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A waveguide with central frequency 868 MHz is used in transmission/reflection operation regime to accurately measure the behaviour of the complex permittivity of high complex permittivity granular materials and it has been frequency-extended up to 3 GHz using the Debye fitted relaxation model. It is shown that for highly granular high permittivity materials a waveguide based transmission/reflection technique is necessary to reduce the uncertainty of the extracted permittivity values. The technique is first described and validated with isopropyl alcohol and then applied to the characterization of cement based materials. This paper provides accurate data on the evolution of the complex permittivity of concrete and mortar from the moment of pouring until air dried condition is achieved.

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