Nonlinear Rheological Characterizations of Reactive Elastomeric Terpolymer-Modified Asphalt Binder Based on Large-Amplitude Oscillatory Shear Test

In this paper, we investigated the nonlinear rheological behavior of two types of modified asphalt binders, namely reactive elastomeric terpolymer-modified asphalt binder (REA) and styrene-butadiene-styrene–modified asphalt binder (SBA), under large strains using large-amplitude oscillatory shear (LAOS) testing. To determine the test strain levels, we conducted strain sweeps at different temperatures and shear frequencies before subjecting the asphalt binders to the LAOS test. Our findings show that the nonlinear critical strain of asphalt binders has a temperature and frequency dependence, with smaller values at lower temperatures and higher frequencies, indicating stronger nonlinear rheological properties. We used Fourier-transform rheology to analyze the relative intensity of higher harmonics of asphalt binders ($I_n/I_1$, $3\le n\le 9$) and found that the nonlinear parameter $I_3/I_1$ increased with shear frequency and strain amplitude, and that the $I_n/I_1$ of REA was much larger than that of SBA. To evaluate the performance of the modified asphalt binders, we used the zero-strain nonlinear parameter $Q_0$ and found that REA had a higher $Q_0$ value than SBA at the same frequency. Furthermore, based on the Lissajous curves at 25°C and $10\mathrm{rad}/\mathrm{s}$, we observed that the aberration degree of the curves increased with increasing strain amplitude. The Lissajous curves of both base asphalt binder (BA) and SBA failed to form a closed ellipse due to sample damage at larger strain levels, which means that BA and SBA are less resistant to large deformations, whereas REA maintained a higher load-bearing capacity. We also observed that both modified asphalt binders exhibited continuous shear-thinning properties. At higher strains, the intermolecular forces in SBA were overcome by shear deformation, whereas the chemical bonds formed between oxygen-containing functional groups and carboxylic acid groups in REA were gradually broken by stretching. LAOS test results demonstrated that REA exhibited higher deformation resistance potential at large strain levels compared with SBA.