Measurement of complex permittivity of asphalt pavement materials

TO facilitate applications of road penetration radar and other nondestructi ve testing technologies on roads, an apparatus was developed for the measur ement of complex permittivity of construction materials. The system consist s of an automatic network analyzer, a sample holder, coaxial cable connecti ons, and data processing software. The sample holder can accommodate either laboratory-prepared or field-drilled asphalt and concrete samples with max imum aggregate sizes up to 19 mm and lengths up to 400 mm. A computer progr am is used to convert the parameters measured by the automatic network anal yzer into the real and imaginary parts of the complex permittivity. The die lectric constants of 43 laboratory-prepared asphalt samples of fairly consi stent bulk densities were measured over the frequency domain of 0.1 MHz to 1.5 GHz. The average dielectric constants were 6.0 +/- 0.15 for dry specime ns and 6.52 +/- 0.99 for soaked samples over the frequency range of 8-900 M Hz. A linear relationship was observed between the gravimetric moisture con tent and dielectric constant up to a moisture content of 1%, with dielectri c constant increasing by 0.62 for every 1% increase of moisture content. Th e results indicate that the asphalt content and mix type did not significan tly affect the dielectric constants, whereas the moisture content was ident ified as the predominant factor. The results provide much needed informatio n on the dielectric properties of asphalt pavement materials.