Mode I Concrete Characterization using Rebar Induction Heating

Reinforced concrete is a composite material consisting in a rebar embedded in a concrete matrix. The structural equilibrium depends of the quality of bond between the two materials as well as the intrinsic quality of each of the components. When the structure is submitted to heating, cracking can occur due to the difference in thermal expansion properties between the two materials. In the present work, a theoretical approach, correlating rebar expansion rate under a heating process, to the fracture properties of concrete is proposed. The validating test consists in a Double Cantilever concrete Beam, with an initial crack length a0, a rebar embedded at a distance a0 from the crack tip. The rebar is heated through an induction process and its expansion induces a crack opening displacement at the level of the concrete. The deformation of the concrete due to the rebar expansion induces at the level of the crack tip, a displacement as well as a stress field, leading to the crack propagation. In order to follow the development of the displacement field at the level of the crack front, a digital camera is used to capture pictures of that zone at various steps (two images per minute) of the heating process. The images are then analysed with image correlation techniques to obtain the displacement field as well as the strain field, and then the time of crack propagation. The critical crack opening displacement, the critical energy release and Stress Intensity Factor corresponding to the time of crack propagation, can be deduced with a good accuracy.