Best Practice for Using RAS in HMA (0-6614-1)

The use of recycled asphalt shingles (RAS) in hot-mix asphalt (HMA) mixtures has the potential to significantly reduce the cost of asphalt paving mixes while conserving energy and preserving the environment. This report documents the best practices for the use of RAS in HMA in terms of RAS processing, characterizing the processed RAS (binder content, gradations, and performance grade [PG]), RAS mix design, production, and field construction. First, a six-step RAS processing guideline was proposed in this study, including collecting, asbestos testing for the tear-off asphalt shingles, sorting, grinding, screening, and storing the processed RAS. Researchers found that the tear-off shingles have higher binder content than manufacture waste shingles. The manufacture waste shingles have a consistent 20 percent binder content than manufacture waste shingles. The manufacture waste shingles have a consistent ranging from 23 percent to 28 percent. Futhermore, the overall RAS variability in terms of asphalt binder content and gradation is low for both manufacture waste and tear-off shingles. Obviously, the RAS binders are very stiff and their high temperature PG is beyond 140°C, and the low temperature PG is above 0°C. This study compared the ignition oven method with the extraction method, and found that, except for one shingle source, both methods produced similar aggregate gradations and asphalt contents. Issues related to RAS mix design, production, and field construction were identified and discussed in this report. One important area needing further investigation is the long-term performance of RAS mixes. Generally, RAS mixes have good rutting resistance, but its resistance to reflective cracking, fatigue cracking, and potential raveling needs to be evaluated. Life-cycle cost analyses should be performed to determine the economic viability of using RAS.