Evaluation of Asphalt Cement Loss Tangent as Surrogate Performance Indicator for Control of Thermal Cracking.

This paper documents and discusses the field validation of a simple performance indicator for specification grading of asphalt cement for thermal cracking. The loss tangent as defined by the ratio of the viscous loss modulus over the elastic storage modulus, G"/G', is able to provide a quantitative measure of the sol/gel nature of asphalt cement. As such it relates closely to how well a material is able to relax stress and is therefore investigated as a surrogate performance indicator for thermal cracking. Extracted asphalt cements from 20 contract sites in eastern and northeastern Ontario were tested in torsion bar geometry to determine their viscoelastic properties. The findings show that the loss tangent was able to distinguish the good from poor performers for this set of materials with 95% accuracy after only a short period of conditioning prior to testing. This is a considerable improvement over the current low temperature bending beam rheometer protocol. In addition to the use of the loss tangent, it is suggestedthat a measure of the critical strain tolerance in the ductile state could be included in order to provide a significantly improved performance grading method.