Stress-dependent behavior and rutting resistance of modified asphalt binders: An MSCR approach

In this paper, the stress-dependent behavior of modified asphalt binders was studied using multiple stress creep recovery (MSCR) tests. A neat binder was modified with different amounts of styrene-butadienestyrene (SBS), ground tire rubber (GTR) or polyphosphoric acid (PPA) to investigate the effects of these modifiers on the stress-dependent behavior of asphalt binders. Two non-standard MSCR testing regimes, each representing different stress levels and varying numbers of cycles, were applied at 64 °C to each of the modified binders. The nonrecoverable creep compliance (Jnr) and the percentage recovery (R) values were calculated at each cycle. In addition, the average Jnr and the average R values were also calculated at each stress level. All of the modified binders studied in this research showed that a higher degree of non-linear behavior is associated to the higher stress levels. Likewise, all of the binders (except those modified with SBS) showed a decreasing trend of average percent recovery as the stress level increased. In the case of the SBS-modified binders exposed to cumulative incremental stress testing conditions, the initially increasing trend in the average percent recovery was followed by a decreasing trend. This might be due to the fact that, initially, the polymer network in the modified binder got stretched until it reached its highest extension capacity. After reaching this point, the polymer network likely started to rearrange itself while still remaining stronger than neat asphalt.