Evaluation of the effect of thermal oxygen aging on base and SBS-modified bitumen at micro and macroscales

This study investigates the changes and relationship between micro and macro properties of base bitumen and styrene-butadiene-styrene (SBS)-modified bitumen during aging. Fourier infrared spectroscopy and atomic force microscopy were used to observe the changes in the microstructure and chemical composition of bitumen during aging and the change of morphology was quantified. The thermal stability of bitumen during aging was also studied via thermogravimetry and differential scanning calorimetry. The results show that with increase in aging severity, bitumen is gradually oxidized and SBS molecules in SBS modified bitumen are gradually degraded. Quantitative analysis of the micromorphology of bitumen shows that the area of bitumen's bee-shaped structure gradually increases as the aging degree increases, and the number and total area of bee-shaped structures gradually decrease. Additionally, pressure aging vessel aging has a great influence on the bee-shaped structure. The addition of SBS modifier will reduce the magnitude of these changes; thus, modified bitumen exhibits better aging resistance. During the aging process, the initial decomposition temperature of the two bitumen types will increase to varying degrees, whereas the maximum decomposition rate temperature remains unchanged. The phase transformation heat absorption of bitumen gradually decreases as it ages, and its thermal stability improves. The addition of SBS modifier will increase the specific heat capacity of bitumen, but this effect will be weakened as it ages. Additionally, there is a good correlation between the micromorphology, chemical composition and macro thermal stability of bitumen.