June 5, 2013
Through the years, there has been an ebb and flow to the use of rubberized asphalt in Michigan – from bumpy beginnings in the 1990s to ongoing research and testing that is exploring the latest developments relevant to recycled tire rubber use in asphalt.
In the 1990s, Michigan explored the use of recycled tire rubber (RTR) under the threat of a national mandate without the participation or inclusion of the local asphalt or tire recycling industry. Both the rubberized asphalt manufacturing and recycled tire rubber supply were not local to Michigan at the time.
However, a study was conducted in 1993 where nine miles of M-50 between Eaton Rapids and Charlotte, MI were paved with several different rubberized materials. A significant portion of the study was dedicated to emission testing, since the technology available at the time often required substantially higher mix temperatures and this was a concern. The emission testing did not substantiate any significant contributions from the RTR per se, more was derived from the base liquid asphalt source. No formal conclusions were reached by the Michigan Department of Natural Resources and the issue went away along with the national mandate.
Fast forward to 2001, an innovative activated tire rubber technology, perhaps ahead of its time, was introduced in a trial project. In the fall of 2001 between October 19 and November 30, about 50,000 tons of mix were placed. Issues arose in production and “pumpability”; the binder with the rubber included was very high in viscosity, was difficult to handle and did not encourage the contractor for repeated use.
The DOT paused its study of RTR for awhile and the Saginaw County Road Commission picked up interest in 2005, placing several small pilot projects in various locations throughout the county through the year 2011, using RTR as a alternative modifier along with a processing agent to lower mix temperatures, reduce viscosity, improve contractor workability and aid in compaction.Projects completed by the Saginaw County Road Commission (SCRC) include:
- Sheridan Road – Fisher to Williamson – 2 Miles – 2005
- Bell Road – Busch to Townline – 1 Mile – 2006
- Curtis Road – Sheridan to Bell – 2 Miles – 2007
- Townline Road – Brennan to Steel – 2 Miles – 2007
- Hackett Road – M-47 to McCarty – 0.75 Mile – 2011
- N. Thomas Road – Geddes to Frost – 1.75 Miles – 2011
- Ferden Road – Frandsche to Sharon – 1.1 Mile – 2011
- Beyer Road – King to Bradley – 0.9 Mile – 2011
- Frank Road – Frankenmuth C.L. to Roedel – 0.5 Miles – 2011
A major shift in asphalt materials cost developed between 2005 and 2011. The cost of liquid asphalt and virgin polymers increased substantially. Both materials are tied to the current price of crude oil. The cost of recycled tire rubber has not been so adversely affected as the feedstock of end of life tires and processing cost experienced little change over the same period of time.
In 2010, the Michigan Department of Environmental Quality began a market development program to re-examine rubberized asphalt on the state agency level and began encouraging projects with grants provided by the scrap tire fund. Materials research and project performance evaluations have been conducted by Michigan State University with testing and trials still underway. The MDEQ Market Development program has funded 24 projects and beneficially reused over 88,000 end of life tires since 2010. A re-introduction training program was provided in February 27, 2012, dubbed the Crumb Rubber Modified Asphalt 101 to provide local stakeholders with the latest information relevant to recycled tire rubber use in asphalt.
Ingham County Road Commission also participated in the market development projects through placement of a test sections on Mt. Hope Road in 2010, Waverly Road in 2011 and Haslett Road in 2012. Dr. Emin Kutay, Assisitant, professor at MSU, was contracted to provide materials characterization and performance testing analysis.
Dr. Kutay has also published an interesting paper demonstrating the relationship between RTR particles, aggregate and asphalt binder in a mix using 3D x-ray microtomography imaging.