Effects of Changing Virgin Binder Grade and Content on High Reclaimed Asphalt Pavement Mixture Properties

Abstract

Most highway agencies have decades of experience with hot-mix asphalt whose percentage of reclaimed asphalt pavement (RAP) has remained low to moderate because of the general perception that RAP mixtures may be more susceptible to various modes of cracking. As the RAP proportion increases, so does the potential for an increase in mixture stiffness and a decrease in resistance to cracking. Two proposed ways to increase the durability of RAP mixtures are to (a) increase the amount of virgin binder in the asphalt mixture and (b) decrease the performance grade of the virgin binder. To assess these options, 0%, 25%, and 50% RAP mixtures at optimum asphalt content were designed with a standard PG 67-22 virgin asphalt binder. These mixtures were tested to evaluate surface cracking, reflection cracking, and rutting with the use of an energy ratio, overlay tester, and asphalt pavement analyzer, respectively. These tests also were conducted on RAP mixtures with 0.25% and 0.50% higher asphalt contents and at the optimum asphalt content with the use of a softer virgin binder. In addition, the linear amplitude sweep methodology was used to assess the fatigue properties of the blended binders. The results showed that, to improve resistance to cracking, the amount of virgin asphalt should be increased by 0.1% for every 10% of RAP binder in the mixture for up to 30% RAP binder. Once the RAP binder exceeds 30%, a softer grade of asphalt should be used to increase the mixture's resistance to cracking. All mixtures should be assessed for rutting susceptibility.