Investigation into material optimization and development for improved ravelling resistant porous asphalt concrete

Ravelling, the loss of aggregate from the pavement surface, is the dominant defect of noise reducing porous asphalt wearing courses. Meso-mechanical simulations of porous asphalt concrete (PAC) under a moving tyre passage were performed to get insight into the in-mixture stresses. The simulation results showed that ravelling developed over a wide range of temperatures and that particularly low or high temperatures were critical. Ravelling resistance at high temperatures strongly depends on the confining stresses that follow from the pavement deflection. However, the tensile strains induced by the combined effect of pavement deflection and thermal contraction are the main cause for ravelling at low temperatures. Material optimization by changing mortar or bitumen properties can result in a significant improvement on ravelling resistance. A flexible bituminous binder with ample relaxation behaviour showed to give an optimal performance for ravelling resistance. Adhesive failure and cohesive failure are the failure mechanisms within the stone contact and the weak link is responsible for ravelling. Adhesive failure is predominant at low temperatures, while cohesive failure is the main cause at high temperatures. Aging mainly enhances the high-temperature ravelling performance, but dramatically degrades low-temperature ravelling performance.