Air blowing of supercritical asphalt fractions

Air blowing of asphalt at higher temperature does not greatly impact such parameters as the softening point-penetration relationship. With new Superpave specification, very good grade asphalts can be produced by air blowing, and the blowing temperature does not seriously impact the grade span. It is shown, however, that the subsequent 88 degreesC hardening and oxidation rates are higher for materials blown at higher temperature, and this is not detected by Superpave specifications. Blowing fluxes with high saturate content may result in higher grade but can cause subsequent susceptibility to oxidative hardening. The mechanism by which air blowing can affect the 88 degreesC hardening rate is related to oxidation kinetics and the tendency of oxidation products to form asphaltenes, causing hardening. For some materials air blown at higher temperature, the subsequent accelerated hardening rate results from an increase in the oxidation rate, while the hardening susceptibility may actually decrease.