Evaluating Rutting and Fatigue Characteristics of Binder Containing SBS and PPA and Their Relationship with the Mixture Stiffness Parameter

The paper assessed the rutting and fatigue resistances of binders containing styrene butadiene styrene (SBS) and polyphosphoric acid (PPA). For this purpose, a performance grade (PG) 58-22 base binder was modified in two manners: SBS polymer and reduced SBS polymer plus PPA. The SBS content of the SBS binder and the PPA content of the SBS+PPA binders were kept constant. Two SBS+PPA binders were investigated, for which the reduced SBS contents were determined differently: one had the same continuous high-temperature PG as the SBS binder, and the other had the same viscosity at 135°C. Multiple stress creep and recovery (MSCR) tests were performed at 40 and 55°C for determining the rutting characteristic, and linear amplitude sweep (LAS) tests were performed at 25°C for determining the fatigue characteristic of the binders. To depict the nonlinearity and predict the rutting resistance more clearly, the high stress levels of 12.8 and 25.6 kPa were added to the MSCR standard procedure. A complex modulus test was also used to evaluate the effectiveness of the new test methods for the SBS and SBS+PPA binders and to relate the results to the mixtures’ stiffness parameters. Based on the results, it is found that the nonlinearity caused by the high stress levels (rutting potential) and the fatigue damage of the SBS binder are less than those of the SBS+PPA binder with the same continuous PG, but are more than those of the SBS+PPA binder with the same viscosity. The results also show good correlations between the binders and mixtures tests data.