Apparent interfacial toughness (AIT) is a critical material property representing the energy required to propagate a crack at the interface of two different materials within a composite, such as concrete. In the context of cement and concrete, AIT is particularly important when evaluating the bond strength between the cement paste and aggregate particles, which can be influenced by various additives and environmental conditions. A high AIT value indicates a strong bond that resists cracking and delamination, which is crucial for the durability and integrity of concrete structures exposed to harsh environments.