The Thermal Oxidative Aging of Petroleum Bitumens and Tars

A study was carried out on the dependence of the adhesive properties and pH of oxidized bitumens and tars, which are raw materials for bitumen production, on the aging time. Changes in the type of oxo compounds and, as a consequence, of the adhesive properties occur in bitumen with increasing extent of oxidation. Rapid formation of asphaltenes, resins, and asphaltogenic acids occurs in high‑melting bitumens upon aging, leading to an improvement in the adhesive properties of the binder. Rapid formation of carboxyl and hydroxyl groups occurs in low‑melting bitumens, which decreases their adhesion to alkaline mineral materials. The rate of aging of tars increases steadily, while the corresponding rate for bitumen traverses a maximum in the first hours of aging. The adhesion index and acidity in combination with the softening point after aging, which is a standard quality indicator, are proposed for use in selecting the component composition of bitumen obtained by “oxidation‑compounding” methods as well as in the development of methods to reduce the aging rate of bitumens in the initial period of use of asphalt concrete coatings and to improve their quality and durability.