Dielectric Constant and Relaxation Time of Asphalt Pavement Materials

Abstract

The static dielectric constant and relaxation time of two asphalt aggregate mixes commonly used as the bearing and wearing courses of asphalt pavements are measured in the frequency range of 0.1 MHz to 1.5 GHz. The measurement is conducted on 70 laboratory-prepared asphalt aggregate specimens using a custom-designed complex permittivity measurement system. The results in the frequency range of 10 MHz and 1.5 GHz indicate that, under dry conditions, the static dielectric constant of the asphalt pavement materials tested in the range of 5–6, whereas the relaxation time is in the range of 100–400 picoseconds. The results show that within the range of field applications the static dielectric constant and relaxation time of asphalt pavement materials are independent of the mix type, density, and asphalt cement content. The moisture content is the predominant parameter controlling both the dielectric constant and relaxation time. When the moisture content of the asphalt samples increase above a characteristic moisture content of 1.2%, both dielectric constant and relaxation time increase considerably with further increase in moisture content.