Case Studies of Practices and Lessons Learned When Using Reclaimed Asphalt Shingles in Asphalt Mixtures

The use of reclaimed asphalt shingles (RAS) in asphalt mixtures dates back to the 1990s. RAS contains four to six times more asphalt binder than reclaimed asphalt pavement (RAP), so it is very attractive from a virgin asphalt binder replacement cost-savings perspective, as well as from a sustainability perspective, since over 50% of the carbon footprint of asphalt mixtures comes from asphalt binder production. Using RAS in asphalt mixtures also prevents it from being landfilled. However, asphalt binder in RAS is significantly stiffer than paving-grade asphalt binder, which can lead to stiff asphalt mixtures with poor cracking resistance. Materials, mixture design, and processing and handling developments have helped improve the success of RAS asphalt mixture use. The performance history of RAS mixtures over the past 20 years has shown that with proper engineering and construction it is comparable to virgin asphalt mixtures. In the current study, observations from field visits to six agencies that regularly use RAS in asphalt mixtures were summarized, identifying positive practices and lessons learned. Different agencies had diverse goals when using RAS; those with rigorous specifications and policies obtained good performance from the mixture, especially when closely monitoring it over time. Field performance reviews of in-service pavements up to 9 years old encompassing RAS or RAS and RAP revealed that with appropriate policy, mixture design, and quality control, good performance was achieved. Limiting RAS dosage, ensuring adequate virgin binder in the mixtures and a sufficiently soft blended binder, along with RAS processing and handling, led to positive performance.