Effect of temperature and humidity environment on the microstructure and physicochemical properties of SBS modified asphalt

Asphalt pavements undergo aging process when exposed to various environmental factors, which affects their service life. Numerous engineering cases have demonstrated that water vapor is a significant cause of aging damage in asphalt pavement during its service period. This study aimed to assess the impact of temperature and humidity on the physicochemical characteristics of asphalt binders. First, asphalt samples were subjected to damp-heat aging conditions using a custom-made environment chamber. The specimens were then investigated through Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and nuclear magnetic resonance hydrogen spectroscopy (NMR). The results suggest that rising temperature accelerates the movement of particles in the system, leading to the generation of more carbonyl and sulfoxide functional groups. Furthermore, higher humidity encourages the formation of hydrogen bonds between the polar groups in asphalt and water molecules, resulting in the generation of more oxygen-containing functional groups. In comparison to variations in humidity, the aging of SBS modified asphalt binder exhibits a higher sensitivity to temperature. Under identical aging conditions, the rise in both carbonyl index and sulfoxide indices is more pronounced in base asphalt binder compared to SBS modified asphalt binder. With the increase in aging duration, temperature, and humidity, the macromolecular content increases, while the content of small and medium-sized molecules decreases. Additionally, the weight-average molecular weight of asphalt shows greater sensitivity to these changes compared to the number-average molecular weight. Following damp-heat aging, asphalt undergoes hydrogen substitution on the aromatic rings, which increases hydrogen content on aliphatic side chains and enhances intermolecular forces. As humidity increases, the large molecular proportion (LMS%) changes in SBS modified asphalt binder are more pronounced than in base asphalt binder. Additionally, the changes in the sulfoxide index are greater in SBS modified asphalt binder than in base asphalt binder. This may suggest that SBS polymers degrade more quickly due to humidity than base asphalt.