Recommendations in Low-Temperature DSR Testing Methods and Data Analysis

Low-temperature binder characterization within the Superpave framework relies primarily on the bending beam rheometer (BBR); however, advancements in dynamic shear rheometer (DSR) technology have enabled growing interest in subzero DSR tests for evaluating stiffness, thermal cracking behavior, and performance grading criteria. Properly implemented low-temperature DSR testing offers potential for quick, consistent testing with minimal required sample volume compared to traditional BBR testing. 

However, this mode of testing introduces unique challenges such as instrument compliance concerns, sensitivity to sample preparation and geometry, and thermal equilibration of the sample.  Further, data analysis of low-temperature DSR data can often include implicit assumptions about low temperature viscoelastic behavior of binders such as viscoelastic linearity and thermo-rheological simplicity. 

This work examines current strategies and practices in low-temperature DSR measurements as well as the challenges, limitations, and assumptions involved. These methods are compared to several techniques for performing low-temperature DSR tests, using criteria by which to measure data quality such as Black Space, instrument compliance calibrations, and thermal analysis from differential scanning calorimetry (DSC). From this evaluation, we propose recommended test parameters, practices, and instrumentation for low-temperature DSR testing as well as methods of assessing data quality and validity. 

Key learning objectives: 

• Identify the primary sources of error in subzero DSR testing
• Evaluate the validity of certain assumptions made during testing
• Use a variety of models and techniques to audit the quality of master curves generated with subzero isotherms