High-Temperature Characterization of Highly Modified Asphalt Binders and Mixtures

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High-Temperature Characterization of Highly Modified Asphalt Binders and Mixtures

Mohseni, Alaeddin / Azari, Haleh

To characterize highly modified asphalt binders under high temperatures, this paper presents an alternative that uses the incremental repeated load permanent deformation (iRLPD) test in lieu of the multiple stress creep recovery (MSCR) test. The rationale for the iRLPD test includes a reduced loading time that better correlates with field-loading conditions, decreased variability of results, and an improved estimation of highly modified binder behavior. Moreover, an iRLPD high-temperature model for the highly modified binder is presented; this model is also correlated to the iRLPD traffic model to provide traffic estimates through the use of the iRLPD mixture parameter. Laboratory results indicate that as the level of binder modification increases, MSCR underestimates the strain response that can lead to overestimation of traffic levels. The study also illustrates the effect of the stress–strain nonlinearity parameter, which increases as the level of binder modification increases. The difference in the permanent strain and recovery response from the two methods is exacerbated by the level of binder modification; however, for neat binders, the MSCR and iRLPD strain ratio approaches unity. The results demonstrate that the permanent strain of polymer modified binder is highly time dependent and thus the loading time for testing asphalt binders should be properly selected. The LTPPBind software seems to underestimate the traffic levels calculated from the iRLPD and MSCR models; nevertheless, the results of iRLPD and LTPPBind are in agreement, insinuating that the LTPPBind model underpredicts the traffic level for neat binders, whereas the MSCR model overpredicts the traffic level for highly modified binders.