This paper verifies the reliability of the numerical methods in reflecting the experimentation in the field of non-destructive testing by infrared thermography. A non-reinforced concrete slab (1 m × 1 m × 0.25 m) containing four defects was used, two of which had the void type and two had honeycombs type. The defects were situated from 5 cm and 10 cm of the surface. The response of the slab to thermal excitation was investigated by determining the variation of temperature at the top surface of defects and at the slab surface by simulation and experimentation. A good correlation was noted between the numerical results and the experimentation for the three studied durations of thermal excitation (30 min, 60 min and 90 min).