The Missouri Department of Transportation has been a pioneer in the use of recycled asphalt pavement in its asphalt mixes, allowing the agency to save money and protect the environment.
When a contractor approached MoDOT in 2003 with the proposal to try recycled tear-off shingles in an asphalt mix, MoDOT stood to save millions of dollars while simultaneously keeping waste out of landfills. MoDOT used an average of 4,170,300 tons of asphalt each year between 2004 and 2014 to build and maintain its state roadways.
“It’s not often that you come across a product that can be used in pavement that is inexpensive, produces a good viable product, saves taxpayers money, and helps the environment, said Sarah Kleinschmit, Field Materials Engineer at MoDOT. “Using recycled shingles is more than win-win!” she said.
Post-consumer RAS was not being used by any other state DOT at the time MoDOT and the contractor began their investigation into the viability of using RAS-containing asphalt mixes. Today, about 20 state DOTs allow or are making efforts to allow using post-consumer RAS in their asphalt mixes. Integrating shingles in asphalt was not a new concept when MoDOT and their contractor used a pilot shingle mix—based on favorable test results—on Route 61/67 in St. Louis County in 2005; manufacture waste recycled asphalt shingles (RAS) were being used at various state DOTs. However, using post-consumer RAS represented an innovative step towards continuing to reduce waste and increase cost-savings for roadway projects.
Testing and Developing RAS Specifications
When MoDOT began investigating the potential for using post-consumer RAS in asphalt mixtures, it began with a literature review and then participated in a demonstration project with the contractor in 2004. MoDOT found results from testing the demonstration mixture favorable enough to launch the pilot project on Route 61/67 in St. Louis County. Though some reflective cracking was visible on the roadway after six years, the pavement’s performance was still deemed favorable by MoDOT.
Another project using manufacture-waste RAS was constructed in Joplin, MO, around the same time and produced similar results. With the initial positive performance of these two text mixtures, a provisional MoDOT specification allowing RAS in asphalt mixes was developed in 2006. In 2008 MoDOT’s added specifications to include different types of asphalt products (surface levels, bituminous mixes, and asphaltic concrete). In 2010, MoDOT added “Roofs to Roads” to its Tracker performance reporting accountability tool.
Key takeaways from MoDOT’s Roofs to Roads efforts:
- Economic savings: RAS saves the state $3 to $5 per ton of asphalt mixture when used between 5 percent and 7 percent RAS. With the average resurfacing project in the state using 30,000 tons of asphalt, the cost savings amounts between $90,000 and $150,000 per project. The reduced cost helps MoDOT resurface more roadways overall.
- Waste reduction: Incorporating RAS in its asphalt mixtures reduced 395,360 tons of shingles from disposal in landfills between 2004 and 2014.
- Innovation breeds innovation: Being open to and encouraging innovation within and around an agency often makes way for continued innovation. MoDOT finds that supporting its staff and contractors to come up with creative solutions to agency problems is a solid recipe for success.
- Recycled does not have to mean lower quality: Fear of inferior quality often accompanies attempts of using recycled materials. However, experience with RAS in asphalt mixes has shown significant economic and raw materials savings without a significant reduction in quality. Quality control is key, especially when ensuring the material meets specifications and is placed during optimal conditions (e.g., above 50°F).
Other State DOTs Using Roofs to Roads
Texas DOT was one of the first states to allow RAS in asphalt mixes and has developed stringent deleterious materials requirements for RAS. Its first RAS testing began in 1990, and Texas DOT developed its RAS program after the Asphalt Shingle Recycling Forum in Chicago, IL, in 2007.
Many examples from various state DOTs can serve as a starting point for other state DOTs interested in RAS. MoDOT recommends keeping any RAS program outcome-based, staying focused on the end result that meets its state’s particular needs (e.g., cheaper mixes, longer lasting pavement, pavement that does not crack, diverting waste from landfills, or all the above). State DOTs can reference other DOTs specifications to help develop their own specifications to include RAS.
The following state DOTs have effectively used RAS in projects:
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Current Efforts and Next Steps
Today, every contractor working for MoDOT has mixtures that incorporate manufacture waste or post-consumer RAS in their asphalt mixes. MoDOT continues to lead the way in using RAS in asphalt mixes by serving as the lead state of the Transportation Pooled Fund Study TPF-5(213), Performance of Recycled Asphalt Shingles in Hot Mix Asphalt.
With the help of partner agencies and other states—including Federal Highway Administration, Minnesota, Iowa, Indiana, California, Colorado, Illinois Tollway, and Wisconsin—this TPF study includes demonstration projects aimed at understanding how RAS affects both the binder and mixture properties of asphalt mixes. The study focuses on quality control practices, grind size of the shingles, and both post-consumer and manufacture waste shingles.
Study results showed that RAS can be successfully used in asphalt mixes; field performance showed no rutting, thermal cracking, or fatigue cracking after two years. Reflective cracking was noted on five of the projects.
Moving forward, MoDOT will continue to use RAS in asphalt mixes, monitoring mix performance and making adjustments as needed. Contractors are excited about the possibilities of using even more shingles in their asphalt mixes and are experimenting with how different grades of virgin binder are affected by the increase in shingles. MoDOT prides itself on encouraging innovation in collaboration with its contractors.
The following additional resource offer more information on recycled asphalt shingles in road construction:
- Construction and Demolition Recycling Association: http://www.cdrecycling.org/ and http://www.shinglerecycling.org/
- MoDOT Construction Specifications
- Iowa State University: Performance of Recycled Asphalt Shingles in Hot Mix Asphalt, Final Report (2013): http://lib.dr.iastate.edu/intrans_reports/19/
For more information on MoDOT’s Roofs to Roads efforts, contact Sarah Kleinschmit, Field Materials Engineer, MoDOT, at [email protected].