Methods Available to Calculate Flow Number Parameter Based on Dynamic Creep Test

The results from the NCHRP 9-19 project recommended three candidate Simple Performance Test (SPT) tests: flow time (FT), flow number (FN), and dynamic modulus |E*| tests. In addition, the dynamic modulus test was selected for the HMA materials characterization input utilized in the 2002 Mechanistic and Empirical (M-E) Guide for Design of New and Rehabilitated Pavement Structures, developed under NCHRP Project 1-37A. The rutting model selected in the M-E design guide for the asphalt concrete layer is based on an empirical relationship between the elastic strain and the plastic strain, where the computation of the elastic strains is derived from the |E*| values. However, as demonstrated from the results presented in this paper, if the |E*| value itself can not differentiate between poor and good performing HMA mixtures in terms of permanent deformation resistance, it is cautioned that the rutting prediction provided in the M-E design guide may not provide the true mixture performance. Currently, there is interest in incorporating flow number as the additional test method. The objective of this research study is to evaluate and compare several methods to be used in calculating the onset of tertiary flow (referred to as flow number (FN) parameter) for asphalt mixtures.