Detection of asphalt binder aging in flexible pavement by ground penetrating radar

In situ dielectric constant variations of hot mix asphalt layers versus time were studied. The dielectric constant of the considered hot mix asphalt layers were nondestructively estimated using ground penetrating radar data collected over a controlled test pavement - the Virginia Smart Road. It was found that the dielectric constant of various hot mix asphalt layers decreased linearly with time but remained within the typical limits. For all tested hot mix asphalt types, the variation slope was relatively small, with a maximum decrease of approximately 0.8 over a one year period. The main cause of the hot mix asphalt dielectric constant decrease versus time was found to be the aging of the asphalt binder, which causes the reduction of its susceptibility to be polarized by the applied electric fields, thus decreasing its ability to store electric energy and consequently decreasing its dielectric constant.