Development of a Model to Estimate Percentage of Reclaimed Asphalt Pavement (RAP) Binder Contribution Based on Design and Performance of Super High RAP Mixes

Abstract

Reclaimed asphalt pavement (RAP) is one of the most recycled materials. The allowed RAP percentage in asphalt mixes is typically limited because of concerns over variability, binder stiffness, cracking performance, and generally the unknown associated with RAP. With abundant RAP stockpiles, the use of higher percentage RAP in asphalt mix may be warranted if performance can meet or exceed low RAP (LR) mixes (20% RAP or lower). In this study, high RAP (HR) mixes (40% RAP) and super high RAP (SHR) mixes (greater than 40% RAP) were designed, and their performance was compared with LR mixes. Mixes that cover two climates, Eastern and Western Washington, were included in this study. A lower performance grade (PG) virgin binder and a bio-based rejuvenator were used in HR and SHR mixes to allow the blended binder to meet the target PG required by the Washington Department of Transportation (WSDOT). Mix volumetrics and binder PGs of these mixes were designed close to each other, indicating the feasibility to produce RAP mixes up to 100% RAP. Overall, the addition of RAP improves the rutting performance but reduces the cracking performance of SHR mixes. Two measures were evaluated to mitigate SHR mixes’ cracking potential, including adding extra 0.5% virgin binder or 50% rejuvenator above the original dose, which improved the cracking performance of SHR mixes but reduced the rutting resistance. Based on these results, a recycled binder contribution model was developed to estimate the percentage of RAP binder contribution based on rutting and cracking performance testing.