Effect of Field Aging on Rheological and Chemical Properties of Asphalt Binder in a Cold and Arid Region

Indoor accelerated aging simulations cannot fully replicate the field aging conditions of asphalt binders. To study the aging behaviors of asphalt binders in field environments, samples with three film thicknesses (3.2 mm, 2.0 mm, and 1.0 mm) were exposed to field conditions (sunlight, heat, oxygen, wind, rain, and dust) for 6 and 12 months. Aging behaviors were evaluated based on rheological and chemical parameters. The results indicated the oxygen content of asphalt binders increased after aging. Specifically, the oxygen-containing polar functional groups in 12-month-aged and 1.0-mm-thick virgin asphalt binders were 26.24% higher than the 6-month-aged samples. The weight-average molecular weight (Mw) of 12-month-aged and 1.0-mm-thick samples was 30% higher than that of 3.2-mm-thick samples. The 1.0-mm-thick samples exhibited the highest sensitivity to field aging time, with a 2.1 times higher average complex modulus and a 16.7 times higher Glover-Rowe (G-R) parameter compared to the 3.2-mm-thick samples after 6 months. Thinner asphalt films facilitated faster air exposure, accelerating the accumulation of oxidation products. The degree of aging decreased with increasing film thickness. Increasing film thickness from 1.0 mm to 2.0 mm and 3.2 mm in 12-month-aged 90# virgin asphalt binder extended the fatigue life by 2.6-fold and 52-fold, respectively. The results underscored that optimizing the film thickness significantly prolongs the pavement service life. Both the number-average molecular weight (Mn) and carbonyl index (IC═O) showed a strong linear relationship with the G* and G-R parameter. Pressure aging vessel aging was equivalent to 0.91 years for the 1.0-mm asphalt binder field aging in Dunhuang. These findings support selecting appropriate film thicknesses for laboratory multifactor aging tests.