Simplifications of the Short-Term USAT Protocol for Neat and Modified Binders: A Rheological Assessment

Abstract

This study evaluates the feasibility of proposed simplifications of the universal simple aging test (USAT) to simulate the short-term aging of asphalt binders (STUSAT). Rutting and fatigue parameters of four neat and four modified binders (two asphalt-rubbers and two polymer-modified ones) were determined after aging the materials in both the STUSAT and the regular rolling thin-film oven test (RTFOT). Rheological tests included multiple stress creep and recovery (MSCR) and linear amplitude sweep (LAS). The fatigue parameter (|G*|.sinδ) and the Glover–Rowe parameter were also determined. Overall, the findings of the MSCR and fatigue parameters for the STUSAT-aged binders are in close agreement with the ones derived from the RTFOT-aged ones. The same can be said for the high performance grades (PG) and the assigned traffic levels for each material. Moreover, STUSAT does not appear to mask the formulations that are overly stress sensitive in the MSCR tests, and it does not seem to penalize the binders that can withstand high traffic levels or modify the classification of the binder according to stress sensitivity. The mass loss for both procedures is equivalent, but STUSAT presented higher variations due to the small amount of sample. The ranking order based on the three fatigue indicators for both aging protocols converged in terms of which are the best and worst materials: polymer-modified binder C1 was the best one, followed by one of the two asphalt-rubbers (B1 or B2), with the neat binders A4, A1, and A2 as the worst materials. These findings suggest that STUSAT is a feasible alternative to regular RTFOT, once the procedure demands a simple set of equipment. Future studies are recommended to validate the applicability of STUSAT using a higher number of asphalt binders. The findings of this paper may provide civil engineers and highway agencies with an easy-to-use, short-term aging test, designated as the short-term universal simple aging test (STUSAT), which is a simplified version of the universal simple aging test (USAT). The test described here is intended to be an alternative to the regular rolling thin-film oven test (RTFOT). It requires only a regular forced-air oven, silicone apparatuses, and aluminum plates to age the binder and simulate the actual aging the material experiences during plant production, hauling, and compaction. This method is especially useful for asphalt laboratories in developing countries, which typically do not have a rolling thin-film oven to conduct the regular short-term aging tests per the ASTM and AASHTO standards. Moreover, STUSAT demands a smaller mass of binder (only 3.0 g) and a lower test time (50 min) when compared with RTFOT. The test temperature (150°C) is also lower than the one in RTFOT (163°C), thereby saving energy and time during the regular operations in the laboratory.