Nano-silica enhanced recycled asphalt mixtures: a sustainable approach to pavement performance optimization

Recycled Asphalt Pavement (RAP) utilization faces challenges including performance variability and moisture susceptibility, particularly at higher percentages. While nanomaterials show promise for enhancing asphalt properties, limited research exists on their combined effects with RAP and rejuvenators. This study addresses the critical need to optimize nano-silica content in rejuvenated high-RAP mixtures to achieve performance equivalent to conventional mixes while maximizing sustainable material utilization. A systematic Taguchi L-9 orthogonal array design evaluated three factors: RAP percentage (15%, 30%, 45%), bitumen content (5%, 5.5%, 6%), and nano-silica content (3%, 5%, 7%). Waste cooking oil (1%) served as rejuvenator for 45% RAP mixtures. Comprehensive testing included Marshall properties, moisture susceptibility (TSR), and rutting resistance. Optimal nano-silica content of 5% consistently enhanced performance across all RAP percentages. Marshall stability increased by 16–25% compared to unmodified mixes. TSR values exceeded 80% minimum requirement, and rutting resistance improved by 25–32%. Statistical models showed strong correlation (R2 = 0.96) between composition and performance. Nano-silica modification enables successful utilization of up to 45% RAP while maintaining superior performance characteristics, providing a sustainable approach to pavement construction with predictable outcomes.