LAUSR

The development of the multiple stress creep and recovery (MSCR) test represented an improvement in the evaluation of the rutting susceptibility of asphalt binders. However, the creep and recovery times of the current test protocol (1 and 9 s, respectively) may not be adequate to predict performance under extremely heavy and slow traffic conditions or to allow full recovery of polymer-modified binders. Highly modified asphalt binders have been increasingly used in pavements under severe traffic and weather conditions, and, because of the higher polymer content in these materials, they can be more sensitive to variations in loading times and stresses. However, the influence of different loading times has not been investigated in detail for these materials yet. In this article, the effect of longer creep and recovery times on the MSCR test was evaluated for a highly modified asphalt binder, and the results were compared with those obtained for a neat asphalt binder and a regular styrene-butadiene-styrene (SBS) modified binder. Tests were carried out at the high performance grading temperature of each binder. and three situations were analyzed: (i) the increase of creep time to 2, 4, and 8 s; (ii) the increase of recovery time to 240 and 500 s; and (iii) the increase of both times simultaneously, to 2/18 s and 3/27 s. The highly modified binder analyzed was more susceptible to variation in creep and recovery times than the other binders and showed considerable increase in compliance due to nonlinear behavior, although there is no evidence that this was caused by the high polymer amount in this material. The results support the need of further investigation in this subject for future refinements in the MSCR test protocol and the specification criteria for slow or standing traffic, so that the susceptibility to longer loading times can be properly considered.