Compared to traditional methods of obtaining pavement layer information from core samples, ground penetrating radar (GPR) can provide accurate and continuous layer thickness measurements and detect subsurface defects. In order to accurately predict pavement layer thickness, the dielectric constant, which is related to the material volumetric properties, has to be known. In-situ dielectric constants of various hot-mix asphalt (HMA) layers from nine interstate or heavy traffic flexible pavement sections were estimated and used to calculate layer thicknesses in this paper. The effect of variation in the dielectric constant the estimated layer thickness was quantified. Due to error accumulation and energy attenuation, the error increases as the layer depth from the surface increases. Utilizing a dielectric constant correction factor, based on field cores, less than 4% average error in layer thickness were obtained. To avoid dependency on cores, an algorithm was developed to estimate the dielectric constant of the entire HMA layer. The developed algorithm requires the use of two air-coupled GPR systems. The new technique allows in-situ estimation of the dielectric constant, while the survey is conducted at highway speed.
Abstract