An improved method to calculate stripping inflection point (SIP) and its application in evaluating moisture susceptibility of asphalt mixtures

Accurately assessing asphalt mixtures’ moisture susceptibility is critical because moisture damage can significantly reduce pavement durability, leading to premature failure and structural integrity of the pavement. The stripping inflection point (SIP), a moisture susceptibility index derived from the Hamburg Wheel Track (HWT) test, has practical merits in evaluating moisture susceptibility. However, current methods for determining the SIP showed low accuracy and high variability due to poor regression quality. Hence, this study aims to propose an improved method for calculating the SIP by modifying existing approaches to better capture the characteristics of rutting curves. Typical asphalt mixtures were used to conduct moisture susceptibility tests. Results from the TSR (T283) test and the Moisture Induced Stress Tester (M.i.S.T) test were used to verify the effectiveness of SIP. Results showed that the proposed model provided a better fit than existing models due to its ability to identify steep upturn tails, and it yielded more reasonable SIP values with much lower variability. In addition, SIP results based on the improved method exhibited a significant correlation with the results from M.i.S.T method, suggesting a promising approach for evaluating the moisture susceptibility of mixtures under field conditions. It is noted that a significant discrepancy was observed between the recommended SIP threshold and existing SIP limits. This indicates the necessity of further assessing the evaluation methods for the moisture susceptibility of mixtures.