Ravelling investigation of porous asphalt concrete based on fatigue characteristics of bitumen–stone adhesion and mortar

Loss of aggregate, called ravelling is the dominant defect type of noise reducing porous asphalt surface wearing courses. Ravelling might be caused by cohesive failure of the bituminous mortar or by adhesive failure in the adhesive zone. This paper describes the result of a testing program into the fatigue resistance and the adhesive zone. Experimental results showed that the adhesive zone between stone and mortar tended to be the weakest link. Image analysis of fractured surfaces showed that such an adhesive zone looked like a bitumen-rich interlayer that connects rigid stone particles with the stiffer mortar. Based on this knowledge it is concluded that improvement of the adhesive zone will result in porous asphalt concrete with improved durability and lifetime.