The effects of signal frequency as well as curing time and moisture content on the dielectric properties of concrete have been investigated. Microwave dielectric material characterization was performed on two ordinary concrete mixtures varying in their aggregate composition and water-to-binder ratio (w/b). Moisture content, complex permittivity and signal attenuation behavior were evaluated in the GHz range over a radio frequency range of 1 to 10 GHz at ages of 28 and 100 days. The results serve as useful information for the spectrum planning of 5G networks in the sub-6 GHz frequency band. The investigations show a strong correlation between the dielectric parameters and moisture content, as well as the internal pore volume of the samples under investigation. With ongoing curing time, the dielectric number decreases steadily due to hydration-related water consumption and evaporation.