Chemo-mechanical evaluation of unmodified binders exposed to extended ageing using Superpave fatigue factor, Linear Amplitude Sweep, and Double-Edge Notched Tension

Cracking remains a critical challenge in flexible pavements, particularly after long-term oxidative ageing of asphalt binders. This study evaluates the cracking susceptibility of twelve unmodified binders from domestic and international sources under extended ageing conditions (20, 40, and 60 h in a pressure ageing vessel). Despite similar grading, significant variability in chemical composition and performance was observed. Cracking behaviour was characterised using the Superpave fatigue factor (G*·sinδ), Linear Amplitude Sweep (LAS), and Double-Edge Notched Tension (DENT) tests. Complementary chemical analysis using SARA fractions and the Gaestel index (GI) revealed systematic compositional shifts, with decreasing aromatics and increasing resins and asphaltenes, resulting in higher GI values. While fatigue parameters showed a decline with ageing, their correlation with GI was inconsistent. In contrast, crack tip opening displacement (CTOD) from the DENT test exhibited a strong and mechanistically consistent correlation with GI (R² = 0.73), effectively distinguishing resilient and embrittled binders. The findings highlight the limitations of fatigue-based parameters and establish CTOD as a reliable chemo-mechanical indicator of cracking susceptibility. Adoption of DENT-based evaluation is recommended for improved durability assessment.