Cement is one of the most useful materials in the world. Concrete made with this material presents many advantages such as workability and durability. However, cement production releases a lot of CO 2. To limit this effect, cement can be replaced by mineral additions. Ground granulated blast-furnace slag (GGBFS), an industrial waste of iron manufacturing, can be recycled as a cementitious material. Moreover, it improves some properties of concrete such as workability, sulphate resistance, etc. However, concrete made with blast-furnace slag presents cracking risk under restraint conditions and can affect the durability by allowing the penetration of aggressive agents. Previous researches have proved that self-healing of cracks can limit this problem. To understand the role of GGBFS on self-healing and the impact of material characteristics on the kinetics of the phenomenon, three compositions of mortar characterized by several GGBFS contents were tested Mortar specimens were cracked at 7 days after casting and stored in water at 23°C. The volume evolution of self-healing products was monitored by X-ray tomography. The hydration degree of mortars was computed from TGA measurements. After one year, SEM with EDS was performed to identify the products formed inside the crack. Results showed that hydration products were formed by the hydration of anhydrous particles on the crack surface. Mortar made with GGBFS presented the best self-healing potential. These results were explained by the material characteristics but also by the evolution of its hydration degree.