Sustainable tunnel constructions in hard rock depend on efficient reinforcement systems but reliable material parameters are, however, not always available for shotcrete (sprayed concrete). Therefore, parameters for ordinary, cast concrete are often used in the design of structural shotcrete. Shotcrete differs from ordinary concrete through its application technique and the addition of accelerators which gives rapid hardening. Early after spraying the material properties of shotcrete, including the bond to the rock, depend on the accelerator and the micro structure formed. In this project the development of bond strength as a function of age for very young shotcrete is studied.