 22 percent. The porous material acts like a French drain, allowing water to drain from the pavement surface faster, increasing lane marking visibility and driver safety.
Click here to see innovation test zones by year.
Summary of Experiment Parameters:
- 2006: Baseline established with 3/8" aggregate, 10% rubber in the oil
- 2006: Various combinations of new/existing road surfaces and traffic volumes
- 2007: Larger rock - 1/2" Aggregate vs. 3/8" Aggregate
- 2007: Higher rubber content - 15% vs. 10% of oil
- 2009: Harder rock
- 2010: Type of rock - Slag vs. granite
Mix design and road surface changes are being tested for effects on:
- Noise Reduction
- Cost Savings/Sustainability
Noise Reduction: Continued testing has shown mixed results. 3/8" aggregate seems to be quieter than 1/2" aggregate and traditional asphalt. Preliminary results show noise reductions of up to 3 dB, but deterioration of the aggregate appears to correlate with increased noise levels over time. Continued testing will be needed to determine if how time and mix changes affect this finding
Colorado Department of Transportation (CDOT) Skid Test: No appreciable difference was detected between the traditional dense graded mixes and tire rubber asphalt
Surface Condition Ratings/Life Cycle: An outside company, RII, established baselines in 2007. Follow up tests will be done in 2010
Accident Rate Comparisons: Statistics compiled in 2008 show a 23.5% decrease in accidents
Appearance, Ride Quality, Rain/Snow Handling - Photo comparisons and public response indicate favorable results. Additional time will be needed to determine if qualities are lost over time and if mix changes affect this finding
Environmental Considerations: Colorado Springs test areas have utilized approximately 452,013 pounds of tire crumb rubber, recycling over 45,000 tires between 2005 and 2009
- The City of Colorado Springs and Pikes Peak Rural Transportation Authority (PPRTA) are partners on this innovative project to explore tire rubber asphalt in a Colorado climate. Nolte Associates is the program management firm that the City has hired to handle the PPRTA contract and develop the project specifications. Schmidt Construction Company and Lafarge North American are the paving contractors hired by the City to lay the tire rubber asphalt.
The City of Colorado Springs and Pikes Peak Rural Transportation Authority (PPRTA) have been recognized for their work with Terminally Blended Tire Rubber Asphalt by several organizations:
- Environmentally Sustainable Paving Practices Award, presented by the Colorado Asphalt Pavement Association in February 24, 2010, for the 2009 TBTRA paving project on Circle Drive. This award was given as part of CAPA's 16th annual statewide "Best in Colorado" Asphalt Pavement Award Program
- 2010 Excellence in Recycling Award: Outstanding Government Recycling/Diversion Program, presented by the Colorado Association for Recycling (CAFR) July, 2010 for the creation of programs that efficiently increase recycling and waste diversion
- The City's TBTRA program was recognized in the International Road Federation's Innovative Practices for Greener Roads CD-rom, website and literature which were published and distributed internationally in 2008
- Nominated for the 2010 Sustainability Champion Award, sponsored by the Colorado Department of Public Health and Environment and the Colorado Environmental Partnership
- TBTRA Program Overview and Technical Presentation
- Technical Paper: Testing Terminal Blend Tire Rubber Asphalt Performance for Safety, Ride Quality, and Cost Released in 2007
- Map of 2006 –2007 Test Areas
- PPRTA Street Division 2009 Year End Report: Pages 91-95 of this report provide a detailed description of the TBTRA paving program, testing plan, and test results
* Additional PowerPoint presentations and test results are available on request
Contact the Colorado Springs Streets Division Offices at 719-385-6819 for more information on the Colorado Springs TBTRA experimental paving program