Interpreting Stress Sensitivity in the Multiple Stress Creep and Recovery Test

Abstract

The original intent of the Jnrdiff 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 Jnrdiff specification for asphalt binders with low Jnr3.2 (mainly less than .5 kPa−1) have been documented, with reported Jnrdiff values greater than 4% in some cases. This paper presents an argument that Jnrdiff is an inaccurate representation of stress sensitivity, unfairly penalizes asphalt binders with low Jnr3.2, and lacks correlation with expected changes in field rutting performance. A new parameter that more appropriately describes stress sensitivity, Jnrslope, is presented. Jnrslope shows a better performance-based relationship to expected changes in rutting and more accurately ranks the study asphalt binders than Jnrdiff. Jnrslope also demonstrates the ability to capture changes in Jnr3.2 with respect to increases in test temperature. Finally, a conceptual, performance-based Jnrslope specification limit is presented. Overall, Jnrslope provides an alternate parameter to accurately interpret and describe stress and temperature sensitivity and demonstrates potential as a performance-based parameter.