Strain-hardening cement-based composite (SHCC) has proved to be a suitable material for repair layers on concrete substrate. Bonded SHCC overlays may bridge cracks in the substrate, and normally exhibit an enhanced resistance to drying shrinkage. In addition to the SHCC material properties, the interface behaviour has a significant influence on the failure process. By varying the interface roughness and bond strength, it is possible to attain a balance between the debonding of the interface and SHCC cracking, and to ensure both monolithic mechanical behaviour of the structure and sufficiently small crack widths in the SHCC overlay. The smaller these crack widths are, the lower the permeability and the greater the self-healing potential of the cracks. In the case of mechanical loading, a rather weak bond may be beneficial, as the crack widths in the SHCC tend to be smaller under such conditions. In the case of drying shrinkage of the SHCC overlay, however, weak bonding may lead to large debonded interface areas, making the use of SHCC inadvisable in such instances