Evaluating Cracking Resistance of Asphalt Binders and Mixtures under Extended Aging through Chemical, Physical, and Fracture-Based Correlations

Cracking is one of the most persistent issues in asphalt pavements. It is intensified by the fact that binders of the same grade also exhibit different long-term performance due to variations in crude source and refining processes. This study evaluates 12 unmodified VG40 binders from different refineries to establish binder–mixture dependence in cracking resistance against extended oxidative aging. Each binder was aged using the rolling thin film oven (RTFO) for short-term aging (STA), while long-term aging (LTA) was performed using a pressure aging vessel (PAV) for 20, 40, and 60 h. Corresponding mixtures, with identical volumetrics and a 13.2 mm nominal maximum aggregate size, were evaluated using the indirect tensile asphalt cracking test under short- and long-term aging. Mixtures showed significant variability, though having identical binder grade, with a decrease in cracking tolerance (CT) index by almost 19% after LTA. Strong correlation between STA and LTA CT index values confirmed that mixtures maintained their relative cracking performance, showing the effect of differences in chemical composition. The Gaestel index (GI) increased from 0.40 at 20 h to 0.47 at 60 h, showing a clear sol-to-gel transformation. Softening-point change ( Δ SP ) differentiated binders into stable ( < 23 ° C ), transitional (23°C–30°C), and severely oxidized ( > 30 ° C ) groups. Change in ductility ( Δ ductility ) quantified the progressive reduction in tensile extensibility. Double-edge-notched tension results depicted a corresponding decline in critical tip opening displacement (CTOD), showing reduced fracture deformability with aging. Cross-parameter relations depicted coherent mechanistic trends among GI, Δ SP , Δ ductility , CTOD, and CT index, confirming that oxidation-driven asphaltene enhancement and maltene reduction govern embrittlement across the properties. Overall, the combined chemical, physical, and fracture-based results show that traditional binder grading is insufficient for unmodified binders, and that chemical and fracture-based criteria are essential to secure reliable long-term cracking performance.