Background
Chemical binders used in asphalt paved surfaces are subject to age hardening, resulting in increased stiffness over time, a major cause of cracking and the subsequent need for re-surfacing. Over the last 40 years, treating the binders with some form of anti-oxidant (AOX) has shown some promise in reducing binder stiffness, but it still is prone to softening at higher temperatures, stiffening at lower temperatures or leaching out over time. To ensure long-term durability, a viable AOX treatment should remain dimensionally stable over a wide temperature range and be environmentally and occupationally safe to use.
AOXADUR
Developed by a team of researchers at the University of Illinois at Urbana-Champaign in 2006, this revolutionary AOX binder treatment consists of three additives to base asphalt: aldehyde, thioester and a caltalyst. A condensation reaction of aldehyde with asphalt to form novolacs, which can act as antioxidants, results in a reduction of age-susceptible polar aromatics in the binder. The thioester serves as a secondary antioxidant, which is highly effective against oxidative degradation of hydrocarbons. Laboratory testing of over 40 binders at the University of Illinois showed that the AOXADUR-modified binder produces the lowest aging index the measurement of asphalt aging potential during service life. Further, the AOXADUR-modified binder showed a dramatic increase in high-temperature stiffness and a substantial decrease in low-temperature stiffness. This improvement in binder properties at both high and low temperatures results in less thermal stress and reduced cracking potential. Finally, the age-fighting characteristics of AOXADUR make it an appealing choice asphalt mixtures containing recycled asphalt pavement (RAP).
With AOXADUR, higher amounts of RAP material can be used, which can lead to a reduction in the amount of new aggregate and asphalt binder required per ton of mixture, leading to economic and environmental benefits and increased sustainability of the roadway materials.