In situ measurements of hot-mix asphalt dielectric properties

Twelve different flexible pavement sections, which comprised different layers/materials, are incorporated in the Virginia Smart Road test facility. These sections provide a good opportunity to explore the feasibility of using ground penetrating radar (GPR) to assess pavements and to verify its practicality. Thirty-one copper plates, serving as a reflecting material, were placed during construction at different layer interfaces throughout the pavement sections. Results show that enough radar energy is reaching the subgrade, but due to low dielectric contrast between some pavement materials, energy is not reflected back. In these cases, the copper plates indicate where the interface between each two layers occurs. Reflections from the copper plates are also used to determine the dielectric constant of pavement materials over the GPR frequency range. This paper presents an overview of the Virginia Smart Road test facility, data obtained from different sections using two GPR systems, and a method to calculate the complex dielectric constant of hot-mix asphalt over the frequency range of 750-1750 MHz using an air-coupled GPR system.