Effects of Stress Levels on Creep and Recovery Behavior of Modified Asphalt Binders with the Same Continuous Performance Grades

Abstract

The study reported in this paper assessed the effects of stress levels on the creep and recovery behavior of modified asphalt binders with the same continuous performance grades (PGs). The modifiers included styrene–butadiene–styrene (SBS) and polyphosphoric acid (PPA). The multiple stress creep and recovery (MSCR) test was applied at 55°C and 70°C and at the PG temperature of each binder to consider a wide range of high temperatures. To further explore the role of applied stresses, the stress of 12.8 kPa was selected as an addition to the MSCR standard procedure. The nonrecoverable compliance (Jnr) and the percentage recovery (R) were calculated at each stress cycle. Comparison of the Jnr values between the corresponding SBS and PPA binders showed that, for the whole temperature range considered, the addition of a higher stress level to the MSCR standard procedure was necessary to increase the stress sensitivities and also to depict the nonlinear behaviors of the modified binders more clearly, especially for the PPA ones. Moreover, the R values showed that, at the PG temperatures of the binders, performance of the MSCR standard procedure made it possible to differentiate between the SBS and PPA binders with similar continuous PGs. At testing temperatures lower than the PGs, a higher stress level should be added to the MSCR standard procedure to differentiate between the elasticity of the corresponding SBS and PPA binders. At temperatures higher than the PGs, stress levels lower than 3.2 kPa should be applied to avoid negative recovery values.