Parametric study on the damage to concrete matrices by induction heating of its reinforcement

Concrete structures may be subjected to repair or local dismantling due to changes in the activity or in case of their damage. Current demolition techniques, besides the required time frame for the renewal, involve remarkable affections due to noise, vibration and dust. This research presents a method to carry out such procedures selectively and efficiently, avoiding noticeable affections on the environment and other users. In addition, it could ease the segregation of the construction materials for better recycling. The study analyses the influence of the position and diameter of the reinforcement, the frequency of the applied magnetic field, the thermal conductivity and the specific heat capacity of the surrounding cementitious matrix and the convection and radiation phenomena on the induction heating process. Depending on the setup, high temperatures (above 700 °C) can be achieved in less than 90 s. However, the frequency and the reinforcement position are the most influential parameters, showing a heating rate up to a 300% faster when increasing the frequency 4 times (from 12 kHz to 48 kHz) and a difference up to 250% in the maximum temperature achieved between rebars aligned and misaligned with the magnetic field. A regression analysis performed on the data obtained provides a prediction model that properly fits (R²=0.979) the expected heating according to the variable parameters. Finally, a real scale column case is simulated and observed that closed stirrups can increase the heating above 1000 °C in just 60 s and induce cracking of the matrix.