Case Study of Step-frequency Radar Application in Evaluation of Complex Pavement Structure

Abstract

The 3D imaging radar technique belongs to a relatively new generation of Ground Penetrating Radars (GPR). It can be used in both versions of equipment i.e. in commonly used pulses of electromagnetic wave scanning and in the step frequency technique, where sampling of the ground response for long sinusoidal signal and for numerous set of frequencies is used. The frequency range selection, as well as other settings of the measuring system (in the step frequency method) belongs to critical features of the procedure and they have influence on results and interpretation.The paper discusses the diagnostic abilities of the 3D imaging technique on the base of data collected over historic pavement section with complex structure of layers. The method of horizontal slices were used to present and analyze the data. The method is particularly efficient in the detection of reinforcement and large infrastructural objects of linear shape. In the case of tested pavement section it is interesting that slices allowed for the detection of joints and cracks characterized by very weak GPR response. In this case several questions appear as to the nature of response generation and the features of the medium structure which are represented in the scattered signal.The presented case study well illustrates possibilities of the GPR technique in interpretation of complex pavement structures and possible mechanisms of cracking process. The present paper describes one case study of the semi-rigid pavement. The GPR analysis of its structure shows possibilities of this technique, illustrating mechanism of the current reflected cracking occurring in asphalt package above the concrete subbase.