Rheological Modelling of Asphalt Viscoelasticity

Abstract

The rheology of asphalt binders is an important factor in the design and construction of roads. As polymer modification is now often required to meet performance demands, the rheological behaviour of the binders has become increasingly complex. Within the past decade, a new method to evaluate these binders and their viscoelasticity has emerged – the Multiple Stress Creep Recovery (MSCR) test. This thesis introduces a simple, lowest-order rheological model — the Standard Linear Fluid (SLF) model — that correctly predicts the MSCR response. It is shown that the SLF parameters can be obtained via a frequency sweep (involving small deformations) with a Dynamic Shear Rheometer. Furthermore, these parameters can be used to distinguish between polymer-modified and unmodified asphalts, just as a MSCR test can. Although the SLF model has all the correct qualitative features, it significantly under-predicts the amount of strain that was recovered in an MSCR test. This discrepancy is attributed to the non-linearity of the material properties. Specifically, the SLF model parameters are determined from small-strain frequency sweeps, while the MSCR test involves large deformations — when non-linearities in material properties begin to appear. An adjustment was made to the elastic element of the SLF model to account for non-linearity in the form of a hyperelastic Mooney-Rivlin solid. This improved the prediction for the recovery portion of the MSCR test considerably, but still not enough to agree with the experimental results at the cost of two additional parameters.