Creep-Recovery Behavior of Asphalt Binders Modified with SBS and PPA

The main objective of this study was to investigate the impact of longer creep-recovery times on the percent recovery (R) and the nonrecoverable compliance (Jnr) of three asphalt cements (AC), or binders, modified with (1) styrene-butadiene-styrene (SBS) copolymer, (2) polyphosphoric acid (PPA), and (3) SBS+PPA. The base material is a 50/70 pen-grade (PG 64-xx) asphalt binder and the modified asphalt binders have the same high-temperature performance grade (PG 76-xx). The impact of longer creep-recovery times was addressed by calculating the percent recovery and the nonrecoverable compliance ratios at the test temperatures of 70°C and 76°C. The multiple stress creep and recovery (MSCR) test was used to determine the R and Jnr values at the stress levels of 0.1 and 3.2 kPa. Two creep-recovery times were used, namely, 1/9 and 2/18 s. The highest R values and the lowest Jnr values can be found in the AC+PPA formulation. The increase in both creep-recovery times caused less impact on the rutting susceptibility of the AC+SBS+PPA than the AC+SBS and the AC+PPA under the same MSCR test conditions.