Investigation on the deterioration process of low temperature properties of asphalt under ultraviolet aging and analysis of its multi-scale action mechanism

The decline in low-temperature properties of asphalt induced by ultraviolet irradiation is a critical factor contributing pavement diseases. To explore the influence and mechanism of ultraviolet aging on low temperature properties of asphalt, multi-scale characterization methods were employed to explore how UV aging alters asphalt properties, including macro cracking behavior, microstructure characterization and molecular dynamic simulation. On this basis, relationships between macro cracking and micro properties of samples were established to reveal the aging mechanism. Test results show that with the prolonged UV aging treatment, G ⁎ , G-R , S , S/m , Burgers model fitting parameters and relaxation time of asphalt rise progressively, while m values, the dissipation energy ratio W l/s and composite compliance J present a decreasing tendency. This proves that UV aging can slow down the stress relaxation rate of asphalt under low temperature conditions. Microscopic tests reveal that UV irradiation accelerates the transformation of light fractions to heavy components, generates more complex aromatic cyclic structures, and enriches carbonyl and sulfoxide functional groups. It also intensifies molecular aggregation, weakens compatibility of polar fractions and raises the proportion of large-size molecules in asphalt. Under the combined effect of above factors, asphalt turns stiffer and more fragile, which means that its low temperature properties has decreased. Lastly, MD simulation results have also verified the above conclusion, which manifests as the increase of glass transition temperature T g . Additionally, UV aging also increases cohesive energy density of asphalt and decreases the free volume fraction, thus enhancing non-bonding interactions between asphalt chains. Under such conditions, mobility of asphalt molecular chains is constrained, endowing it with solid-like characteristics, which in turn reduces the stress relaxation capacity under external loading and significantly increases the cracking risk.