Minimum Virgin Binder Content Needed in Recycled Superpave Mixtures to Resist Fatigue Cracking and Moisture Damage

Abstract

Use of recycled materials such as recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) in hot-mix asphalt (HMA) is common now due to their economy and sustainability. However, the effects of RAP and RAS on mixture performance are not fully known. In this research, three recycled Superpave mixture with 9.5 and 19 mm nominal maximum aggregate size (NMAS) were studied as control mixtures. Binder grades in mixtures containing higher percentages of recycled materials (RAP and RAS) were established using a blending chart. Nine laboratory-designed mixtures with different virgin binder contents were evaluated for potential early fatigue cracking using the dynamic modulus and simplified viscoelastic continuum damage direct tension fatigue tests. Moisture susceptibility of the mixtures was evaluated using the Hamburg wheel tracking and modified Lottman tests. Decreased virgin binder content resulted in inferior moisture and rutting performance for 9.5-mm mixtures. Similar fatigue performance was predicted for the mixtures made with the same source of materials regardless of NMAS. In general, mixtures with virgin binder content of 65% of total effective asphalt content and higher showed better performance properties.