Study of ravelling failure on dense graded asphalt pavement

Ravelling is the loss of bond between aggregates and asphalt binder. This distress is more common in porous asphalt concrete when the voids content is 20% or more. However, premature pavement failure in terms of ravelling on a dense graded asphalt concrete pavement in China occurred within 3 years after the pavement was opened to traffic. The objective of this paper is to determine the cause of this distress. A preliminary investigation did not find evidence of either inadequate design- or construction-related issues. Detailed investigations were undertaken to identify the possible cause of failures. Cores and material samples were also tested in the laboratory. The results indicated that the asphalt mixture at this section fully met the specified requirements of a conventional mixture. The adhesions between binder and aggregate also met the specified requirements and the air void content of the mixture was 5·3%. X-ray diffraction indicated that some aggregates contained illite and kaolinite, which are expansive clays. It was found that this was the primary reason for the distress. Although selection of proper aggregate materials and quantities is standard practice, there is a need to include requirements for contamination by weathered products in the crushed stone.