As for OPC, the primary hydration product which is formed is an Aluminum-inserted-Calcium-Silicate-Hydrate, C-A-S-H, phase gel . The structure of the C-A-S-H formed depends on the slag composition but mostly on the activator used. For example, the NaOHactivation usually leads to a more crystalline gel with a higher Al incorporation than with sodium silicates . Furthermore, more cross-linked gels are observed when sodium silicates or sodium carbonate are used as activators than when NaOH is used . Fernández-Jiménez et al. also found longer linear chains in the C-A-S-H precipitated in presence of NaOH. Moreover, in the case of low Ca-environments, another type of aluminosilicate gel can form, the N-A-S-H gel . This hydrate has a very disordered and cross-linked structure, similar to an amorphous zeolite. Compared to C-A-S-H, it contains a low quantity of Ca and significantly more alkali (Na or K).