In situ measurements of hot-mix asphalt dielectric properties

Twelve different flexible pavement sections, which comprised different laye rs/materials, are incorporated in the Virginia Smart Road test facility. Th ese sections provide a good opportunity to explore the feasibility of using ground penetrating radar (GPR) to assess pavements and to verify its pract icality. Thirty-one copper plates, serving as a reflecting material, were p laced during construction at different layer interfaces throughout the pave ment sections. Results show that enough radar energy is reaching the subgra de, but due to low dielectric contrast between some pavement materials, ene rgy 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 mater ials over the GPR frequency range. This paper presents an overview of the V irginia Smart Road test facility, data obtained from different sections usi ng two GPR systems, and a method to calculate the complex dielectric consta nt of hot-mix asphalt over the frequency range of 750-1750 MHz using an air -coupled GPR system. (C) 2001 Elsevier Science Ltd. All rights reserved.