OXIDATION CHEMISTRY IN ASPHALT†

Abstract A possible mechanism of asphalt oxidation with O2 or photo-excited O2 is presented herein. The oxidation reaction will occur via an allowed reaction pathway -charge-transfer (CT) complexes. Oxidation reactions transform the sulfur-containing compounds from electron donors to electron acceptors - sulfoxides. These new electron acceptors form CT complexes with electron donors, particularly nitrogen-containing compounds and aromatic compounds. An increase in the average molecular weight after oxidation of asphalt may be due to the formation of CT complex. Treatment with H2SO4 or p-chloranil increases the electron acceptor concentration in asphalt. The resulting products show extremely large increases in viscosity. ESR studies show decreases in the signal intensity ratio of vanadyl porphyrins to free radicals in asphalt after oxidation. The decrease in this ratio may be due to the formation of CT complexes. The introduction of deactivating groups such as nitro or fluoro functional groups, or hydroquinone in asphalt will increase the elastic recovery of original asphalt and thin film oven test residues. These results suggest that the rheological properties of asphalt can be strongly affected by controlling the formation of CT complexes.