Testing Protocols to Ensure Performance of High Asphalt Binder Replacement Mixes Using RAP and RAS

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt concrete (AC) mixtures can reduce demand for virgin aggregates and asphalt binder, bringing environmental and economic benefits. However, replacing virgin asphalt binder in AC mixtures poses challenges in terms of mixture volumetrics and low-temperature cracking, fatigue cracking, and other deterioration related to cracking. To counter these effects, softer virgin asphalt binder grades or modifying agents are used to improve production consistency. The purpose of this study was to develop and evaluate protocols, procedures, and specifications for testing engineering properties and performance of AC mixtures with high amounts (up to 60%) of RAP and RAS. The criteria for selection of the test method were (1) statistically significant spread in test outcome, representing a mix’s cracking resistance; (2) applicability and seamless implementation; (3) correlation to other independent test methods and engineering intuition; and (4) correlation to field performance. A practical test method, the Illinois modified semi-circular bending test (IL-SCB) was developed that can be readily implemented to quantify AC mixture’s cracking potential. In addition, a flexibility index (FI) was introduced to determine cracking resistance in a consistent way. The IL-SCB showed consistent and repeatable trends for changes in AC mix design properties. The developed FI was shown to provide greater separation between AC mixes to capture some of the changes that could not be captured by fracture energy alone. This approach does not enforce any limits on any AC mixture design characteristics, such as RAP and RAS content, or other alternative materials or technologies. Instead, it categorizes AC mixes based on their performance index. Hence, this approach encourages innovation and sustainability at the same time.