Strain recovery rate and absolute per cent recovery of polymer-modified asphalt binders

Multiple Stress Creep and Recovery (MSCR) test was conducted on four different types of polymer-modified asphalt (PMA) with three different performance grade (PG) levels, at two stress levels (0.1 and 3.2 kPa) and four temperatures (58°C, 64°C, 70°C and 76°C). Strain recovery rates, absolute per cent recovery and creep compliance recovery rate of the PMAs at near instantaneous (NI) and near steady-state (NSS) regions were estimated and analysed. Higher levels of applied stress and temperature have induced a correspondingly higher rate of strain recovery both at NI (RR_NI) and NSS, due to additional rebound energy accompanying more sustained deformation. Similar but mild strain recovery rate trend was observed with increasing PG. The strain recovery rate is inversely proportional to the per cent strain recovered, for a given temperature and applied stress, both at NI and at NSS region. An absolute per cent recovery at NI (%R_NI) and NSS (%R_NSS) was estimated in terms of the strain recovery rates. The %R_NI is relatively constant for all rest periods, and can be obtained within the first 2 seconds of the creep-recovery cycle. Finally, even though the conventional MSCR parameters (i.e. J_nr and R) showed statistically significant correlation with the AC rutting, some strain recovery rate base parameters (%R_NI and %R_NSS) demonstrate a statistically better correlation with the AC rutting.