Comparison of the fatigue failure behaviour for asphalt binder using both cyclic and monotonic loading modes

The objective of this paper is to investigate and compare the fatigue failure characteristics of neat and modified asphalt binders using both cyclic and monotonic loading modes, and further discuss the potential possibility of using the monotonic test for binder fatigue resistance ranking of purchase specification. The cyclic linear amplitude sweep (LAS) test (AASHTO TP 101) has been introduced to quantify the strain at peak stress, and also to predict the strain-controlled binder fatigue life from applying the simplified-viscoelastic continuum damage modeling (S-VECD) approach. Although the LAS is getting acceptance, the mathematical fitting approach is very complicated and require advanced curve fitting and analysis procedure. A simple alternative for characterizing binder failure properties is the use of monotonic loading as described in the binder yield energy test (BYET) and dynamic shear rheometer-elastic recovery (DSR-ER) test (AASHTO TP 123). In this study the BYET based failure strain is found to most efficiently correlate to the LAS based failure strain and predicted fatigue life. However, the multiple-peak phenomenon observed in the BYET stress-strain curves of some of the complex modified binders makes it very difficult to clearly identify the failure parameters. Results collected in this study show that using the DSR-ER test results can be a good addition to the BYET to predict fatigue life of a number of highly modified binders as estimated from the complex LAS mathematical procedure. Therefore, the combined use of the monotonic BYET and DSR-ER tests is recommended as an alternative to the cyclic LAS test for ranking the fatigue resistance of modified asphalt binders in routine practice.