Semnan University Press Journal of Transportation Infrastructure Engineering 2423-5350 11 3 2025 10 23 Performance Evaluation of Nano Silica Used in Asphalt Mixture: Focus on the Content and Aging of Recycled Asphalt Pavement Performance Evaluation of Nano Silica Used in Asphalt Mixture: Focus on the Content and Aging of Recycled Asphalt Pavement 1 20 9864 10.22075/jtie.2025.37817.1724 FA Esmaeil Taheri Ph.D. Candidate, Faculty of Civil Engineering, Semnan University, Semnan, I. R. Iran. Gholamali Shafabakhsh Professor, Department of Road and Transportation, Faculty of Civil Engineering, Semnan University, Semnan, I. R. Iran. Mostafa Sadeghnejad Assistant Professor, Department of Civil Engineering, University of Guilan, Rasht, I. R. Iran. Journal Article 2025 05 24 Incorporating recycled asphalt pavement (RAP) into asphalt mixtures is a common practice for sustainability. However, aging and hardening of the RAP binder can compromise performance. Aged RAP is stiffer, less flexible, and more prone to cracking. This research investigates the combined effects of RAP content, RAP age, and nano-silica (SiO₂) addition on asphalt performance, focusing on fracture resistance, fatigue resistance, and moisture susceptibility. Asphalt mixtures containing 25%, 50%, and 75% RAP were evaluated using RAP aged 5 and 10 years. Nano-SiO₂was incorporated at 0%, 1%, 1.5%, and 2%. Performance evaluations included semi-circular bending test for fracture resistance, indirect tensile fatigue test for fatigue resistance, and tensile strength ratio (TSR) test for moisture susceptibility. The findings indicated that nano-SiO₂significantly enhanced fracture and fatigue resistance, especially at lower RAP content. At 25% RAP, 1.5% and 2% nano-SiO₂improved both fracture and fatigue resistance by 15%-20%. Notable enhancements were observed for mixtures with 50% and 75% RAP, with optimal results at 2% nano-silica. Furthermore, nano-SiO₂improved moisture resistance, increasing TSR values above 80%. Nano-silica effectively mitigated aging effects, particularly in mixtures with higher RAP content. Based on this analysis, utilizing 25%-50% RAP combined with 1.5% nano-SiO₂is advisable for producing high-performance asphalt mixtures. Incorporating recycled asphalt pavement (RAP) into asphalt mixtures is a common practice for sustainability. However, aging and hardening of the RAP binder can compromise performance. Aged RAP is stiffer, less flexible, and more prone to cracking. This research investigates the combined effects of RAP content, RAP age, and nano-silica (SiO₂) addition on asphalt performance, focusing on fracture resistance, fatigue resistance, and moisture susceptibility. Asphalt mixtures containing 25%, 50%, and 75% RAP were evaluated using RAP aged 5 and 10 years. Nano-SiO₂was incorporated at 0%, 1%, 1.5%, and 2%. Performance evaluations included semi-circular bending test for fracture resistance, indirect tensile fatigue test for fatigue resistance, and tensile strength ratio (TSR) test for moisture susceptibility. The findings indicated that nano-SiO₂significantly enhanced fracture and fatigue resistance, especially at lower RAP content. At 25% RAP, 1.5% and 2% nano-SiO₂improved both fracture and fatigue resistance by 15%-20%. Notable enhancements were observed for mixtures with 50% and 75% RAP, with optimal results at 2% nano-silica. Furthermore, nano-SiO₂improved moisture resistance, increasing TSR values above 80%. Nano-silica effectively mitigated aging effects, particularly in mixtures with higher RAP content. Based on this analysis, utilizing 25%-50% RAP combined with 1.5% nano-SiO₂is advisable for producing high-performance asphalt mixtures. https://jtie.semnan.ac.ir/article_9864_1dac5cabe30aac580312c1c3c104e8a4.pdf