# Effect and Mechanism of Red Mud on the Aging Resistance of Asphalt

## TL;DR

This study shows that adding sintered red mud to asphalt improves its resistance to aging caused by heat, oxidation, and UV exposure.

## Contribution

The novel finding is that 4% sintered red mud provides anti-aging properties comparable to commercial agents by adsorbing light components and blocking UV.

## Key findings

- Asphalt with 4% sintered red mud shows the lowest increase in softening point and aging indices after thermo-oxidative and UV aging.
- Sintered red mud selectively adsorbs light asphalt components, preventing conversion to heavier fractions during aging.
- UV-vis analysis confirms sintered red mud provides effective UV shielding, reducing UV-induced damage.

## Abstract

The primary objective of this study is to investigate the effect and mechanism of replacing limestone powder with red mud as a filler on asphalt aging resistance. The microstructure and porosity characteristics of limestone powder, Bayer process red mud, and sintered red mud were analyzed. Asphalt mastics were then prepared using these fillers. The effect of red mud on the aging resistance of asphalt was evaluated by comparing the conventional physical properties, rheological behavior, and functional groups of the asphalt mastics before and after aging. Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and ultraviolet-visible spectroscopy (UV-Vis) were further employed to elucidate the underlying anti-aging mechanisms. The results indicate that the asphalt mastic containing 4% sintered red mud exhibits the strongest resistance to both thermo-oxidative and UV aging. It shows the lowest increments in softening point, viscosity aging index, and complex modulus aging index, with performance comparable to a commercial anti-aging agent. FTIR and GPC analyses reveal that sintered red mud selectively adsorbs light asphalt components, thereby inhibiting their conversion into heavier fractions during thermo-oxidative aging. UV-vis analysis demonstrates that sintered red mud provides effective UV shielding within the asphalt mastic, substantially mitigating UV-induced damage. In summary, the incorporation of 4% sintered red mud can significantly delay both thermo-oxidative and UV aging processes in asphalt mastics, thereby effectively enhancing the aging resistance of asphalt pavement.