The Shear Strength of the Interface Between Rock and Printable Concrete At Super-Young Ages

3D concrete printing has the potential to replace shotcrete to construct tunnel linings in hard rock tunnels. The shear strength of the interface between rock and printed concrete is vital, especially at super-young ages. However, traditional methods for testing the shear strength of the interface, e.g., direct shear test, are time-consuming and result in a high variability for fast-hardening printed concrete. A fast bond shear test was newly proposed to test the shear strength of the interface. Each test can be completed in one minute, with another two minutes for preparing the next test. With the 3-minute test, the influence of the matrix composition, the age of printed matrices, and the interface roughness of rock substrate on the shear strength of the interface can be studied.