Oxidative aging of long-life asphalt pavements in Hong Kong

Hong Kong (HK) is currently developing a new flexible pavement design standard with the goal of building long-life pavement in the future. Long-life pavement is expected to last for at least 40 years without major structural damage. The design of long-life flexible pavement has been traditionally focused on structural design, in particular the control of tensile strain at the bottom of Asphalt Concrete (AC) layer and compressive strain at the top of subgrade. Changes of fundamental asphalt binder properties and performance due to its oxidative aging throughout the pavement structure often receive little attention. However, understanding the evolution of asphalt binder properties is critically important for long-life pavement design. It not only affects the load-induced mechanistic responses of the flexible pavement system, but also the fracture and cracking potentials of the binder per se. In this study, AC samples were taken from a heavily trafficked road in HK that has been in service for 36 years with only being periodically resurfaced. The cores were cut into six slices and asphalt binders were extracted and recovered for the analysis of their aging characteristics by using Gel Permeation Chromatography (GPC), Fourier Transform Infrared spectroscopy (FTIR), and Dynamic Shear Rheometer (DSR). The analysis results indicate that oxidative aging penetrates deep into the asphalt pavement layers, but there are variations in the extent of aging. In general, asphalt binder is severely aged at different depths, but at certain locations it exhibits less aging. The causes of the aging variations need to be further researched.