Techniques for Determining Errors in Asphalt Binder Rheological Data

Abstract

Numerous new methods for specifying asphalt binders, based on more complex theoretical approaches, have emerged in the past years, and researchers are increasingly using these methods for studying asphalt binders. These methods require an increased degree of accuracy and precision in the laboratory data. A number of simple techniques are detailed that can be successfully used to identify errors in rheological data obtained for asphalt binders. Asphalt binders do not exhibit sudden changes in their behavior with respect to time or temperature. Therefore, any discontinuities revealed by the visual inspection of the test data in graphical format can be attributed to testing errors. A powerful yet simple tool in identifying potential problems with the dynamic shear rheometer test data is the Black diagram. The Black diagram is a plot of phase angle versus log | G*|, which, unlike master curves, does not require shifting of the data generated at different temperatures. However, pseudo Black diagrams should not be used with the bending beam rheometer (BBR) data because of the errors in calculating m-values associated with the use of the polynomial approximation. The c-coefficient can be used for a quick check of BBR data on the basis of the fact that the slope of the m-values decreases as the test temperature decreases. For the direct tension test, the secant modulus calculated from the stress-strain data provides a better tool to identify errors in the test data.