An interview with Dr. Kimberly “Kimmie” Lyons of the South Carolina Department of Transportation
The South Carolina Department of Transportation (SCDOT) has more than three decades of experience evaluating and using recycled tire rubber in asphalt technologies. Through ongoing research and field applications, the agency has focused on improving pavement performance while supporting sustainability and the beneficial use of recycled materials.
Performance First, Sustainability Included
According to Dr. Kimberly “Kimmie” Lyons, SCDOT adopted rubberized asphalt as part of a broader effort to improve pavement performance, sustainability, and long-term cost efficiency. Rubber modification can enhance resistance to cracking and rutting, reduce roadway noise, and help extend pavement service life while incorporating recycled tire rubber.
A Clemson University Connection
Lyons was first introduced to rubberized asphalt during her graduate research at Clemson University, where she studied rubberized Open Graded Friction Course (OGFC) for SCDOT. Her academic research provided a foundation for understanding the benefits and applications of rubberized asphalt, while the ongoing partnership between Clemson University and SCDOT has helped advance expertise and research related to recycled tire rubber in asphalt mixtures throughout South Carolina.
More Than Thirty Years of Experience
SCDOT’s evaluation of crumb tire rubber in asphalt mixtures dates back to 1991. Over time, the agency’s specifications evolved to allow ground tire rubber (GTR) to be added to liquid asphalt at supplier terminals using a controlled wet process. When properly incorporated, the process can improve the performance characteristics of standard asphalt binders to levels comparable with polymer-modified asphalt.
While the wet process remains an option, contractor use has been limited due to material handling challenges and additional equipment maintenance requirements. Through years of implementation, SCDOT identified proper mix design, temperature control, and contractor experience as key factors in achieving consistent performance.
Today’s Rubberized Asphalt Applications
SCDOT currently permits both dry-process and wet-process rubberized asphalt technologies. Applications include dense-graded asphalt mixtures produced using the dry process, stone matrix asphalt (SMA) mixes that use rubber as a durability additive, and stress absorbing membrane interlayer (SAMI) treatments designed to reduce reflective cracking prior to asphalt overlays.
These applications are used to improve durability, enhance resistance to cracking and rutting, and extend pavement life.
Learning from Others
SCDOT’s program has benefited from collaboration with other transportation agencies, particularly the Georgia Department of Transportation. By reviewing performance data, specifications, and lessons learned from Georgia, SCDOT gained valuable insights that helped reduce implementation risks and support informed decision-making.
Overcoming Challenges
One of the primary challenges has been limited contractor familiarity with rubberized asphalt, along with concerns related to mix design consistency and rubber introduction methods. To address these issues, SCDOT has emphasized contractor training, clear specifications, pilot projects, and ongoing communication between contractors and agency staff. These efforts have helped improve consistency and confidence in implementation.
Looking Ahead
SCDOT’s experience demonstrates that recycled tire rubber can be successfully incorporated into paving programs when supported by research, well-developed specifications, contractor engagement, and long-term commitment. From early wet-process evaluations to today’s dry-process mixtures, SMA applications, and SAMI treatments, South Carolina continues to build on decades of experience using recycled tire rubber to deliver both pavement performance and sustainability benefits.
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Key Takeaways
- SCDOT has more than 30 years of experience evaluating and using recycled tire rubber in asphalt applications, with research dating back to 1991.
- Rubberized asphalt supports both performance and sustainability goals by improving resistance to cracking and rutting while incorporating recycled tire materials.
- Ground tire rubber (GTR) can be used through both wet-process and dry-process technologies, providing flexibility for different pavement applications.
- Current SCDOT applications include dense-graded asphalt mixtures, stone matrix asphalt (SMA), and stress-absorbing membrane interlayer (SAMI) treatments.
- Proper mix design, temperature control, and contractor expertise are essential to achieving consistent performance from rubberized asphalt.
- Collaboration with Clemson University and the Georgia Department of Transportation has helped advance research, refine specifications, and support successful implementation.
- Contractor training, pilot projects, and clear specifications have been key to overcoming implementation challenges and improving adoption.
- SCDOT's long-term experience demonstrates that recycled tire rubber can deliver both pavement performance and environmental benefits when supported by research and best practices.
Frequently Asked Questions (FAQs)
Q: What is rubberized asphalt?
A: Rubberized asphalt is asphalt pavement that incorporates ground tire rubber (GTR) from recycled scrap tires. The rubber can be added through either wet-process or dry-process technologies to enhance pavement performance and durability.
Q: Why does SCDOT use recycled tire rubber in asphalt?
A: SCDOT uses recycled tire rubber to improve pavement performance, extend pavement life, increase resistance to cracking and rutting, reduce roadway noise, and support sustainability initiatives through the beneficial use of recycled materials.
Q: How long has South Carolina used rubberized asphalt?
A: SCDOT has been evaluating and using recycled tire rubber in asphalt mixtures since 1991, making it one of the longest-running rubberized asphalt programs in the Southeast.
Q: What are the benefits of ground tire rubber (GTR) in asphalt?
A: Ground tire rubber can improve durability, reduce cracking and rutting, enhance pavement longevity, and provide an environmentally responsible outlet for recycled scrap tires.
Q: What rubberized asphalt applications does SCDOT currently allow?
A: SCDOT permits both dry-process and wet-process rubberized asphalt technologies, including dense-graded asphalt mixtures, stone matrix asphalt (SMA) mixes, and stress absorbing membrane interlayer (SAMI) treatments.
Q: What challenges are associated with rubberized asphalt?
A: Some challenges include contractor familiarity, mix design consistency, and material handling requirements. SCDOT has addressed these challenges through training, specifications, pilot projects, and increased collaboration with contractors.
Q: How does recycled tire rubber contribute to sustainability?
A: Using recycled tire rubber in asphalt helps divert scrap tires from the waste stream while creating a valuable material that can improve pavement performance and support sustainable infrastructure development.
Q: What can other transportation agencies learn from SCDOT's experience?
A: SCDOT's experience shows that successful rubberized asphalt programs are built on research, performance testing, clear specifications, contractor engagement, and long-term commitment to continuous improvement.