This paper deals with the effect of concrete carbonation on the propagation and dispersion of EM electromagnetic waves. Capacitive probes working at low frequency (around 33 MHz) and GPR (antenna nominal frequency of 1.5 GHz) could provide useful information for reinforced concrete structure monitoring. So, in order to better understand the phenomena involved by concrete carbonation, the results of 2 complementary experimental campaigns are analyzed. First, the dispersion curves of the complex permittivity are measured for carbonated and non-carbonated samples by an EM cylindrical coaxial cell. Due to carbonation, the permittivity decreases, and the dispersion is slightly reduced. Second, it is confirmed by GPR and capacitive measurements on slabs, that the real part of the permittivity decreases and that the radar signal amplitude increase.