Interpreting Stress Sensitivity in the Multiple Stress Creep and Recovery Test

The original intent of the $J_{nrdiff}$ limit applied to multiple stress creep and recovery test results was to ensure that an asphalt binder does not fail if, under real-world application, it experienced higher stresses or temperatures than what was considered in the laboratory. In recent years, challenges meeting the $J_{nrdiff}$ specification for asphalt binders with low $J_{nr3.2}$ (mainly less than $0.5{\mathrm{kPa}}^{-1}$) have been documented, with reported $J_{nrdiff}$ values greater than 400% in some cases. This paper presents an argument that $J_{nrdiff}$ is an inaccurate representation of stress sensitivity, unfairly penalizes asphalt binders with low $J_{nr3.2}$, and lacks correlation with expected changes in field rutting performance. A new parameter that more appropriately describes stress sensitivity, $J_{nrslope}$, is presented. $J_{nrslope}$ shows a better performance-based relationship to expected changes in rutting and more accurately ranks the study asphalt binders than $J_{nrdiff}$. $J_{nrslope}$ also demonstrates the ability to capture changes in $J_{nr3.2}$ with respect to increases in test temperature. Finally, a conceptual, performance-based $J_{nrslope}$ specification limit is presented. Overall, $J_{nrslope}$ provides an alternate parameter to accurately interpret and describe stress and temperature sensitivity and demonstrates potential as a performance-based parameter.