Further exploration of the pavement oxidation model – Diffusion-reaction balance in asphalt

•Pavement oxidation model simulate asphalt oxidative aging including both diffusion and reaction.•Asphalt oxidative reaction results asphalt hardening.•Diffusion transports oxygen to reaction, but suffers from asphalt hardening.•Asphalt oxidative aging could be controlled by either diffusion or reaction or both. Oxygen diffusion and oxidative reaction are two main factors in asphalt oxidative aging discovered by experiment, but the dynamic balance between them could not be easily studied by experimental methods due to its comprehensiveness. A pavement oxidation model was utilized to simulate this process in asphalt: oxygen molecules penetrate into the asphalt film and then react with the asphalt molecules. In some special cases, diffusion or reaction can become the determination step of asphalt oxidative aging. Another factor, asphalt hardening, which is a result of oxidative reaction, slows the oxygen diffusion seriously and consequently. With the help of the model simulation, the efforts of binder reaction kinetics, hardening properties and temperature on this balance have been studied and discussed in detail. A new standard for asphalt binder, solely from oxidation aspect, includes high activation energy, low hardening susceptibility and high hardening intercept. A new idea of anti-oxidant development was proposed. By decreasing oxygen diffusion, asphalt oxidation can be slowed down, but only works for oxygen diffusion determined cases.