Full range of mode I and II cracking performance of asphalt mixtures containing low to high reclaimed asphalt pavement (RAP) contents; modified by recycling agent and substituting of a softer binder

Reclaimed asphalt pavement (RAP) is a recycled material that can decrease the consumption of virgin materials; however, it increases stiffness and brittleness, resulting in cracking. In this regard adding recycling agents and using soft binders can be a solution. In this study, base binder (PG 64-22) with recycling agent and softer binder (PG 58-22) are used to enhance the fracture behavior of asphalt mixtures containing low to high RAP contents (20, 40, and 60%). The fracture test was performed using a semi-circular bending (SCB) specimen under pure mode I, two mixed mode I and II, and pure mode II loading. Also, the effect of air voids content is reviewed. Results show that the addition of RAP in mixtures prepared with PG 64-22 binder and recycling agent increases the fracture toughness from 1.22 to 1.25, 1.27, and 130 MPa√m, and reduces the fracture energy from 3.46 to 3.44, 3.36, and 3.24 KJ/m2 (respectively for of 20, 40 and 60% substitution). By comparing the effect of binder types, although the fracture toughness of mixtures prepared with PG 58-22 binder was lower than mixtures prepared with PG 64-22 binder and recycling agent (at most 11% lower), but the fracture energy of mixtures prepared with PG 58-22 binder was superior (6 to 19% higher). Based on the data, regression equations of linear trends were extracted, and the relationship between fracture toughness and fracture energy data was clustered and formalized.