Revised Index–Volumetrics Relationship for Cracking and Its Four Corners

This study aims to improve the reliability of the index–volumetrics relationship (IVR) function used to predict the cracking performance of asphalt mixtures based on field-measurable volumetric parameters. The conventional IVR model, which utilizes in-place voids in mineral aggregate and in-place voids filled with asphalt, has shown inconsistent trends, particularly in the relationship between the cracking index and air void content. To address this limitation, two new parameters were proposed: in-place air void content V a and effective asphalt content P be , based on their independence and linear relationship with cracking performance. Eight mixtures from different states were used to develop and verify the revised IVR function. IVR performance was assessed through calibration using four volumetric conditions (so-called “four corners”) and independent verification. The revised IVR exhibited enhanced consistency and alignment with theoretical expectations. In addition, a random combination analysis was conducted to evaluate the effect of different four-corner selections on model behavior. The findings showed that selecting well-distributed calibration points across the V a – P be domain significantly improved the revised model’s prediction accuracy. A new four-corner design is proposed that balances aggregate gradation, design air void content, and performance test air void content. The results of this study contribute to a more robust framework for developing IVRs for balanced mix design and performance-related specifications in asphalt pavement design and construction.