<p>Concrete production affects sustainability, and using recycled aggregates (RA) is one way to reduce its impact, RA are increasingly explored as an alternative to conventional aggregates. While many studies have examined partial replacement, the fracture behaviour of fully replaced recycled aggregate concrete (RAC) remains insufficiently understood, particularly regarding its non-linear fracture properties. This study investigates the fracture mechanics of RAC in comparison with conventional aggregate concrete (CAC), with a focus on crack propagation, fracture process zone (FPZ) characteristics, and critical crack tip behaviour. Digital Image Correlation (DIC) was employed as a non-contact measurement technique to capture strain localization and crack development. The results reveal that RAC exhibits distinct fracture mechanisms, with cracks initiating not only at the interfacial transition zone but also within weak recycled aggregates. Compared to CAC, RAC demonstrated a wider and longer FPZ, higher strain densification near the crack tip, and altered crack propagation paths. Validation through size effect analysis confirmed differences in fracture energy and toughness. These findings highlight the unique failure behaviour of fully replaced RAC, providing new insights into its structural performance and supporting its role as a sustainable alternative in concrete construction.</p>