Fast-Rate–Constant-Rate Oxidation Kinetics Model for Asphalt Binders

Asphalt oxidative aging at constant temperature is characterized by a declining fast-rate period and a constant-rate period. While constant-rate reaction kinetics are known for many asphalt materials, much less is known about the equally important fast-rate region. Fifteen modified and unmodified asphalts were aged at five temperatures in 1 atm air, with samples collected during both fast-rate and constant-rate periods. Arrhenius kinetics parameters were obtained for both reactions; an additional parameter characterizes the total oxidation that occurs by the fast-rate, first-order reaction. Interestingly, the data show correlations between the kinetics parameters. Viscosity hardening in response to oxidation, as characterized by hardening susceptibility, is not significantly different for the two aging periods for a single binder. Therefore, the combined first-order, zero-order oxidation model together with hardening susceptibility is capable of modeling asphalt oxidation and hardening. Such a capability ...