Use of the multiple stress creep recovery (MSCR) test to characterize the rutting potential of asphalt binders: A literature review

Abstract

The multiple stress creep recovery (MSCR) test has been recently accepted to improve the rutting assessment of the Superpave performance grading (PG) system. The non-recoverable creep compliance and the percent recovery are two major parameters obtained from the MSCR test. The non-recoverable creep compliance measured at 3.2 kPa is used as a measure of the resistance of an asphalt binder to permanent deformation under repeated loading condition. The percent recovery is employed to identify the presence of elastic response and stress dependence of tested asphalt binders. Despite its success in rutting characterization, the MSCR test has received a lot of debates mainly about the test protocol and analysis method. Examples of the most argued problems are the creep and recovery time, the number of creep and recovery cycles and the stress levels. Considerable efforts have been made to refine the MSCR test protocol in recent years, such as increase of creep time and/or recovery time, addition of more creep and recovery cycles and use of a higher stress level. Mechanistic modeling of the MSCR test has also been proposed to separate the full viscoplastic strain from the total strain by employing the Schapery’s nonlinear viscoelastic theory and the modified superposition principle. All of these efforts are aimed at a better characterization of the rutting performance of asphalt binders. This paper provides a review of the MSCR test from its development, validation to new improvements in test protocol and analysis method. Such a literature review is useful in developing a comprehensive understanding of the MSCR test and proposing a better MSCR test protocol than the one being currently used.