Interpreting Stress Sensitivity in the Multiple Stress Creep and Recovery Test: Fid-Bau Portal

Interpreting Stress Sensitivity in the Multiple Stress Creep and Recovery Test

Stempihar, Jeffrey / Gundla, Akshay / Underwood, B. Shane

The original intent of the $J_{n r d i f f}$ 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 $J_{n r d i f f}$ specification for asphalt binders with low $J_{n r 3.2}$ (mainly less than $0.5 {kPa}^{- 1}$ ) have been documented, with reported $J_{n r d i f f}$ values greater than 400% in some cases. This paper presents an argument that $J_{n r d i f f}$ is an inaccurate representation of stress sensitivity, unfairly penalizes asphalt binders with low $J_{n r 3.2}$ , and lacks correlation with expected changes in field rutting performance. A new parameter that more appropriately describes stress sensitivity, $J_{n r s l o p e}$ , is presented. $J_{n r s l o p e}$ shows a better performance-based relationship to expected changes in rutting and more accurately ranks the study asphalt binders than $J_{n r d i f f}$ . $J_{n r s l o p e}$ also demonstrates the ability to capture changes in $J_{n r 3.2}$ with respect to increases in test temperature. Finally, a conceptual, performance-based $J_{n r s l o p e}$ specification limit is presented. Overall, $J_{n r s l o p e}$ provides an alternate parameter to accurately interpret and describe stress and temperature sensitivity and demonstrates potential as a performance-based parameter.