GPR abilities in investigation of the pavement transversal cracks

• A list of common GPR indications of cracks was created.
• Indications were linked with probable features of crack structure and activity.
• The major reasons of poor visibility of cracks were studied and described.
• Conditions of effective use of GPR in cracks inspection were characterized.

This paper describes the results of an investigation into the capabilities of the GPR technique within the field of pavement crack diagnostics. Initially, laboratory tests were performed on prototypes simulating idealized cracks. Next, long-term visual observation and repeated GPR scanning were performed, on three roads of semi-rigid construction, several hundreds of meters long and subjected to heavy traffic. Furthermore, a road of rigid construction was tested, having a more than 70-year history of use. In several cases the cracks were probed by drillings, in order to recognize structures responsible for signal generation, or to explain reasons of signal lacking.The main result of this work is a list of GPR indications of cracks, which can be noticed on echograms. It was created through a correlation of the visually-observed cracks with the corresponding echograms, with decimeter accuracy. Several types of GPR responses were classified and linked to possible categories of crack structures, or to processes associated with the presence of cracks (as crumbling, erosion, and lithological alterations). The poor visibility of cracks was also studied, due to small crack size, or to the blurred character of the damaged area, or else to masking effects related to coarse grains in the asphalt mixture.The efficiency of the proposed method for the identification and localization of cracks is higher when a long-term GPR observation is performed.