Comparative Analysis of Fatigue Performance in Asphalt Concrete Modified with Nano-Alumina and Nano-Silica

This comprehensive study undertakes a two-tiered comparative analysis to systematically evaluate the fatigue and cracking performance of a 40-50 penetration grade asphalt binder and its corresponding asphalt concrete mixtures, modified with varying dosages (2%, 4%, and 6% by binder weight) of Nano-Alumina (NA) and Nano-Silica (NS). The experimental methodology involved extensive binder-level testing, including the evaluation of physical properties (penetration, softening point, ductility), rheological behavior (Rotational Viscosity (RV)), and fatigue characteristics using the Superpave parameter G* sin δ and the advanced Linear Amplitude Sweep (LAS) test. Furthermore, compatibility was assessed via storage stability and Scanning Electron Microscopy (SEM). The research culminated in mixture-level performance evaluation using the Indirect Tensile Cracking Test (IDEAL-CT) to derive the Cracking Tolerance Index (CT-Index), Flexibility Index (FI), and Crack Resistance Index (CRI). The results confirmed that both nanomaterials significantly enhance binder stiffness and thermal stability. Nano-Alumina (NA) consistently induced the most profound stiffening effect, reflected by a major reduction in penetration. Rheological and LAS testing indicated that NA provides a stable and progressive, dose-proportional enhancement in fatigue life from 2% to 6%, attributed to the formation of a sustained nanoscale reinforcement network. Conversely, Nano-Silica (NS) exhibited a potent viscosity-building effect due to its high surface area, achieving superior initial cracking tolerance and fatigue life at low concentrations (2% to 4%). Crucially, the study identified a narrow optimal range for NS; concentrations at 6% led to an adverse reduction in fatigue resistance (G* sin δ increase) and diminished flexibility, suggesting a constraint imposed by excessive stiffening and potential particle agglomeration. Mixture-level IDEAL-CT results further validated these trends: NA offered a balanced overall contribution, maximizing the CT-Index at 6% and CRI at 4%, while NS yielded an exceptionally high CT- Index value at 2% but showed a decline in performance at higher contents. The overall findings recommend an optimal practical dosage of 2-4% for NS and 4-6% for NA, underscoring the necessity of material-specific optimization for achieving enhanced durability and fatigue life under repeated loading.