Ku band ground penetrating radar for asphalt layer measurement

This study presents a new asphalt radar, operating in the band from 13 to 17 GHz, intended for mobile road surveying of road pavement surface layers. A wide frequency band is required since new asphalt overlays are very thin in Finland being less than 50 mm in thickness. Therefore, sufficient spatial resolution of the radar system is required so that the subgrade would not affect the measurement result of the surface course. This study presents new results of the measurement campaign carried out on a newly-laid highway lane in Finland during summer 2014. The permittivity values on the trial section of the lane varied between 2.1 and 6.4. Two samples were drilled from the road in order to obtain reference permittivity values, measured in a laboratory using a 7 to 17 GHz scanner producing a 2D image of the permittivity. The permittivity values obtained using the scanner varied between 4.3 and 9.5 and they relate to the structural variation of the permittivity with a 5 mmx5 mm resolution. The results indicate that permittivity values can be used for monitoring the change in asphalt density condition when it is performed as a follow-up survey.