City of Colorado Springs / Streets / Pavement Rehabilitation/Resurfacing / Tire Rubber Asphalt
Open Graded Terminal Blend Tire Rubber Asphalt
Terminal Blend Tire Rubber Asphalt 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). 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 (outside of the environmental sustainability consideration) include a smoother ride, reduced noise inside and outside the vehicle, and better safety during rain storms due to increased drainage with less standing water and splash back. However, the most compelling possible benefit is that of durability and the potential to reduce street resurfacing expenses by extending the life of Colorado Springs roads.
Tire rubber asphalt has some unique characteristics. For example, it requires warmer surface temperatures than standard asphalt to be applied, specifically, 65 degrees or above. Tire rubber asphalt is also tackier than traditional asphalt, so water trucks spray the surface to bring the temperature down to 135 degrees before vehicles may drive on the new surface.
Manufacturing method being tried by Colorado Springs:
Terminal Blend 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. Local contractors do not require specialized equipment to use this product. Unlike most traditional densely graded asphalt mixes, which have three to four percent voids (air pockets), city's mixes have voids ranging from 18 to 22 percent. The porous material allows water to drain from the pavement surface faster.
2006 innovation test zones of about 25 lanes:
- Union Boulevard from about 600 feet north of Austin Bluffs Parkway to Academy Boulevard: This high-volume section was milled and overlaid with a 1½ inch layer of traditional dense graded asphalt followed by a one inch cap of terminal blend tire rubber asphalt. This mix used 10 percent tire rubber content and 3/8 inch aggregate.
- Chelton Road from Airport Road to Marion Drive (one block south of Palmer Park Boulevard): This low-volume section was milled and overlaid with traditional asphalt followed by a one inch layer of tire rubber asphalt. This mix used 10 percent tire rubber content and 3/8 inch aggregate.
- Wooten Road from Platte Avenue to Galley Road: In this section, half of the road was milled and overlaid with new traditional asphalt, followed by a one inch layer of tire rubber asphalt. The other half of the road had a one inch layer of tire rubber asphalt placed over the top of the existing asphalt, after crack sealing the surface. This mix used 10 percent tire rubber content and 3/8 inch aggregate.
- Briargate Parkway eastbound from Lexington Drive to Union Boulevard: In this section a one inch layer of tire rubber asphalt was placed over the top of the existing surface. This mix used 10 percent tire rubber content and 3/8 inch aggregate.
2007 innovation test zones of about 27 lanes:
- All lanes on Union Boulevard from Pikes Peak Avenue to 1000 feet south of Austin Bluffs Parkway: In this section, as part of the Union Improvement Project, a 1¼ inch layer of tire rubber asphalt was placed over the top of a new 1 1/2 inch layer of traditional asphalt. This mix used 15 percent tire rubber content and 1/2 inch aggregate.
Testing:
- Noise Reduction: Continued testing has shown mixed results. 3/8" aggregate seems to be quiter than 1/2" aggregate and traditional asphalt. Continued testing will be needed to determine if noise-reducing qualities are lost over time and how 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.
- 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.
- Evironmental Considerations: Colorado Springs test areas have utilized 225,173 pounds of tire crumb rubber, recycling 2,000 to 2,300 tires.
Cost:
So far, using tire rubber asphalt has been more expensive for the City than using traditional asphalt. However, the product will pay for itself if adding one inch of tire rubber asphalt over traditional asphalt pavement extends road life by two years. In Colorado Springs and along the front range, generally the road life of traditional asphalt is eight to ten years.
Partners:
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. Schmidt Construction Company is the paving contractor the City has hired to lay down the tire rubber asphalt; they performed this work last year as well.
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The City's Tire Rubber Aspalt mix is a porous material that allows water to drain from the pavement surface faster for enhanced safety during rain storms due to increased drainage with less standing water and splash back.
Pictured here is tire crumb rubber, old tires crumbled with all the metal pieces removed, which gets melted into the asphalt mix to create tire rubber asphalt.
Pavement contractors use standard equipment to apply tire rubber asphalt. |
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