Recycled binder availability (RBA) is the proportion of total recycled binder in a reclaimed asphalt pavement (RAP) source that is available to blend with virgin asphalt. RAP binder locked inside of an agglomeration is ‘unavailable’ whereas the binder within the peripheral mastic coating of an agglomeration is ‘available’. However, RBA is not accounted for in the majority of state highway agencies’ design procedures The innovation developed through this project is a practical method to quantify the extent of agglomeration in a given RAP source, and in turn, the RBA using comparative sieve analysis of RAP and recovered RAP aggregate. Several sieve analysis procedural variables were evaluated. The RBA derived from a washed sieve analysis of RAP conditioned at 100°C demonstrated favorable agreement with recycled binder contribution (RBC) measurements, making it the recommended procedure for implementation. The close agreement between RBA and RBC results suggests that all available RAP binder is activated in asphalt mixtures produced at typical production conditions. Tracer-based microscopy analysis of asphalt mixtures fabricated using alternative preheating and conditioning procedures further indicates that RBC in asphalt mixtures does not vary significantly with laboratory production conditions. Consequently, the results suggest promise that the RBA results reflect RBC in asphalt mixtures produced under variable conditions. Statistical analyses indicate that RBA cannot be predicted from the commonly measured constituent RAP properties, thereby suggesting that the established sieve analysis procedure is necessary to precisely quantify source-specific RBA. While exhibiting statistical distinctions, the majority of sources exhibited RBA values near 60 percent, implying that a constant value of 60 percent could serve as a pragmatic alternative when sieve analysis measurements are not possible. The effects of RBA on asphalt mixture design were evaluated by comparing the composition and performance of control asphalt mixtures designed under the assumption of 100 percent RBA with those redesigned according to the availability adjusted mixture design (AAMD) method. The AAMD method generally produced mixtures with enhanced cracking resistance and similar rutting resistance compared to the control mixtures. Also, virgin mixtures and AAMD RAP mixtures prepared with similar available volumetric and effective properties yielded similar cracking resistance performance, suggesting potential for applying the AAMD method to counteract RAP’s detrimental effects on cracking resistance.

The Final Report is available.