Influence of Aging and Temperature on Intrinsic Healing of Asphalt Binders

It is well recognized that asphalt binders have the ability to self-heal or reverse microdamage during rest periods between load cycles. The ability of an asphalt mixture to self-heal depends on the physical and chemical properties of the asphalt binder, mixture properties, magnitude of damage before the rest period, and external conditions such as temperature. A thorough understanding of the healing mechanism is required to develop a comprehensive damage model that accounts for both fracture and healing on the basis of material properties and external factors such as temperature. Previous studies have hypothesized that healing was a two-step process comprising microcrack closing, referred to as crack wetting, and strength gain, referred to as intrinsic healing. Intrinsic healing or strength gain was further demonstrated to be the sum of two components: instantaneous strength gain immediately on wetting and time-dependent strength gain. A test method using the dynamic shear rheometer was developed to measure the rate of intrinsic healing, which was modeled with a modified form of the Avrami equation. The influence of temperature and aging on the rate of intrinsic healing of asphalt binders was investigated. The intrinsic healing of three asphalt binders was measured at three temperatures and two aging conditions. Results support the hypothesis that time-dependent intrinsic healing increases with an increase in temperature and that the overall capacity of the asphalt binder to heal decreases with aging of the asphalt binder.