Dielectric Properties of Asphalt Pavement

This paper describes dielectric properties of asphalt pavement that were studied in the process of developing a roller mountable microwave asphalt pavement density sensor as part of the National Cooperative Highway Research Program IDEA project. This new sensor involves simultaneously measuring reflected microwave signals from the asphalt pavement in front of and behind the vibratory roller. As the reflected signal and penetration depth of microwaves depend on the dielectric properties of asphalt pavement, temperature, and frequency dependencies of the permittivity and loss of asphalt, samples of different densities were studied in the frequency range from 100 Hz to 12 GHz. Results show that (1) permittivity and loss depend on frequency and temperature; (ii) the higher the pavement density, the higher the permittivity; (iii) permittivity slightly increases with temperature; (iv) moisture strongly increases permittivity and loss at low frequencies and only slightly at microwave frequencies; and (v) the penetration depth of microwaves in asphalt pavement is about 12-14 cm at 8 GHz and only about 4 cm at 30 GHz.