ABSTRACT
ABSTRACT: This paper presents the results of a round robin test (RRT) on binder fatigue, with data received from 11 participating laboratories. Most data were obtained with a Dynamic Shear Rheometer (DSR) equipment, one laboratory used a tension-compression test. In a first stage, the RRT consisted of three binders, two unmodified binders and one polymer modified binder. These three binders had almost the same stiffness level at the testing conditions, 10°C and 10 Hz. Fatigue tests were conducted at three strain levels, and each strain level was measured in three repeats. For each test it was asked to follow the small strain stiffness during an equilibration time of 30 minutes. A second stage of this RRT including two more binders is foreseen. The same three binders were also tested in two and in four point bending mix fatigue tests. The analysis was separated into two parts, in a first part the repeatability and reproducibility of the small strain equilibrium stiffness was evaluated and in a second part the fatigue data were analyzed. Small strain stiffness data showed that the repeatability and reproducibility of G* is still not very high, and possible reasons are under evaluation. The analysis of the fatigue data showed that the overall reproducibility was not good. But when all participants that did in some way not follow the preparation procedure or that had problems with recording, were excluded, it was found that for 6 of the participating laboratories the fatigue properties gave good repeatability and reproducibility levels, for the two unmodified binders in this study. Each laboratory could distinguish the better fatigue life of the polymer modified binder compared to the unmodified binders as was also confirmed by mixture tests. This shows that the binder behavior plays an important role in the fatigue behavior of the mix, and that a binder test should be able to evaluate this role. The binder fatigue test can be used as a surrogate test for mixture fatigue, implying considerable time savings in sample preparation, however the testing of the binders is still time consuming.
