Simplified Testing Method for Evaluation of Asphalt Mixtures for their Susceptibility to Permanent Deformation

Abstract

The accumulation of permanent deformation in the asphalt surfacing layer is considered to be the major cause of rutting in flexible pavements. Thus testing and methods of evaluation of mixtures for their susceptibility to permanent deformation have become important issues. This article reports further development of a mixture evaluation procedure previously suggested by the authors. The study considered the use of a simplified testing method, in which a slightly modified NAT (Nottingham Asphalt Tester) is used to measure axial and radial strains resulting from loading of cylindrical asphalt specimens. Two types of mixtures, Ab 16 (asphalt concrete) and Ska 16 (stone mastic asphalt) are considered in the study. Tests were conducted on specimens produced in the laboratory using both the repeated load triaxial test and Nottingham Asphalt Tester. The results of the tests were used to rank the two mixtures in terms of their resistance to permanent deformation. The two mixtures were also laid as a surfacing layer on a main road in southern Norway and rutting measurements were conducted in the field. Although the major part of the rutting is believed to come from studded tire wear, the relative performance of the two mixtures in terms of total rutting agrees with the ranking provided by the tests and the suggested evaluation procedure.