Phase Stability Evaluation of Highly Modified Asphalt with High Vinyl Content Copolymer

This study evaluated whether use of a high-vinyl styrene-butadiene-styrene (SBS) copolymer can provide adequate phase stability to highly modified asphalt (HiMA). An asphalt binder was modified with 7.5 % high-vinyl SBS to produce HiMA. A conventional polymer-modified asphalt was produced with 4 % SBS without vinyl and, together with the base asphalt, considered as reference samples. In the first phase, samples were analyzed considering unaged and short-term aged conditions. The experimental procedure analyzed binder morphology using fluorescence microscopy and determined chemical functional groups through Fourier transform infrared spectroscopy (FTIR). Rheological behavior at intermediate temperatures was evaluated concerning dynamic shear modulus, phase angle, and linear amplitude sweep (LAS) tests at 20°C. High-temperature properties, including apparent viscosity, performance grade, aging index, and multiple stress creep and recovery (MSCR) test, were also assessed. In the second phase, unaged asphalt binders were subjected to storage stability test, and the top and bottom sections were evaluated through fluorescence microscopy, FTIR, LAS, and MSCR tests. The samples with 7.5 % high vinyl SBS exhibited enhanced fatigue tolerance in the LAS test compared to base asphalt (14.35 times higher at 15 % shear strain) and samples with 4 % SBS without vinyl (6.62 times higher at 15 % shear strain). Additionally, it displayed superior resistance to deformation accumulation at high temperatures (ε10 parameter from MSCR) compared to base asphalt (99.65 % smaller at 64°C) and samples with 4 % SBS without vinyl (93.05 % smaller at 64°C). However, the storage stability of the asphalt samples with 7.5 % high vinyl SBS was compromised due to phase separation, severely impacting the rheological performance at intermediate and high temperatures. It was concluded that the incorporation of high levels positively impacts mechanical/rheological performance, but the molecular characteristics of the high vinyl SBS are not capable of providing adequate storage stability at a content of 7.5 %.