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 (6–19% 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.