Inspection and depth sizing of surface-initiated cracking for preventive maintenance of asphalt pavements

Adequate monitoring and timely treatment of partial-depth, surface-initiated cracks are essential in order to prolong the life cycle of pavement structures. Therefore, methodologies to precisely identify and assess the progression of top-down cracking (TDC) depth are fundamental. For this purpose, a calibrated model for ultrasound inspection of various types of bituminous mixtures for paving (semi-dense asphalt concrete AC-S, stone mastic asphalt SMA, and porous asphalt PA) is proposed to assess the depth and extent of top-down propagated macro-cracks in asphalt pavements. Extensive laboratory measurements were recorded on specimens of the different materials, thicknesses, temperatures and distances between sensors, with varying crack depths. The laboratory results were compared with in situ tests and with the theoretical approach. The application of the calibrated model allowed an appraisal of the depth of TDC with sufficient precision for a routine practical application regarding pavement maintenance. This non-destructive, inexpensive and easy-to-implement methodology for on-site identification and evaluation of TDC depth in asphalt pavements ensures straightforward implementation on non-prepared surfaces and provides sufficient reliability in the laboratory and on in-service pavements.