Microwave absorption of hardened cement paste

The absorption of microwaves by hardened cement paste has been studied in the frequency range of 8.5 GHz to 12.3 GHz (x-band). Preliminary experiments have been carried out using the free wave method. Much smaller specimens can be used with a conventional experimental set-up with the help of rectangular wave-guides with a cross section of 10×22.8 mm². A new method to determine the complex permittivity from absorption data has been developed. ge′ and ?″ are determined as a function of moisture content, temperature and duration of hydration. Results and further possible application of this method are discussed.