The use of recycled asphalt pavement (RAP) in hot-mix asphalt leads to significant environmental and economical benefits. The major benefits are realized through reduced demand for new or virgin aggregates and asphalt binders. A limited amount of research has been performed to investigate the effects of RAP on the low temperature fracture characteristics of asphalt mixtures. However, this is an important subject, since the inclusion of RAP in Hot-Mix Asphalt (HMA) has the potential to increase mixture stiffness and brittleness unless properly compensated for. Most design procedures for mixtures consisting of RAP recommend an asphalt binder grade adjustment to compensate for the aged binder through the use of a softer virgin binder. This study evaluates the validity of this grade adjustment procedure in the context of four RAP materials using mixture fracture testing. The RAP materials used in this study were chosen from a larger database of materials to represent a wide variety of binder aging levels. Various fracture tests for asphalt concrete were identified through literature review. The disk-shaped compact tension (DC(T)) test, as standardized in ASTM D7313-07b, was used in this study to characterize mixture fracture energy. DC(T) fracture tests were conducted on various asphalt mixtures, namely: a control mixture with no RAP, manufactured with PG 64-22 asphalt binder; four mixtures containing 30% RAP from different sources, with an adjusted virgin binder grade of PG 58-28, and; a reference mixture containing no RAP, manufactured using PG 58-28 binder. The test results indicate significant reduction in the fracture energy of asphalt mixtures with 30% RAP and no virgin binder grade compensation. The reduction in fracture energy was surprisingly consistent between the four RAP sources irrespective of the significantly different RAP binder stiffnesses that were determined to be present in these mixtures through binder recovery and testing. However, when the RAP mixtures were produced using a softer virgin binder (PG 58-28), the measured fracture energy was higher than the control mixture. The study provides some assurance that adequate cracking resistance can be maintained in mixtures containing 30% RAP when designed properly, and demonstrates how fracture testing with ASTM D7313-07b can be used in the design and control of RAP mixtures, particularly where cracking is of concern. © Chinese Society of Pavement Engineering.
