Intermediate-temperature cracking performance evaluation of asphalt mixtures

This study examines the influence of specimen thickness and air void content on asphalt cracking performance using the Multi-Stage Semi-Circular Bending Dynamic (MSSD) test and the Indirect Tensile Asphalt Cracking Test (Ideal-CT). Results indicate that MSSD slope and intercept indicators were largely unaffected by thickness variations, making them reliable for fatigue resistance assessments. In contrast, Dissipated Energy and the Ideal-CT Index were highly sensitive to thickness, requiring standardization (preferably at 50 mm) or correction factors for accurate evaluations. Air void content had a significant effect on all cracking indicators. Higher air voids increased MSSD slope values and decreased ABS intercept values, Dissipated Energy, and Stiffness Reduction, confirming that excessive voids weaken asphalt mixtures. The Ideal-CT Index, however, unexpectedly increased with air void content, contradicting expected field performance and raising concerns about its reliability for real-world cracking assessments. The findings highlight the importance of standardizing air void content within 4–7% to ensure reliable test results and meaningful comparisons. Paris’ Law parameters (slope and absolute intercept) and stiffness modulus reduction were identified as the most robust indicators for fatigue resistance due to their low sensitivity to thickness variations. Given the inconsistencies observed in the Ideal-CT Index, further research is needed to determine its applicability in field evaluations. Overall, the study reinforces the advantages of the MSSD test in providing more precise and field-relevant cracking performance.