Proposed asphalt binder fatigue criteria for various traffic conditions using the LAS or the G-R parameters

The linear amplitude sweep (LAS) test has been used widely in the last decade as an effective tool for evaluating the fatigue behavior of asphalt binders. However, a simple to follow criteria to be included in a standard specification has not been proposed yet. Recently, the Glover-Rowe (G-R) parameter has also been introduced with limiting values as a measure of binder cracking resistance and its change with oxidative aging. These two approaches differ in the time required for testing, the range in strain used and temperature of the tests required to derive the binder acceptance parameters. In addition, there is confusion about what could be the specification acceptance limits to be used and how to consider the temperature of pavement, and traffic volume and traffic speed in the specification criteria. In this study, the calculation procedure of the G-R parameter is simplified by using the data from the strain amplitude sweep, and the frequency sweep, used in the LAS test (AASHTO TP101). This new method of calculation eliminates the need for the time-consuming procedure that requires lower temperatures and low frequency conditions. The calculation procedure is also used to determine the dependency of the G-R parameter on strain level during the test and to derive acceptance criteria as a function of traffic speed and volume similar to the MSCR criteria. Thirty-six types of modified asphalt subjected to PAV aging are used in this study. For eight types of these asphalts, mixtures were prepared and subjected to three periods of oven aging conditions. By comparing the G-R index with the LAS fatigue life of the asphalt binder and the Flexibility Index value of the asphalt mixture, it is shown that there is a strong correlation between the selected binder fatigue parameters and mixture performance. It is also confirmed that strain levels play a very important role in defining the fatigue life of a binder. Following the concept of Jnr limits for different traffic grades used for the MSCR test, the threshold values of the allowable strain in LAS results, or a maximum allowable G-R limits, under different traffic volume and speed conditions are defined. The approach used in the study allows a determination of which traffic and speed conditions an asphalt binder can tolerate can be made in a relatively short time. Similar to the MSCR, four fatigue grades including S, H, V, and E are used in the proposed criteria.