Investigating the Nonlinear Behaviour of Neat and Modified Binders Through Large Amplitude Oscillatory Shear (LAOS) Testing

Asphalt Cements (ACs) are typically characterized within their Linear Viscoelastic (LVE) range, where they are treated as thermo-rheologically simple materials. Such assumption simplifies characterization of asphalt behaviour over a wider range of time- and temperature-varying conditions by applying time-temperature superposition principle. However, the LVE-based tests cannot capture the nonlinear behaviour of binders under larger strains, which is an important aspect towards proper characterization of flexible pavement materials. Nowadays, various modification techniques are employed to engineer the desired rheology of asphalt cements, which also signifies the need for better understanding the nonlinear behaviour of modified binders. Therefore, the Large Amplitude Oscillatory Shear (LAOS) testing and Fourier Transform (FT) analysis, originally rooted in polymer science, were utilized in this study to characterize the nonlinearity of neat and modified ACs. To this end, the neat asphalt cements were treated with either 0.5% of a warm mix asphalt (WMA) additive or 4.0% of an elastomer. The elastomer used is Styrene-Butadiene-Styrene (SBS) based polymer. The specimens were then aged in the laboratory to simulate the short- and long-term aging process prior to performing the LAOS strain testing. The results obtained at the intermediate temperature were used in the FT Analysis to quantify the nonlinearity of the ACs. This technique can be successfully used to distinguish the contribution of nonlinearity from other factors such as damage.