Project Details

Increase in travel demand, reduced availability of virgin materials and budgetary constraints have prompted the use of waste materials in new asphalt mixes. Recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) are the two waste materials that receive the most importance as they offer a partial substitute for virgin aggregates and asphalt binder. Mixtures incorporating higher amounts of RAP or RAS will have higher stiffness due to blending of aged and virgin binders. This results in the mixture being more susceptible to cracking, therefore limiting the amount of recycled material that can be added to asphalt mixtures. The current state of practice in the industry is to place limits on the percentage by weight of total mixture that has been replaced by RAP, RAS, or a combination of both. The need exists to determine if changes in specifications are warranted to limit recycled materials based on the percent recycled binder they contribute to the total binder percentage instead of the percent by total weight of mixture.  The main objectives of this study are to determine recycled binder limits for S9.5C and S9.5D mixes which use a virgin binder grade of PG 70-22 and PG 76-22, respectively. In this study, limits for allowable recycled binder were determined by conducting dynamic shear rheometer (DSR) tests at high and intermediate temperatures. Blending charts were developed and regression analysis was done to estimate the allowable recycled binder limits for virgin binders to satisfy the performance grade (PG) specifications for S9.5C and S9.5D mixes. These limits were used to design recycled asphalt concrete mixtures. These mixtures were tested using the Asphalt Mixture Performance Tester (AMPT) for measuring dynamic modulus. The dynamic modulus values of the mixtures and rheological properties of blended binders were used to predict the performance of the mixtures with respect to fatigue cracking and rutting using AASHTOWare Pavement M-E Design software. The predicted performance data and binder test results were used to determine limits for the recycled materials based on the recycled binder percentage in the mix.