Investigating the durability and low-temperature performance of asphalt mixtures modified with hydrophobic and hydrophilic nano-alumina

This study investigates the effects of hydrophobic and hydrophilic nano-alumina on the durability and low-temperature performance of asphalt mixtures. Asphalt binders (50–70 penetration grade and 4.5% SBS-modified) were modified with 2% and 5% nano-alumina and tested for binder properties (penetration, softening point, kinematic and dynamic viscosity, ductility, DMA for Tg) and mixture properties (Marshall stability, moisture susceptibility, low-temperature IDT at 0°C and −20°C). No single concentration universally optimises all properties; however, hydrophilic nano-alumina (HPi) generally enhanced moisture resistance and long-term Marshall stability, while hydrophobic (HPb) improved unaged softening point. Low-temperature performance improved for 50–70 but degraded for SBS-modified mixtures. Aging dominated long-term behaviour, often overshadowing nano benefits. These findings highlight that the effectiveness of nano-alumina modification depends on the asphalt binder type, nano-alumina surface chemistry, and aging conditions, necessitating a performance-based selection approach.