A simple stepwise method to determine and evaluate the initiation of tertiary flow for asphalt mixtures under dynamic creep test

A number of research studies have focused on the linkage between material properties and pavement performance. Part of the efforts in this research was the development of Superpave simple performance tests (SPT). One of the Superpave SPT is the repeated loading or dynamic creep test. The output of this test is the flow number, which is the initiation of tertiary flow. A common method in examining the flow number is to locate the lowest point in the strain rate versus cycle number curve, or the minimum value of the strain rate. However, this method may provide confusion due to the variation in the test data. Researchers have been trying to discover new effective methods for determining flow number. Their efforts have led to the development of several excellent approaches. However, these methods need to be more refined in order to improve the user-friendliness to engineers, researchers, and even students. A new simple stepwise method was developed and evaluated in this paper. In this process, it was assumed that the strain would only be maintained at the same point or increased over the load cycle number. Then, the flow number at the minimum point of new strain rate versus cycle number was determined. The flow number results from this new method are simpler and more practical compared to other methods for determining the flow number. In addition, the rate of deformation at the secondary stage was correlated well with the flow number using this method.