The nation's current state of infrastructure is at an increasing rate of disrepair with new methods of cost-effective rehabilitation being considered over timely and costly reconstruction. Externally bonding carbon fiber-reinforced polymer (CFRP) plates to the tension side of a flexural reinforced concrete beam has been one such method that has proven effective and reliable due to the outstanding performance and various advantages in CFRP materials. Gaps in long-term durability studies have been the major reason why this strengthening technique has not seen more success. It is fundamental and crucial that the mechanism of the bond interface between concrete and the strengthening material be thoroughly tested and understood. It is the intention of this study to further increase the knowledge and understanding of the long-term durability of the concrete/adhesive interface while being exposed to various aggressive environments in such externally bonded systems. In this study, an environment-assisted subcritical debonding testing (EASD) program is carried out to evaluate the long-term durability of the interface. EASE is adopted because it allows for interaction with environmental species, making it possible to measure important parameters of the reaction kinetics at the crack tip and to learn more about the degradation mechanism of the interface. EASD testing is carried out using a static split wedge specimen together with a digital image correlation system. Results show that subcritical cracking does exist along the interface between the epoxy and concrete. Temperature has significant effects on the subcritical debonding growth.