Impact of the Interlayer Scabbing on Asphalt Pavement Performance

A full-scale experiment was conducted at the Florida Department of Transportation's accelerated pavement testing (APT) facility to identify factors affecting the occurrence of interlayer scabbing and the impact of scabbing on pavement performances. Two experimental parameters-interlayer bonding condition of existing asphalt layers and milling thickness-were considered for the first objective. For the second objective, core specimens were obtained after the hot mix asphalt overlay on sections where scabbing was present and not present to compare their interlayer bonding strengths. In addition, APT was utilized to assess the rutting and cracking performance of the test sections. Test results indicated that the occurrence of scabbing is highly dependent on the interlayer bonding condition of the existing asphalt layers and milling depths. Once scabs form after milling, the scabs result in a weak or variable bond with the new overlay. Also, the accelerated loading using heavy vehicle simulator generated approximately 30% greater rut-depth and longitudinal cracks along the edge of the wheel path on the test sections with interlayer scabbing. In consideration of the reduced performance of the test sections with interlayer scabbing, the authors suggest preventing or removing the scabbing before the asphalt overlay.