A Comparative Study for Creep and Recovery Behavior Characterization of Modified Bitumens Using the MSCR Test

In recent decades, the application of modified bitumens has experienced tremendous growth. However, due to the varying modification mechanism of different modifiers, the creep and recovery properties of modified bitumen have not been comprehensively understood. This study aims to evaluate the creep and recovery properties of several representative modified bitumens using the multi-stress creep recovery (MSCR) test. The MSCR test can highlight the unique delayed elasticity of modified bitumen and it uses a high stress level, which is more comparable to the field. In particular, this test also aims to identify the effects of different aging conditions. To do so, a total of 15 bitumens, including 7 elastomeric-modified bitumens, 5 non-elastomeric-modified bitumens, and 3 plain bitumens, were prepared and examined. Furthermore, 10 different aging conditions were considered. The results suggest that the generation mechanism of elasticity varies for different modified bitumens. There are two types of elasticities, which are energy elasticity and entropy elasticity, and their differences need more attention in the road bitumen material community. Aging changes the percentages of contributions from energy elasticity and entropy elasticity to the bitumen's overall recovery performance. The increase in "bad" energy elasticity may compensate for part of the "good" entropy elasticity loss, but overall, the bitumen's recovery rate is decreasing and the ratio of energy elasticity is increasing, which might hinder the bitumen's road performance.