Study On Ageing/Hardening Mechanism Of Petroleum Asphalt

As an important material in road construction, the research,development and production of asphalt for pavement has been taken seriously in the world. The ageing/hardening of asphalt has significant impact on performance of asphalt, which relates to the life of road. In this paper, two 70# heavy traffic road asphalts from different sources and straight-run processes and 50# asphalt from oxidation process were selected. The changes of composition and property of asphalt had been studied by using the method of rolling thin-film ageing, and structural changes had also been studied by IR, GPC and other means in order to reveal the ageing mechanism of asphalt. The experimental results showed that:1. In the ageing of asphalt, the composition of asphalt generally had transformed into heavier component by aromatics→resins→asphaltenes route, which led to the decrease of plasticity and ductility of asphalt. It manifested as higher softening point, lower penetration, smaller ductility, larger viscosity. The overall property became harder.2. The ageing of asphalt was first-order reaction, and the dynamic process could be better characterized using the content change of n-pentane asphaltenes. Compared with SZ36-1 70# and JDS 70# straight-run asphalt, SZ36-1 50# oxidation asphalt had larger reaction rate constant, which showed relatively high ageing rate and poor anti-ageing ability. SZ36-1 70# and JDS 70# had similar anti-ageing ability.3. Different asphalts had different molecular weight distributions and changes. But on the whole, the molecular weight and molecular dispersity of asphalt aged increased significantly, and the entire molecular weight distribution tended to continuous distribution. The weight average molecular weight is more sensitive to aging than the number average molecular weight. It mainly occurred condensation reaction during the ageing of asphalt. The strong association had emerged between resins and asphaltenes, which drived the colloid system gradually changing to the solid.4. IR spectroscopy confirmed the aging of asphalt is a slow self-oxidation process. The ageing reaction was on radical reaction mechanism, and the contents of carbonyl and sulfoxide increased in ageing. Through the analysis of impact of ageing on resins and asphaltenes from the role of charge transfer, hydrogen bonding and dipole interaction, it was suggested that dissociation and substitution were predominant reaction types that occurred in the short-time ageing, and the association, aromatization, cyclization and dealkylation took place in the further ageing, which caused that molecular polarity and aromaticity of asphalt increased and the association between the molecules enhanced.