Samples from both wear and binder layers of common bitouminous concrete were radiated with intense electromagnetic fields at 2.45GHz in a laboratory microwave oven: the observed heating rate was similar to that of an equal volume of water put in the same conditions. Information useful for the comprehension of this behaviour were obtained by exposing individual constituents (bitumen and aggregates) to microwaves and by means of broad band dielectric spectroscopy performed on both concrete and single constituents. Collected data show that bitumen is the less dissipative component of the concrete, while the nature of aggregates and the effects of interfacial polarisation seem to be at the basis of both the finite dissipation observed in the radiofrequencies region of the spectra and the efficient heating obtained with microwaves.
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