Improvement of a coreless method to calculate the average dielectric value of the whole asphalt layer of a road pavement

The need for more effective road condition management policies and practices has been growing rapidly over the last few years. A key word in this development is “focus” and for that more accurate and reliable continuous NDT survey methods, such as GPR, are needed. In asphalt thickness surveys a problem has been how to calculate/estimate the dielectric value of the asphalt. Thus far this has been done using drill cores or using the surface reflection technique. Within this context, this study is aimed at defining an accurate coreless method to calculate the average dielectric value of the whole asphalt layer of a road pavement using GPR (horn antennas). To accomplish this, the WARR (Wide Angle Reflection and Refraction) technique is applied. The principle is based on the resolution of a system of two nonlinear equations with two unknowns (asphalt thickness and electromagnetic wave velocity) using reflection the different time shift. An initial validation under controlled conditions was conducted and then followed by a series of measurements on a dedicated test field in order to validate and check the accuracy of the results given by our calculations. The results obtained are promising and a series of tests on real roads are under preparation.