The multiple stress creep and recovery (MSCR) test is a result of refinements in the repeated creep and recovery test by the United States Federal Highway Administration (FHWA) with the main objectives of (a) analyzing and controlling the stress dependence of asphalt binders; (b) quantifying the magnitude of the elastic reponse of the asphalt binder and its rutting potential; and (c) determining the adequate traffic level for each asphalt binder at the high pavement temperature. The standard test protocol (ASTM D7405, AASHTO TP70) utilizes a dynamic shear rheometer (DSR) to apply subsequent loading-unloading cycles (10 or 20 cycles, depending on the standard and the stress level) on an asphalt binder sample with a diameter of 25 mm and a gap height of 1 mm, such that each cycle includes a creep time of 1 s and a recovery time of 9 s.Although the MSCR test constitutes a substantial improvement over the dynamic oscillatory shear test and the determination of the Superpave® binder rutting parameter G*/sin´, the standard procedure has major limitations. One of these limitations is the recovery time of 9 s, which may not be long enough to fully capture the recoverable strain of asphalt binders. Another problem is the proportion 1:9 for the creep and recovery times, since research studies with asphalt mixtures showed that the recovery time must be from 20 to 30 times longer than the creep time to obtain a complete characterization of the rheological behavior of the asphalt binder.This research project is intended to contribute to the industry and the university sectors in the following aspects: (a) to present an in-depth study about the creep-recovery behavior of asphalt binders modified with different types of additives and the same high-temperature performance grade (PG 76-xx); (b) to clarify some issues concerning the effects of the delayed elasticity on the rheological properties of short-term aged asphalt binders; and (c) to determine, as a function of a predefined creep time, the recovery time at which the delayed elasticity of the asphalt binders is fully recovered and does not have any more influence on the rheological properties of the materials.
News published in Agência FAPESP Newsletter about the scholarship: