Influence of radiant energy source on bitumen oxidation

Abstract

AbstractBy use of the steady change in infra‐red absorption of the carbonyl functional groups of bitumen with increase of radiant energy flux, the oxidation rates of four air‐blown bitumens of coating grade have been obtained for the three sources of radiation, carbon arc, xenon arc, and sunlight. Differences in the pattern of oxidation for the much used carbon arc compared with both xenon‐arc and solar irradiation were found, whereas the last two sources induced nearly identical behaviour in the bitumens. Continuous measurement of the intensity of the solar radiation by pyroheliometry has indicated that the oxidation rates are directly proportional to intensity, sensitive to very low intensities and independent of diurnal changes. Potassium ferrioxalate dosimetry has shown that the intensity of the xenon‐arc irradiation as used in a weatherometer simulated that of summer sunshine extremely well, whereas the carbon‐arc irradiation, as used in the ASTM method of evaluation of weatherometer durability of bitumens, had a fivefold greater intensity. This increased intensity changed the pattern of rate of bitumen oxidation rather than simply accelerating the steady‐state oxidation rates.