The objectives of this research are to (1) evaluate the effectiveness of recycling agents in HMA and WMA mixtures with high RAS, RAP, or combined RAS/RAP binder ratios through a coordinated program of laboratory and field experiments; (2) propose revisions to several relevant AASHTO specifications and test methods; and (3) develop training and workshop materials and deliver one workshop.
Since current practice generally limits recycled binder ratios to 0.3 or less, the scope of this research shall encompass asphalt mixtures prepared with recycling agents and RAS, RAP, or combined RAS/RAP at recycled binder ratios between 0.3 and 0.5. The performance of binders and mixtures containing recycling agents shall be compared to that of equivalent binders and mixtures (1) without recycling agents and (2) without RAS and RAP. It is anticipated that the majority of mixture testing in this research will be conducted on plant-mixed, laboratory-compacted (PMLC) specimens obtained from trial batches or production runs prepared in asphalt mix plants. Consistent laboratory conditioning procedures shall be applied to all specimens and changes in mixture properties with aging in the field shall be quantified. Field test sections shall be documented such that long-term performance studies can be conducted with these sections in future NCHRP research projects.