Experimental Investigation on the Fatigue Damage Behaviour of Modified Bituminous Binders and Mastics

With respect to the minimization of fatigue cracking in flexible pavements, it is widely recognized that current SUPERPAVE specification criteria do not allow a reliable ranking of the fatigue resistance of bituminous binders. Thus, an alternative characterization procedure, based on the use of time sweep testing protocols and on the concept of Dissipated Energy Ratio (DER), has been proposed within NCHRP Project 9-10. However, the true significance of test results still needs to be thoroughly understood in order to define new acceptance and grading criteria. In this paper the Authors present the results obtained during an experimental investigation which addressed the issue of fatigue damage of modified binders and mastics. In particular, the objective of the study was to highlight, by means of time sweep tests, the effects on the fatigue behaviour caused by variations of the type and dosage of the polymer used as a chemical modifier. Moreover, the same kind of test was carried out on bituminous mastics in order to gain a better understanding of the role played by mineral filler in the fatigue performance of the binding matrix. In the analysis of test results, for a more complete description of the damage behaviour of the materials during cyclic loading, a new parameter, based on dissipated energy data, was introduced. Such a parameter, called Relative Crack Propagation Amplitude (RCPA), proved to be especially useful in highlighting the peculiar effects caused by the creation within the binder mass of an effective fatigue-resistant polymer network, in differentiating the consequences deriving from the use of different polymer types and dosages, and in comparing the performance of mastics with that of the corresponding binders.