Evaluation and comparison of flow number calculation methods

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. The FN indicates the onset of shear deformation in asphalt mixtures, which is a significant parameter in evaluating rutting in the field; however, its variability has limited its implementation. The FN is obtained from the repeated load permanent deformation laboratory test. To evaluate and compare the methods, permanent deformation data from tests performed on 12 mixtures were analysed in terms of within- and between-sample variability and their ability to determine whether a tertiary stage was reached or not. The results showed that for modified and unmodified asphalt mixtures the Francken model has lowest variability and may be used as the final method for calculating FN.